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WORKS  OF  PROF.  I.  0.  BAKER    | 

PUBUSBED  BY 

JOHN 

WILEY  &  SONS. 

Ntnih^'Edii 
600  paga, 

udHKH^TcMini  Ihs  Bsrlni  fowa 
MuonrrSlnicliirc-Subiiilv  AplfM 

(o  Egim  uid  6  [aJ^Di  plate*,  cloth. 

Editlan.  R«viKd  and  Gieallf  Enluied.  umo,  U  + 

ATrMtlMVO 

^^^. . 

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A  TREATISE 


MASONRY  CONSTRUCTION. 


IBA  0.  BAKEE,  0.  E.,  D.  Ehq'o, 

FBOTKSeOB  OJ  OiriL  BNfllNBSiKISa,  UKtVKBHITT  Of  ILLQIOIB. 


J/INTS  BDITIOS,  REVISED  ASD  PABTIALLT  REWRITTSJU. 

TWELFTH  THOUSAND. 


NEW   VORK: 

JOHN    WILEY  &    SONS. 

London:  CHAPMAN    ft    HALL,   LiumD. 

1906 


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mjt  o.  BAXOL 


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234481 

m  20  1320  t^o.3-icc. 

.- .•'^ 

PREFACE. 


The  present  Tolnme  is  an  outgrowth  of  the  needs  of  the  snthor'B 
own  claBB-room.  The  matter  is  eaeentially  that  presented  to  hi& 
classes  for  3  namber  of  years  past,  a  considerable  part  having  been, 
used  in  the  form  of  a  blue-print  manuscript  text-book.  It  is  now 
published  for  the  greater  convenience  of  his  own  stadents,  and  with 
the  hope  that  it  may  be  useful  bo  others.  The  author  knows  of  no 
work  which  treats  of  any  considerable  part  of  the  field  covered  by 
this  volume.   Nearly  all  of  the  matter  is  believed  to  be  entirely  new. 

The  object  has  been  to  develop  principles  and  methods  and  to 
give  Boch  esamples  as  illustrate  them,  rather  than  to  accumulate 
details  or  to  describe  individual  structures.  The  underlying  prin- 
ciples of  ordinary  practice  are  explained  ;  and,  where  needed,  ways 
are  pointed  out  whereby  it  may  be  improved.  The  common  theo- 
ries are  compared  with  the  results  of  actual  practice ;  and  only 
those  are  recommended  which  have  been  verified  by  ezperimeDts 
or  experience,  since  true  theory  and  good  practice  are  always 
in  accord.  The  author  has  had  the  benefit  of  suggestions  and 
advice  from  practical  masons  and  engineers,  and  believes  that  the 
information  here  presented  is  reliable,  and  that  the  examples  cited 
represent  good  practice.  The  general  prices  are  the  average  of  a 
large  number  actually  paid  ;  and  the  special  prices  are  representa- 
tive. The  structures  illustrated  are  actual  ones.  The  accredited 
illustrations  are  from  well-authenticated  copies  of  working  drawings, 
,  and  are  presented  without  any  modification  whatever ;  while  those 
not  accredited  are  representative  of  practice  so  common  that  a  single 
name  could  not  properly  be  attached. 

In  the  preparation  of  the  book  the  endeavor  has  been  to  observe 
a  logical  order  and  a  due  proportion  between  different  parts.  Groat 
care  has  been  taken  in  classifying  and  arranging  the  matter.  It 
will  be  helpful  to  the  reader  to  notice  that  the  volume  is  divided 
successively  into  parts,  chapters,  articles,  sections  having  small-cap- 
ital black-face  side-heads,  sections  having  lower-case  black-face  side- 
heads,  sections  having  lower-case  italic  side-heads,  and  sections  hav- 
ing simply  the  aerial  number.     In  some  cases  the  major  snbdivis> 


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iona  of  the  sections  are  indicated  by  small  numerals.  The  constant 
aim  has  been  to  present  the  subject  clearly  and  concisely. 

Every  precantion  has  been  taken  to  present  the  work  in  a  form 
ior  convenient  practical  use  and  ready  reference.  Nnmeroas  cross 
references  are  given  by  section  number;  and  whenever  a  figure  or  a 
table  is  mentioned,  the  citation  is  accompanied  by  the  number  of 
the  page  on  which  it  may  be  foond.  The  table  of  contents  shows 
the  general  scope  of  the  book  ;  the  running  title  assists  in  finding 
the  different  parts ;  and  a  very  full  index  makes  everything  in  the 
book  easy  of  access.  There  are  also  a  number  of  helps  for  the 
gtudent,  which  the  experienced  teacher  will  not  fail  to  recognize 
and  appreciate. 

Although  the  book  has  been  specially  arranged  for  engineering 
and  architectnral  students,  it  is  hoped  that  the  information  con- 
cerning the  strengths  of  the  materials,  the  data  for  focilitating  the 
making  of  estimates,  the  plans,  the  tables  of  dimensions,  and  the 
costs  of  actual  stmctures,  will  prove  useful  to  the  man  of  experience. 
'Considering  the  large  amonnt  of  practical  details  presented  and 
the  great  difference  in  the  methods  employed  by  various  construc- 
tors, it  is  probable  that  practical  men  will  find  much  to  criticiaa 
The  views  here  expressed  are,  however,  the  results  of  obserration 
thronghoot  the  entire  country,  and  of  consultation  and  correspond- 
ence with  many  prominent  and  practical  men,  and  represent  average 
good  practice.  The  experienced  engineer  may  possibly  also  feel 
that  some  subjects  should  have  been  treated  more  fully ;  but  it  is 
neither  wise  nor  possible  to  give  in  a  single  volume  minute  details. 
These  belong  to  technical  journals,  proceedings  of  societies,  and 
special  reports  of  particular  work. 

No  pains  have  been  spared  in  verifying  data  and  checking  re- 
sults. The  tables  of  cubic  contents  have  been  computed  by  differ- 
ent proceeses  by  at  least  two  persons,  and  to  at  least  one  more  place 
than  is  recorded.  Should  any  error,  either  of  printer  or  author, 
be  discovered — as  is  very  possible  in  a  work  of  so  much  detail, 
despite  the  greiit  care  used,— the  writer  will  be  greatly  obliged  by 
;prompt  notification  of  the  same. 

The  author  gratefully  acknowledges  his  indebtedness  to  many 
■engineers  for  advice  and  data,  and  to  his  former  pupil  and  present 
eo-laborer,  Prof.  A,  N.  Talbot,  for  many  valuable  su^estiona. 

OsAHFAiOK,  III.,  Julj  9,  1889. 


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PREFACE  rOR  NINTH  EDITION. 


Thb  order  of  the  snbdiTiBJons  of  Art.  3,  Chap.  I,  has  been 
changed,  and  pages  7-11  have  been  rewritten.  Chapter  III — Cement 
and  Lime — and  Chapter  IV — Mortar  and  Concrete— have  been 
entirely  revrittea.  Chapter  IIIa — Sand,  Gravel,  and  Broken 
Stone — has  been  added.  The  Definitions  of  Kinds  of  Masonry— 
pages  136  and  137 — have  been  rewritten  and  new  illustrations  hare 
been  prepared.  The  specifications  for  the  different  classea  of  stou« 
masonry — paged  142, 144,  and  147 — have  been  rewritten.  Many 
minor  changes  have  been  made  in  varions  parts  of  the  book. 
CsAxrueif,  lu.,  June  27,  ISMi 


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TABLE  OF  CONTENTS. 


f  PART  I.      THE    MATERIALS. 

CHAPTER  I.    MATUBAL  STONE. 
IimiODCOTioii 1 

ABT.  1.     REQinBITBS  TOR  GoOD  BCILDINO  Btohb. S 

Aki.  3.    TxBTDio  Bdildins  Btoss. (L 

Waight -«. 

BardnMi  and  Tougkneu. T 

Strength.     Crushing  Strength.     TransverM  Slraogtb.     Elaitlcltf .  .      & 
DurtMlitj/,    Destructive  Agents :  mecbanlcal,  cbemical.    ResiBting 
Agenia :  chemical  composition,  physicnl  structure,  Beasouing.    Meth- 
ods of  Testing  Durability:  absorptiTe power,  methods  and  results; 
effect  of  frost,  methods  and  results;  eflect  of  atmoephere,  methods 

uid  results.    Methods  of  Preserving 14 

^KT.  S.    Ci.AsaiFiCATioK  AKD  DKscRrt-noN  of  Bcildiko  Stones.  .     .    Si& 
Classlflcatlon :  geological,  chemical,  physical.    Description  of  Trap, 
Or(uiit«,  Marble,  Limsstose,  and  Sandstone.    Location  of  Quarries. 
Weight  of  Stone. 

CHAPTER  n.    BRICK. 
Process  of  mannfacture.    Classillcatlon.    Requisites  for  good  Brick. 

Uethods  of  Testing :  absorbing  power,  tiaosverge  strength,  crashing 
Strength;  results.     Size.     Cost SS. 

CHAPTER  in.    LIME  AND  CEMENT. 

CliABBIFlCATIOIt 48 

Abt.  1.    CoMHOH  Limb. 4IK 

Heibods  of  manufacturing,  t«tlng,  and  preserving.    Cost, 

Art.  2.    Htdbaouc  Limb. 61 

Art.  8.    Htdraulig  Cembnt. 61 

Description  :  Portland,  Natural,  Pozzuolana.    Weight.    Cost. 

Art.  4.    Ubthods  or  Tstmna  Htdbauwc  Cekekt 0& 

Color,  Thoroughness  of  Buniiug,  Aclivllj,  Soundness,  Finsneas, 
Strength. 


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TABLE  OP   CONTENTS. 


Abt.  6.    Speoifioatiohb  tob  Ceuent 07 

Quality :  Oermau,  EnglUb,  French,  Americui,  Phllkdelphla-  De- 
liverj  Bud  Stonge. 

CHAPTER  niA.    SAND,  GRAVEL,  AND  BROKEN  STONE. 

Art.  ].    Band. ' 7t>a 

Requisites  for  Good  Sand :  Durabllitj,  SharpDea*.  Cleanaew,  Fine- 
ness, Voids.    Btone  ScreeolDgs.    Cost,    Welgbl. 

Art.  2.     Qbatbl  and  Bbokbn  Stokb 7M 

Qrarel.    Broken  Stone.    Voids.    Weight.    Cost. 


PART  II.   PREPARING  AND  USING  THE  MATERIALS. 

CHAPTER  IV.    MORTAR.  CONCRETE,  AND  ABTinCIAL  STONE. 

.Abt.  1    MoBTAR. 81 

Lime  HoTtar.  Cement  Hortar  :  proportions  and  preparation. 
Data  forEitlmal«8.  Strength  :  tensile,  compresBlve,  adhesire.  Cost. 
ESect  of  Re- tempering.  Lime  with  Cemeot.  Moitar  Impervious  to 
Water.    Effect  of  Freezfng. 

Abt.  3.    Coscretb lOO 

Hortar.  Aggregate.  Proportions :  theoiy,  determination,  data 
forMttmateB     Mixing.    Laying.    Strength.    Coat. 

Abt.  8.    Abtificial  Stone 1136 

Portland.    McMuriiie.    Prear.    Raosome.    Borel. 

CHAPTER  V.    QUARRTINO. 
Methods  of  Quarrying ;  by  band  tools  ;  by  explosives, — the  drills, 
the  explosives  ;  by  cbonneliDg  and  wedging. 116 

CHAPTEB  VI.    STONE  CUTTINa. 

Abt.  1.    Tools. 19S 

Eighteen  hand  tools  illustrated  and  described.  Machine  tools  de- 
scribed. 

Akt.  i.    Hbtbods  of  FoBifTNa  thb  Biirfaces 139 

Four  metliods  Illustrated  and  described, 

Abt.  8.    Methods  of  Fiitibhino  the  Surfaces. 181 

Eight  methods  Illustrated  and  described. 

CHAPTER  VII.  STONE  MASONBY. 
Deflultions:  parts  of  tbewall,  kinds  of  masonry.  Ashlar  Masonry: 
dressing,  bond,  backing,  pointing,  mortar  required,  when  employed, 
specifications.  Squnred-stone  Masonry :  description,  mortar  required. 
speciflcatjous.  Hubble  Ma.4onry :  description,  mortar  required,  when 
employed,  apeciflcalions.     Slope-wall  Masoniy.    Slone  Paving.     Rip- 


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?  CONTENTS. 


np.  SireDgth  of  Stooe  MaBoury :  examples,  safe  preesure.  Ueas- 
uremeot  of  masour;.  Cost:  quarrjliig,  dressing,  price  of  stone; 
examples— U.  8.  public  buildlogs,  rellroada.  tmmela,  bridge  piers, 
arch  culyerlB ;  summary. 1 

CHAPTER  Vin.  BRICK  MASONRY. 
Horlar.  Bond.  CompressiTe  Strength :  results  of  eiperimeniB, 
aafe  pressure.  TrHnaverse  Strength :  strain  on  liatcl.  Ueasurement 
of  Brick-work.  Data  for  Estimates :  brick,  labor,  mortar  requii^. 
Cost.  Speclfloitlons :  for  btiUdinifH,  sewera,  arches.  Brick  e*.  Stone 
MasoDty.    Brick  Maaonry  Impervious  to  Water.    EfQoreBcence.  .    .  1 


PABT  III.    FOUNDATIONS. 
CHAPTER  IX.    INTRODUCTORY. 
DxmnTioirs,  add  Plah  or  Propobrd  Dibcdbsion.     .    .    .    .  li 
CHAPTER  S.    ORDINARY  FOUNDATIONS. 

Odtlinx  of  Comtmtb. li 

Abt.  I.    Thb  Boil 11 

Examioation  of  the  Bite.  Bearing  power  of  Soils  :  rock,  clay,  sand, 
seml-liquld  aoilii ;  summnry.  Methods  of  ImproTlng  Bearing  Power: 
increasing  depth,  drainage,  springs,  consolidating  the  Boll,  sand  piles, 
layen  of  sand. 

Abt.  2.    DsmeinMO  thk  Poormos. V 

Load  to  be  Supported.  Area  Required,  Center  of  Pressure  and 
Center  of  Base.  Independent  Piets.  Effect  of  Wind.  Offsets  for 
Masonry  Footings.    Timber.F90tbigi.    Sleel-r»11  Footings.    Inverted 

AbT.  8.     PHEFABIVa  THE  Bkd. 3 

On  Rock.  On  Firm  Earth.  In  Wet  Qronnd :  coffer-dam,  con- 
crete, grillage. 

CHAPTER  KI.    PILE  FOUNDATIONS. 

Dbtinitiorb.      ...  9 

Abt.  1.  DKSCRiPTtuiia.  AHD  Methods  or  Dritthb  Piles.  ....  3 
Deecriplion  :  Iron  piles ;  screw  piles  ;  disk  piles ;  sheet  piles  ;  bear 
ing  piles,— speciHcations,  caps  and  aboes,  splicing.  Pile  Driving  Ma- 
chines: drop  iiaramer, — friction  clutch,  nipper;  sleam-hainmer,  drop- 
hammer  w,  steam-hammer ;  gunpowder  pile-drivers ;  driving  with 
dynamilc;  driving  with  water  Jet;  jetM.  hammer.  Cost  of  Piles. 
Cost  of  Pile  Driving:  railroad  construction,  bridge  construction, 
bridge  repairs,  foundations,  harbor  and  river  work. 


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TABLE   OF  C0HTEW18. 


Abt.  3.    Bearido  PowBtt  o?  Ptleb. 388 

Hetbods  of  DelerminiDg  Supporting  Power.  Batlonal  Formula. 
CompuisoD  of  Empiricul  Formulas:  BeAufoy'i,  Nyslrom's,  Moaon'S, 
Sander's,  McAlpine'a,  Traulwlne's.  tbe  Author's.  SuppottlDg  Power 
Determined  by  Experimeot ;  examples,  factor  of  eattty ;  Bupporting 
power  or  screw  and  disk  plles^ 

Abt.  8.    Arrahoehbnt  or  thb  Foundation. 350 

position  of  Piles.  Bawing-off.  Fialshing  Foundation:  piles  and 
grillage,  piles  and  concrete,  lateral  yielding.  Cuablng's  Pile  Founda- 
aon. 

CHAPTER  XII.    FOUNDATIONS  UNDER  WATER. 
Difficulties  to  be  OrBRCoxE.    Oihtjnb  or  Contsntb.  .    .  367 

Abt.  1.    The  Coffbr-Dak  Process 368 

Construction  of  tbe  Dam.  Leakage,  pumps.  Preparing  the 
Foundation 

Art.  S.    The  Crib  abd  Opeit  Caibbok  {"bocess 266 

Deflaitlona.  PriDciple,  Consiructlon  of  tbe  Caisson.  Construc- 
tion of  the  Crib.    Excavating  tne  Site. 

Akt.  8,    Drbdgino  throooh  Wells. 871 

Principle.  Excavator,  Noted  Examples:  Poughkeepale,  Atcba- 
falaya,aud  Hawhesbury  bridges;  brick  cylinders.  Frictional  Reust- 
ance.     Coat.  • 

Abt.  4.    Pnedhatic  Frocebs STiS- 

Vacuum  Process.  Plenum  Process.  History.  Pneumatic  Hies, 
bearing  power.  Pneumalic  CsissouH :  the  caisson,  Ibe  crib,  thecoSer- 
dam,  machinery,  air-lock.  Excavators;  sand  lift,  mud-pump,  water 
column,  blasting.  Rate  of  Sinking.  Quidlng  tbe  Caisson.  Noted 
Examples:  Havre  deOrace,  Blair,  St  Louis,  Brooklyn.  Forth  Bridges. 
Pbysiologicsl  Effects  of  Compressed  Air,  Examples  of  Cost :  at 
Havre  de  Grace,  Blair,  and  Brooklyn,  and  in  Europe. 

Art.  5.    The  FRBBziNa  Process. 807 

PriDcipIe.    History,    Details  of  Process.    Examples.    Advantages. 

Art.  6.    Compabisom  of  Methods. 809 


PART  IV.    MASONKY  STKUCTURE8. 

CHAPTER  Xm.    MASONRY  DAMS. 

Classification  op  Dams. 811 

Abt.  1.    Stabilitv  of  Gbavitv  Dams 3ia 

Principles.  Stability  against  Sliding;  destroying  forces,  resisting 
forces,  co-etlicient  of  friction,  condilion  of  equilibrium,  factor  of 
safety.  Stability  against  Overturning :  by  moments. -^overturning  mo- 


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TABLB   OF   COyrSKTS. 


ment,  realattng  moment,  condltloa  for  equilibrium,  factor  of  safety ; 
by  resolution  of  forces.  Btablllt;  Bgalust  Crushing :  method  of  flnd* 
log  maximum  pressure,  tenalou  od  masonry,  limiting  pressure. 

Abt.  3.    Oirn.niB8  of  the  Desioii 834 

Width  on  Top.  The  Profile :  theory,  examples.  The  Plan ; 
straight  crest  e«.  straight  toe  ;  gravity  t».  arch  dams ;  curved  gravity 
dams.    Quality  of  Hasotuy.    BlbIiogt«phy. 

Abt.  8.    RocK-E^LL  Dams. .^  8Sl 

Wood.    EartlL    Bock-fill  aad  utasoniy  dams  compared. 

CHAPTER  XIV.    RETAIHISQ  WALLS. 

Definltloni.    Methods  of  Failure.    Difficulties. 888 

Abt.  1.    Theoketical  PoBuuiiAS 84C 

The    Three    Assumptloiis.      Theories:   Coulomb's,    Weyraach's, 

AsT.  3.    EupiucAi,  Rules US 

Bnglish  Rules.  American  Rules.  Details  of  Construction  :  quality 
of  masonry,  drainage,  land  ties,  relieving  archee. 

CHAPTER  XV.    BRIDGE  ABUTMENTS. 

DUcussloD  of  General  Forms.    Quality  of  Masonry.    Foundation. 

Wing  Abutment, —design,  and  table  of  contents  of  various  sizes. 

U  -Abutment,— design  and  table  of  contents  of  varlotu  sizes.  T-Abut. 

ment, — design  and  table  of  contents  of  various  sizes 808 

CHAPTER  IVI.    BRIDGE  PIERS. 
Sblectioh  or  Sits  and  ABRAnaBMEirT  or  Sfaits.       ...  866 

Art.  1.    Thbobt  of  Stability 887 

Methods  of  fUlure.  Stability  against  Sliding :  effect  of  wind,  cur- 
rent, ice;  rcslstiug  forces.  Btabll it j against  Overturning:  by  mo- 
ments ;  by  resolution  of  forces.  Stability  against  Crushing.  Example 
of  method  of  computing  stability. 

Abt.  S.    DsrAiLe  or  Corbtbuctioh 877 

Dimensions :  on  lop,  at  bottom.  Batter.  Cross  Section.  Spcclflca- 
tlons.  Examples :  (^ro.  Grand  Forks,  Blair,  Henderson,  St.  Croix 
River ;  iron  tubular ;  wooden  barrel.  Tables  of  Contents  of  different 
styles  and  sizes  of  bridge  piers.     Specifications. 

CHAPTER  XVn.    CULVERTa 

Abt.  1.    Water  Wat  Re4UIEEd 891 

The  Factors.  The  Formulas :  Meyer's,  Talbot's.  Pmctioal  method 
of  finding  area  of  water  way. 

Abt.  2.    Box  Ain>  Pipe  Culvxbts. 896 

Sfens  Son  Culvert :  foundntlou,  end  walls,  cover,  spec! B cations. 


ovGoQi^lc 


TABLE   07   CONTENTS. 


ExuDples:  Siuidard,  West  Shore,  Cuudlon.    Table  ot  Conteols  and 
cosl  of  the  TsriouB  Btyle»  bdcI  sixea 8M 

VilTified  Pipe  Oalwrlt :  CooBtructloa.  Example.  I^ble  of  Cod- 
tents 407 

Iron  Pipe  OuUierlt :  ConBCriictlon.  Blze  and  Weight  of  Pipe.  Ex- 
unplw  ;  A.,  T.  Ss  B.  F..  and  C,  B.  Sc  Q.  slaodards.  Tahle  of  Quan- 
tity of  Materials  Required 413 

Timber  CtUf>erl :    C,  M.  &  St.  P.  standard  box  cnlverta.    C,  U.  & 

Q.  standard  barrel  culvert. 417 

Art.  8.    Abcb  CTn.TKRT 419 

Qeoenl  Form :  qjlay  of  wfng  walls,  joluing  wings  and  body,  seg- 
mental M,  semi-circular.  Examples :  diagrams  illuniatlng  details,  and 
also  tables  giving  dimenalona,  and  contents,  and  cost,  of  all  dzes  of 
each  of  the  standard  forms  of  the  Illinois  Central.  C.  E.  &  N.,  A.,  T. 
&S.-F.  (both  semi-circular  and  segmental),  and  a  standard  form. 
Specifications. 

CHAPTER  XVra.    MASONRY  ARCHES, 
Deflnitions:  parts  and  kinds  of  arches;  line  of  resistance.  .    .     .     .  440 

Art.  1.    Thbori  of  tkb  HASotniT  Arch 444 

External  Forces.  Methods  of  Failure.  Criteria  ot  Safety:  sliding, 
rotation,  crushlug, — unit,  pressure,  open  joints.  Location  of  Line  of 
Resistance :  hypothesis  of  least  prossure  ;  hypothesis  of  least  crown 
thrust,  joint  of  rupture ;  Winkler's  hypothesis ;  Navier's  principle. 
Rational  Theory  of  the  Arch:  symmetrical  load,— two  methods; 
unsymmetrical  load ;  criterion  for  line  of  resistance.  Scheffler's 
Theory :  two  examples ;  erroneous  application  ;  reliability  of.  Ran- 
kine's  Theory  :  curvature  of  linear  aich,  method  of  testing  stability, 
reiiabillty.  Other  Theories.  Theory  of  the  Elastic  Arch.  StablUty 
ot  Abutments  and  Piers. 

Art.  2.    Rules  Drrivkd  frou  Practick 4M 

Empirical  Formulas :  thickness  of  the  arch  at  the  crown,— Ameri' 
can,  French.  English  practice;  thicknessatthespringing,— American, 
French,  English  practice ;  dimensions  of  abutments.  Dimensions  of 
Actual  Arches  and  Abutments.  Illustrations  of  Arches.  Minor  De- 
tails :  backing,  spandrel  fliling.  drainage.  Brick  Arches ;  bond  ;  ex- 
amples,—tunnel,  Philadelphia  sewers,  Washington  sew  era.  Specifica- 
tions: stone  arches,  brick  arches. 

Art.  6.    Arch  Ckntrrs. SU| 

Load  to  be  supported,  method  of  computing.  Outline  forms  of 
Centera :  solid  rib,  built  rib,  braced  wooden  rib,  trussed  frame.  Ex- 
amples: centers  for  Vosburg  tunnel,  stone  bridges,  and  Cabin  John 
Arch.    Striking  Centers:  method,  time. 


ovGoQi^lc 


TABLE  OF   COHTZNIB, 


APPENDIX   I.     SPECIFICATIONS  FOB  MASONBY. 


Ofiiieral  R&IIroad  IKuoaty.  ,  . 
HiMOUTj  of  Railroad  Building*.  . 
Architectural  Haaonry 


APPENDIX  II.    SFPPLEMENTABY  NOTES. 

Labor  Bequired  !d  QuanrlDg. 544 

Coat  of  Cutting  Qranite. MS 

Coat  of  Laying  Cut  Stone. C45 

Coat  of  Breaking  Stone  for  Concrete 64$ 

Coit  of  Imboddlng  Large  Stones  in  Concrete. M7 

Cnublng  SlrenglL  of  Sewer  Pipe. 647 

Holding  Power  of  Dilft-botta. 547 


ovGoQi^lc 


jvGooi^le- 


MASONBT  C0NSTRU0TI02SI. 


DJTEODTJCnON. 

Ukdeb  this  geaeni  head  vill  be  diBoaBsed  the  snbjecta  nlating 
to  the  use  of  atone  and  brick  as  employed  by  the  en^neer  or  archi- 
tect in  the  conetraction  of  boildings,  retaining  walls,  bridge  piers, 
cnlverts,  arches,  etc.,  indnding  the  fonndations  for  the  samo, 
For  conTenience,  the  snhject  will  he  divided  as  follows  : 

Part     I.  Description  and  Characteristics  of  the  Material*. 

Put  IL  Methods  of  Preparing  and  XTsing  the  Materiaia. 

Part  III.  Foundations. 

ftrt  TV.  MaeoQr;  Structaree. 


ovGoQi^lc 


■*  nu  flnt  ooat  of  muoniy  Bhould  be  Its  oaljr  cceL  ThonriiMipentiactuic* 
decay  and  drift  nway,  though  emiMukmeDts  abould  crumble  uid  wvib  ouL 
uuaamjr  ahoold  itiuia  u  one  great  mow  ol  loUd  rock,  firm  and  enduring.* 


ovGoQi^lc 


PART   I. 

THE  MATERIAIA 


NATURAL  STONE. 

Art.  1.  BBQUiBrrBS  fob  Good  Buildino  Stonb. 

1.  The  qnalities  ThJoh  are  most  important  in  stone  uaed  lor 
Donstrnction  are  cheapness,  durability,  strength,  and  beanty. 

2.  CHlAmsB.  The  primary  factor  which  detflrminee  the  Talne 
of  a  stone  for  strnctand  purposes  is  its  cheapness.  The  items  which 
contribute  to  the  cheapness  of  a  stone  are  abundance,  proximity  of 
quarries  to  place  of  use,  facility  of  transportation,  and  the  ease  with, 
which  it  is  quarried  and  worked. 

The  wide  distribution  and  the  great  rariety  of  good  building 
etone  in  this  country  are  snch  that  suitable  stone  should  everywhere 
be  cheap.  That  such  is  not  the  case  is  probably  due  either  to  a 
lack  of  the  developme'it  of  home  resources  or  to  a  lack  of  con  fidence 
in  home  products.  The  several  State  and  Govenunent  geological 
surreys  have  done  much  to  increase  oar  knowledge  of  the  building 
stones  of  this  country. 

The  lack  of  confidence  in  home  resources  has  very  frequently 
caused  stones  of  demonstrated  good  quality  to  be  carried  far  and 
wide,  and  frequently  to  be  laid  down  upon  the  outcropping  ledges 
of  material  in  every  way  their  equal.  The  first  stone  house  erected 
in  San  Francisco,  for  example,  was  built  of  Btone  bronght  from 
China ;  and  at  the  present  day  the  granites  mostly  employed  there 
are  bronght  from  New  England  or  from  Scotland,  Yet  then  are 
no  stones  in  onr  country  more  to  be  recommended  than  the  Califor- 
nia granites.  Some  of  the  prominent  public  and  private  buildings 
in  Oinoiunati  are  oonetructed  of  stone  that  was  carried  by  water  and 


ov($OOi^lc 


i  HATUBAI.  BTOTTB.  [CHAP.   I. 

railway  a  distance  of  aboat  1500  miles.  Withia  150  miles  of  Cin- 
cinnati, in  the  snb-carboniferouB  limestone  district  of  Kentncky, 
there  are  very  extensive  deposits  of  dolomitic  limestone  that  aSord 
a  beaatifnl  building  stone,  which  can  be  quarried  at  no  more  ex< 
pense  than  that  of  the  granite  of  Maine.  Moreover,  this  dolomitfi 
is  easily  carved,  and  requires  not  more  than  one  third  the  labor  to 
give  it  a  surface  that  is  needed  by  granite.  Experience  has  shown 
that  the  endurance  of  this  stone  under  the  influence  of  weather  is 
very  great ;  yet  because  it  has  lacked  authoritative  indorsement 
there  has  been  little  market  for  it,  and  lack  of  confidence  in  it  bat 
led  to  the  transportation  half-way  across  the  continent  of  a  stent 
little,  if  any,  superior  to  it. 

Development  of  local  resources  follows  in  the  wake  of  good  in- 
formation concerning  them,  for  the  lack  of  confidence  in  home  prod- 
ucts can  not  be  attributed  to  prejudice. 

The  facility  with  which  a  stone  may  be  quarried  and  worked  is 
an  element  affecting  cheapness.  To  be  cheaply  worked,  a  stone 
must  uot  only  be  as  soft  as  durability  will  allow,  but  it  should  have, 
no  flaws,  knots,  or  b&rd  crystals. 

3.  I>tnABI£ITT.  Next  in  importance  after  cheapness  is  dura- 
bility.  Bock  is  supposed  to  be  the  typo  of  all  that  is  unchangeable 
and  lasting ;  but  the  truth  is  that,  unless  a  stone  is  suited  to  the 
conditions  in  which  it  is  placed,  there  are  few  substances  more  liable 
to  decay  and  utter  failure.  The  durability  of  stone  is  a  subject 
upon  which  there  is  very  little  reliable  knowledge.  The  question 
of  endurance  under  the  action  of  weather  and  other  forces  can  not 
be  readily  determined.  The  external  aspect  of  th§  stone  may  fail 
to  give  any  clue  to  it ;  nor  can  all  the  testa  we  yet  know  determine 
to  a  certainty,  in  the  laboratory,  just  how  a  given  rock  will  with- 
stand the  effect  of  onr  variable  climate  and  the  gases  of  our  cities. 
If  our  land  were  what  is  known  as  a  rainless  country,  and  if  the 
temperature  were  uniform  throughout  the  year,  the  selection  of  a 
durable  building  stone  would  be  much  simplified.  The  cities  o' 
northern  Europe  are  full  of  failures  in  the  stones  of  importan 
structures.  The  most  costly  building  erected  in  modem  times,  per- 
haps the  most  costly  edifice  reared  since  the  Great  Pyramid, — tht 
Parliament  House  in  London, — was  built  of  a  stone  taken  on  tfat 
recommendation  of  a  committee  representing  the  best  scientific  and 
tochDical  skill  of  Great  Britain,     The  stone  selected  woa  submitted 


ovGoQi^lc 


ABT.   2.J  TESTS   UP  BUILDmrS   STONES,  5 

torarioQs  teste,  but  the  corroding  inflnence of  a  Ijondonatmc^phere 
was  overlooked.  The  great  strnctare  was  built,  and  now  it  seems 
questionable  whether  it  can  be  made  to  eodure  oe  long  as  a  timber 
building  would  stand,  so  great  is  the  effect  of  the  gases  of  the 
atmosphere  upon  the  stone.  This  is  only  one  of  the  numerous  in- 
stances that  might  be  cited  in  which  a  neglect  to  consider  the 
climatic  conditions  of  a  particular  locality  in  selecting  a  building 
material  has  proved  disastrous, 

"The  great  difference  which  may  exist  in  the  durability  of  stones- 
ol  the  same  kind,  presenting  little  difference  in  appearance,  is 
strikingly  exemplified  at  Oxford,  England,  where  Christ  Church 
Cathedral,  built  in  the  twelfth  or  thirteenth  century  of  oolite  from 
a  quarry  about  fifteen  miles  away,  is  in  good  preservation,  while 
many  colleges  only  two  or  three  centuries  old,  built  also  of  oolite 
from  a  quarry  in  the  neighborhood  of  Oxford,  are  rapidly  cmmbling 
to  pieces. "  * 

4.  Stbevoth.  The  strength  of  stone  is  in  some  instances  a 
cardinal  quality,  aa  when  it  is  to  form  piers  or  columns  to  support 
great  weights,  or  capstones  that  span  considerable  intervals.  It  is 
also  an  indispensable  attribute  of  stone  that  is  to  be  exposed  to 
mechanical  violence  or  unusual  wear,  as  in  steps,  lintels,  door- jambs, 
e*c. 

5.  Beautt.  This  element  is  of  more  importance  to  the  archi- 
tect thau  to , the  engineer;  and  yet  the  latter  can  not  afford  to 
neglect  entirely  the  element  of  beauty  in  the  design  of  his  most 
utilitarian  structures.  The  stone  should  have  a  durable  and  pleas- 
ing color. 

Art,  3.  Tests  of  the  Quautt  of  Bitildikg  Stones. 
9.  As  a  general  mie,  the  densest,  hardest,  and  most  uniform 
stone  will  most  nearly  meet  the  preceding  requisites  for  a  good 
building  stone.  The  fitness  of  stone  for  structural  purposes  can  bt 
determined  approximately  by  examining  a  fresh  fracture.  It  should 
be  bright,  clean,  and  sharp,  without  loose  grains,  and  free  from  any 
dull,  earthy  appearance.  The  stone  should  contain  no  "  drys,"  i.e., 
seams  containing  material  not  tlioroughly  cemented  together,  nor 
"crow-foots,"  i.e.,  veins  containing  dark-colored,  uncemented 
material. 

*  BauUne's  CItQ  Engineering,  p.  862. 


ovGoQi^lc 


6  NATURAL   STONE.  [OHAP.  I. 

The  more  form&t  tests  employed  to  determine  the  qaalitiee  of  a 
building  stone  are:  (1)  veight  or  density,  (S)  hardness  and  tough- 
neaa,  (3)  strength,  (4)  darability. 

1.  Wmght  of  Stone. 

7.  Weight  or  dennty  is  an  important  property,  since  npon  it 
depends  to  a  large  extent  the  strength  and  dnrabilit;  of  the  stone. 

If  it  is  desired  to  find  the  exact  weight  per  cabic  foot  of  a  given 
stone,  it  is  generally  easier  to  find  its  specific  gravity  first,  and  then 
mnltiply  by  62.4, — weight,  in  pounds,  of  a  cabio  foot  of  water. 
Tjiis  method  obriates,  on  the  one  hand,  the  expense  of  dressing  a 
sample  to  regular  dimensions,  or,  on  the  other,  hand,  the  in- 
aocnracy  of  meosaring  a  roagh,  irregalar  piece.  Kotice,  howcTer, 
that  this  method  determines  the  weight  of  a  onbic  foot  of  the  solid 
stone,  which  will  be  more  than  the  weight  of  a  cubic  foot  of  the 
material  as  used  for  stractaral  parposes.  In  finding  the  specific 
gravity  there  is  some  difficnity  in  getting  the  correct  displacement 
of  porona  stones, — and  all  stones  are  more  or  less  poruns.  There 
are  varione  methods  of  overcoming  this  difficulty,  which  give 
slightly  diSerent  resnlta.  The  following  method,  recommended  by 
General  Gillmore,  is  most  frequently  nsed: 

All  loose  grains  and  sharp  comers  haying  been  removed  from 
the  sample  and  its  weight  taken,  it  is  immersed  in  water  and 
weighed  there  after  all  babbling  has  ceased.  It  is  then  taken  ont 
of  tiie  water,  and,  after  being  compressed  lightly  in  bibalons  paper 
to  absorb  the  water  on  its  surface,  is  weighed  again.  The  specific 
gravity  is  found  by  dividing  the  weight  of  the  dry  stone  by  the 
difference  between  the  weight  of  the  saturated  stone  in  air  and  in 
water.    Or  expressing  this  in  s  formnla, 

W 
Specific  gravity  =  ^^  _^  ^, 

in  which  W^  representfl  the  weight  of  dry  stone  in  air,  W,  the 
weight  of  saturated  stone  in  air,  If,  the  weight  of  stone  immersed 
in  water. 

The  following  table  containa  the  weight  of  the  atones  most  fre- 
qnently  met  with. 


ovGoQi^lc 


iBT.  2.] 


TZaXS   OF   BriLOING    BTOKEB. 

TABLE  1. 
Wbioht  of  BmLDisG  Btokbb. 


PODMM  FEB  CUHIO 

Foot. 

lUn. 

Hu. 

Mod. 

161 
14« 
167 

1B7 
160 

178 
174 
180 
161 
176 

170 

174 

2.   HaBDHEBB  AHD  TorOHNESS. 

8.  The  apparent  hardness  of  a  etone  dependB  upon  (1)  the 
.  hardness  of  its  component  minerals  and  (2)  their  state  of  aggrega- 
tion. The  hardness  of  the  component  minerals  is  determined  by 
the  resistance  they  offer  to  being  scratched ;  and  Tariss  from  that 
of  talc  which  can  easily  be  scratched  with  the  thnmb-nail,  to  that 
:  of  qnartz  which  scratches  glass.  Bat  however  hard  tiie  mineral 
constituents  of  a  stotie  are,  the  apparent  hardness  of  the  stone  itself 
depends  npon  the  state  of  aggregation  of  the  particles.  Many 
rocks  composed  of  hard  materials  work  readily,  because  their  grains 
are  loosely  coherent;  while  others  composed  of  softer  materials  are 
qnite  toagh  and  difiBcalt  to  work,  owing  to  the  tenacity  with  which 
the  particles  adhere  to  each  other.  Obviously  a  stone  in  which  the 
grains  adhere  closely  and  strongly  one  to  another  will  be  stronger 
and  more  dnrable  than  one  which  is  loose  textured  and  friable. 

The  toughness  of  a  stone  depends  upon  the  force  with  which  the 
particles  of  the  component  minerals  are  held  together. 
'  Both  hardness  and  toughness  should  exist  in  a  stone  used  for 
fltoops,  pavements,  road-metal,  the  facing  of  piers,  etc.  Ko  experi- 
ments have  been  made  in  this  country  to  test  the  resisting  power  of 
atone  when  exposed  to  the  different  kinds  of  service.  A  table  of  the 
resistance  of  stones  to  abrasion  is  often  quoted,*  but  as  it  contains 
only  foreign  stones,  which  are  described  by  local  names,  it  is  not  of 
much  value. 

*  For  enunple,  Habui's  Olvtl  Engineering,  p.  IS. 


ovGoQi^lc 


8  KATUR1.L  8T0NB.  [CHAP.  I. 

3.    STHSNarH. 

TTnder  thia  head  will  be  included  (1)  ornihing  or  compreaaifd 
Btreogth,  (2)  transYerse  strength,  (3)  elasticity.  Usually,  when 
simply  the  strength  la  referred  to,  the  crashing  strength  is  intended. 

9.  CBTTSHnro  Stbevoth.  The  crushing  strength  of  a  stone  is 
tested  by  applying  measured  force  to  cubes  nntil  they  are  cmahed. 
The  resnlts  for  the  crushing  strength  vary  greatly  with  the  details 
of  the  experiments.  Several  points,  which  should  not  be  neglected 
either  in  planning  a  series  of  experiments  or  in  using  the  results 
obtained  by  experiment,  will  be  taken  up  separately,  although  they 
are  not  entirely  independent. 

10.  Form  of  Test  Specimen.  Experiments  show  that  all  brittle 
materials  when  subjected  to  a  oompresBive  load  fail  by  shearing  on 
certain  definite  angles.  For  brick  or  stone,  the  plane  of  rupture 
makes  an  angle  of  about  60°  with  the  direction  of  the  compressing 
force.  For  this  reason,  the  theoretically  best  form  of  test  specimen 
would  be  a  prism  having  a  height  of  about  one  and  a  halt  times  the 
least  lateral  dimension.  The  result  is  not  materially  different  if 
the  height  is  three  or  four  times  the  least  lateral  dimenBion.  But 
if  the  test  specimen  is  broader  than  high,  the  material  is  not  free 
to  fail  along  the  above  plane  of  rupture,  and  conseqaently  the 
strength  per  unit  of  bed-area  is  greater  than  when  the  height  is 
greater  than  the  breadth. 

However,  notwithstanding  the  fact  that  theoretically  the  teat 
specimen  should  be  higher  than  broad,  it  is  quite  the  universal 
custom  t«  determine  the  crushing  strength  of  stone  by  testing 
cubes. 

11.  Blie  of  the  Gabe.  Although  the  cube  is  the  form  of  test 
specimen  generally  adopted,  there  is  not  equal  unanimity  as  to  the 
size  of  the  cube;  but  it  is  oonclnsiTely  proven  that  the  strength  per 
square  inch  of  bed-area  is  independent  of  the  size  of  the  cube,  and 
therefore  the  size  of  the  test  specimen  is  immaterial. 

General  Gillmore,  in  1875,  made  two  sets  of  experiments  which 
seems  to  prove  that  the  relation  between  the  crushing  stongth  and 
the  size  of  the  cube  can  be  expressed  by  the  formaU 

ID  which  y  is  the  total  crushing  pressure  in  pounds  per  square  inch 
0 


ovGoQi^lc 


ABT.  2.]  STBBNQTH  OB   BniLDINQ   BTONES.  ft 

of  bed-oreft,  a  is  the  crashlDg  prearare  of  a  l-inch  cnbe  of  the  Bome- 
material,  and  x  is  the  length  Id  inches  of  an  edge  of  the  cnbe  under 
trial.  For  tvo  sampleB  of  Berea  (Ohio)  aandatone,  a  was  7000  and 
flSOO  IbB.,  respectively.* 

Besnlta  by  other  obaervers  with  better  machines,  particularly  by 
General  Gillmore  f  with  the  large  and  accurate  testing-machine  at 
Watertown  (Masa.)  Arsenal,  X  uniformly  show  this  sappoaed  law  to 
be  without  any  foundation.  Unfortunately  the  above  relation 
between  strength  and  bed-area  ie  frequently  quoted,  and  has  found 
a  wide  acceptance  among  engineers  and  architects. 

Two  inches  is  the  moat  common  size  of  the  cube  for  oompression 
tests. 

12.  Cushions.  Homogeneous  stones  in  small  cubes  appear  in 
all  cases  to  break  as  shown  in  Fig.  1.  The 
forms  of  the  fragments  a  and  b  are,  approxi- 
mately, either  conical  or  pyramidal.  The 
more  or  less  disk-shaped  pieces  e  and  d  are 
detached  from  the  sides  of  the  cnbe  with  a 
kind  of  explosion.  In  the  angles  «  and  /,  the 
stone  ia  generally  found  crushed  and  ground 
into  powder.  This  general  form  of  breakage 
occurs  also  in  non-homogeneons  stones  when  ?">■  i- 

crushed  on  their  beds,  but  in  this  case  the  modification  which  the- 
grain  of  the  stone  produces  mnst  be  taken  into  account. 

The  nature  of  the  material  in  contact  with  the  stone  while- 
nnder  pressure  is  a  matter  of  great  moment.  If  the  materials  which 
press  upon  the  top  and  bottom  of  the  specimen  are  soft  and  yielding 
and  press  out  sidewise,  they  introduce  horizontal  forces  which 
materially  diminish  the  apparent  crnshing  strength  of  the  stone. 
If  the  pressing  surfaces  are  hard  and  unyielding,  the  resistance  of 
these  surfaces  adds  considerable  to  the  apparent  strength. 

■  Report  on  Btrengtb  of  Batlding  Stona,  Appendix,  Baport  of  Obltt  ot  EngiDeeta- 
of  U.  8.  A.  (or  187t 

tNotos  OD  the  ComprsBBlTe  BeBlstanoe  at  Ftaestons,  Brlok  Plan,  HydiauUa 
Caments,  H ort&rs,  and  Oonaret«,  Q.  A.  OlUmore.    John  Wile;  A  Sons,  New  York, 

ises. 

{Report  OD  the  " Teste  of  Metals,"  etc.,  tor  tha  year  ending  JaoeSO,  ISSi,  pp. 
Ue,  166,  IST,  197,  312,  918,  316;  the  aama  being  Sen.  Ex.  Doo.  No.  85,  49th  Cong., 
Xet  SesBloD.  For  a  dlseosBlon  at  Uiese  data  by  the  antboT,  see  ^igtauriag  JfrnM, 
VoLzlz.pp.  Sll-SU. 


ovGoQi^lc 


10  NATURAL  STOKE.  [CHAP.  L 

Formerly  steel,  wood,  lead,  and  leather  were  mnch  nsed  oa 
pressing  snifaces.  Under  certain  limitations,  the  relative  crashing 
strengths  of  atones  with  these  different  pressing  sarfacee  are  100, 
89,  65,  and  62  respectively.* 

Testa  of  the  strength  of  blocks  of  stone  are  nsefal  only  tn  com- 
paring different  stones,  and  give  no  idea  of  the  strei^gth  of  strnct- 
nres  bnilt  of  snch  stone  (see  §  246)  or  of  the  crnabing  strength  of 
etone  in  large  masses  in  its  native  bed  (see  §  273). 

Then,  since  it  is  not  possible  to  have  the  stone  under  the  same 
conditions  while  being  tested  that  it  is  in  the  actual  atroctnre,  it  is 
best  to  test  tbe  stone  under  conditions  that  can  be  accnrately 
deacribed  and  readily  duplicated.  Therefore  it  ia  rapidly  coming  to 
be  tbe  custom  to  test^  the  stone  between  metal  pres^ng  surfaces. 
Under  these  conditions  the  strength  of  tbe  specimen  will  vary  greatly 
with  tbe  degree  of  smootfaneBS  of  its  bed-anid!aceB.  Hence,  to  obtain 
definite  and  precise  resnlts,  these  enrfaces  abootd  be  robbed  or 
gronnd  perfectly  smooth;  bat  as  this  is  tedions  and  expensive,  it  is 
qnite  common  to  rednce  tbe  bed-snrfaces  to  planes  by  plastering 
them  with  a  thin  coat  of  plaster  of  Paris.  With  the  stronger 
etoDea,  specimens  with  plastered  bed  will  show  less  strength  than 
those  having  rubbed  beds,  and  this  difference  will  vary  also  with 
the  length  of  time  tbe  plaster  is  allowed  to  harden.  With  a 
stone  having  a  atrengtb  of  5,000  to  6,000  pounds  per  square  inch, 
allowing  the  plaster  to  attain  its  maximnm  strength,  this  differ- 
ence varied  from  5  to  30  per  cent.,  the  mean  for  ten  trials  being 
almost  10  per  cent,  of  the  strength  of  the  specimen  with  rubbed 
beds. 

13.  Sreuing  the  Cube.  It  is  well  known  that  even  large 
atones  can  be  broken  by  striking  a  number  of  comparatively  light 
blows  along  an;  particular  line ;  in  which  case  tbe  force  of  the  blows 
gradu^Iy  weakens  tbe  cohesion  of  tbe  particles.  This  principle  finds 
application  in  the  preparation  of  teat  specimens  of  atone.  If  the 
specimen  ia  dressed  by  hand,  the  coDcnssion  of  the  tool  greatly 
affects  ita  internal  conditions,  particnlarly  with  test  specimens  of 
small  dimensions.  With  3-incb  onbea,  t^e  tool-dreseed  specimen 
uaually  shows  only  abont  60  per  cent,  of  the  strength  of  the  sawed 


ovGoQi^lc 


»■] 


STRENGTH    OF    UUILDINQ   STONES. 


11 


.sample.     The  sawed  Bample  most  nearly  represente  the  conditions 
•of  ftctaal  practice. 

Unfortuaatelj,  experimenters  seldom  state  whether  the 
^specimens  were  tool-dressed  or  sawed.  The  disintegrating 
'effect  of  the  tool  in  dressiog  ia  greater  with  small  than  with 
large  specimens.  This  may  acconnt  for  the  difference  in 
:strength  of  different  sizes  of  test  Bpeoimen  as  seems  to  be 
jhown  by   some   experiments. 

AU  stones  are  strongest  when  laid  on  their  natural  bed, 
i.«.,  when  the  pressure  is  perpendicular  to  the  stratification ;  • 
■and  with  sedimentary  rocka  there  is  a  very  great  difference 
in  the  two  positions.  Hence,  in  preparing  the  test  specimen 
the  natural  bed  should  be  marked,  and  the  cube  should  be 
-tested  upon  its  native  bed. 

14.  Data  en  Cmihlng  Strength.  The  strength  of  the  principal 
classes  of  building  stone  in  use  in  the  United  States  is  about  as 
iollowa  : 

TABLE  L 


CBUBKiMa  Stekhoth 

or  UuBsa  o> 

Stoitb. 

Knna  or  Snn. 

Pounds  per  Bqiuralncb. 

TootpwSq 

ivafooL 

Ko. 

1U< 

MIo.. 

Mmx. 

Trap  Bocki  of  N.  J 

20,000 
18,000 
8,000 
7,000 
5,000 

£4,000 
31.000 
30,000 
30.000 
15.000 

1,440 
860 
580 
500 
860 

1,780 
1,010 
1,440 

1,060 

16.  Cruihing  Strength  of  Slabe.  Only  a  few  experiments  have 
been  made  to  determine  the  crushing  strength  of  slabs  of  stone. 
The  strength  per  square  inch  of  bed-snr^e  was  considerably 
greater  than  that  for  cubes ;  but  a  study  of  the  results  of  all  of  the 
reliable  experiments  •  fails  to  discover  any  simple  relation  between 


"  tor  ISU—aeo.  Ex.  Doo.  No.  35, 49th 


ovGoQi^lc 


12  NATDEAL  STOITB.  [CHAP.    L 

the  oriisliing  etrength  of  cubes  aad  dabs.  It  is  probable  that  the 
effect  of  the  precming  sarface  is  80  great  as  to  completely  maek  the 
TariatioQ  due  to  height  of  Bpecimeu.  More  experiments  on  this 
flnbject  are  very  much  needed. 

16.  TSAXSVIBSE  Strxvoth.  When  stones  are  used  tor  lintels, 
etc,  their  transverse  strength  becomes  important.  The  ability  of  a 
stone  to  resist  as  a  beam  depends  upon  its  tensile  strength,  since 
that  is  always  mnch  less  than  its  compressive  strength.  A  knowl- 
edge of  the  relative  tensile  and  compreaaive  strength  of  stones  is 
valnable  in  interpreting  the  effect  of  different  pressing  surfaces  in 
compreasiye  tests,  and  also  in  determining  the  thickness  required 
for  lintels,  sidewalks,  cover-stones  for  box  culverts,  thickness  o£ 
footing  courses,  etc. 

Owing  to  the  smalt  cross  section  of  the  specimen  employed  in 
determining  the  transverse  strength  of  stones, — usually  a  bar  1  inch 
square, — the  manner  of  dressing  the  sample  affects  the  apparent 
transverse  strength  to  a  greater  degree  than  the  compressive  strength' 
(see  §  13);  and  it  is  even  more  unfortunate,  since  the  strength  of 
the  stone  as  used  in  actual  practice  is  nearly  proportional  to  the 
strength  of  sawed  samples. 

The  following  formulas  are  useful  in  computing  the  breaking 
load  of  a  slab  of  stone.  Let  W  represent  the  concentrated  center 
load  plus  half  of  the  weight  of  the  beam  itself,  in  pounds ;  and  let 
/>,  d,  and  I  represent  the  breadth,  depth,  and  length,  in  inches, 
respectively.  Let  R  =  the  modulus  of  rupture,  in  lbs.  per  sq.  in. ;, 
let  C  =■  the  weight,  in  pounds,  required  to  break  a  bar  1  inch 
square  and  1  foot  long  between  bearings ;  and  let  L  =  the  lengthi 
of  the  beam  in  feet.     Then 

The  equivalent  unifomdy  distributed  weight  is  equal  to  twice  the- 
concentrated  center  load. 

Table  3  on  the  following  page  gives  the  values  of  R,  the  mod- 
ulus of  rupture,  and  of  C,  the  co-efficient  of  transverse  strength, 
required  in  the  above  formulas. 

Example, — To  illustrate  the  method  of  using  the  above  formulas, 
assume  that  it  is  desired  to  know  the  breaking  load  for  a  limestone 
Blab  3  inches  thick,  4  feet  wide,  and  6  feet  long.    Then  d  =  48 ;. 


ovGoQi^lc 


ABT.   2.] 


emXSQ^  OF   BUILDINO  STONES. 


TABLE  8. 
TbjUibtbbsb  Strxkoth  ot  Stohx,  Brick,  and  Uobtas. 


HooDura  or  Buftcbb. 


Blue^tone  flagging 

Granite 

Limestone 

"      oolitic,  from  Ind.,  sawed. 
Jfarble 


Slate 

Brick  (§69). 

Concrete— see  g  Iff^. 

Mortar,  neat  Portland.  1  jeaj  old. 
Uortar,  1  part  Portland  cement,  1 

part  sand.  1  jear  old 

Hortar,  1  part  Portland  cement,  3 

parts  sand,  1  ^ear  old 

Uortar,  neat  Rosendale,  1  year 
Hortar,  1  part  Rosendale  cement, 

1  part  sand,  1  year  old 

Uortar,  1  part  Rosendale  cement, 

3  parts  sand,  1  year  old ... . 


860 

3,700 

900 

1,800 

140 

1,500 

2,190 

2,888 

144 

2.160 

676 

1.260 

1,800 

5.400 

M9 

800 

1.168* 

»46» 

e88» 

416 

600 

848 

586 

888 

406 

((  =  3 ;  /  =  73  ;  R  =  1500  lbs.,— the  "averse"  value  from  the 
tahle; — and  C  =  83.     Substituting  these  values,  we  have 

W=ll^R  =  L|i^X_9i500  =  6000  poundfl; 

or,  using  the  other  form, 

W=  ^C  =  ^^^3  =  5976  pounds, 

vrhich  agrees  with  the  preceding  except  for  omitted  decimals. 
Hence  the  breaking  toad  for  average  quality  of  limestone  is  6000 
ponnds  concentrated  along  a  line  half-waj  between  the  ends ;  the 
QnLformly  distributed  load  is  twice  this,  or  13,000  pounds.    The 


D.qitizeabyG00l^lc 


14  HATi/RAL  8T0NB.  [CHAP    I, 

question  of  what  margin  ahoald  ba  allowed  for  safety  is  one  that  caix 
not  be  determined  in  the  abstract ;  it  depends  upon  the  accnracy 
with  which  the  maximum  load  is  estimated,  upon  the  manner  the 
load  is  applied — whether  with  shock  or  not, — upon  the  care  with 
which  the  stone  was  selected,  etc  This  subject  will  be  discussed 
farther  in  connection  with  the  use  of  the  data  of  the  above  table  in 
subsequent  parts  of  this  volume. 

17,  Elasticitt.  But  very  few  experiments  have  been  made  to 
determine  the  co-efficient  of  elasticity,  the  elastic  limit,  and  the 
"  set "  of  stone.  Data  on  these  points  would  be  valuable  in  deter- 
mining the  effect  of  combining  masonry  and  metal,  of  joining 
different  kinds  of  masonry,  or  of  joining  new  masonry  to  old  ;  in 
calculating  the  effect  of  loading  a  masonry  arch ;  in  proport)'>ning 
abutments  and  piers  of  railroad  bridges  subject  to  shock,  etc 
The  following  is  all  the  data  that  can  be  found: 
TABLE  4. 
Co-KmcisNT  07  Blabticitt  of  Stonb,  Brick,  asd  Uobtab. 


Haverstrew  Freestone  * 

Portland  &toue  (oClite  limeBtoDe)! 

Martlet 

Portland  GrantteJ. 

Blatef 

Graflon  Limestone} 

Richmond  Qranitet 

Brick,  medium— mesD  of  IS  experiments* 

Louisville  Cement  Mortar,  4  months  old :  t 

Neat  cemenl 

1  part  cement,  1  part  sand. 

I  part  cement,  3  parts  sand 

Ulster  Co.  (N.  Y.)   Cement  Uortar,  S3   monthe 
old:" 

8  parts  cement,  8  porta  sand 

1  part  cement,  8  parts  sand 

hvtland  Cement  Mortar,  32  months  old* 


950,000 
1,680,000 
8,600,000 
S,G00,O00 
7,000,000 
8,000,000 
18,000,000 
8,600,000 

800,000 

600.000 

1,800,00P 


eu.oop 

686.000 


1,  as  quoted  hj  Stonej. 


ovGoQi^lc 


ART.   i.}  BTBBNOTH  OF  BUILDINQ  8T01TBS.  16 

18.  BiBLiaeEAPHIOAI.  A  large  nnmber  of  testa  bave  been 
applied  to  the  boilding  stones  of  tbe  United  States.  For  the 
results  and  detuls  of  some  of  the  more  important  of  these  tests 
see:  Report  on  Strength  of  Sailding  Stoae,  den.  Q.  A.  Gillmore, 
Appen.  II,  Beport  of  Chief  of  Engineers,  U.  S.  A.,  for  1875; 
Tenth  Ceosna  of  the  XS.  8.,  Vol.  X,  Beport  on  the  Qnarr; 
IndnBtry,  pp.  330-35;  the  several  annnal  reports  of  tests  made 
with  the  V.  S.  Ooverament  testing  machine  at  the  Watertown 
(Mass.)  Arsenal,  pablished  by  the  U.  S.  War  Department  under 
the  title  Report  on  Tests  of  Metals  and  Other  Materials; 
Transactions  of  the  American  Society  of  Civil  Engineers,  Vol.  II, 
pp.  146-Sl  and  pp.  187-9^;  Jourital  of  the  Association  of  En- 
gineering Societies,  Vol.  V,  pp.  176-79,  Vol.  IX,  pp.  33-43; 
Engineering  Jfews,  Vol.  XXXI,  p.  135  (Fe£.  16,  1884);  and  the 
reports  of  the  various  State  Geological  Sarveys,  and  the  com- 
missioners of  the  varions  State  capitols  and  of  other  pnblio 
buildings. 

By  vay  of  comparison  the  following  reports  of  tests  of  building 
stones  of  Great  Britain  may  be  interesting:  Prooeedinga  of  the 
Inatitnte  of  Civil  Engineers,  Vol.  CVII  (1891-98),  pp.  341-69; 
abstract  of  the  above,  Engineerinff  Mws,  Vol.  XXVIII,  pp.  279-82 
(Sept.  22,  1892). 

In  consnlting  the  above  references  or  in  nsing  the  results,  the 
details  of  the  manner  of  making  of  the  experiments  shonld  be 
kept  clearly  in  mind,  particalarly  the  method  of  pieparing  and. 
bedding  the  specimen, 

4.    DUKABILTTT. 

19.  *'  Although  the  art  of  bnilding  has  been  practiced  from  the 
earliest  times,  and  constant  demands  have  been  made  in  every  age 
for  the  means  of  determining  the  best  matenals,  yet  the  process  of 
ascertaining  the  durability  of  stone  appears  to  have  received  but 
little  definite  scientific  attention,  and  the  processes  usually  employed 
for  solving  this  question  are  still  in  a  very  unsatisfactory  state. 
Hardly  any  department  of  technical  science  is  so  much  neglected  as 
that  which  embraces  the  study  of  the  nature  of  stone,  and  all  the 
raried  resources  of  litbology  in  chemical,  microscopical,  and  physical 
methods  of  investigation,  woDderfuUy  developed  within  the  last 


ovGoQi^lc 


t6  NATURAL  STONE.  [CHAP.  I 

quarter  century,  have  never  yet  been  properly  applied  to  the  aeleo- 
tion  and  protection  of  atone  used  for  building  purposeB."  * 

Examples  of  the  rapid  decay  of  building  atones  have  already  been 
referred  to,  and  numerouB  others  oonld  be  cited,  in  vhich  a  stone 
vbich  it  was  snppoeed  would  last  forever  has  abready  begun  to 
decay.  In  every  way,  the  question  of  durability  is  of  more  interest 
to  the  architect  than  to  the  engineer ;  although  it  is  of  enough 
importance  to  the  latter  to  warrant  a  brief  discussion  here. 

20.  Sebtaiictite  Aoehtb.  The  destructive  i^ents  may  be  clas- 
sified as  mechanical,  chemical,  and  organic.  The  last  are  onim- 
portont,  and  will  not  be  considered  here. 

'  81.  Mechanical  A^ots.  For  our  climate  the  mechanical  agents 
are  the  most  efficient.  These  are  frost,  wind,  rain,  fire,  pressure, 
and  friction. 

The  action  of  frost  is  usually  one  of  the  main  causes  of  rapid 
decay.  Two  elements  are  involved, — the  friability  of  the  material 
«nd  its  power  of  absorbing  moisture.  In  addition  to  the  alter- 
nate freezing  and  thawing,  the  constant  variations  of  temperature 
from  day  to  day,  and  even  from  hour  to  hour,  give  rise  to  molecular 
motions  which  affect  the  durability  of  stone  as  a  building  material. 
This  effect  is  greatest  in  isolated  columns, — as  monuments,  bridge 
piers,  etc. 

The  effect  of  rain  depends  upon  the  solvent  action  of  the  gases 
which  it  contains,  and  upon  its  mechanical  eSect  in  the  wear  of 
pattering  drops  and  streams  triclding  down  the  face  of  the  wall. 

A  gentle  breeze  dries  out  the  moisture  of  a  building  stone  and 
tends 'to  preserve  it;  but  a  violent  wind  wears  it  away  by  dashing 
sand  grains,  street  dust,  ice  particles,  etc.,  against  its  face.  The 
extreme  of  such  action  is  illustrated  by  the  vast  erosion  of  the  sand- 
stone in  the  plateaus  of  Colorado,  Arizona,  etc.,  into  tabular  miias, 
isolated  pillars,  and  groteequely-shaped  hills,  by  the  erosive  force  of 
sand  grains  borne  by  the  winds.  The  effect  is  similar  to  that  of  the 
sand  blast  as  used  in  various  processes  of  manufacture.  A  violent 
wind  also  forces  the  rain-water,  with  all  the  corrosive  acids  it  con- 
tains, into  the  pores  of  stones,  and  carries  off  the  loosened  grains, 
thus  keeping  a  fresh  surface  of  the  stone  exposed.  Again,  the 
swaying  of  tall  edifices  by  the  wind  must  cause  a  continual  motion, 

■  Tamil  Ceanu  o(  the  U.  S.,  Tot.  X,  Bepcet  on  tbe  Qomtt  lD^utEr,Tb  Ml 


ovGoQi^lc 


ART.    3.]  DUaABlLITT   OF   BUILDINO   STOSES.  17 

not  only  in  tlie  joints  between  tlie  blocks,  bat  among  the  grains  of 
the  stoneB  themaelrea.  Many  of  these  have  a  certain  degree  o( 
fiexibility,  it  is  true;  and  yet  the  play  of  the  grains  mnat  gradually 
increase,  and  a  tendency  to  disintegration  result. 

Experience  in  great  fires  in  the  cities  shows  that  there  is  no 
stone  which  can  withstand  the  fierce  heat  o£  a  maes  of  burning 
buildiogs.  Sandstones  seem  to  be  the  least  aSected  by  great  heat, 
and  granite  most. 

Frictiou  aBects  sidewalks,  pavements,  etc.,  and  has  already 
been  referred  tr>  (§  8).  It  may  also  aSect  bridge  piers,  sea-walls, 
docks,  etc. 

The  efiect  of  pressure  in  destroying  stone  is  one  of  the  Ic^t 
importance,  provided  the  load  to  be  borne  does  not  too  nearly  eqnnl 
the  crushing  strength.  The  pressure  to  which  stone  is  subjected 
does  not  generally  exceed  one  tenth  of  the  ultimate  strength  as 
determined  by  methods  already  described. 

22.  Chemical  Agents.  The  principal  ones  are  acids.  Every 
constituent  of  stone,  except  quartz,  is  subject  to  attack  by  acids; 
and  the  carbonates,  which  enter  as  chief  constituents  or  as  cement- 
ing materials,  yield  very  readily  to  such  action.  Oxygen  and  am- 
monia by  their  chemical  action  tend  to  destroy  stones.  In  cities  or 
manufacturing  districts  sulphur  acids  and  carbonic  acid  hare  a 
very  marked  effect.  These  all  result  from  the  combustion  of  gas, 
coal,  etc.,  and  some  are  also  the  residuary  gases  of  many  kinds  of 
manufactories.  The  nitric  acid  in  tbe  rain  and  the  atmosphere 
exerts  a  perceptible  infinence  in  destroying  building  stone. 

23.  BsBiBTHro  Abektb.  The  durability  of  a  building  stone  de- 
pends upon  three  conditions;  viz.,  the  chemical  and  mineralogical 
nature  of  its  constituents,  its  physical  structure,  and  the  character 
and  position  of  its  exposed  surfaces. 

24.  Chemical  Composition.  The  chemical  composition  of  the 
principal  constituent  mineral  and  of  the  cementing  material  has  an 
important  effect  upon  the  durability  of  a  etone. 

A  siliceous  stone,  other  things  being  equal,  is  more  durable  than 
a  limestone;  but  the  durability  of  the  former  plainly  depends  upon 
the  state  of  aggregation  of  the  individual  grains  and  their  cement- 
ing bond,  ae  well  as  on  the  chemical  relation  of  the  silica  to  the 
other  chemical  ingredients.  A  dolomitic  limestone  is  more  durable 
thkn  a  pure  limestone. 


ovGoQi^lc 


18  KATCBAL  STONE.  [CHAP.   T. 

A  stone  that  absorbs  moisture  abundantly  and  rapidly  is  apt  to 
be  iajttred  by  alternate  freezing  and  thawing;  hence  clayey  conetit- 
iients  are  injnrions.  An  argillaceous  stone  is  generally  compact, 
and  often  baa  no  pores  visible  to  the  eye;  yet  such  will  disintegrate 
rapidly  either  by  freezing  and  thawing,  or  by  corrosive  vapors. 

The  presence  of  calcium  carbonate,  as  in  some  forms  of  marble 
and  in  earthy  limestones,  renders  a  building  material  liable  to  rapid 
attack  by  acid  vapors.  In  some  sandstones  the  cementing  material 
is  the  hydrated  form  of  ferric  oxide,  which  is  solnble  and  easily 
removed.  Sandstones  in  which  the  cementing  material  is  siliceous 
are  likely  to  be  the  most  durable,  although  they  are  not  so  easily 
worked  as  the  former,  A  stone  that  hae  a  high  per  cent,  of  alumina 
(if  it  be  also  non-cry stalUne),  or  of  organic  matter,  or  of  protoxide 
of  iron,  will  usually  disintegrate  rapidly.  Such  stones  are  gen- 
erally of  a  bluish  color. 

26.  Seasoning.  The  thorough  drying  of  a  atone  before,  and  the 
preservation  of  this  drynesa  after,  its  insertion  in  masonry  are  com- 
monly recognized  as  important  factors  of  its  durability;  bnt  the 
exact  nature  of  the  process  of  seasoning,  and  of  the  composition 
of  the  quarry-sap  removed  by  thorough  drying,  have  never  been 
determined.  The  quarry  water  may  contain  little  else  than  ordinary 
well-water,  or  may  bo  a  solution  more  or  less  nearly  saturated,  at  the 
ordinary  temperature,  with  carbonate  of  calcium,  silica,  double  salts 
of  calcium  and  magnesium,  etc.  In  the  latter  case,  hardening  re- 
sults from  the  drying,  and  an  exact  knowledge  of  its  nature  might 
throw  important  light  on  the  best  means  for  the  artificial  preserva- 
tion of  stone.  Again,  water  may  exist  in  large  quantity,  in  chemical 
combination,  in  the  silicates  {e.g.,  chlorite,  kaolin,  etc.),  or  in  the 
hydrated  iron  oxides  which  constitute  the  cement  of  a  building 
stone. 

26.  Physical  StrnotiiTe.  The  physical  properties  which  con- 
tribute to  durability  are  hardness,  toughness,  homogeneity,  con- 
tiguity of  the  grains,  and  the  structure — whether  crystalline  or 
amorphous. 

Although  hardness  (resistance  to  crushing)  is  often  regarded  as 
■the  moat  important  element,  yet  resistance  to  weathering  does  not 
necessarily  depend  upon  hardness  alone,  bnt  upon  hardness  and  the 
non-absorbent  properties  of  the  store.  A  hard  material  of  close 
and  firm  texture  is,  however,  in  those  qualities  at  least,  especially 


ovGoQi^lc 


AllT.    2.J  BURaBILITT:    op   BUILDIKG    S10KE8.  19 

fitted  to  resist  friction,  as  in  stoops,  pavements,  iind  road  metal,  and 
the  wear  of  rain-drope,  dripping  rain-water,  the  blows  of  the  waves, 
etc 

Porosity  is  an  objectionable  element.  An  excessive  porosity  in- 
creases the  layer  of  decomposition  which  is  caused  by  the  acids  of 
the  atmosphere  and  of  the  rain,  and  also  deepens  the  penetration  of 
frost  and  promotes  its  work  of  disintegration. 

If  the  constituents  of  a  rock  differ  greatly  in  hardnese,  texture^ 
solubility,  porosity,  etc.,  the  weathering  is  unequal,  the  surface  ia 
roughened,  and  the  sensibility  of  the  stone  to  the  action  of  frost  is. 
increased. 

The  principle  which  obtains  in  applying  an  artificial  cement, 
snch  aaglue,  in  the  thinnest  film  in  order  to  secure  the  greatest 
binding  force  finds  its  analogy  in  the  building  stones.  The  thinner 
the  films  of  the  natural  cement  and  the  closer  the  grains  of  the  pre- 
dominant minerals,  the  stronger  and  more  durable  the  stone.  One- 
source  of  weakness  in  the  .famous  brown-stone  of  Hew  York  City- 
lies  in  the  separation  of  the  rounded  grains  of  quartz  and  feldspar 
by  a  superabundance  of  ocherous  cement.  Of  course  the  further 
separation  prodaced  by  fissure,  looseness  of  lamination,  empty 
cavities  and  geodea,  'and  excess  of  mica  tends  to  deteriorate  still 
further  a  weak  building  stone. 

Experience  has  generally  shown  that  a  crystalline  structure  re- 
sists atmospheric  attack  better  than  an  amorphous  one,  This  prin- 
ciple has  been  abundantly  illustrated  in  the  buildings  of  New  York 
City.  The  same  fact  is  generally  true  with  the  sedimentary  rocks 
also,  a  crystalline  limestone  or  good  marble  I'esisting  erosion  better 
than  earthy  limestone.  A  stone  that  is  compactly  and  finely  granular 
will  exfoliate  more  easily  by  freezing  and  thawing  than  one  that  is 
coarse-grained.  A  stone  that  is  laminar  in  structure  absorbs  mois- 
ture unequally  and  will  be  seriously  affected  by  unequal  expansion 
and  contraction, — especially  by  freezing  and  thawing.  Such  a  stone 
will  gradually  separate  into  sheets.  A  stone  that  has  a  granular 
texture,  as  contrasted  with  one  that  is  crystalline  or  fibrous,  will 
crumble  sooner  by  frost  and  by  chemical  agents,  because  of  the 
easy  dislodgment  of  the  individual  grains. 

The  condition  of  the  surface,  whether  rough  or  polished,  in- 
fluences the  durability, — the  smoother  surface  being  the  better. 


ovGoQi^lc 


20  NiXUBAL   6T0KB.  [CHAP.   I. 

The  stone  is  more  durable  if  the  exposed  Burfoce  is  vertical  than  if 
mclmed.     The  lamination  of  the  stone  should  be  horizontal. 

27.  HZTEODS  OF  TESTISO  StTBABILITT.  It  hus  long  been  recog- 
nized that  there  are  two  ways  in  which  we  can  'form  a'  Judgment  of 
the  durability  of  a  building  stone,  and  these  may  be  distinguished 
as  natural  and  artificial. 

28.  Natural  Hethoda.  These  must  always  take  the  precedence 
whenever  they  can  be  used,  becai^e  they  iuTolve  (1)  the  exaot 
ftgenciea  concerned  in  the  atmospheric  attack  npon  stone,  and  (S) 
Jong  periods  of  time  &r  beyond  the  reach  of  artificial  experiment. 

One  method  is  to  visit  the  quarry  and  observe  whether  the  ledges 
that  have  been  exposed  to  the  weather  are  deejdy  corroded,  or 
whether  these  old  surfaces  are  still  fresh.  In  applying  this  test, 
consideration  must  be  given  to  the  modifying  effect  of  geological 
phenomena.  It  has  been  pointed  out  that  "the  length  of  time  the 
ledges  hare  been  exposed,  and  the  changes  of  actions  to  which 
they  may  have  been  subjected  during  long  geological  periods,  are 
unknown;  and  since  different  quarries  may  not  have  been  exposed 
to  the  same  action,  they  do  not  always  afford  definite  data  for  re- 
liable comparative  estimates  of  durability,' except  where  different 
specimens  occur  in  the  same  quarry." 

North  of  the  glacial  limit,  all  the  products  of  decomposition 
have  been  planed  away  and  deposited  as  drift-formation  over  the 
length  and  breadth  of  the  land.  The  rocks  are  therefore,  in  gen- 
eral, quite  fresh  in  appearance,  and  possess  only  a  slight  depth  of 
cap  or  worthless  rock.  The  same  classes  of  rock,  however,  in  the 
South  are  covered  with  rotten  products  from  long  ages  of  atmos- 
pheric action. 

A  study  of  the  surfaces  of  old  buildings,  bridge  piers,  monu- 
ments, tombetonee,  etc.,  which  have  been  exposed  to  atmospheric 
influences  for  years,  is  one  of  the  beet  sources  of  reliable  information 
concerning  the  durability  of  stone.  A  durable  stone  will  retain  the 
tool-marks  made  in  working  it,  and  preserve  its  edges  and  corners 
sharp  and  true. 

29.  Artificial  Hethods  of  Testing  IhirabiUty.  The  older  but 
less  satisfactory  methods  are:  determining  (1)  the  reeistance  to 
crushing,  (2)  the  absorptive  ]>ower,  (3)  the  resistance  to  the  expan- 
iiion  of  frost,  by  saturating  the  stone  with  some  solution  which  will 
crystallize  in  the  pores  of  the  stone  and  produce  an  effect  similar  to 
frost,  (4)  the  aolntolity  in  acids,  and  (5)  microscopical  examination. 


ovGoQi^lc 


AKT.   2.J  DUKABILITY    OF   BLILDISQ   STONEB.  Sil 

SO.  Absorptive  Power.  The  ratio  of  absorption  dependslargely 
OB  the  density, — a  dense  stone  absorbing  less  water  than  a  lighter, 
more  poroae  one.  Compactness  is  therefore  a  matter  of  impor- 
tance, especially  in  cold  climates;  for  if  the  water  in  a  stone  is  onco 
allowed  to  freeze,  it  destroys  the  surface,  and  the  stone  veryspeedUy 
crnmblee  away.  Other  things  being  eqnal,  the  less  the  absorption 
the  better  the  stone. 

To  determine  the  absorptive  power,  dry  the  specimen  and  weigh 
it  carefully;  then  soak  it  in  water  for  34  hours,  and  weigh  again. 
The  increase  in  weight  will  be  the  amonnt  of  absorption.  Table  4 
shows  the  weight  of  water  absorbed  by  the  stone  as  compared  with 
the  weight  of  the  dry  stone — that  is,  if  300  units  of  dry  stone  weigh 
301  units  after  immersion,  the  absorption  is  1  in  300,  and  is  recorded 

68  1-300. 

Dr.  Hiram  A.  Cntting,  State  Greologist  of  Vermont,  determined 
the  absorptive  power  *  by  placing  the  specimens  in  water  under  th» 
receiver  of  an  air-pnmp,  and  found  the  ratio  of  absorption  a  littl» 
larger  than  is  given  in  the  following  table.  It  is  believed  that  the 
results  given  below  more  nearly  represent  the  conditions  of  actual 
practice.  The  values  in  the  "  Mai."  column  are  the  means  of  two- 
or  three  of  the  largest  results,  and  those  in  the  "Min."  column  of 
two  or  three  of  the  smallest.  The  value  in  the  last  column  is  tha 
mean  for  20  or  more  specimens. 

TABLE   C. 
Abbobftivk  Power  of  Stone,  Brick,  akd  IfosTAs. 


^^^^ 

RiTio  or  AoKoamo*. 

Uu. 

um. 

Avenge 

1-150 
1-150 
1-30 
1-15 
1-4 

1-a 

0 

0 
1-500 
1-840 
1-50 
1-10 

1-768 

1-^oa 

1-88 
1-U     ' 
1-10 
1-4 

31.  Sffoet  of  Frost.     To  determine  the  probable  effect  of  froet 
npon  s  stone,  carefully  wash,  dry,  and  weigh  samples,  and  then  wet 
■  Van  Nostnuid'*  Englo'g  Ha(.,  voL  zzlv.  pp.  401-0G> 


ovGoQi^lc 


93  '  NATURAL   8T0NB,  [CHAP.   I. 

them  and  expose  to  alternate  freezing  and. thawing,  after  which 
wash,  dry,  and  weigh  again.  The  Ices  in  weight  meaanres  the  rela- 
tive durability. 

A  quicker  w&y  of  accompli ehing  essentially  the  aame  result  is  to 
heat  the  specimens  to  500°  or  600°  F.,  and  plunge  them,  while  liot, 
.    into  cold  water.     The  following  comparatiTO  resnlts  were  obtained 
bj  the  latter  method  :  * 

RateUte  R>Uo  ot  LoM, 

White  brick 1 

Red  brick 3 

BrowD-stoue  (gandsioue  [rom  Conn.) 5 

Kova  ScDtU  s&ndaione 14 

32.  Brard'i  Tert.  Bmrd's  method  of  deteruiining  the  effect  of 
frost  is  much  used,  although  it  does  not  exactly  conform  to  the  con- 
-ditions  met  with  in  nature.  It  consiBts  in  weighing  carefully  some 
«mall  pieces  of  the  stone,  which  are  then  boiled  in  a  concentrated 
■solation  of  sulphate  of  soda  and  afterwards  hung  up  for  a  few  days 
in  the  open  air.  The  salt  crystallizes  in  the  pores  of  the  stone, 
-expands,  and  produces  an  effect  somewhat  similar  to  frost,  as  it 
causes  small  pieces  to  separate  in  the  form  of  dust.  The  specimens 
are  again  weighed,  aud  those  which  suffer  the  smallest  loss  of  weight 
are  the  best.  The  teat  is  often  repeated  several  times.  It  will  be 
'Soeu  that  this  method  depends  upon  the  assumption  that  the  action 
■of  the  salt  in  crystallizing  is  similar  to  that  of  water  in  freezing. 
This  is  not  entirely  correct,  since  it  substitutes  chemical  and 
mechanical  action  for  merely  mechanical,  to  disintegrate  the  stone, 
thus  giving  the  specimen  a  worse  character  than  it  really  deserves. 
The  following  results  were  obtained  by  this  method:  f 

fietoUve  Ratio  ot  LOM. 

Hard  brick 1 

Light  dove-colored  ssadstone  from  Seneca,  OliJo. ...    2 

Coarse-graiaed  BandMone  from  Nova  BcotU S 

Coane-graiaed  sandsUme  from  Little  Falls,  N.  J S 

Coarse  dolomite  marble  from  Pleasantville,  N.  T. . . .    7 

,  Coaise-gTHined  sandstone  from  Conn. IS 

Boft  brick 16 

.  Fine-gratned  BudMone  from  Conn. 19 

•  Tenth  Censng  of  thaU.  8.,  ToL  x.,  Repeat  on  the  Qnurr  Indnstrr,  P- 3S1  For 
3  table  showing  eesenUalljr  the  same  remilta,  aoe  Tan  Noettand's  Eni^'g  Mag.,  toU 
xlT.  p.  537. 

t  Tenth  CeniBB,  voL  X.,  Report  of  the  Qoairr  JnAtMzj,  p.  SSG. 


ovGoQi^lc 


A[{T.   2.]  DURABILITT  OF  sniLDINQ  BT0NB8.  33 

S3.  Effect  of  the  Atmoaphere.  To  determine  the  effect  of  the 
atmosphere  of  a  Urge  city,  where  coal  ia  used  for  fuel,  soak  clean 
«inall  pieces  of  the  stone  for  several  days  in  water  which  contains  one 
per  cent,  of  sulphuric  and  hydrochloric  acids,  agitating  frequently. 
If  the  stone  contains  any  earthy  matter  likely  to  be  dissolved  by  the 
gases  of  the  atmosphere,  the  water  will  be  more  or  less  cloady  or 
mnddy.    The  following  results  were  obtained  by  this  method:  * 

BslatlTS  Ratio  of  LOM. 

White  brick 1 

Bed  brick S 

NovaBcolta  atone ft 

Brown-sloae 80 

34.  Microsoopical  Examinatioo.  It  is  now  held  that  the  best 
method  of  determining  the  probable  durability  of  a  building  stone 
is  to  study  its  surface,  or  thin,  transpai-ent  slices,  under  a  micro- 
scope. This  method  of  study  in  recent  years  has  been  most  fruit- 
ful in  developing  interesting  and  vainable  knowledge  of  a  scientifio 
and  truly  practical  character.  An  examination  of  a  section  by  means 
of  the  microscope  will  show,  not  merely  the  various  substances  which 
compose  it,  bnt  also  the  method  according  to  which  they  are 
arranged  and  by  which  they  are  attached  to  one  another.  For 
example,  "pyrites  ia  considered  to  be  the  enemy  of  the  quarryman 
and  constructor,  since  it  decomposes  with  ease,  bnd  stains  and  dis* 
colors  the  rock.  Pyrites  in  sharp,  well-defined  crystals  sometimes 
decomposes  with  great  difficulty.  If  a  crystal  or  grain  of  pyrites  is 
embedded  in  soft,  porous,  light-colored  sandstones,  like  those  which 
come  from  Ohio,  its  presence  will  with  certainty  soon  demonstrate 
itself  by  the  black  spot  which  will  form  about  it  in  the  porons 
stone,  and  which  will  permanently  disfigure  and  mar  its  beauty. 
If  the  same  grain  of  pyrites  is  situated  in  a  very  hard,  compact,  noU' 
absorbent  stone,  the  constituent  minerals  of  which  are  not  rifted  or 
cracked,  this  grain  of  pyrites  may  decompose  and  the  products  be 
washed  away,  leaving  the  stone  untarnished." 

36.  KETEODB  of  Pbesebtiho.  Yitruvins,  the  Boman  architect, 
two  thousand  years  ^o  recommended  that  stone  should  be  quarned 
in  summer  when  driest,  and  that  it  should  be  seasoned  by  being 
allowed  to  lie  two  years  before  being  used,  so  as  to  allow  the  nataial 

*  Tenth  Ccmsni,  toL  z^  fieport  on  the  Qtuur;  ludaaOT,  p.  381 


ovGoQi^lc 


24  NATURAL  BTONE.  [CHAF.   1. 

Bap  to  evaponite.  It  is  a  notable  fact,  tbat  in  the  erection  of  St 
Fanl's  Cathedral  in  London,  England,  Sir  Christopher  Wren  re- 
quired  that  the  stone,  after  being  quarried,  should  be  exp(»ed  for 
three  years  on  the  sea-beach,  before  its  introduction  into  th& 
building. 

The  surfaces  of  buildings  are  often  covered  vith  a  coating  of 
paintj  coal-tar,  oil,  panifiBne,  soap  and  alum,  rosin,  etc.,  to  preeerTo, 
them. 

Another  method  of  treatment  consists  in  bathing  the  st^ine  ia 
euccessive  solutions,  the  chemical  actions  bringing  about  the  forma- 
tion of  JDBoluble  silicates  in  the  pores  of  the  stone.  For  example,  if 
a  stone  front  is  first  washed  with  an  alkaline  fluid  to  remove  dirt,. 
and  this  followed  by  a  succession  of  baths  of  silicate  of  soda  or 
potash,  and  the  surface  is  then  bathed  in  a  solution  of  chloride  of 
lime,  an  insoluble  lime  silicate  is  formed.  The  soluble  salt  is  then 
washed  away,  and  the  insoluble  silicate  forms  a  durable  cement  and 
checks  disintegration.  If  lime-water  is  substituted  for  chloride  ot 
lime,  there  is  no  soluble  chloride  to  wash  away. 

There  are  a  great  many  applications  that  have  been  used  for  the 
prevention  of  the  decay  of  building  stones,  as  paint,  oil,  coal-tar, 
bees-wax,  rosin,  paraffine,  etc.,  and  numerous  chemical  preparations 
similar  to  that  mentioned  in  the  paragraph  just  above ;  but  all  are 
expensive,  and  none  have  proved  fairly  satisfactory.* 

It  has  already  been  stated  that,  in  order  to  resist  the  eSects  of 
both  pressure  and  weathering,  a  stone  should  be  placed  on  its  nat- 
□ral  bed.  This  simple  precaution  adds  considerably  to  the  dara~ 
bility  of  any  stone. 


Abt.  3.  Classificatioit  akd  Deschiption  of  Bcildinq  Stones. 

36.  CUBsmoAtloV.  Building  stones  are  variously  classified 
according  to  geological  position,  physical  structure,  oud  chemical 
composition. 

37.  OeaJ<^cal  Classification.  The  geological  position  of  rocks 
iias  but  little  connection  with  their  properties  aa  building  materials. 
As  a  general  rule,  the  more  ancient  rocks  are  the  stronger  and  the 

*  For  on  elaborate  and  valuable  article  by  Prof.  Eggleston  on  the  causes  ot  il«cap 
and  the  metbods  of  preserrtng  building  aloDes,  see  Trans.  Am,  8oc.  of  C.  S.,  voL 
XT.  pp'  UT-TM ;  and  for  a  disciiaBloa  on  the  same,  see  Baine  volume,  pp.  TD5-1S. 


ovGoQi^lc 


ART.   3.]  DBSCBIPTIOH  OF  BUILDINQ  STONES.  35 

more  darable ;  but  to  this  there  are  many  ezoeptions.  Accordjt^ 
to  the  Qsoal  geological  claaaification,  rocks  are  divided  into  igneons, 
metamorphic,  and  aedimentary.  Qreenstone,  basalt,  and  lava  are 
eiampleB  of  igneoae  rocks ;  granite;  marblo,  and  slate,  of  meta- 
morphic ;  and  sandBtone,  limeBtoae,  and  clay,  of  sedimentary.  Al- 
though clay  can  hardly  be  classed  with  building  stones,  it  is  not 
entirely  oat  of  place  in  this  connection,  since  it  is  employed  in 
making  bricks  and  cement,  which  are  important  elements  of 
masonry. 

38.  Fhyaioal  Claasifloation.  With  respect  to  the  atmctnral 
character  of  large  masses,  rocks  are  divided  into  stratified  and  aa- 
Btratifled. 

la  their  more  iniaute  structure  the  unstratified  rocks  present, 
for  the  most  part,  an  aggregate  of  crystalline  grains,  firmly  adhering 
together.    Granite,  trap,  basalt,  and  lava  are  examples  of  this  class. 

In  the  more  minute  structure  of  stratified  rocks,  the  following 
Tarieties  are  distinguished :  1.  Compact  crystalline  structure ;  ac- 
companied by  great  strength  and  durability,  as  in  quartz-rock  and 
marble.  2.  Slaty  structure,  easily  split  into  thin  layers ;  accom- 
panied by  both  extremes  of  strength  and  durability,  clay-elate  and 
hornblende-slate  being  the  strongest  and  most  durable.  3.  The 
granular  cry</oiiine,. structure,  in  which  crystalline  grains  either 
adhere  firmly  together,  as  in  gneiss,  or  are  cemented  into  one  masi 
by  some  other  material,  ae  in  sandstone ;  accompanied  by  all  degree* 
of  compactness,  porosity,  strength,  and  durability,  the  lowest  ex- 
treme being  sand.  4.  The  compact  granular  structure,  in  which 
the  grains  are  too  small  to  be  visible  to  the  unaided  eye,  as  in  blue 
limestone  ;  accompanied  by  considerable  strength  and  durability. 
fi-  Porous,  granular  structure,  in  which  the  grains  are  not  crystal* 
line,  and  are  often,  if  not  always,  minute  shells  cemented  together; 
Accompanied  by  a  low  degree  of  strength  and  durability.  6.  The 
conglomerate  structure,  where  fragmente  of  one  material  are  embed- 
ded in  a  mass  of  another,  as  graywacke;  accompanied  by  all  degrees 
of  strength  and  durability. 

A  study  of  the  fractured  surface  of  a  stone  is  one  means  of 
determining  its  structural  character.  The  even  fracture,  when  the 
surfaces  of  division  are  pianos  in  definite  positions,  is  characteristic 
of  a  cryetaUine  structure.  The  uneven  fracture,  when  the  broken 
nirface  presents  sharp  projections,  is  characteristic  of  a  granular 


ovGoQi^lc 


CO  NATUEAL   STOKE.  [CHAP.    I. 

BtixLctare.  The  slaty  fracture  gives  an  even  aar&oe  for  planes  ol 
divisioQ  parallel  to  the  lamination,  and  uneven  for  other  directions 
of  division.  The  conchoidal  fracture  preeeitts  smooth  concave  and 
'wnvex  surfaces,  and  is  characteristic  of  a  hard  and  compact  atrnct- 
are.  The  earthy  fracture  leaves  a  roagh,  dull  snrbce,  and  indi- 
cates Boftress  and  brittleaesa. 

'  39.  Chemical  Clauifloation.  Stones  are  divided  into  three 
classes  with  respect  to  their  chemical  composition,  each  distin- 
guished by  the  earth  which  forms  its  chief  constituent ,  viz.,  sili- 
ceous stones,  argillaceous  stones,  and  calcareous  Etoues. 

Siliceous  Stones  ore  those  in  which  silica  is  the  characteristic  earthy 
constituent.  With  a  few  exceptions  their  structure  is  crystalline- 
granular,  and  the  crystalline  grains  contained  in  them  are  hard  and 
durable ;  hence  weakness  and  decay  iu  them  generally  arise  from 
the  decomposition  or  disintegration  of  some  softer  and  more  perish- 
able material,  by  which  the  grains  are  cemented  together,  or,  when 
they  are  porous,  by  the  freezing  of  water  in  their  pores.  The  prm- 
«ipal  siliceous  stones  are  granite,  syenite,  gneiBS,  mica-slate,  green- 
stone, baealt,  trap,  porpliyry,  quartz-rook,  hornbleude-alate,  ana 
sandstone. 

Argillaceous  or  Clayey  Stones  are  those  in  which  alnmina,  although 
it  may  not  always  be  the  most  abundant  constituent,  exiets  in  suf- 
ficient quantity  to  give  the  stone  its  characteristic  properties.  The 
principal  kiuds  are  slate  and  graywacke-slatsk 

Calcareous  Stones  are  those  in  which  carbonate  of  lime  pre- 
dominates. They  eflorveace  with  the  dilute  mineral  acids,  which 
oombine  with  the  lime  and  set  free  carbonic  acid  gas.  Sulphurio 
acid  forms  an  insoluble  compound  with  the  lime.  Nitric  and  mu- 
riatic acids  form  compounds  with  it,  which  are  soluble  iu  water. 
By  the  action  of  intense  heat  the  carbonic  acid  is  expelled  in  gas- 
eous form,  and  the  lime  is  left  in  its  caustic  or  alkaline  state,  when 
it  is  called  quicklime.  Some  calcareous  stones  consist  of  pure  car- 
bonate of  lime ;  in  others  it  is  mixed  with  sand,  clay,  and  oxide 
of  iron,  or  combined  with  carbonate  of  magnesia.  The  durability 
of  calcareous  stones  depends  upon  their  compactness,  those  which 
are  porous  being  disintegrated  by  the  freezing  of  water,  and  by  the 
chemical  action  of  an  acid  atmosphere.  They  are,  for  the  most 
part,  easily  wrought.     The  principal  calcareous  stones  are  nurble, 


ovGoQi^lc 


AKT.    3,]  DESCaiPTIOS    OF   BUILDIKO  STONES.  37 

«ompact  limeetone,  granul&r  limestone  (the  calcareous  stone  of  tht 
geological  classification),  fiad  magnesian  limeBtone  or  dolomite. 

40.  SlHBIPTIOV  OF  BuiLDDie  BTOITZB.  A  few  of  the  mora 
prominent  classes  of  building  stones  will  now  be  briefly  deecribed. 

41.  Trap.  Although  trap  is  the  strongest  oi  builiiing  material^ 
and  exceodingly  durable,  it  is  little  used,  owing  to  the  great  diffi- 
culty with  which  it  is  quarried  and  wrought.  It  ia  an  exceedingly 
tough  rock,  and,  being  generally  without  cleav^e  oi-  bedding,  is 
especially  intractable  under  the  hammer  or  chisel.  It  is,  however, 
fometimes  used  with  excellent  effect  in  cyclopean  architecture,  the 
blocks  of  various  shapes  and  sizes  being  fitted  together  with  no 
effort  to  form  regular  courses.  The  "  Palisades"  (the  bluff  skirting 
the  western  shore  of  the  Hudson  River,  opposite  and  above  New 
York)  are  composed  of  trap-rock, — much  used  for  road-metal,  street 
pavements,  and  railroad  ballast. 

42.  Granite.  Granite  is  the  strongest  and  most  durable  of  all 
ihe  stones  in  commpn  use.  It  generally  breaks  with  regularity, 
and  may  be  quarried  in  simple  shapes  with  facility  ;  but  it  ia  ex- 
tremely hard  and  tough,  and  therefore  can  only  be  wrought  into 
elaborate  forme  with  a  great  expenditore  of  labor.  For  this  reason 
the  use  of  granite  is  somewhat  limited.  Its  strength  and  durability 
commend  it,  however,  for  foundations,  docks,  piers,  eta,  and  for 
massive  buildings ;  and  for  these  purposes  it  is  in  nse  the  world 
over. 

The  larger  portion  of  our  granites  are  some  shade  of  gray  in 
color,  though  pink  and  red  varieties  are  not  uncommon,  and  black 
Tarieties  occasionally  occur.  They  vary  in  texture  from  very  fine 
«nd  hom<^;eneous  to  coarsely  porphyritio  rocks,  in  which  the  indi- 
vidual grains  are  an  inch  or  more  in  length.  Excellent  granites  are 
ionnd  in  New  England,  throughout  the  Alleghany  belt,  in  the 
Rocky  Mountains,  and  in  the  Sierra  Nevada.  Very  large  granite 
,  ijuarrioe  exist  at  Vinalhaven,  Maine ;  Gloucester  and  Quincy,  Ma^ 
sachoeette;  and  at  Concord,  New  Hampshire.  These  quarries  fur- 
nish nearly  all  the  granite  nsed  in  this  country.  An  excellent 
granite,  which  ie  largely  nsed  at  Chicago  and  in  the  Northwest,  is 
found  at  St.  Olond,  Minnesota. 

At  the  Vinalhaven  quarry  a  single  block  300  feet  long,  20  feet 
vide^  and  6  to  10  feet  thick  was  blasted  out,  being  afterwards  broken 
tip.     Until  recently  the  largest  single  block  ever  quarried  and 


ovGoQi^lc 


ZB  HATCRAL  8T0SB,  [CQAP.    tt 

dressed  in  tbiB  conntrj  was  that  used  for  the  General  Wool  Mcnn- 
ment,  now  in  Troy,  New  York,  which  measured,  when  completed,. 
60  feet  in  he^ht  bj  5^  feet  square  at  the  baae,  being  only  9  feet 
shorter  than  the  Egyptian  Obelisk  now  in  Central  Park,  New  York> 
la  1887  the  Bodwell  Qranite  Company  took  ont  from  ita  qDarrieB  in: 
Maine  a  granite  shaft  115  feet  long,  10  feet  square  at  the  base,  and 
weighing  850  tons.  It  is  claimed  that  this  is  the  largest  single 
quarried  stone  on  record. 

43.  Marbles.  In  common  langnage,  any  limestone  which  will  take' 
a  good  polish  is  called  a  marble  ;  but  the  name  is  properly  applied 
only  to  limestones  which  have  been  exposed  to  metamorphic  action,, 
and  have  thereby  been  rendered  more  crystalline  in  texture,  and 
have  had  their  color  more  or  less  modified  or  totally  removed. 
Marbles  exhibit  great  diversity  of  color  and  texture.  They  are- 
pure  white,  mottled  white,  gray,  blue,  black,  red,  yellow,  or  mot- 
tled with  various  mixtures  of  these  colors.  Marble  is  confessedly 
the  moat  beautiful  of  all  building  materials,  but  is  chiefly  employed 
for  interior  decorations. 

44,  Iiimeitoues.  Limestones  are  composed  chiefly  or  Li^^ly  of 
carbonate  of  lime.  There  are  many  varieties  of  limestone,  which 
difFer  in  color,  composition,  and  value  for  engineering  and  building 
purposes,  owing  to  the  differences  in  the  character  of  the  deposita 
and  chemical  combinations  entering  into  them^  "If  the  rock  is 
compact,  fine-grained,  and  has  been  deposited  by  chemical  agencies, 
we  have  a  variety  of  limestone  known  as  travertine.  If  it  contains 
much  sand,  and  baa  a  more  or  less  concfaoidal  fracture,  we  have  a 
siliceous  limestone.  If  the  silica  ia  very  fine-grained,  it  is  hom- 
stona  If  the  silica  is  distributed  in  nodules  or  flakes,  either  in 
seams  or  throughout  the  mass,  it  is  cherty  limestone;  if  it  contains 
sihca  and  clay  in  about  equal  proportions,  hydraulic  limestone ;  if 
clay  alone  is  the  principal  impurity,  argillaceous  limestone ;  if  iron 
is  the  principal  impurity,  ferruginous  limestone  ;  if  iron  and  clay 
exceed  the  lime,  ironstone.  If  the  ironstone  is  decomposed,  and 
the  iron  hydrntcd,  it  is  rottcnstone;  if  carbonate  of  magnesia  forms 
one  third  or  less,  magnesian  limestone  ;  if  carbonate  of  magnesia 
forms  more  than  one  third,  dolomitic  limestone." 

The  lighter-colored  and  fine-grained  limestones,  when  sawed  and 
used  as  ashlars,  are  deservedly  esteemed  as  among  our  best  building 
materials.     The;  are,  however,  less  easily  and  accurately  worked 


ovGoQi^lc 


ART.  3.]  DE8CEIPTI0N   OF    BL'ILllINO  STONES.  29 

under  tiie  chisel  than  BandBtones,  and  for  this  reason  and  their 
greater  rarity  are  &a  less  generally  nsed.  The  gray  limestones,  like 
that  of  Lockport,  New  York,  when  hammer-dressed,  have  the  ap- 
pearance of  light  granite,  and,  mnce  they  are  easily  wrought,  they 
are  advantageously  used  for  trimmings  in  buildings  of  brick. 

Some  of  the  softer  limestones  possess  qualities  which  Bpecially 
commend  them  for  bailding  material?.  For  example,  the  cream- 
colored  limestone  of  the  Paris  basin  {calcaire  grassier)  is  so  soft  that 
it  may  be  dressed  with  great  facility,  and  yet  hardens  on  exposure, 
and  is  a  durable  stone.  Walls  laid  up  of  this  material  are  frequently 
planed  down  to  a  common  surface,  and  elaborately  ornamented  at 
«mall  expense.  The  Topeka  stone,  found  and  now  largely  nsed  in 
Kansas,  has  the  same  qualities.  It  may  be  sawed'  out  in  blocks 
Almost  as  easily  as  wood,  and  yet  is  handsome  and  durable  when 
placed  in  position.  The  Bermuda  stone  and  eoquina  are  treated  in 
the  same  way. 

Large  quantities  of  limestones  and  dolomites  are  quarried  in 
nearly  all  of  the  Western  States.  These  are  mostly  of  a  d^II  grayish 
color,  and  their  uses  are  chiefly  local.  The  light-colored  oolitio 
limestone  of  Bedford,  Indiana,  is,  however,  an  exception  to  this 
rule.  Not  only  are  the  lasting  qualities  fair  and  the  color  pleasing, 
but  its  fine  even  grain  and  softness  render  it  admirably  adapted  for 
carved  work.  It  has  been  very  widely  used  within  the  last  few 
years.  This  stone  is  often  found  in  layers  20  and  30  feet  thick,  and 
is  much  used  for  bridge  piers  and  other  massive  work.  There  ai-e 
noted  limestone  quarriesat  Dayton  and  Sandusky,  Ohio;  at  Bedford, 
Ellettsville,  and  Salem,  Indiana;  at  Joliot,  Lemont,  Orafton,  and 
Chester,  Illinois;  and  at  Cottonwood,  Kansas. 

46.  Sandstoaes.  "  Sandstones  vary  much  in  color  and  fitness  for 
architectural  purposes,  but  they  include  some  of  the  most  beautiful, 
durable,  rnd  highly  valued  materials  used  in  construction.  What- 
ever their  differences,  they  have  this  in  common,  that  they  are 
chiefly  composed  of  sand — that  is,  grains  of  quartz — to  a  greater  or 
less  degree  cemented  and  consolidated.  They  also  frequently  con- 
tain other  ingredients,  as  lime,  iron,  alumina,  manganese,  etc,  by 
which  the  color  and  texture  are  modified.  Where  a  sandstone  is 
composed  exclusively  of  grains  of  quartz,  without  foreign  matter,  it 
may  be  snow-white  in  color.  Examples  of  this  variety  are  known 
in  miiny  localities.     They  are  rarely  nsed  for  building,  though  capa* 


ovGoQi^lc 


30  NATURAL  8T0HB.  [OHAP.   I. 

ble  ot  feeing  employed  for  that  purpose  with  excellent  effect.  They 
bnye  been  more  generally  valued  as  famishing  material  fortheman- 
niacture  of  glass.  The  color  of  sandstones  is  frequently  bright  and 
handsome,  and  couBtitntes  one  of  the  many  qualities  which  have 
rendered  them  so  popular.  It  is  UBually  caused  by  iron;  when  gray, 
blue,  or  green,  by  the  protoxide,  as  carbonate  or  silicate ;  when 
brown,  by  the  hydrated  oxide ;  when  red,  by  the  anhydrous  oxide. 
The  purple  sandstones  usually  derive  tbia  shade  of  color  from  s 
amall  quantity  of  manganese. 

"  The  texture  of  sandstones  varies  with  the  coarseness  of  the 
sand  of  which  they  are  composed,  and  the  degree  to  which  it  is  con- 
solidated. Usually  the  material  which  unites  the  grains  of  sand 
is  silica;  and  this  is  the  best  of  all  cements.  This  silica  has  been 
deposited  from  solntion,  and  sometimes  fills  &I1  the  interstices  be> 
tween  the  grains.  If  the  process  of  consolidation  has  been  carried 
fill  enough,  or  the  quartz  grains  have  been  cemented  by  fusion,  the 
sandstone  is  converted  into  quartzite, — one  of  the  strongest  and  most 
dnrable  of  rocks,  but,  in  the  ratio  of  its  compactness,  difBcult  to- 
work.  Lime  and  iron  often  act  as  cements  in  sandstones,  but  both- 
are  more  soluble  and  less  strong  than  silica.  Hence  the  finest  and 
most  indestructible  sandstones  are  such  as  consist  exclusively  of 
~  grains  of  quartz  united  by  siliceous  cement.  In  some  sandstones 
part  of  the  grains  are  fragments  of  feldspar,  and  these,  being  liable 
to  decomposition,  are  elements  of  weakness  in  the  stone.  The  very 
fine-grained  sandstones  often  contain  a  lat^e  amount  of  clay,  and 
thus,  though  very  haiidsome,  are  generally  less  strong  than  those- 
which  are  more  purely  siliceous. 

"  The  durability  of  sandstones  varies  with  both  their  physical 
and  chemical  composition.  When  nearly  pure  silica  and  well  ce- 
mented, sandstones  are  as  resistant  to  weather  as  granite,  and  very 
much  less  affected  by  the  action  of  fire.  Taken  as  a  whole,  they 
may  be  regarded  as  among  the  most  dnrable  of  building  materials. 
When  first  taken  from  the  quarry,  and  saturated  with  quarry  water 
(a  weak  solution  of  silica),  they  are  frequently  very  soft,  but  on  ex- 
posure become  much  harder  by  the  precipitation  of  the  soluble  silica 
contained  in  them. 

48.  "Since  they  form  an  important  part  of  all  the  groups  of 
sedimentary  rocks,  sandstones  are  abundant  in  nearly  all  countries; 
EUid  as  they  are  quarried  with  great  ease,  and  are  wrought  with  th» 


ovGoQi^lc 


ART.   3.]  DBSCRIPTIOK   07  BUILDING  810X18.  3t 

hammer  and  ofaiael  vith  much  greater  facility  than  limeatonesr 
grauitee,  and  moat  other  kinds  of  rocks,  these  qualities,  joined  to 
their  rarioas  and  pleasant  colors  and  their  durability,  hare  mada 
them  the  most  popular  and  nsefnl  of  building  stonea.  In  the 
United  States,  we  hare  a  rer;  large  number  of  sandBtonea  which  are 
"jxtensively  used  for  building  purposes. 

"  Among  these  may  be  mentioned  the  Dorchesier  stove  of  New 
Brnnswiok,  and  Brown-stone  of  Connecticut  and  New  Jersey. 
These  have  been  much  used  in  the  boiIdingB  of  the  Atlantic  cities. 
The  latter  has  been  very  popular,  but  experience  has  shown  it  to  b& 
Berioualy  lackiug  in  durability. 

"  Among  the  sandstones  most  frequently  employed  in  the  build- 
ing of  the  interior  are  : — 

1.  "  The  Ohio  stone,  derived  from  the  Berea  grit,  a  member  of 
the  Lower  Carboniferous  series  in  Northern  Ohio.  The  principal 
quarries  are  located  at  Amherst  and  Berea.  The  stone  from  Am- 
herst IB  generally  light  drab  in  color,  Tory  homogeneous  in  testure„ 
and  composed  of  nearly  pure  silica.  It  is  very  resistant  to  fire  and 
weathering,  and  is,  on  the  whole,  one  of  the  best  and  handsomest 
building  stones  known.  The  Berea  stone  is  lighter  in  color  than 
tiie  Amherst,  but  sometimes  contains  sulphide  of  iron,  and  is  then 
liable  to  stain  and  decompose. 

2.  '■'  The  Waverly  sandstone,  also  derived  from  the  Lower  Car- 
tioniferona  seriea,  comes  from  Southern  Ohio.  This  is  a  fine- 
grained hom<^neous  stone  of  a  light-drab  or  dove  color,  works  with 
facility,  and  is  very  handsome  and  durable.  It  forms  the  material 
of  which  many  of  the  finest  buildings  of  Cincinnati  are  constructed, 
and  is,  justly,  highly  esteemed  there  and  elsewhere. 

3.  "  The  Lake  Superior  sandstone  is  a  dark,  piirpliah-brown 
stone  of  the  Potsdam  ago,  quarried  at  Bass  Island,  Marquette,  etc 
This  is  rather  a  coarse  stone,  of  medium  strength,  but  homogeneous 
and  durable,  and  one  much  used  in  the  Lake  cities. 

4.  "TheBt.  ffeneftefti  s/one  is  a  fine-grained  sandstone  of  a  del- 
icate drab  Or  straw  color,  very  homogeneous  in  tone  and  texture. 
It  is  quarried  at  St.  Genevieve,  Missouri,  and  is  one  of  the  hand- 
somest of  all  our  sandstones. 

6.  "  The  Medina  sandstone,  v\ao)y  forms  the  base  of  the  Upper 
Silurian  seriefi  in  Western  New  York,  furnishes  a  remarkably  strong 


ovGoQi^lc 


32  katural  stoke.  [chap,  l 

And  dnrable  stone,  mncii  used  forpaTement  and  corbing  in  the 
Luke  cities. 

6.  "  The  coal-measures  of  Pennsylvania,  Ohio,  and  other  Western 
States  sapply  exceUent  Bandstonee  foT  building  purposes  at  a  large 
number  of  localities.  These  vary  in  color  from  white  to  dark  red 
or  purple,  though  generally  gray  or  drab.  While  strong  and 
durable,  they  are  mostly  coarser  and  less  handsome  than  the  sand- 
stones which  have  been  ennmerated  above.  This  is  the  scarce  from 
which  are  derived  the  sandstones  used  in  purely  engineering  stmct- 
nres. "  • 

47.  Other  Hames.  There  is  a  great  variety  of  names  of  more 
or  less  local  application,  derived  from  the  appearance  of  the  stone, 
the  use  to  which  it  is  put,  etc.,  which  it  would  be  impossible  to 
classify.  The  same  stone  often  passes  under  entirely  different 
names  in  difEerent  localities;  and  stones  entirely  different  in  their 
«ssential  characteristics  often  pass  under  the  same  name. 

48.  LocATloir  of  ftlTAKBlzs.  For  information  coaceming  the 
location  of  quarries,  character  of  product,  etc.,  see:  Tenth  Censas 
«f  the  U.  S.,  Vol.  X,  Beport  on  Quarry  ludnstry,  pp.  107-363; 
Report  of  Smithsonian  Institution,  1885-86,  Part  II,  pp.*357-^488; 
Merrill's  Stones  for  Building  and  Decoration,  pp.  45-312 — substan- 
tially the  same  as  the  preceding — and  the  reports  of  the  various 
State  geological  surveys. 

49.  Cost.    See  §§  226-38. 

•  Frirf.  1.  B.  KewbaiTT. 


ovGoQi^lc 


CHAPTER  IL 
BRICK. 

61.  Bbice  is  made  by  snbmittiiig  clay,  which  has  been  prepared 
properly  and  moulded  into  shape,  to  a  temperature  which  oonrerts 
it  into  a  semi-vitriSed  mass. 

Common  brick  is  a  moat  valuable  substitute  for  stone.  Its 
-comparative  cheapness,  the  ease  with  which  it  is  transported  and 
handled,  and  the  facility  with  which  it  ia  worked  into  structures  of 
«ny  desired  form,  are  its  valuable  characteristics.  It  is,  when  prop- 
erly made,  nearly  aa  strong  as  the  best  building  stone.  It  is  but 
slightly  affected  by  change  of  temperature  or  of  humidity;  and  ia 
also  lighter  than  stone. 

Notwithstanding  the  good  qnalities  which  recommend  brick  as 
a  substitute  for  stone,  it  is  very  little  used  in  engineering  structures. 
It  is  employed  in  the  construction  of  sewers  and  bridge  piers,  and 
for  the  lining  of  tunnels.  Brick  could  many  times  be  profitably 
sabstituted  for  iron,  stone,  or  timber  in  engineering  Btructnres. 
This  is  especially  true  since  recent  improvements  in  the  process  of 
manufacture  have  decreased  the  cost  while  they  have  increased  the 
'quality  and  the  uniformity  of  the  product.  The  advantages  of 
employing  brick-work  inst(«d  of  stone  masonry  will  be  discussed  in 
■connection  with  brick  masonry  in  Chapter  VIII.  Probably  one 
thing  which  has  prevented  the  more  general  use  of  brick  in  engi- 
neering is  the  variable  quality  of  the  product  and  the  trouble  of 
proper  inspection. 

S2.  Fbocssb  of  XAvrrTAcnmE.  The  Clay.  The  quality  of  the 
brick  depends  primarily  upon  the  kind  of  clay.  Common  clays,  of 
which  the  common  brick  is  made,  consist  principally  of  silicate  of 
alumina;  bat  they  also  usually  contain  lime,  mf^nesia,  and  oxide 
of  iron.  The  latter  ingredient  is  useful,  improving  the  product  by 
giving  it  hardness  and  strength;  hence  the  red  brick  of  the  Eastern 
States  18  often  of  better  quality  than  the  white  and  yellow  brick 
jnade  in  the  West.     Silicate  of  lime  renders  the  clay  too  fusible,' 


ovGoQi^lc 


34  BEICK.  [CHAP.  II. 

and  causes  the  bricks  to  soften  and  to  become  distorted  in  tbe  pro- 
cees  of  buming.  Carbonate  of  lime  is  certain  to  decompose  iii 
bnrning,  and  tbe  caustic  lime  left  behind  absorbs  moistare,  prevents 
the  adherence  of  the  mortar,  and  promotes  disintegration. 

Uncombined  silica,  if  not  in  excess,  is  beneficial,  as  it  preserres 
the  form  of  the  briclc  at  high  temperatures.  In  excess  it  destroys 
the  cohesion,  and  renders  the  bricks  brittle  and  weak.  Twenty-fira 
per  cent,  of  silica  is  a  good  proportion. 

63.  Moulding.  Id  the  old  process  the  cla;  is  tempered  with 
water  and  mixed  to  a  plastic  state  in  a  pit  with  a  tempering  wheel, 
or  in  a  primitive  pug-mill;  and  tlaen  the  soft,  plastic  clay  is  pressed 
into  the  moulda  by  band.  This-  method  is  so  slow  and  laborioaa 
that  it  has  beeu  almost  entirely  displaced  by  more  economical  and 
expeditious  ones  in  which  the  work  ia  done  wholly  by  machinery. 
There  is-  a  great  variety  of  machines  for  preparing  and  moulding 
the  clay,  which,  however,  may  be  grouped  into  three  classes,  accord- 
ing to  the  condition  of  the  clay  when  moulded:  (1)  soft-mud 
machines,  for  which  the  clay  is  reduced  to  a  soft  mud  by  adding 
about  one  quarter  of  its  volume  of  water;  (S)  stiff-mud  machines, 
for  which  the  clay  <■;  reduced  to  a  stiff  mud;  and  (8)  dry-clay 
machines,  with  which  the  dry,  or  nearly  dry,  clay  is  forced  into  the 
moulds  by  a  heavy  pressure  without  having  been  reduced  to  a  plastic 
mass.  These  machines  may  also  be  divided  into  two  classes,  aocord* 
ing  to  tlie  method  of  filling  the  moulds:  (1)  Those  in  which  a  con- 

.  ttnuons  stream  of  clay  is  forced  from  the  pug-mill  through  a  die 
and  is  afterwards  cut  up  into  bricks;  and  {'i)  those  in  which  the 
clay  is  forced  into  moulds  moving  under  the  nozzle  of  the  pug-mill. 

64.  Burning.     The  time  of  burning  varies  with  the  character  of 
/the  clay,  the  form  and  size  of  kiln,  and  the  kind  of  fuel.     With  the 

older  processes  of  burning,  the  brick,  when  dry  enough,  is  built  up 
in  sections — by  brick -makers  called  "  arches, " — which  are  usually 
about  5  bricks  {3i  feet)  wide,  30  to  40  bricks  (30  to  30  feet)  deep, 
and  from  35  to  50  courses  high.  Each  section  or  "arch"  has  an 
opening— called  an  "eye" — at  the  bottom  in  the  center  of  its  width, 
which  runs  entirely  through  the  kiln,  and  in  which  the  fuel  used  in 
burning  is  placed.  After  the  bricks  are  thus  stacked  up,  tbe  entire 
pile  is  enclosed  with  a  wall  of  green  brick,  and  the  joints  between 
the  casing  bricks  are  carefnlly  stopped  with  mud.  Bumiug,  includ- 
ing drying,  occupies  from  6  to  15  days.     The  brick  ia  first  subjected 


D.qitizeabyG00l^lc 


CLASSIFICATION   OF   COUUON   BBICE.  &^ 

to  a  moderate  heat,  and  when  all  moistnre  has  been  expelled,  the 
heat  i8  increased  slowly  until  the  "arch-brick,"  i.  e.,  those  next  to 
the  "eye,"  attain  a  white  heat.  This  temperature  is  kept  up  until 
the  burning  is  complete.  Finally,  all  oponinga  are  closed,  and  tha 
mass  slowly  cools. 

With  the  more  modeiii  processes  of  burning,  the  principal  yards 
have  permanent  kilns.  These  are  usually  either  a  rectangular  space 
eurronnded,  except  for  very  wide  doors  at  the  ends,  by  permanent 
brick  walls  having  fire-boxes  on  the  outside;  or  the  kiln  may  bo 
entirely  enclosed — above  as  well  as  on  the  sides — with  brick  masonry. 
The  latter  are  usaally  circular,  and  are  sometimes  made  in  com- 
partments, each  of  which  has  a  separate  entrance  and  independent 
connection  with  the  chimney.  The  latter  may  be  built  within  the 
kiln  or  entirely  outside,  but  a  downward  draught  is  invariably 
secured.  The  fuel,  nsnally  fine  coal,  is  placed  near  the  top  of  the 
kiln,  and  the  down  draught  causes  a  free  circulation  of  the  fiame 
and  heated  gases  about  the  material  being  burned.  While  some 
compartments  are  being  fired  others  are  being  filled,  and  still 
others  are  being  emptied. 

55.  FiBE  Buck.  Fire  bricks  are  osed  whenever  very  higb 
temperatures  are  to  be  resisted.  They  are  made  either  of  a  veiy 
nearly  pure  clay,  or  of  a  mixture  of  pure  clay  and  clean  sand,  or,  in 
rare  casee,  of  nearly  pure  silica  cemented  with  a  small  propoition 
,  of  clay.  The  presence  of  oxide  of  iron  is  very 'injurious,  and,  as  a 
rnle,  the  presence  of  G  per  cent,  justifies  the  rejection  of  the  brick. 
In  specifications  it  should  generally  be  stipulated  that  fire  brick 
should  contain  less  than  6  per  cent,  of  oxide  of  iron,  and  less  tliao 
an  aggregate  of  3  per  cent,  of  combined  lime,  soda,  potash,  and 
ma^csia.  The  sulphide  of  iron — pyrites — is  even  worse  in  its 
effect  on  fire  brick  than  the  substances  first  named. 

When  intended  to  resist  only  extremely  high  heat,  silica  should 
be  in  excess;  and  if  to  be  exposed  to  the  action  of  metallic  oxides, 
which  would  tend  to  unite  with  silica,  alumina  should  be  in  excess. 

Good  fire  brick  should  be  uniform  in  size,  regular  in  shape, 
homogeneous  in  textnre  and  composition,  eaeily  cat,  strong,  and 
infasible. 

66.  CLAMincATioH  07  COHOir  Bbiok.  Bricks  are  classified 
according  to  (1)  the  way  in  which  they  are  moulded;  (H)  their 
position  In  the  kiln  while  being  burned;  and  (3)  their  form  or  use. 


ovGoQi^lc 


96  BBicE.  [chap.  n. 

■I-  The  method  of  moulding  givee  rise  to  the  following  terms: 

8o/t-mud  Brick.  One  moulded  from  claj  which  has  been  reduced 
to  &  soft  mnd  by  adding  water.  It  may  be  either  hand-monlded  or 
machine-monl  ded. 

Sliff-mud  Brick,  One  moulded  from  clay  in  the  condition  of 
stift  mud.     It  is  always  machine-moulded. 

Pressed  Brick.     One  moulded  from  dry  or  semi-dry  clay. 

Re-pressed  Brick,  A  soft-mud  brick  which,  after  being  par- 
tially dried,  has  been  subjected  to  an  enormous  pressure.  It  is 
ako  called,  but  less  appropriately,  pressed  brick.  The  object  of 
the  re-preaeing  is  to  render  the  form  more  regular  and  to  increase 
the  strength  and  density. 

Slop  Brick.  In  moulding  brick  by  hand,  the  monlds  are  some- 
times dipped  into  water  just  before  being  filled  with  clay,  to  pre- 
Tent  the  mnd  from  sticking  to  them,  Brick  moulded  by  this 
process  is  known  as  slop  brick.  It  is  deficient  in  color,  and  has  a 
■comparatively  smooth  surface,  with  rounded  edges  and  comers. 
*rhiB  kind  of  brick  is  now  seldom  made. 

Snnded  Brick.  Ordinarily,  in  making  soft-mud  brick,  sand  is 
sprinkled  into  the  moulds  to  prevent  the  clay  from  sticking ;  the 
brick  is  then  called  sanded  brick.  The  sand  on  the  surface  is  of  no 
serious  advantage  or  disadvantage.  In  hand -mo  aiding,  when  sand 
is  used  for  this  purpose,  it  is  certain  to  become  mixed  with  the  clay 
and  occur  in  streaks  in  the  finished  hrick,  which  is  very  undesira- 
ble ;  and  owing  to  details  of  the  process,  which  it  is  here  unneces- 
jwry  to  explain,  every  third  brick  is  especially  bad. 

Machine-made  Brick.  Brick  is  frequently  described  as  "ma- 
chine-made;" but  this  is  very  indefinite,  since  all  grad^  and  kinds 
are  made  by  machinei^. 

a*  When  brick  was  generally  burned  in  the  old-style  np-draught 
kiln,  the  classification  according  to  position  was  important ;  but 
with  the  new  styles  of  kilna  and  improved  methods  of  burning,  the 
quality  is  bo  nearly  uniform  throughout  the  kiln,  that  tiie  classifica- 
tion is  less  important.  Three  grades  of  brick  are  taken  from  the 
-©Id-stylo  kiln: 

A  ri'h  or  Clinker  Bricks.  Those  which  form  the  tops  and  sides  of 
the  arches  in  which  the  fire  is  built.  Being  over-hnmed  and  par- 
iially  vitrified,  they  ta%  hard,  brittle,  and  vre^k. 


ovGoQi^lc 


BEQCISITES  FOU  OOOD  BRIOE.  37 

Bodi/,  Cherry,  or  Bard  Bricks.  Those  taken  from  the  interior' 
of  the  pile.    The  best  bricks  in  the  kiln. 

Salmon,  Pale,  or  Soft  Bricks.  Those  which  form  the  exterior  of 
the  mass.  Being  underburned,  the;  are  too  soft  for  ordinary  work, 
nnlesB  it  be  for  filling.  The  terms  salmon  and  pale  refer  to  the 
color  of  the  brick,  and  hence  are  not  applicable  to  a  brick  made  of 
a  clay  that  does  not  bum  red.  Although  nearly  all  brick  clajs  burn- 
red,  yet  the  localities  where  the  contrary  is  true  are  suEBciently 
nnmeroiiB  to  make  it  desirable  to  use  a  diSerent  term  in  dcsignating- 
the  quality.  There  is,  necessarily,  no  relation  between  color,  and 
strength  and  density.  Briok-makers  naturally  iiave  a  prejudice 
against  the  term  soft  brick,  which  doubtteas  explains  the  nearly 
uniTersal  prevalence  of  the  lesa  appropriate  term — salmon. 

3.  The  form  or  use  of  toiokB  glres  rise  to  fha  fblloving  daadfr 
cation: — 

Compass  Brick.  Those  having  one  edge  ehorter  than  the  other. 
Used  in  lining  shafts,  etc. 

Feather-edge  Brick.  Those  of  which  one  edge  is  tMnner  thtut 
the  other.  Used  in  arches ;  and  more  properly,  but  leas  frequently, 
called  vouSEoif  brick. 

Face  Brick.  Those  which,  owing  to  tiniformity  of  size  and 
color,  are  snitable  for  the  face  of  the  wall  of  buildings.  Sometimet 
face  bricks  are  simply  the  bent  ordinary  brick ;  bat  generally  the 
term  is  applied  only  to  re-preased  or  pressed  brick  made  specially  tor 
this  purpose.    They  are  a  little  larger  than  ordinary  bricks  (g  62), 

Sewer  Brick.  Ordinary  hard  brick,  smooth,  and  r^alar  in 
form. 

Paving  Brick.  Very  hard,  ordinary  brick.  A  Titrifled  ola} 
block,  very  much  larger  than  ordinary  brick,  is  sometimes  used  fot 
paving,  and  is  called  a  paving  hriok,  but  mora  often,  and  more 
properly,  a  brick  paving-block. 

57.  ExqinilTU  TOB  OooD  BXIOX.  1.  A  good  brick  ehonld  have 
plane  faces,  parallel  aides,  and  ahnrp  edges  and  angles.  2.  It  should 
be  of  fine,  compact,  nniform  texture ;  shoald  be  quite  hard;  and 
should  give  a  clear  ringing  sound  when  stmck  a  sharp  blow,  3,  It 
shoald  not  absorb  more  than  one  tenth  of  ite  weight  of  water.  4. 
Its  specific  gravity  should  be  2  or  more.  5.  The  crnshing  strength 
tft  half  brick,  when  ground  fiat  and  pressed  botweec  thick  metal 


ovGoQi^lc 


38  BKiCK.  [chap.  n. 

plfttes,  shoold  be  at  least  7,000  poanda  per  square  inch.    6.  Its  mod* 
aim  of  rupture  shotild  be  at  least  1,000  pounds  per  square  inch. 

1.  lu  regularity  of  form  re-pressed  brick  racks  first,  dry-cla; 
briclE  next,  then  stifi-mud  brick,  and  soft-mud  brick  last.  Begu- 
Urit;  of  form  depends  largely  upon  the  method  of  burning. 

2.  The  compactness  and  uniformity  of  testare,  which  greatly 
inSnence  the  durability  of  brick,  depend  mainly  upon  the  method 
of  moulding.  As  a  general  rule,  hand-moulded  bricks  are  best  in 
iMb  respect,  since  the  clay  in  them  is  more  uniformly  tempered  b&- 
fore  being  moulded ;  bnt  this  advantage  is  partially  neutralized  by 
the  presence  of  sand  seams  (§  56).  Machine-moulded  soft-mud 
bricks  rank  next  in  compactness  and  uniformity  of  testnre.  Then 
oome  machine -moulded  stiff-mud  bricks,  which  Tary  greatly  in 
durability  with  the  kind  of  machine  used  in  their  maaufactnre. 
By  some  of  the  machines,  the  brick  is  moulded  in  layers  (parallel  to 
Any  face,  according  to  the  kind  of  machine),  which  are  not  thor- 
oughly cemented,  and  which  separate  under  the  action  of  the  frost. 
Jn  compactness,  the  dry -clay  "brick  comes  last.  However,  the  rela- 
tire  value  of  the  products  made  by  the  different  processes  varies 
-with  the  nature  of  the  clay  used. 

3.  The  absorptive  power  is  one  of  the  most  important  elements, 
since  it  greatly  affects  the  durability  of  the  brick,  particularly  its 
redfitance  to  the  effect  of  frost  (see  §§  31  and  33).  Very  soft,  un- 
der-burned brick  will  absorb  from  25  to  33  per  cent,  of  their  weight 
«f  water.  IVeak,  light-red  ones,  such  as  are  frequently  used  in  fill- 
ing in  the  interior  of  walls,  will  absorb  about  20  to  25  per  cent. ; 
while  the  best  brick  wilt  absorb  only  4  or  5  per  cent.  A  brick  may 
be  called  good  which  will  absorb  not  more  than  10  per  cent  See 
Table  9  (page  45). 

4.  The  specific  gravity  of  a  brick  does  not  indicate  its  quality^ 
and  depends  mainly  upon  the  amount  of  burning  and  the  kind  of 
fnel  employed.  Over-barned  arch  lirinks,  being  both  smaller  and 
heavier  than  the  better  body  bricks,  have  a  considerably  greater 
Bpecifio  gravity,  although  inferior  in  quality. 

6.  The  crashing  strength  is  not  a  certain  index  of  the  value  of  a 
brick,  although  it  is  always  one  of  the  'tems  determined  in  testing 
brick — if  a  testiog-machine  is  at  hand.  For  any  kind  of  service, 
the  durability  of  a  brick  is  of  gre»tcr  importance  than  its  ability 
to  resist  crushing, — the  latter  is  only  remotely  connected  with  doi^ 


ovGoo^^lc 


ABSORBING   POWER.  89    . 

Iiility.  Teets  of  the  crashing  etreagth  of  iudividnal  bricks  are  dw> 
fnl  only  in  comparing  different  kinds  of  brick,  and  give  do  idea  o( 
the  strength  of  walls  built  of  such  bricks  (see  §  246).  Furthermore, 
the  crushing  strength  can  not  be  determined  accurately,  since  it 
Taries  greatlv  with  the  size  of  the  specimen  and  with  the  details  of 
the  experiments  (see  §  60). 

6.  Owing  to  both  the  nature  of  the  quality  tested  and  the  facility 
with  which  sncb  a  test  can  be  made,  the  determination  of  the 
transTerse  strength  is  one  of  the  best  means  of  judging  of  the 
tioality  of  a  brick.  The  transverse  strength  depends  mainly  npon  , 
tiie  toughness  of  the  brick, — a  quality  of  prime  importance  in  bricks 
nsed  for  paving,  and  also  a  quality  greatly  affecting  the  resistance  to 
frost. 

68.  ABBOiaiKQ  POWZB.  The  less  the  amount  of  water  absorbed 
1^  a  brick  the  greater,  in  all  probability,  will  be  its  durability. 
The  amount  of  water  absorbed  is,  then,  an  important  consideration 
in  determining  the  quality  of  a  brick.  There  are  different  metboda 
in  nse  for  determining  the  amount  of  water  taken  up  by  a  brick, 
and  these  lead  to  slightly  different  results.  Some  experimenters  dry 
the  bricks  in  a  hot-air  chamber,  while  some  dry  them  simply  by  ex- 
posing them  in  a  dry  room;  some  experimenters  immerse  the  bricks 
in  water  in  the  open  air,  while  others  immerse  them  uuder  the  re- 
oeiver  of  an  air-pump;  some  immerse  whole  brick,  and  some  use 
small  pieces;  and,  again,  some  dry  the  surface  with  bibulous  paper, 
while  others  allow  the  surface  to  dry  by  evaporation.  Air-drying 
most  nearly  represents  the  conditions  of  actual  exposure  in  ma- 
sonry strnctures,  since  water  not  expelled  in  that  way  is  in  such  a 
condition  as  not  to  do  any  harm  by  freezing.  Immersion  in  the 
open  air  more  nearly  represents  actual  practice  than  immersion  in 
a  vacuum.  The  conditions  of  actual  practice  arc  beet  represented 
by  testing  whole  brick,  since  some  kinds  have  a  more  or  less  im- 
penriouB  skin.  Drying  the  surface  by  evaporation  is  more  accurate 
than  drying  it  with  paper;  however,  neither  process  is  susceptible 
of  mathematical  accuracy. 

The  absorbing  power  given  in  Table  9,  page  45,  was  determined 
by  (I)  drying  whole  brick  in  a  steam-heated  room  for  three  weeks, 
(2)  weighing  and  (3)  immersing  them  in  water  for  forty-four 
hours;  and  then  (4)  drying  for  four  hours — until  all  the  water  on 
the  surface  was  evaporated, — and,  finally,  (5)  again  weighing  them. 


ovGoQi^lc 


.40  BBiOE.  [chap.  n:. 

The  results  in  the  table  represent  the  mean  of  sereral  obseiratioiis. 
If  the  brick  had  been  kiln-dried,  or  weighed  before  the  surface 
water  waa  entirely  remoTed,  the  apparent  absorption  woold  hava 
been  greater. 

Comparing  the  absorbing  power  of  brick  as  given  in  the  table 
on  page  45  with  that  of  stone  on  page  20,  we  see  the  absorbing^ 
power  of  the  best  briok  is  abont  equal  to  that  of  average  lime- 
stone and  sandstone,  and  mach  greater  than  marble  and  granite. 
For  a  method  of  rendering  brick  non-abeorbent,  see  g§  368-64. 

69.  TkUTBTIBIE  BtbUQIX.  The  experiments  necessary  to 
determine  the  transverse  strength  of  brick  are  easily  made  (§  16)> 
give  definite  results,  and  furnish  valuable  information  coucerain^ 
the  practical  value  of  the  brick;  hence  this  test  is  one  of  the  best  la 
use. 

Table  6  gives  the  results  of  ezperiments  made  by  the  anther  on 

Illinois  brick.  The  averages  represent  the  results  of  from  six  to  fifteea 

TABLE  6. 

Tkaksvebbb  SntEROTH  or  Iixciou  Bbick. 

(Somiiurind  from  Table  •,  pass  «.) 


u^' 

.„„..„. 

HomiLoa  or  RDmu  Dt 

Laa.FBBS«.lF.> 

TaBaaSracnani.* 

M^ 

Mi„. 

ATtrace. 

Haz. 

Mta. 

A«r. 

' 

Soft-clHV.  hand-moulded, 
-best  50)1  in  kllii 

Soft-clay ,  machine- mould- 
ed,-bert  OMinkilD.... 

Stifl-clay,  mftchine-mould- 
ed,-be»t  SOK  in  kiln. . . . 

2.388 

3.8B4 

1,475 

406 

4,848 

846 

1.136 

764 

160 

S.a86 

1,409 

i.Tia 

1,114 

SS6 

8.817 

134 

143 

83 
37 
341 

47 

68 

43 

8 

134 

78 
OS 

experiments  on  brick  from  three  localities.  The  "Max."  and 
"Min."  columns  contain  the  average  of  the  two  highest  and  the 
two  lowest  results  respectively. 

The  results  in  Table  7  were  obtained  under  the  direction  of  the 
Ohief  Engineer  of  the  Lehigh  Valley  R.  B.     Each  result  represents 

*  For  deaniUoD,  aee  f  16, 


ovGoQi^lc 


OBUSHINO  STBENGTH.  41. 

the  mean  of  seven  to  nine  experiments  on  bricka  from  different: 
locatitiea.     The  results  in  Table   6  are  oonuderabl;  greater  thao 

TABLE  7. 
TBAnerKSSB  Btsesoth 


HoDDLUB  or  Bomru  if 
Lbb.  PM>  64-  I>. 

Co-stfiohmt  of  Tuhb- 

«»i. 

HiD. 

Arencs. 

Ifu. 

Uln. 

Athmb- 

M4 
645 
444 

1,048 
710 
004 
269 

1.8I» 
800 
697 
878 

86 
30 

68 
8S 
38 
10 

Medium 

Soft 

8» 

thoBe  in  Table  7,  the  difference  being  dne  probably  more  to  recent 
improTements  in  the  manofactnre  of  brick  and  to  the  method  of 
selection  than  to  locality.  The  brick  from  irhich  the  reenlta  in 
Table  6  were  derived  were  obtained  from  mannfactarerswell  known 
for  the  high  quality  of  their  products. 

ea  CBTnmvo  STBrarOTH.  It  has  already  been  explained  (g§  7 
to  14)  that  the  results  for  the  crushing  strength  of  stone  vary 
greatly  with  the  details  of  the  experiments;  but  this  difference  is 
even  greater  in  the  case  of  brick  than  in  that  of  stone.  In  testing 
stone  the  nniform  practice  is  to  test  onbes  (§  10)  whoso  taoee  are 
carefolly  dressed  to  parallel  planes.  In  testing  brick  there  is  no 
settled  custom.  (1)  Some  experimenters  test  half  brick  while  others 
test  whole  ones;  (3)  some  grind  the  preesed  surfaces  accurately  to 
planes,  and  some  level  up  the  surfaces  by  putting  on  a  thin  coat  of 
plasterof  P&nB,  while  others  leave  them  in  the  rough;  and  (3)  some 
test  the  brick  set  on  end,  some  on  the  side,  and  others  laid  flat- 
wise. 

1.  From  a  series  of  experiments*  on  soft  brick,  the  author  con- 
cludes that  the  crushing  strength  per  square  inch  of  a  quarter  of  a 
brick  is  about,  half  that  of  a  whole  one;  and  that  a  half  brick  is 
about  two  thirds,  and  three  quarters  of  a  brick  about  fiee  sixths,  as 
strong  per  square  inch  as  a  whole  one ;  or,  in  other  words,  the 
strength  of  a  quarter,  a  half,  abd  three  quarters  of  a  brick,  and  a 

*  JSyiRMriiy  JAiM,  ToL  icxLp.  88. 


ovGoQi^lc 


42  BRICK.  [chap.  II. 

whole  one,  are  to  each  other  as  3,  4,  5,  and  6  respectively.  The 
reason  for  thie  difference  is  apparent  if  a  whole  brick  be  conceived 
«B  being  made  up  of  a  number  of  cnbea  placed  side  by  aide,  in  whiuh 
case  it  is  clear  that  the  interior  cubes  will  be  strotiger  than  the 
exterior  ones  because  of  the  side  support  derived  from  the  latter. 
For  experiments  showing  the  marked  effect  of  this  lateral  support, 
see  §  373.  The  quarter  brick  and  the  half  brick  have  lees  of  this 
lateral  support  than  the  whole  one,  and  hence  have  correspondingly 
less  crushing  strength. 

2.  The  strength  of  the  specimen  will  vary  greatly  with  the  degree 
of  smoothness  of  its  bed-sur&ces.  To  determine  the  difference 
between  reducing  the  pressed  surfaces  to  a  plane  and  leaving  them 
in  the  rough,  the  author  selected  six  bricks  of  regular  form  and 
apparently  of  the  same  strength,  and  tested  three  in  the  rough  and 
the  other  three  after  having  reduced  the  pressed  surfaces  to  planes 
by  laying  on  a  coating  of  plaster  of  Paris,  which,  after  drying,  was 
ground  off  to  a  plane.  The  amount  of  plaster  remaining  on  the 
aurfaces  was  just  sufficient  to  fill  up  the  depressions.  Both  sets 
were  tested  in  a  hydraulic  press  between  cast-iron,  parallel  (self- 
adjusting),  pressing  surfaces.  The  average  strength  of  those  that 
were  plastered  was  2.06  times  the  strength  of  those  that  were  not 
plastered.  This  difference  will  vary  with  the  relative  strength  of 
the  brick  and  the  plaster.  The  average  strength  of  the  bricks  whose 
surfaces  were  plastered  was  9,170  pounds  per  square  inch,  which  is 
more  than  that  of  the  plaster  used;  and  therefore  it  is  highly 
probable  that  if  the  surfaces  had  been  reduced  to  planes  by  grind- 
ing, the  difference  in  strength  would  have  been  still  greater.  See 
also  the  last  paragraph  of  §  12. 

3.  As  before  stated,  some  experimenters  test  brick  flatwise,  some 
edgewise,  and  some  endwise.  Since  bricks  are  generally  employed 
in  such  s  position  that  the  pressure  is  on  the  broadest  face,  it  seems 
a  little  more  satisfactory  to  lay  the  brick  flatwise  while  testing  it; 
but  since  the  only  object  in  determining  the  crushing  strength  of 
brick  is  to  ascertain  the  relative  strength  of  different  bricks, — the 
crushing  strength  of  the  brick  is  only  remotely  connected  with  the 
crushing  strength  of  the  brick-masonry  (§  246), — the  position  of  the 
brick  while  being  tested  is  not  a  matter  of  vital  importance.  Doubt- 
less the  principal  reason  for  testing  them  on  end  or  edgewise  is  to 
bring  them  within  the  capacity  of  the  testing-machine.     Howevei^ 


ovGoQi^lc 


OaUSHINO  8TBENQTH.  43 

tbere  is  one  good  reason  against  testing  brick  flatwise;  viz.,  all 
homogeneous  grannlar  bodies  fail  under  oompreesion  by  shearing 
along  planes  at  about  45°  with  the  pressed  surfaces,  and  hence  if 
ihe  height  is  not  snfficient  to  allow  the  shearing  etreasea  to  act 
freely,  an  abnormal  strength  is  developed.     See  also  §  10. 

The  relative  strength  of  brick  tested  m  the  three  positions — flat- 
wise, edgewise,  and  endwise — ^varies  somewhat  with  the  details  of 
the  ezperimeats;  bnt  it  ie  reasonably  well  settled  that  the  strength 
-of  homogeneous  brick  flatwise  between  steel  or  cast-iron  pressing 
snrtaces  is  one  and  a  half  to  two  times  as  much  as  when  the  brick  is 
-tested  on  end.  A  few  experiments  by  theauthor*  seem  to  indicate 
that  the  strength  edgewise  is  a  little  more  than  a  mean  between  the 
atrength  flatwise  and  endwise.  If  the  bnck  is  laminated  (see  para- 
graph 3,  §  57),  the  relative  strength  for  the  three  positions — flat- 
wise, edgewise,  and  endwise— will  vary  greatly  with  the  direction  of 
the  grain. 

61.  Comparatively  few  experiments  have  been  made  to  deter- 
mine the  strength  of  brick,  and  they  are  far  from  satisfactory,  since 
the  manner  of  making  the  experiment  is  seldom  recorded.  The 
differences  in  the  details  of  the  experiments,  together  with  the 
differences  in  the  quality  of  the  bricks  themselves,  are  suf&cient  to 
«anse  a  wide  variation  in  the  results  obtained  by  different  observers. 
The  following  data  are  given  for  reference  and  comparisons. 

The  results  in  Table  8  (page  44)  were  made  with  the  17.  S. 
testing-machine  at  the  Watertown  (Mass.)  ArsenaLf  In  each 
experiment  the  pressed  sur&ces  were  "  carefully  ground  flat  and 
«et  in  a  thin  facing  of  plaster  of  Paris,  and  then  tested  between  steel 
pressing  sarfaces." 

The  experiments  given  in  Table  9  (page  45)  were  made  by  the 
anther,  on  Illinois  brick.  The  bricks  were  crushed  between  self- 
adjusting  cast-iron  pressing  surfaces.  Although  No,  II  shows  an 
average  absorption,  a  moderate  transverse  strength,  and  a  high  crush- 
ing strength,  this  particular  brand  of  brick  disintegrated  rapidly  by 
the  frost.  This  is  characteristic  of  this  class  of  brick,  and  is  caused 
by  the  clay's  being  forced  into  the  moulds  or  through  the  die  in  such  a 
wayas  to  leave  the  brick  in  laminee,  not  well  cemented  together.  A 
critical  examination  of  the  brick  with  the  unaided  eye  gave  no  indi- 


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jvGooi^le 


46  BBICE.  [CSAP.  n. 

cation  of  a  lamiD&ted  Btructure,  and  yet  compressing  the  brick  ia 
two  positions — sidewisu  and  edgewise — never  failed  to  reveal  auch 
Btructure.  The  crushing  strength  in  the  table  was  obtained  whett 
the  preBsure  was  applied  to  the  edges  of  the  laminie.  la  experi- 
ments Nos.  13, 13,  and  1 4  the  pressed  surfaces  were  so  nearly  mathe- 
matical planes  that  possibly  these  bricks  stood  more  than  they  would 
haTe  done  if  their  beds  had  been  plastered.  The  strength  of  No.  15 
was  beyond  the  capacity  of  the  machine;  a  whole  brick,  on  end,  stood 
11,083  ibs.  persq.  in.  without  any  cracks  or  snapping  sounds — which 
usually  occur  at  about  half  of  the  ultimate  strength. 

Rankine  says  thivt  "  strong  red  brick,  when  set  on  end,  should 
require  at  least  1,100  Iba.  per  aq.  in.  to  crush  them;  weak  red  ones, 
550  to  800  lbs.  persq.  in.;  and  fire  bricks,  1,700  lbs.  per.  sq.  in."* 

Experiments  on  the  brick  in  general  use  in  Berlin  gave  for 
"  ordinary"  brick,  on  edge,  a  atrengtii  of  2,930  lbs.  per  eq.  in.;  and 
for  "  selected"  brick,  3,C70  lbs.  per  sq.  in.f 

The  brick  used  in  the  New  York  reservoir,  when  laid  flat  and 
packed  with  sand,  showed  an  average  strength,  for  fonr  specimens, 
of  2,770  lbs.  per  sq.  in.;  and  two  samples  tested  between  wood 
averaged  2,660  lbs.  per  sq.  In.t  Prof.  Pikeg  tested  half  brick  flat- 
wise between  sheets  of  pasteboard  with  the  following  results:  St. 
Louis  brick,  6,417  lbs.  per  sq.  in.  (the  average  of  six  trials);  and 
pressed  brick,  2,519  lbs,  per  sq.  in.  (the  averse  of  thirteen  sam- 
ples from  ten  localities). 

62.  SIZE  AST)  Weight.  In  England  the  legal  standard  size  for 
brick  is  8J  X  4f  X  2J  inches.  In  Scotland  the  average  size  is 
about  9^  X  4i  X  H  inches;  in  Germany,  9J  X  4}  x  2|  inches;  in 
Austria,  llj  X  5J-  X  2jE  inches;  in  Cuba,  11  X  5^  X  2^  inches;  and 
in  South  America,  12J  X  6J  X  2i  inches. 

In  the  United  States  there  is  no  legal  standard,  and  the  dimen- 
sions vary  with  the  maker.  In  the  Eastern  States  8i  X  4  X  2i 
inches  is  a  common  size  for  brick,  of  which  23  make  a  cubic  foot; 
but  in  the  West  the  dimensions  are  usually  a  little  smaller.  The 
National  Brick-makers'  Association  in  1887  and  the  National 
>  Civil  En^ne«ring,  pp.  866  and  T69. 

f  Van  Nostrand's  Engineering  Magnzlnu,  vol,  xxzlv.  p.  340.  From  ftbetjscta  of 
the  Inst,  of  C.  E. 

X  Jonr.  Frank,  Inst,,  vol.  Ixv.  p.  333;  aUo  TninB.  Am.  Soo.  of  C.  B.,  vol.  U.  pp. 
195-86. 

i  Jour.  Assoc.  Engineering  Boo.,  vol.  iv.  pp.  368-67. 


ovGoQi^lc 


SIZE,  WKIGHT,    ASD   COST,  4? 

Traders  and  Builders'  Aasociation  ia  1889  adopted  8i  X  4  X  3^ 
inches  as  the  standard  size  for  common  brick,  and  8|  X  4^  X  2^ 
for  face  brick.  The  price  should  vary  with  the  size.  If,  reckoned 
according  to  cnbic  contents,  brick  8x4x3  inches  is  worth  tlO 
per  thoosand,  brick  8i  X  4^  x  %i  is  worth  tl3.33  per  thousand, 
and  8^  X  4^  X  3^  is  worth  llo  per  thousand.  Further,  where  brick 
is  laid  by  the  thousand,  small  bricks  are  doubly  expensive.  Since 
bricks  shrink  in  burning,  in  proporiiion  to  the  temperature  to  which 
they  are  exposed,  the  amount  differing  with  the  different  kinds  of 
clays,  it  is  impossible  to  have  the  size  exactly  uniform.  Be-pressed 
and  machine-monlded  bricks  are  more  nearly  aniform  in  size  than 
hand- moulded. 

The  size  of  brick  and  the  thickness  of  the  mortar  joint  should 
be  such  that  brick  may  be  laid  fiat,  edgewise,  or  set  vertically,  and 
still  fit  exactly     These  proportions  are  seldom  realized. 

Re-pressed  brick  weighs  about  150  lbs.  per  en.  ft. ;  common 
hard  brick,  125 ;  inferior,  soft  brick,  100.  Common  bricks  will 
average  about  H  lbs.  each. 

63.  Con.  Brick  is  sold  by  the  thousand.  At  Chicago,  in  1687, 
the  "  best  Bewer"  brick  cost  $9 ;  common  brick,  from  W  to  17. 


ovGoQi^lc 


CHAPTEB  IIL 
UME  AND  CEMENT. 

64,  Cl^ABSIilCATIOK.  Considered  as  materialB  for  nae  in  th* 
^bnilder's  art,  the  prodacts  of  calcination  of  limestone  are  classified 
as  common  lime,  hydraulic  lime,  and  hydraulic  cement.  If  the 
limestone  is  nearly  pure  carbonate  of  lime,  the  produot  la  common 
lime,  which  will  slake  npon  the  addition  of  water,  and  mortar  made 
'of  it  will  harden  by  absorbing  carbonic  acid  from  the  air,  but  will 
not  barden  under  water.  If  the  limestone  contains  more  impari- 
ties,  the  prodnct  is  hydraulic  lime,  which  will  slake  npon  the  addi- 
'4ion  of  water,  and  mortar  made  of  it  will  harden  either  in  air  or 
under  water  by  the  chemical  action  between  the  hydranlic  lime  and 
4he  water  used  in  making  the  mortar.  If  the  limestone  contains 
■still  more  impurities,  the  product  is  hydraulic  cement,  which  will 
not  slake  upon  the  addition  of  water  but  most  be  reduced  to  a  paste 
by  grinding,  and  which  will  set  either  in  air  or  under  water  by  the 
-chemical  action  between  the  cement  and  the  water  used  in  making 
the  mortar. '  Common  lime  is  BometimoB  called  air-lime,  because  a 
paste  or  mortar  made  from  it  requires  exposure  to  the  air  to  enable 
it  to  "  set,"  or  harden.  The  hydraulic  limes  and  cements  are  also 
-called  water-limes  and  water-cements,  from  their  property  of 
hardening  under  water. 

Common  lime  is  nsed  in  making  the  mortar  for  most  architect- 
nral  masonry,  and  until  recently  it  was  generally  employed  in 
-engineering  masonry;  but  the  opinion  is  rapidly  gaining  ground 
■that  only  cement  mortar  should  be  employed  in  engineering  struct- 
ures requiring  great  strength  or  being  subject  to  shock.  On  most 
first-clues  railroads  hydraulic  cement  mortar  is  used  in  all  masonry 
fltrnctures.  This  change  in  practice  is  largely  due  to  the  better 
appreciation  of  the  superiority  of  hydranlic  cement  as  a  building 
material.  Although  it  has  been  manufactured  for  about  fifty 
years,  the  amount  nsed  was  comparatiTely  limited  until  withiu 
'recent  years.     At  present  large  quantities  are    imported  from 


ovGoQi^lc 


AST.  1.]  COUHON    LIUE.  49 

Sarope,  and  very  much  more  is  made  in  thia  coantrj.     Hydranlio 
lime  is  neither  manafaotared  nor  nsed  id  this  coantrj. 

The  following  discuBsiOD  coDcerning  common  sad  hydiaallo 
limes  is  given  as  preliminary  to  the  stndy  of  hydraulic  cemente 
rather  than  becanse  of  the  importance  of  these  materials  in  engineer- 
ing constrncti>n 

Abt.  1.  COUUOK  LiHK. 

65.  DEflOXHTioir.  The  limestones  which  famish  the  common 
lime  are  seldom,  if  erer,  pure;  bat  osnally  contain,  besides  the  car- 
bonate of  lime,  from  3  to  10  per  cent,  of  imparities, — snch  as  silica, 
alumina,  magnesia,  oxide  of  maagaaese,  and  traces  of  the  alkalies. 
Lime — varioasly  designated  as  common  lime,  qaickltme,  or  osnstia 
lime — is  a  protoxide  of  calcium,  and  is  prodnced  when  marble,  or 
any  other  variety  of  pare  or  nearly  pare  carbonate  of  lime,  is 
calcined  with  a  heat  of  sufficient  intensity  and  dnration  to  expel 
the  carbonic  acid.  It  has  a  specific  gravi^  of  ^.3,  is  amorphoos, 
highly  canstic,  has  a  great  avidity  for  water,  and  when  bronght  into 
contact  with  it  will  rapidly  absorb  nearly  a  quarter  of  its  weight  of 
that  anbstanoe.  This  absorption  is  accompanied  and  followed  by  a 
great  elevation  of  tempeiatare,  by  the  evolution  of  hot  and  slightly 
caustic  vapor,  by  the  bnrsting  of  the  lime  into  pieces;  and  finally 
the  lime  ia  reduced  to  a  powder,  the  volnme  of  which  is  from  two 
and  a  half  to  three  and  a  half  times  the  volame  of  the  original  lime 
— the  increase  of  bulk  being  proportional  to  the  purity  of  the  lime- 
stone. In  this  condition  the  lime  is  said  to  be  slaked,  and  is  ready 
for  nse  in  making  mortar. 

The  paste  of  common  lime  is  unctuous  and  impalpable  to  sight 
-and  touch ;  hence  these  limes  are  sometimes  called  fat  or  rich  limes, 
as  distingaished  from  others  known  as  poor  or  meager  limes.  These 
latter  asnally  contain  more  or  less  silica  and  a  greater  proportion  of 
«ther  impurities  than  the  fat  limes.  In  slaking  they  exhibit  a  more 
moderate  elevation  of  temperature;  evolve  less  vapor;  are  seldom 
reduced  to  an  impalpable  homogeneous  powder;  yield  thin  paste ; 
and  expand  less.  They  are  less  valuable  for  mortar  than  the  fat 
limes,'  but  are  extensively  employed  as  fertilizers.  When  used  for 
building  pnrposee  they  should,  if  practicable,  be  reduced  to  powder 
by  grinding,  in  order  to  remove  all  diuiger  of  sabseqaent  slsJdng. 


ovGoQi^lc 


60  LIMB  AND   CEKENT.  [CHAP.  Ill: 

66.  Tumo.  Good  lime  may  be  known  by  the  following 
oharacteristios:  1.  Freedom  from  cinders  and  clinkers,  with  not 
more  than  10  percent,  of  other  impnrities, — as  silica,  ainmina,  etc. 
2.  Chiefly  in  hard  lamps,  with  bnt  little  dust.  3.  Slakes  readily 
in  water,  forming  a  very  fine  smooth  paste,  withoat  any  residue. 
i.  DissoWes  in  soft  water,  when  this  is  added  in  sufficient  qnanti- 
ties.  These  simple  tests  can  be  readily  applied  to  any  sample  of 
lime. 

67.  PSXBSETDTO.  As  lime  abstracts  water  from  the  atmospher^- 
aud  is  thereby  slaked,  it  soon  cmmblea  into  a  fine  powder,  losing- 
all  those  qn^tiee  which  render  it  of  valae  for  mortar.  On  thi» 
account  great  care  mast  be  taken  that  the  lime  to  be  need  is  freshly 
bamed,  as  may  be  known  by  its  being  in  hard  Inmpa  rather  than 
in  powder.  Lime  is  shipped  either  in  bnlk  or  in  casks.  Tf  in  bulk, 
it  is  impossible  to  preserve  it  for  any  considerable  time;  if  in  casitSr 
it  may  be  preserved  for  some  time  by  storing  in  a  dry  place. 

Common  lime,  when  mixed  to  a  paste  with  water,  may  be  kept 
tor  ut  indefinite  time  in  that  condition  without  deterioration,  it 
protected  from  contact  with  the  air  so  that  it  will  not  dry  np.  It 
is  cnstomary  to  keep  the  lime  paste  in  casks,  or  in  the  wide,  shallow 
boxes  in  which  it  was  staked,  or  heaped  np  on  the  gronnd,  covered 
over  with  the  sand  to  be  subsequently  incorporated  with  it  in  mak- 
ing mortar.  It  is  conTenient  for  some  parpoees  to  keep  the  slaked 
lime  on  hand  in  s  state  of  powder,  which  may  be  done  in  caska 
under  cover,  or  in  bnlk  in  a  room  set  apart  for  that  purpose.  The 
common  Hmes  contain  imparities  which  prevent  a  thorongh, 
uniform,  and  prompt  slaking  of  the  entire  mass,  and  hence  the 
necessity  of  slaking  some  days  before  the  lime  is  to  be  used,  to 
avoid  all  danger  to  the  masonry  by  subsequent  enlargement  of 
Tolnme  and  change  of  condition. 

A  paste  or  mortar  of  common  lime  will  not  harden  under  water, 
nor  in  continuously  damp  places  esclnded  from  contact  with  the 
air.  It  will  slowly  harden  in  the  air,  from  the  surface  toward  the 
interior,  by  desiccation  and  the  gradnal  absorption  of  carbonic-acid 
gas,  by  which  process  is  formed  a  snbcarbonate  with  an  excess  of 
bydrated  base. 

68.  Con.  Lime  is  sold  by  the  barrel  (about  230  pounds  net), 
or  by  the  bushel  (75  pounds).  At  Chicago  the  average  price,  in 
1898,  was  from  55  to  60  centa  per  barrel. 


ovGoQi^lc 


XKt.  2.]  ETDRAULIC   LIKB. 


Abt.  2.  Htdkaulic  Like. 


69.  SbsobiptioN-  Hydraulic  lime  is  like  common  lime  in  that 
it  will  Blake,  and  differs  from  it  in  that  it  will  harden  under  water. 
Hydraulic  lime  may  be  either  argillaceona  or  Biliceons.  The  former 
ia  derived  from  limeatonea  contaJning .  from  10  to  KO  per  cent,  of 
day,  homogeneoDBly  mixed  with  oarbonate  of  lime  as  the  principal 
In^^ient;  the  Utter  from  siliceous  limeBtones  containing  from  12 
to  18  per  cent,  of  silica.  Small  percentages  of  oxides  of  iron,  car- 
bonates of  magueeia,  etc.,  are  generally  present. 

Daring  the  bnrning,  the  carbonic  acid  is  expelled,  and  the  silica 
and  alamina  entering  into  combination  with  a  portion  of  the  lime 
form  both  the  aUioate  and  the  alnminate  of  lime,  learing  in  the 
bnrnt  prodoot  an  exoesB  of  quick  or  oanstic  lime,  which  indacea 
slaking,  and  b«comes  hydrate  of  lime  when  broaght  into  contact 
with  water.  The  prodnot  owes  its  hydranlioity  to  the  crystallizing 
energy  of  the  alnminate  and  the  silicate  of  lime. 

Hydraolio  lime  is  slaked  by  sprinkling  with  just  sufficient  water 
to  slake  the  free  lime.  The  free  lime  has  a  greater  aridity  for  the 
water  than  the  bydranlio  elements,  and  ooQseqnently  the  former 
absorbs  the  water,  expands,  and  diaintegratea  the  whole  mass  while 
the  hydranlic  ingredients  are  not  affected.  Hydraulic  lime  ia 
Qsaally  slaked,  screened,  and  packed  in  socks  or  barrels  before 
being  sent  to  market.  .  It  may  be  kept  without  injury  in  this  form 
as  long  as  it  is  protected  from  moisture  and  air. 

No  hydrsolic  lime  is  manufactured  in  the  United  States.  It  is 
manufactured  in  sereral  localities  in  Europe,  notably  at  TeiJ  and 
Scillj,  in  France,  from  which  places  large  quantities  were  formerly 
brought  to  this  country. 

Abt.  3.  Htdraulio  GsicEin:. 

70.  CLASsmcATioir.  Hydraulic  cement  may  be  divided  accord- 
ing to  the  method  of  manufacture  into  three  classes,  viz. :  Portland 
cement,  natural  cement,  and  pozzaolana.  The  first  two  differ  from 
the  third  in  that  the  ingredients  of  which  the  first  two  are  composed 
must  be  roasted  before  they  acqaire  the  property  of  hardening  under 
water,  while  the  iugredients  of  the  third  need  only  to  be  pnlrerized 
and  mixed  with  water  to  a  paste. 


ovGoQi^lc 


03  LIMB   AND   CEMENT.  [CHAV.  III. 

71.  Portland.  Portland  cement  is  prodaced  by  calcining  a 
mixtore  containing  from  75  to  80  per  cent,  of  carbonate  of  lime  and 
30  to  33  per  cent,  of  claj,  at  snch  a  high  temperatare  that  the  silica 
and  alamina  of  the  clay  combines  with  the  lime  of  the  limestone. 
As  the  quantity  of  nncombined  lime  is  not  Bnf&oient  to  oaose  the 
mass  to  slake  to  a  powder  apon  the  addition  of  vater,  the  cement 
mnst  be  redoced  to  powder  by  grinding. 

To  aecore  a  complete  chemical  combination  of  the  clay  and  the 
lime,  it  ia  necessary  that  the  raw  materials  shall  be  rednoed  to  a 
powder  and  be  thoroughly  mixed  before  baming,  and  also  necessary 
that  the  calcination  shall  take  place  at  a  high  temperature.  These 
are  the  distingniahing  characteristics  of  the  mannfacture  of  Portland 


In  a  general  way  Portland  cement  differs  from  natural  cement 
iby  being  heavier,  slower  setting,,  and  stronger. 

72.  Portland  cement  derives  its  name  from  the  resemblance 
which  hardened  mortar  made  of  it  bears  to  a  stone  found  in  the  isle 
of  Portland,  oS  the  south  coast  of  England.  Portland  cement  was 
made  first  in  England  about  1843,  and  in  America  about  1874. 

Until  recent  years  nearly  all  the  Portland  cement  used  in  this 
country  was  imported,  but  at  present  (1898)  about  one  fifth  of  the 
-consumption  is  of  domestic  manufacture.  The  beat  American 
Portland  ia  better  than  the  best  imported,  and  is  sold  equally  cheap. 
In  1896  Portland  cement  was  made  at  twenty-six  places  in  the 
TJnited  States.  Kaw  material  suitable  for  the  manufacture  of  Port- 
land cement  exists  in  great  abundance  in  nature,  and  with  proper 
«are  a  high-class  Portland  cement  may  be  produced  in  almost  any 
part  of  the  country. 

In  recent  years  the  amotint  of  cement  nsed  in  this  country  has 
greatly  increased,  but  the  proportion  of  Portland  used  has  increased 
at  a  much  more  rapid  rate.  In  1887  only  about  one  fifth  was 
Portland,  while  in  1897  one  third  was  Portland. 

73.  5'atnral  Cement.  Tfatural  cement  is  produced  by  calcining 
at  a  comparatively  low  temperatare  either  a  natural  argillaceous 
limestone  or  a  natural  magnesian  limestone  without  pulverization 
or  the  admixture  of  other  materials.  The  stone  ia  qnarried,  broken 
into  pieces,  and  burned  in  a  kiln.  The  burnt  cement  is  then 
crushed  into  small  fragments,  ground,  packed,  and  sent  to  market. 

In  the  process  of  manufacture  natural  cement  is  distiagnished 


ovGoQi^lc 


AKT.  3.]  HYDRADLIC   CBUENT.  53 

from  Portland,  in  nsing  a  natnrsl  instead  of  an  artificial  mistnre 
and  in  calcining  at  a  lower  temperature.  As  a  prodnct,  natural 
cement  is  distingaisbed  from  Portland  in  weighing  less,  being  less 
strong,  and  as  a  rule  setting  more  qaickly. 

In  Enrope  in  making  tbis  class  of  cement  argillaceona  limeetono 
is  generally  need,  and  the  product  is  called  Boman  cement.  In  the 
United  States  magnesian  limestone  is  usually  employed  in  making 
this  cement;  and  formerly  there  was  great  diversity  in  the  term 
used  to  designate  the  product,  domestic,  American,  and  natural 
being  employed.  In  the  early  editions  of  this  rolnme,  the  antbor 
called  this  class  of  cement  Rosendale,  from  the  place  where  it  was 
first  made  in  this  conntry — Boseudale,  Ulster  Co.,  N.  Y.  The 
term  natural  is  now  quite  generally  used,  and  on  the  whole  it  seems 
the  best. 

74.  In  1896  natural  cement  was  made  in  sizty-eight  places  in 
serenteen  states  in  this  conntry,  and  it  may  safely  be  assumed  that 
there  is  no  very  large  area  in  which  a  atone  can  nqt  be  fonnd  from 
which  some  grade  of  natural  cement  can  be  made. 

Kearly  one  half  of  the  natural  cement  made  in  this  conntry 
comes  from  Ulster  Co.,  N.  Y.,  and  nearly  half  of  ihe  remainder 
comes  from  near  Louisville,  Kentucky. 

76.  PozznoLAlTA.  Pozznolana  is  a  term  applied  to  a  combina- 
tion of  silica  and  alumina  which,  when  mixed  with  common  lime 
and  made  into  mortar,  has  the  property  of  hardening  under  water. 
There  are  several  classes  of  materials  possessing  this  property. 

Pozznolana  proper  is  a  material  of  volcanic  origin,  and  is  the 
first  substance  known  to  possess  the  peculiar  property  of  hydrau- 
licity.  The  discovery  was  made  at  Pozzuoli,  near  the  base  of 
Monnt  Vesuvius, — hence  the  name.  Vitruvius  and  Pliny  both 
mention  that  pozzuolana  was  extensively  nsed  by  the  Romans  befor» 
their  day;  and  Yitmvius  gives  a  formula  for  its  use  in  monolithic 
masonry,  which  with  slight  variations  has  been  followed  in  Italy 
ever  since.  It  is  as  follows:  "  12  parts  pozznolana,  well  pulverized; 
6  parts  qnartzoee  sand,  well  washed;  and  9  parts  rich  lime,  well 
slaked." 

Trass  is  a  volcanic  earth  closely  resembling  pozzaolana,  and  is 
employed  substantially  in  the  same  way.  It  is  found  on  the  Rhine 
between  Mayeuce  and  Cologne,  and  in  various  localities  in  Holland. 

Argnes  is  a  species  of  ocheroos  sand  containing  so  large  a  pro- 


ovGoQi^lc 


64  LIMB   AND   CKUBKT.  [CHAP.III.  ' 

portion  of  olay  that  it  con  be  mixed  into  a  pute  with  water  withont 
the  addition  of  lime,  and  used  in  that  stats  for  common  mortar. 
Mixed  with  rich  lime  it  yields  hydrealic  mortar  of  considerable 
energy. 

Brick  dnst  mixed  with  common  lime  produces  a  feebly  hydraulic 
mortur. 

76.  Slag  Cement.  Slag  cement  is  by  far  the  most  important  of 
the  pozznolana  cements.  It  is  the  prodnct  obtained  by  mixing 
powdered  slaked  lime  and  finely  pnlrerized  blast-f  ornace  slag.  The 
amonnt  of  slag  cement  mannfactared  is  very  small  as  compared 
with  Portland  or  natural  cemeot,  and  apparently  mnch  more  is 
mauofactared  in  Earope  than  in  America.  Probably  most  of  the 
so-called  pozznolana  cements  are  slag  cements.  It  is  claimed  that 
«lag  cement  mortar  will  not  stain  the  stone  laid  with  it. 

77.  WEiaHT.  Cement  ix  generally  sold  by  the  barrel,  althongh 
not  necesBarily  ih  a  barrel.  Imported  cement  is  always  sold  in 
barrels,  but  American  cement  is  sold  in  barrels,  or  in  bags,  or  leas 
frequently  in  bulk. 

Portland  cemeat  usually  weighs  400  pounds  per  barrel  gross, 
aod  370  to  380  pounds  net.  A  bag  of  Portland  usually  weighs  95 
pounds,  of  which  four  are  counted  a  barrel. 

Natural  cement  made  in  or  near  Rosendale,  K.  Y.,  weighs  318 
pounds  per  barrel  gross,  and  300  net.  Cement  made  in  Akron, 
N.  Y.,  Milwaukee,  Wis.,  Utioa,  111.,  LouisTille,  Ky.,  weighs  285 
pounds  per  barrel  gross,  and  265  net.  Cloth  bags  usually  contain 
■one  third,  and  paper  bags  one  fourth  of  a  barrel. 

Slag  oement  weighs  from  335  to  350  pounds  net  per  barrel. 

78.  Cost,  The  price  of  hydraulic  cement  has  decreased  greatly 
in  recent  years,  owing  chieSy  to  the  development  of  the  cement 
industry  in  this  country.  At  present  the  competition  among 
-domestic  manufacturers  gOTems  the  price.  In  1898  the  prices  in 
car-load  lots  were  about  as  follows: 

Imported  Portland  cement  at  Atlantic  ports  11.50  to  t3  per 
barrel  in  wood,  and  at  Chicago  t2  to  13.50.  American  Portland  at 
eastern  mills  is  II. SO  to  11.75  in  wood,  and  in  the  Mississippi  valley 
$1.75  to  t%.  The  price  in  paper  bags  is  about  10  cents  per  barrel 
less  than  in  wood,  and  about  15  cents  per  barrel  cheaper  in  cloth 
bags  than  in  wood— provided  the  cloth  bags  are  returned  to  the 
jnill,  freight  prepud. 


ovGoQi^lc. 


ABT.  4.]  TESTS  OF   CEUEXT.  56 

Natural  cement  in  the  Rosendale  (N.  Y.)  district  costs  f.  o.  b. 
mills  50  cents  per  barrel  {300  poanda  net)  in  bnlk,  60  cents  in 
paper,  and  70  cents  in  vood.  The  price  at  the  western  mills  in 
recent  years  va&  50  cents  per  barrel  (265  poands  net)  in  cloth  (the 
sacks  to  be  returned,  freight  prepaid),  55  cents  in  paper,  aud  60 
■cents  in  wood. 

Slag  cement  is  made  in  this  country  only  at  Chicago,  where  it 
«ell8  at  prices  bnt  little  below  those  of  similar  grades  of  Portland 
■cements.  The  imported  pozzaolana  sells  sabstantially  the  Bame  as 
-similar  grades  of  Portland. 

Art.  4,  Tests  of'Cement. 

79.  The  yalne  of  a  cement  Taries  greatly  with  the  chemical 
composition,  the  temperstnre  of  calcination,  the  fineness  of  grind- 
ing, etc. ;  and  a  slight  variation  in  any  one  of  theee  items  may 
greatly  affect  the  physical  properties  of  the  product.  Unless  the 
process  of  manafactnre  is  conducted  with  the  ntmost  care,  two  lots 
of  cement  of  the  same  brand  are  liable  to  differ  considerably  in 
physical  properties.  Therefore  the  testing  of  cement  to  determine 
its  fitness  for  the  nse  proposed  is  a  matter  of  very  great  importance. 
The  properties  of  a  cement  which  are  examined  to  determine  its 
-constractive  valne  are:  (1)  color,  (2)  thoronghness  of  barning,  (3) 
iiotiTity,  (4)  soundness,  (5)  finenesB,  (6)  stieagth. 

80.  CoLOB.  The  color  of  the  cement  powder  indicates  but 
little,  since  it  is  cbie&y  dne  to  oxides  of  iron  and  manganese,  which 
in  no  way  affect  the  cementitiona  valne;  bnt  for  any  given  brand, 
Tariations  in  shade  may  indicate  differences  in  the  character  of  the 
Tock  or  in  the  degree  of  barning. 

With  Portland  cement,  gray  or  greenish  gray  is  generally  con- 
sidered beat;  bluish  gray  indicates  a  probable  excess  of  lime,  and 
brown  an  excess  of  clay.  An  nndne  proportion  of  under-burned 
material  is  generally  indicated  by  a  yellowish  shade,  with  a  znarked 
difference  between  the  color  of  the  hard-bnrned,  ongronnd  particles 
retained  by  a  fine  sieve  and  the  finer  cement  which  passes  throngh 
the  sieve. 

Natural  oemeuts  are  usually  brown,  but  vary  from  very  light  to 
very  dark. 

Slag  cement  has  a  manve  tint — a  delicate  lilac. 


ovGoQi^lc 


66  IIME  AND  CEMEST.  [CHAP.  III. 

SI.  TEOKOUOrorEBB  of  BUBimtQ.  The  higher  the  temperatorO' 
of  baming  the  greater  the  weight  of  the  cliaker  (the  ungronnd 
cement).  Tiro  methodB  have  been  employed  in  ntilizing  this  priu- 
ciple  as  a  test  of  the  thoronghnesB  of  barning,  viz. :  (1)  determine 
the  weight  of  a  unit  of  volume  of  the  groond  cement,  and  (2) 
determine  the  specific  gravity  of  the  cement. 

83.  Weight.  For  any  particular  cement  the  weight  varies  with 
the  temperatare  of  burning,  the  degree  of  fineness  in  grinding,  and 
the  density  of  packing.  Other  things  being  the  same,  the  harder- 
burned  varieties  are  the  heavier.  The  finer  a  cement  is  groand  the 
more  bnlky  it  becomes,  and  conseqnently  the  less  it  weighs.  Kence 
light  weight  may  be  canaed  by  laudable  fine  grinding  or  by  objec- 
tionable nnder-buming. 

The  weight  per  nnit  of  volume  ia  usually  determined  by  sifting: 
thecementintoameasnre,  and  striking  the  top  level  with  a  straight- 
edge. In  careful  work  the  height  of  fail  and  the  size  of  the  meas- 
nring  vessel  are  specified.  The  weight  per  cabic  foot  is  neither 
exactly  constant,  nor  can  it  be  determined  precisely;  and  is  of  very 
little  service  in  determining  the  valae  of  a  cement.  However,  it  is 
often  specified  as  one  of  the  requirements  to  be  fulfilled.  The  fol* 
lowing  valnes,  determined  by  sifting  the  cement  with  a  fall  of  thre» 
feet  into  a  box  having  a  capacity  of  one  tenth  of  a  cubic  foot,  may 
be  taken  as  fair  averages  for  ordinary  cements.  The  difference  in 
weight  for  any  particnlar  kind  is  mainly  dne  to  s  difference  in  fine- 
ness: 

Portland  TO  to  90  lbs.  per  cublo  foot,  or  Oi  to  112  lbs.  per  buKhel. 
Kalural  CO  to  S6  lbs.  per  cubic  foot,  or  63  lo   70  lbs.  per  busheL 

Specifications  for  the  reception  of  cement  frequently  specify  the 
net  weight  per  barrel;  but  this  ia  a  specification  for  quantity  and 
not  quality. 

83.  Specific  Gravity.  The  determination  of  the  ^ecific  gravity 
of  a  cement  is  the  only  real  test  of  the  thoroughness  of  burning. 
The  specific  gravity  is  determined  by  immersing  a  known  weight 
of  the  cement  in  a  liquid  which  will  not  act  upon  it  (usually  turpen- 
tine or  benzine),  and  obtaining  the  volume  of  the  liquid  displaced. 
The  specific  gravity  is  equal  to  the  weight  of  the  cement  (in 
grammes)  divided  by  the  displaced  volume  (in  cubic  centimetres). 

A  variety  of  forms  of  apparatus  for  use  in  making  this  test  ar& 


ovGoQi^lc 


ART.  4.]  TBSTS   OP  CEMEHT.  57 

npOQ  the  market,  bnt  as  Beveral  of  the  volameters  in  ordinary  nse 
iti  chemical  and  physical  laboratories  are  snitable  for  this  porpose, 
it  is  unneceaaary  to  describe  any  of  them  here.  Ab  a  alight  differ- 
ence in  specific  gravity  is  frequently  accompanied  by  a  considerable 
difference  in  the  qnality  of  the  cement,  great  care  is  necessary  in 
making  the  test.  It  is  necessary  that  all  the  air-bnbblea  contained 
in  the  cement  powder  be  eliminated,  bo  that  the  volume  obtained 
be  that  of  the  cement  particles  only.  The  cement  shoald  be  passed 
through  a  sieve,  say  No,  80,  to  eliminate  the  lamps.  The  tempera- 
ture of  the  liquid  should  not  he  above  60"  Fahr.,  and  should  not 
change  during  the  test.  A  change  of  1°  C  in  the  turpentine 
between  the  readings  of  the  volumeter  will  make  a  difference  of 
0.08  in  the  resulting  specific  gravity. 

The  specific  gravity  of  Portland  cement  varies  from  3.00  to  3.S5, 
usually  betweeu  3.05  and  3.17.  Natural  cement  varies  from  %,75  to 
3.05,  and  is  asnally  between  2.80  and  3.00.  Slag  cement  has  a 
specific  gravity  of  2.72  to  2.76.  The  specific  gravity  of  cement 
decreases  with  age  owing  to  the  absorption  of  water  and  carbonic  acid 
from  the  air. 

German  authorities  state  that  the  specific  gravity  of  fresh  Fort- 
land  cement  is  between  3.13  and  3.^5.  English  specifications  re- 
quire 3.10  for  fresh  Fortland  and  3.07  for  cement  3  months  old. 
By  the  specifications  of  the  Canadian  Society  of  Civil  Engineers 
the  minimum  for  fresh  Portland  is  3.09.  Many  specifications  fix 
3.00  or  3.05  for  the  lower  limit. 

84.  AcnriTT.  When  cement  powder  is  mixed  with  water  to  a 
plastic  condition  and  allowed  to  stand,  the  cement  chemically  com- 
bines with  the  water  and  the  entire  mass  gradually  becomes  firm 
and  hard.  This  process  of  solidifying  is  called  setting.  Cements 
differ  very  widely  in  their  rate  and  manner  of  selling.  Some 
occnpy  bat  a  few  minutes  in  the  operation,  while  others  require 
several  hours.  Some  begin  to  set  comparatively  early  and  take 
considerable  time  to  complete  the  process,  while  others  stand  con- 
siderahle  time  without  apparent  change  and  then  set  very  quickly. 

A  knowledge  of  the  activity  of  a  cement  is  of  importance  both 
in  testing  and  in  using  a  cement,  since  its  strength  ia  seriously 
impaired  if  the  mortar  is  distnrbed  after  it  has  begun  to  set. 
Ordinarily  the  moderately  slow-setting  cements  are  preferable,  since 
they  need  not  be  handled  so  rapidly  and  may  be  mixed  in  larger 


ovGoQi^lc 


^58  LIUE  AND   CEUENT.  [CHAP.  III. 

qnaa titles;  bat  in  some  cases  it  is  necessary  to  nse  a  rapid-setting 

-  cement,  as  for  example  vben  an  Inflow  of  water  is  to  be  prevented. 

To  determine  the  rate  of  setting,  points  have  been  arbitrarily 

fixed  where  the  set  Is  said  to  begin  and  to  end.     It  is  very  difficnlt 

to  determine  these  points  with  exactness,  particalarly  the  latter; 

bnt  an  exact  determioation  is  not  necessary  to  jadge  of  the  fitness 

«f  a  cement  for  a  partlcnlar  use.     For  this  purpose  it  is  ordinarily 

snfficient.to  say  that  a  mortar  has  begun  to  set  when  It  has  lost  its 
..plasticity,  i.e.,  when  its  form  cannot  be  altered  without  prodacing 
■  a  fracture-;  and  that  it  has  set  hard  when  It  will  resist  a  slight 

pressure  of  the  thnmb-nail.  Cements  will  increase  iu  hardness  long 
'.after  they  can  not  be  indented  with  the  thnmb-nail. 

For  an  accurate  determination  of  rate  of  set  two  standards  are 

in  nse,  viz. :  Oillmore's  and  the  Qerman. 

S6.  Gillmore'i  Test.     Mix  the  cement  with  water  to  a  stifE 
aplastic  mortar  (see  §§  103-4),  and  make  a  cake  or  pat  2  or  3  inches 

in  diameter  and  about  ^  inch  thick.     The  mortar  is  said  to  have  - 

begun  to  set  when  it  will  just  support  a  wire  ^^-iuch  in  diameter 
"weighing  J  pound,  and  to  have  "  set  hard  "  when  it  will  bear  a  jfj- 

inch  wire  weigliing  1  pound,  A  loaded  wire  used  for  this  purpose 
iis. frequently  called  a  Vicat  needle,  after  Vicat,  its  inventor.     The 

interval  between  the  time  of  adding  the  water  and  the  time  when 
■the  light  wire  is  just  supported  is  the  time  of  beginning  to  set,  and 

the  interval  between  the  time  the  light  wire  ia  supported  and  the 
'time  when  the  heavy  one  is  just  supported  is  the  time  of  setting, 

86.  German  Teat.*    "  A  slow-setting  cement  (one  setting  in  not 
'less  than  two  hoars)  shall  be  mixed  three  minutes,  and  a  qnick- 

setting  cement  (one  setting  in  less  than  two  hours)  one  minute,  with 

water  to  a  stiS  paste.    The  consistency  of  the  cement  paste  for  this 

cake  shall  be  such  that,  when  wrought  with  a  trowel  on  the  plate, 
'  the  paste  will  only  begin  to  ran  towards  the  edge  of  the  same  after 

the  paste  haa  been  repeatedly  jarred.     As  a  rule,  27  to  30  per  cent. 

of  water  will  suffice  to  give  the  necessary  consistency  to  a  Portland 

cement  paste,  f 

"  For  the  exact  determination  of  the  time  of  beginning  to  aet, 

and  for  determining  the  time  of  setting,  a  standard  needle  300 

■Bpaclfleatlonsot  the  Fmsslan  Hlnlatsr  of  Pnblto  Works,  lalj  38,  IBST. 
t  Apparentl;  this  mortar  la  more  moist  thui  the  "plaatlo  mortar"  ordlnaTQf 
.  empLoyed  ia  tbls  0001X17  {■««  tt  103-1). 


ovGoQi^lc 


ABT.  4.]  TESTS   OF   CEMENT.  59 

£raiiLmee  (11  oz.)  in  weight  and  1  squaro  luillimetire  (0.0006  square 
inch)  in  cross-section  is  used.  A  metal  ring  4  centimetres  (1.575 
inches)  in  height  and  8  centimetres  (3.15  inchee)  clear  diameter 
(inside)  la  placed  on  a  glass  plate,  filled  with  cement  paste  of  the 
above  coDstatency,  and  brcoght  under  the  needle.*  The  moment 
at  which  the  needle  is  no  longer  capable  of  completely  penetrating 
the  cement  cake  is  considered  the  beginning  of  the  time  of  setting. 
The  time  elapaing  between  this  and  the  moment  when  the  standard 
needle  no  longer  leaves  an  appreciable  impreaeion  on  the  hardened 
«ake  is  considered  the  time  of  setting." 

To  facilitate  the  making  of  this  teat,  an  apparatos  ia  provided 
which  GonBista  of  a  light  rod  freely  sliding  throngh  an  arm;  and 
carrying  in  its  lower  end  the  penetrating  needle.  The  amoaut  of 
penetration  is  read  by  an  index  moving  over  a  gradnated  scale. 

87.  Elements  Affecting  Bate  of  Set.  The  amount  of  water 
employed  is  important.  For  data  as  to  the  amoant  of  water  to  be 
oaed,  see  gg  103-1.     The  less  the  water,  the  more  rapid  the  set. 

It  is  nsnally  specified  that  the  temperature  of  tbe  water  and  air 
shall  be  from  eo"  to  65"  F.  The  higher  the  temperatnre,  the  more 
rapid  the  set.  To  prevent  the  anrface  of  the  teat  specimen  from 
^  hardening  by  drying,  it  ia  specified  that  the  pat  shall  be  immersed 
in  water  at  60°  to  66°  F.  The  setting  under  water  is  much  alower 
than  in  air  even  thongh  the  air  be  aatnrated  with  moiatnre  and  be 
at  the  aame  temperatnre  as  the  water,  dne  to  the  mechanical  action 
of  the  water. 

Other  things  being  the  same,  the  finer  the  cement  is  ground  the 
-quicker  it  sets. 

Cements  nsually  become  slower  setting  with  age,  particularly  if 
exposed  to  the  air — Portlands  nsnally  but  slightly. 

The  standard  testa  for  activity  are  usually  made  on  neat  cement 
on  accoant  of  the  interference  of  the  sand  grains  with  the  descent 
of  the  needle.  The  rate  of  setting  of  neat  mortar  gives  bat  little 
Indication  of  what  the  action  may  be  with  aand.  Sand  increases 
the  time  of  aetting — but  very  differently  for  different  cements. 
With  some  cements  a  mortar  composed  of  one  part  cement  to  three 
parts  sand  will  require  twice  as  long  to  set  as  a  neat  mortar,  whits 
with  other  cements  the  time  will  be  eight  or  ten  times  as  long. 


ovGoQi^lc 


60  LIUB   AND   CEKBNT.  [CHAP.  III. 

Sulphate  of  lime  (plaster  of  Paria)  greatly  influences  the  rate  of 
Betting  of  PortJand  cements.  The  addition  of  1  or  2  per  cent  i» 
sufficient  to  change  the  time  of  setting  from  a  few  mianteG  to  aeveral 
hours.  Cement  vhich  has  been  made  slow-setting  by  the  addition  of 
sulphate  of  lime,  nsaally  becomes  quick -setting  again  after  exposure 
to  the  air;  cement  which  has  not  had  its  time  of  setting  changed 
by  the  addition  of  sulphate  of  lime,  usually  becomes  slower  setting 
with  age  and  may  finally  lose  the  power  of  setting.  Cement  which 
has  become  slow-setting  by  the  addition  of  sulphate  of  lime  will 
become  quick-setting  if  mixed  with  a  solution  of  carbonate  of 
soda. 

A  weak  solution  of  chloride  of  lime  usually  cansee  the  cement 
to  set  more  slowly;  while  a  strong  solution  usually  accelerates  the 
rate  of  setting. 

SB.  Time  of  Bet.  A  few  of  the  quickest  natural  cements  when 
'  tested  neat  with  the  minimum  of  water  will  begin  to  set  in  5  to  10 
minutes,  and  set  hard  in  15  to  20  miautes;  while  the  majority  will 
begin  to  set  in  30  to  30  mtDutes  and  will  set  hard  in  40  to  60 
minutes;  and  a  few  of  the  slowest  will  not  begin  to  set  under  60 
minutes. 

The  quickest  of  the  Portlands  will  begin  to  set  in  20  to  40  min- 
utes; but  the  majority  will  not  begin  to  set  nnder  2  or  3  hours, 
and  will  not  set  hard  nnder  6  or  8  hours.  The  18S7  standard 
Qerman  specifications  reject  a  Portland  cement  which  begins  to 
set  in  less  than  30  minutes  or  which  sets  hard  in  less  than 
3  hours. 

89.  SOTnrsMEBB.  Sonndneaa  refers  to  me  ability  of  a  cement  to 
retain  its  strength  and  form  unimpaired  for  an  indefinite  period. 
SouuduesB  is  a  most  important  element;  since  if  a  cement  ultimately 
loses  its  streugth  it  is  worthless,  and  if  it  Anally  expands  it  becomes 
a  destructive  agent.  A  cement  may  be  unsound  because  of  the 
presence  in  it  of  some  active  elements  which  cause  the  mortar  to 
expand  or  contract  in  setting,  or  the  unsoundness  may  be  dne  to 
exterior  agencies  which  act  upon  the  ingredients  of  the  cement. 
Most  unsound  cements  fail  by  swelling  and  cracking  under  the 
action  of  expansires;  but  sometimes  the  mortar  fails  by  a  gradual 
softening  of  the  mass  without  material  change  of  form.  The  ex- 
pansive action  is  usually  dne  to  free  lime  or  free  magnesia  in  the 
oement,  but  may  be  caused  by  sulphur  compounds.     The  priuoipal 


ovGoQi^lc 


JlSI.  4.]  TB3TS   OF   CBUEITT.       .  61 

«xterior  agencies  acting  npon  a  cement  are  air,  sea-water,  and 
■extremes  of  heat  and  cold. 

The  presence  of  small  quantities  of  free  lime  in  the  cement  is  a 
freqnent  «aase  of  ansoandneas.  The  lime  slakes,  and  caasee  the 
mortar  to  svell  and  crack — and  perhaps  finall;  disintegrate.  The 
-degree  of  heat  employed  in  the  burning,  and  the  fiaeness,  modify 
the  effect  of  the  free  lime.  Lime  bnrned  at  a  high  heat  slakes 
more  slowly  than  when  barned  at  a  low  temperatare,  and  is  there- 
fore more  likely  to  be  iajarions.  Finely  gronnd  lime  slakes  more 
qaickly  than  coarsely  gronnd,  and  hence  with  fine  cement  the  lime 
may  slake  before  the  cement  has  set,  and  therefore  do  no  harm. 
The  lime  in  finely  gronnd  cements  will  air-slake  sooner  than  that  ia 
-coarsely  gronnd. 

Free  magnesia  in  cement  acts  very  mnch  like  free  lime.  The 
action  of  the  magnesia  is  mach  slower  than  that  of  lime,  and  hence 
its  presence  is  a  more  serions  defect,  since  it  is  less  likely  to  be 
detected  before  the  cement  is  ased.  The  effect  of  magnesia  in 
cement  is  not  thoronghly  understood,  bat  seems  to  vary  with  the 
composition  of  the  cement,  the  degree  of  burning,  and  the  amount 
of  water  used  in  mixing.  It  was  formerly  held  that  1(  or  2  per 
cent,  of  magnesia  in  Portland  cement  was  dangerous;  bnt  it  is  now 
known  that  5  per  cent,  is  not  injnrions,  while  8  per  cent,  may  pro- 
duce expansion.  Since  many  of  tbe  natnral  cements  are  made  of 
magnesinm  limestone,  they  contain  mnch  more  magnesia  than 
Portland  cements;  bnt  chemists  are  not  agreed  as  to  the  manner  in 
which  the  different  constituents  are  combined,  and  consequently  are 
not  agreed  either  as  to  the  amount  or  effect  of  free  m^nesia  in  such 
a  cement.  Fortunately,  it  is  not  necessary  to  resort  to  a  chemical 
analysis  to  determine  the  amonnt  of  lime  or  magnesia  present,  for 
a  cement  which  snccesaf ally  stands  the  ordinary  test  for  soundness 
-(§  92)  for  7,  or  at  moat  28  days,  may  be  used  with  reasonable  con- 
'fidence. 

The  effect  of  lime  and  magnesia  seems  to  be  more  seriona 
in  water  than  in  air,  and  greater  in  sea-water'  than  in  fresh 
water. 

90.  The  action  of  sulphur  in  a  cement  is  extremely  rariable, 
depending  upon  the  state  in  which  it  may  exist  and  upon  the 
natnre  of  the  cement.  Sulphur  may  occur  naturally  in  the  cement 
or  may  be  added  in  the  form  of  sulphate  of  lime  (plaster  of  Paris) 


ovGoQi^lc 


63  LIHK   AKD    CEMENT,  [CHA.P.  III^ 

to  rotard  the  time  of  set  (§  87).  TJnder  certfun  conditioiu  the 
Bnlphnr  ma;  form  snlphides,  which  on  espoeare  to  the  air  oxidize 
and  form  aalphates  and  canae  the  mortar  to  decrease  in  strength. 
Many,  if  not  all,  of  tbe  slag  cements  contain  an  excess  of  salphides, 
and  are  therefore  nnfit  for  oae  in  the  air,  particularly  a  very  dry 
atmoephere,  althongh  under  water  they  may  give  satisfactory  reaalta 
and  compare  favorably  with  Forthind  cement. 

91.  Teita  of  BoundBeu.  Sereral  methods  of  testing  sonndness 
have  been  recommended.  Of  those  mentioned  below,  tbe  first  two 
are  called  cold  tests,  since  the  mortar  is  tested  at  ordinary  tempera- 
tares;  and  the  others  accelerated  or  hot  tests. 

92.  Th«  Fat  Test.  The  ordinary  method  of  testing  sonndness- 
is  to  make  small  cakea  or  pats  of  neat  mortw  3  or  4  inches  in 
diameter,  aboot  half  an  inch  thick  and  h&riog  thin  edges,  upon  a- 
sheet  of  glass,  and  examine  from  day  to  day,  for  38  days  (if 
possible),  to  see  if  they  show  any  cracks  or  signs  of  distortion. 
The  amount  of  water  nsed  in  mixing  (see  §  104)  within  reason- 
able limits  seems  to  have  no  material  effect  on  the  rosnlt.  The 
German  standard  specifioations  reqnire  the  cake  to  be  kept  24 
honrs  in  a  closed  box  or  nnder  a  damp  cloth,  and  then  stored  in 
water.  The  French,  to  make  snre  that  the  pats  do  not  get  dry 
before  immeraion,  recommend  that  the  cakes  be  immersed  immedi- 
ately after  mixing  without  waiting  for  the  mortar  to  set.  Some- 
really  sound  natural  cements  will  disintegrate  if  immersed  before 
setting  has  begun. 

The  first  evidence  of  had  quality  is  the  loosening  of  the  pat  from 
the  glass,  which  generally  takes  place,  if  at  all,  within  one  or  two 
days.  Good  cement  will  remain  firmly  attached  to  the  glass  for  two- 
weeks  at  least.  The  cracks  due  to  expansion  occur  usually  at  the 
edges  of  the  pat,  and  radiate  from  the  center.  These  cracks  should 
not  be  confnsed  with  irregular  hair-like  shrinkage  cracks,  which 
appear  over  the  entire  surface  when  the  pats  are  made  too  wet  and 
dry  oat  too  much  while  setting. 

93.  A  cement  high  in  snlphides,  as  for  example  one  made  of 
blast-furnace  slag,  will  successfully  pass  the  above,  the  usual,  test 
for  soundness;  and  still  the  mortar  when  exposed  in  the  air  will 
show  a  marked  decrease  in  strength  and  perhaps  finally  dis- 
integrate. The  presence  of  an  excess  of  snlphides  may  be  sns- 
peoted   in   any  cement  made-  from   blast-fnmace  slag.     A    slag 


ovGoQi^lc 


AET.  4.]  TEBT3  OF  CBMBNT.  .  63: 

cemeiit  u  indicated  by  a  manve  or  delicate  lilac  tint  of  the  dry- 
powder. 

Tlierefore,  in  making  the  pat  teat,  it  is  wise  to  expose  a  pat  in 
the  air  as  well  as  one  under  water.  Any  ealphidea  in  the  cement. 
will  be  revealed  by  brown  or  yellowish  blotches  on  the  pat  exposed 
in  air,  and  also  by  a  greenish  color  of  the  interior  of  the  pat  exposed 
nnder  water.  The  pat  in  air  is  not  as  good  a  test  of  expansives  as- 
the  pat  ander  water,  owing  to  a  possible  deficiency  of  water  and  to^ 
greater  shrinkage  cracks. 

If  there  are  any  considerable  indications  of  anlphidee,  before- 
accepting  the  cement  a  chemical  analysis  shonld  be  made  to  deter- 
'  mine  the  snlphnr  and  the  probable  nltimato  action  of  the  cement. 
Any  cement  containing  sulphides  in  appreciable  quantities  is  at. 
least  doubtfal  and  shonld  probably  be  rejected.  Slag  cements- 
asQally  contain  1  to  1.5  per  cent,  of  snlphides. 

Another  excellent  method  of  examining  for  the  presence  of  enl- 
phidea  is,  in  making  the  test  for  tensile  strength  (gg  99-111^),  ta 
store  part  of  the  briqnettes  in  air  and  part  in  water.  Any  material, 
difierence  in  strength  between  the  two  lots  is  sufficient  ground  for- 
rejecting  the  cement  for  nse  in  a  dry  place.  Of  course  due  con- 
aideratiou  should  be  given  to  the  possible  effect  of  evaporation  of: 
water  from  the  briqnettea  stored  in  air, 

64.  Expansion  Test,  Various  experimenters  test  the  soundness 
of  cement  by  measaring  the  expansion  of  a  bar  of  cement  mortar. 
The  French  Commission  recommend  the  measnremeat  of  the  expan- 
sion of  a  bar  33  inches  long  by  ^  inch  square,  or  the  measurement 
of  the  increase  of  circumference  of  a  cylinder.  The  German 
standard  tests  require  the  measarement  of  the  increase  in  length  of 
a  prism  i  inches  long  by  3  inches  square.  The  apparatus  for 
m^ing  these  tests  can  be  had  in  the  market.  The  testa  require 
very  delicate  manipulation  to  secure  reliable  reanlte. 

96.  Accelerated  Testt.  The  ordinary  teats  extending  over  a 
reaeonable  period,  sometimes  fail  to  detect  unsoundness;  and  many 
efforts  have  been  made  to  utilize  heat  to  accelerate  the  action,  with 
a  Tiew  of  determining  from  the  effect  of  heat  during  a  short  tim^ 
what  would  be  the  action  in  a  longer  period  under  normal  condi- 
tions. Some  of  these  tests  have  been  fairly  succesafnl,  but  none 
have  been  extensively  employed.  It  is  difficult  to  interpret  the 
teste,  as  the  results  vary  with  the  per  cent  of  lime,  magnesia,  snt- 


ovGoQi^lc 


«4  LIMB   AKD   CEIIEKT.  [CHAP.  III. 

phatfis,  «tc.,  present,  aod  with  their  proportions  relatire  to  eacb 
other  and  to  the  whole.  There  is  a  great  diversity  as  to  the  value 
of  accelerated  tests.  Many  natural  cemeots  which  go  all  to  pieces 
in  the  accelerated  tests,  particularly  the  boiling  test,  still  stand 
well  in  octnal  service.  This  is  a  strong  argnmeot  against  drawing 
adverse  conclnsions  from  accelerated  tests  when  applied  to  Portland 
cement. 

The  warm-water  lest,  proposed  by  Mr.  Faija,*  a  British 
Authority,  is  made  with  a  covered  vessel  partly  fall  of  water 
maintained  at  a  temperatare  of  100°  to  116°  F.,  in  the  upper 
part  of  which  the  pat  tg  placed  until  set.  When  the  pat  is 
set,  it  is  placed  in  the  water  for  24  honrs.  If  the  cement  remains 
firmly  attached  to  the  glass  and  shows  no  cracks,  it  is  very  probably 
sound. 

The  hot-water  test,  proposed  by  Mr.  Maclay.f  an  American 
authority,  is  snbstantislly  like  Faija's  test  above,  except  that 
Maclay  recommends  195°  to  300°  F. 

The  hailing  test,  suggested  by  Professor  Tetmajer,  the  Swiss 
authority,  consists  in  placing  the  mortar  in  cold  water  immediately 
after  mixing,  then  gradually  raising  the  temperature  to  boiling 
after  about  an  hoar,  and  boiling  for  three  hours.  The  test 
apecimeu  consists  of  s  small  ball  of  such  a  consistency  that  when 
flattened  to  half  its  diameter  it  neither  cracks  nor  runs  at  the 
edges. 

The  kiln  tetts  consist  of  exposing  a  small  cake  of  cement 
mortar,  after  it  has  set,  to  a  temperature  of  110°  to  120°  G. 
{166°  to  248°  F.)  in  a  drying  oven  until  all  tlie  water  is  driven  off. 
If  no  edge  cracks  appear,  the  cement  is  considered  of  constant 
Tolume. 

The  flame  test  is  mads  by  placing  a  ball  of  the  cement  paste, 
About  2  inches  in  diameter,  on  a  wire  gauge  and  applying  the 
flame  of  a  Sanson  barner  gradually  nntil  at  the  end  of  an  hour  the 
temperature  is  about  90°  C.  (194°  F.).  The  heat  is  then  in- 
creased until  the  lower  part  of  the  ball  becomes  red-hot.  The 
appearance  of  oraoks  probably  indicates  the  presence  of  an  expansive 
element. 


ovGoQi^lc 


ART.  4.J  TESTS  OF  CEMBKT.  65 

The  chloride-of-lime  lest  is  to  mix  the  paste  for  the  cakes  with 
■A  solution  of  40  grammee  of  calciom  chloride  per  liter  of  vater, 
allow  to  Bet,  immerBe  in  the  same  solntion  for  34  honre,  and  then 
■«za[nine  tor  checking  and  softening.  The  chloride  of  lime  accel- 
erates the  hydration  of  the  free  lime.  The  chloride  in  the  eolation 
Qsed  in  mixing  causes  the  slaking  before  setting  of  only  so  mocb  of 
the  free  lime  as  is  not  objectionable  in  the  cement.  The  chloride 
of  calcium  has  no  effect  upon  free  magnesia. 

96.  FUTEHESB.  The  question  of  fineness  is  wholly  a  matter  of 
eoonomy.  Oement  until  ground  is  a  mass  of  partially  Titrified 
clinker,  which  is  not  affected  by  water,  and  which  has  no  setting 
power.  It  is  only  after  it  is  ground  that  the  addition  of  water 
indnces  crystallization.  Gonseqaently  the  coarse  particles  in  a 
cement  have  no  setting  power  whatever,  and  may  for  practical 
purposes  be  considered  as  so  mnch  sand  and  essentially  an  adnl- 
(eraot. 

There  is  another  reason  why  cement  shonld  be  well  ground.  A 
mortar  or  concrete  being  composed  of  a  certain  quantity  of  inert 
material  bound  together  by  cement,  it  is  evident  that  to  secure  a 
strong  mortar  or  concrete  it  is  essential  that  each  piece  of  aggregate 
■ball  be  entirely  surrounded  by  the  cementing  material,  bo  that  no 
two  piecee  are  in  actual  contact.  Obviously,  then,  the  finer  a 
cement  the  greater  surface  will  a  given  weight  cover,  and  the  more 
economy  will  there  be  in  its  use. 

Fine  cement  can  be  produced  by  the  maanfacturers  in  three 
ways:  1,  by  supplying  the  mill  with  comparatively  soft,  under-burnt 
took,  which  is  easily  reduced  to  powder;  2,  by  more  thorough 
grinding;  or  3,  by  bolting  through  a  sieve  and  returning  the 
unground  particles  to  the  mill.  The  first  process  pmduces  an  in- 
ferior quality  of  cement,  while  the  second  and  third  add  to  the  cost 
of  manufacture. 

It  ia  possible  to  reduce  a  cement  to  an  impalpable  powder,  but 
the  proper  degree  of  fineness  is  reached  when  it  becomes  cheaper  to 
nse  more  cement  in  proportion  to  the  aggregate  tban  to  pay  the 
extra  coat  of  additional  grinding. 

97.  Heasoring  Fineness.  The  degree  of  fineness  is  determined 
by  weighing  the  per  cent,  which  will  not  pass  through  sieves  of  a 
specified  number  of  meshes  per  square  inch.  In  the  paat,  three 
.sieves  have  been  used  for  this  purpose,  viz.,  sieves  having  60,  75, 


ovGoQi^lc 


66  LIME   AMD   CEMENT.  [CHAP.  III. 

and  100  meshes  per  linear  inch,  or  2,500,  5,625,  and  10,000  meshes, 
per  sqaare  inch  reapectirely.  These  sieves  are  nsnally  referred  to 
by  the  nnmber  of  meshes  per  linear  inch,  the  first  being  known  aa 
No.  SO,  the  second  as  No.  75,  and  the  third  aa  No.  100.  In  each 
case  the  diameter  of  the  mesh  is  abont  eqaal  to  that  of  the  wire. 
The  per  cent,  left  on  the  coareer  sieves  has  no  special  significance, 
and  hence  the  use  of  more  than  one  sieve  has  been  a!mos1  aban- 
doned. More  recently  in  this  conntry  a  No.  120  sieve  (14,400 
meahea  per  square  inch)  has  been  employed,  and  sometimes  a 
No.  200.  On  the  continent  of  Enrope  the  sieve  generally  used  has 
70  mesbes  per  linear  centimetre,  corresponding  to  175  meshes  per 
linear  inch  (30,625  per  square  inch). 

9S.  Data  on  Fi&eneu.  Nearly  all  Portland  cements  are  so 
ground  as  not  to  leave  more  than  20  per  cent,  on  a  No.  100  sieve, 
and  many  of  them  will  not  leave  more  than  10  per  cent,  ob  & 
No.  100  sieve  or  more  than  20  per  cent,  on  a  No.  200  sieve;  and 
some  mannfactarers  claim  less  than  10  per  cent,  on  a  No.  200  sieve. 
As  a  rule,  American  Portlands  are  finer  gronod  than  German,  and 
German  finer  than  English. 

Most  of  the  natural  cements  are  nsually  gronnd  so  as  to  give 
not  more  than  20  per  cent,  on  the  No.  100  sieve,  and  many  of  them 
will  not  leave  more  than  10  per  cent,  on  the  No.  100  sieve,  and  a 
few  vill  leave  only  10  per  cent,  on  the  No.  200  sieve. 

A  common  specification  is  that  not  more  than  10  per  cent,  shall 
be  left  on  a  No.  50  sieve.  Such  a  test  simply  prevents  the  adultera- 
tion of  the  cement  with  very  coarse  particles,  but  does  not  insure 
any  considerable  proportion  of  impalpable  powder  (approximately 
that  which  will  pass  a  No.  200  sieve),  which  alone  gives  value  to 
the  cement,* 

Since  the  natural  cement  is  not  so  hard  burned  as  the  Portland, 
there  is  more  impalpable  powder  in  proportion  to  the  per  cent,  left 
on  the  teat  sieve  than  with  the  Portland;  and  consequently  a  severe 
test  for   fineness  is  not  as  important  for  natural  cement  as  for 

*Tbcre  hae  receutly  been  iatrodac^  an  article  called  sand-oemeDt,  which  la 
made  by  mixing  oement  and  silica  aand  and  gricdlng  the  mixture.  The  grind' 
iDg  ot  Uie  mixture  greatly  Increases  the  flneness  ot  the  cement.  A  mixture  at 
1  part  Dement  and  3  parts  silica  sand  when  reground  will  carry  nearly  as  much 
sand  as  the  original  pure  cement,  which  shows  the  strildng  sSeot  of  tlie  Teiy 
Aoe  grinding  ot  the  cement. 


ovGoQi^lc 


ART.  4.]  TESTS  OF   CEMENT.  67 

Portland,  Farther,  since  nataral  cement  is  mnob  clieaper  than 
Portland,  it  is  more  economical  to  use  more  cement  than  to 
require  extra  flneneBS.  Again,  since  nataral  cement  is  weaker, 
it  IB  not  ordinarily  naed  with  as  large  a  proportion  of  sand  as 
Portland,  and  henoe  fineness  is  not  aa  important  with  nataral  as  with 
Portland. 

For  varions  specifications  for  fineness,  see  Art.  5,  pages  78d- 
78&,  partionlarly  Tables  10c  and  lOd,  pages  78/,  78g. 

99.  TeitsILB  Stkeksth.  The  strength  of  .cement  mortar  is 
nsnally  determined  by  submitting  a  specimen  having  a  cross  section 
of  1  square  inch  to  a  tensile  stress.  The  reason  for  adopting  tensile 
teste  instead  of  compresBive  is  the  greater  ease  of  making  the  former 
and  the  less  variation  in  the  resnltB.  Mortar  is  eight  to  ten  times 
as  strong  in  compression  as  in  teosion. 

The  accnrate  determination  of  the  tensile  strength  of  cement  is 
a  mnch  less  simple  process  than  at  first  appears.  Many  things, 
apparently  of  minor  importance,  exert  snch  a  marked  infiuence  apon 
the  results  that  it  ia  only  by  the  greatest  care  that  trustworthy  testa 
can  he  made.  The  rariations  in  the  resnlts  of  different  experienced. 
operators  working  by  the  same  method  and  upon  the  same  material 
are  frequently  very  large.  In  one  particular  test  case,*  the  lowest 
of  nine  results  was  but  30  per  cent,  of  the  highest,  the  remainder 
being  evenly  distributed  between  the  two  extremes.  Similar  varia- 
tions are  not  at  all  unusual.  The  variation  is  chiefly  due  to  differ- 
ences in  making  the  test  specimen.  Unfortunately,  there  is  at 
present  no  detailed  standard  method  of  procedure  in  making  the 
tests,  and  conseqnently  all  that  can  be  done  is  to  observe  with  the 
most  oonscientions  care  the  rules  that  have  been  formnlated,  and 
draw  the  specifications  in  accordance  with  the  personal  equation  of 
the  one  to  make  the  tests. 

100.  Heat  vs.  Sand  Tests.  It  is  very  common  to  test  neat-cement 
mortar,  but  there  are  two  serious  objections  to  this  practice.  First, 
most  neat  cements  decrease  in  tensQe  strength  after  a  time.  This 
decrease  seems  to  be  due  to  a  change  in  the  molecular  structure  of 
the  cement,  the  crystals  growing  larger  with  increase  of  age,  thna 
producing  a  crowding  which  results  in  a  decrease  of  the  tensile 
strength.    This  decrease  is  most  marked  with  high-grade  Portlands 

'Engineering  2ltat,  ToL  zxxv.  pp.  IBIMil. 


ovGoQi^lc 


68  LIUB   AND   CEMENT.  [CHAK  III. 

vbich  attain  their  strength  rapidly,  and  naaally  occurs  between 
three  months  and  a  year.  A  second  objection  to  neat  teste  is  that 
coarselj-gronnd  cements  show  greater  strength  than  finely-groand 
cements,  although  the  latter  mixed  with  the  osoal  proportion  of 
sand  will  give  the  greater  strength. 

On  the  other  hand,  more  skill  is  required  to  secare  uniform 
resalts  with  sand  than  with  neat  cement. 

101.  The  Sand.  The  quality  of  the  sand  employed  is  of  great 
importance,  for  sands  looking  alike  and  sifted  through  the  same 
sieve  gire  reenlts  varying  30  to  40  per  cent. 

The  standard  sand  employed  in  the  official  Oerman  testa  is  a 
natnral  quartz  sand  obtained  at  Freienwalde  on  the  Oder,  paasmg 
a  sieve  of  60  meshes  per  square  centimetre  (ZO  per  linear  inch)  and 
canght  upon  a  sieve  of  120  meshes  per  square  centimetre  (SS  per 
linear  inch).  The  standard  "sand"  recommended  by  the  Com- 
mittee of  the  American  Society  of  Civil  Engineers  is  crushed  quartz, 
used  in  tbe  maanfacture  of  sand-paper,  which  passes  a  No.  20  sieve 
(wire  Ko.  28  Stnba's  gangs)  and  is  caught  on  a  Ko.  HO  sieve  (wire 
ifo.  30  Stnbs's  gauge),  the  grains  being  from  0.03  to  0.03  inch  in 


The  crushed  quartz  consists  of  sharp,  glossy  splinters,  while  the 
standard  German  sand  is  composed  of  nearly  spherical  grains  having 
a  rough  surface  like  ground  glass.  The  quartz  contains  about  50 
per  cent,  of  voids,  while  the  German  standard  sand  oontMns  only 
about  40  (see  Table  10^,  page  79t.)  The  crushed  qaartz  will  give 
less  strength  than  standard  sand.  Ordinarily  common  building  sand 
will  give  a  higher  strength  than  standard  sand,  since  nsually  tbe 
former  oonslsta  of  grains  having  a  greater  variety  of  sizes,  and  con- 
eeqnently  there  are  fewer  voids  to  be  filled  by  the  cement  (see  Table 
lO^r,  page  79i.) 

102.  The  Amonnt  of  Water.  Tbe  amount  of  water  necessary 
to  make  the  strongest  mortar  varies  with  each  cement.  It  is  com- 
monly expressed  in  per  cents,  by  weight,  although  in  part  at  least 
it  depends  upon  volume.  The  Tariation  in  the  amonnt  of  water 
required  depends  upon  the  degree  of  fineness,  the  specific  gravity, 
the  weight  per  nnit  of  Tolume,  and  the  chemical  composition.  If 
the  cement  ia  coarsely  ground,  the  voids  are  less,  and  consequently 
the  volume  of  water  reqnired  is  less.  If  the  specific  gravity  of  one 
.cement  is  greater  than  that  of  another,  equal  volumes  of  cement 


ovGoQi^lc 


ART.  4.]  TESTS   OF   CKMBNT.  69 

vill  reqaire  different  Tolnmesof  water.  The  chemical  composition 
has  the  greatest  inSaeDce  upon  the  amount  of  water  neceBsary. 
Part  of  the  water  is  req aired  to  combine  chemically  with  the  cement, 
and  part  acts  physically  in  reducing  the  cement  to  a  plastic  mass; 
and  the  portion  required  for  each  of  these  effects  differs  with  differ- 
ent cements.  The  dryness  and  porosity  of  the  sand  mb.y  also 
appreciably  affect  the  quantity  of  water  required.  The  finer  the 
sand,  the  greater  the  amount  of  water  required.  Again,  the  same 
consistency  may  be  arrived  at  in  two  ways — by  using  a  small  quan- 
tity of  water  and  working  thoronghly,  or  by  using  a  larger 
quantity  and  working  less.  (For  instrnotions  coQcerning  mixing, 
see  §  106). 

Attempts  have  been  made  to  eetabliab  a  standard  consistency, 
hut  there  is  no  constant  relation  between  the  consistency  and  the 
maximum  strength.  With  one  cement  a  particular  consistenoy  may 
give  maximum  strength,  while  with  another  cement  a  different  con- 
sistency may  be  required  to  develop  the  greatest  strength.  The 
relationship  between  consistency  and  strength  will  vary  also  with 
the  details  of  the  experiment.  In  reporting  the  results  of  tests  the 
quantity  of  water  employed  should  be  stated. 

There  are  two  distinct  standards  of  consistency  for  the  mortar 
employed  in  testing  cements, — the  plastio  and  the  dry. 

103.  Plastic  Mortar.  This  grade  of  mortar  is  that  com- 
monly employed  in  the  United  States  and  England,  and  is  fre- 
qnently  naed  in  France.*  Tbere  are  two  methods  of  identifying 
this  degree  of  consistency,  viz. :  the  Tetmajer  method  and  the 
Boulogne  method.  The  Tetmajer  method  reqnires  more  water 
than  the  Boulogne  method — for  Portland  this  excess  is  abont  3 
per  cent,  of  the  weight  of  the  cement,  and  for  natural  abont  S 
per  cent. 

The  Tetmajer  method  is  much  used  on  the  continent  of  Europe. 
It  is  as  follows:  The  plasticity  shall  be  such  that  a  rod  0.1  of  an 
inch  in  diameter  and  weighing  0.66  pounds  will  penetrate  1.35 
inches  into  a  box  3  inches  in  diameter  and  1.57  inches  deep,  filled 
with  the  mortar.f 

The  Boulogne  method  is  treqnently  used  in  France.     It  is  aa 

*  Bee  loot  note,  page  71. 

f  For  Ml  Ulustratloa  ot  tbe  apparatua,  sea  Trans,  Amer.  Soo.  ot  0,  E.,  toL  z^ 
P.U. 


ovGoQi^lc 


70  LIME  AND   CEMENT.  [CHAP.  III. 

folIoTH:  *  "  The  qnantity  of  water  ie  aficertaiQed  bj  a  prelimioarT' 
experiment.  It  is  recommended  to  commence  with  a  rather  anmller 
qnantity  of  water  than  may  be  ultimately  raqnired,  and  then  to 
make  freeh  miiinga  with  a  Blight  additional  qnantity  of  vat«r. 
The  mortar  is  to  be  Tigoronsly  worked  for  five  minntes  with  a  trowel 
on  a  marble  dab  to  bring  it  to  the  required  consiBtency,  after  which 
the  foar  following  testa  are  to  be  applied  to  determine  whether  the 
proportion  of  water  is  correct:  1.  The  consistency  of  the  mortar 
shonld  not  change  if  it  be  ganged  for  an  additional  period  of  three 
minntes  after  the  initial  five  minates.  Z.  A  small  qaantity  of  the 
mortar  dropped  from  the  trowel  upon  the  marble  slab  from  a  height 
of  aboat  0.50  metres  (20  inches)  Bhoald  leave  the  trowel  clean,  and 
retun  its  form  approximately  without  cracking.  3.  A  small  qnan- 
tity of  the  mortar  worked  gently  in  the  hands  should  be  easUy 
moulded  into  a  ball,  on  the  surface  of  which  water  ahoald  appear. 
When  this  ball  is  dropped  from  a  height  of  0.50  metres  (20  inches), 
it  should  retain  a  rounded  shape  without  cracking.  4.  If  a  slightly 
smaller  quantity  of  water  be  nsed,  the  mortar  should  he  ornmbly, 
Mid  crack  when  dropped  upon  the  slab.  On  the  other  hand,  the 
addition  of  a  further  qnantity  of  water — 1  to  2  per  cent,  of  the 
weight  of  the  cement — would  soften  the  mortar,  rendering  it  more 
sticky,  and  preventing  it  from  retaining  its  form  when  allowed  to 
fall  upon  the  slab." 

104.  With  any  particular  cement  the  exact  amount  of  water  to 
prodnce  the  above  degree  of  plasticity  can  be  determined  only  by 
trial,  but  as  a  rule  the  qnanti^  reqnJred  by  the  Boulogne  method 
will  he  about  as  follows: 

For  neat  cement:  Portland,  23  to  36  percent.-,  natural,  from 
30  to  40,  usually  from  32  to  36  per  cent. 

For  1  part  cement  to  1  part  sand:  Portland  cement,  13  to  15 
per  cent,  of  the  total  weight  of  cement  and  sand;  natnral,  1?  to 
20,  usnally  18  to  19  per  cent. 

For  1  part  cement  to  2  parts  sand:  Portland,  12  to  13  per  cent. 
of  the  total  weight  of  the  sand  and  cement;  natural,  12  to  16, 
DBoally  13  to  15  per  cent. 

For  1  part  cement  to  3  parts  sand:  Portland,  11  to  12  per  cent. 

■  From  alMttacU  of  lust  at  C.  K. 


ovGoQi^lc 


ART.  4.]  TESTS  OF   CEHEtTT.  71 

at  the  total  weight  of  the  sand  and  cement;  nataral,  1%  to  13  pel 
«ent. 

106.  Dry  Mortar.  This,  grade  at  mortar  is  employed  in  the 
Oerman  and  French  *  governmental  teste  of  tensile  strength.  The 
rales  for  the  identification  of  this  degree  of  consistency  are  not  vei; 
Bpecific.  "  Dry  mortars"  are  nsnally  described  as  being"  as  damp 
as  moist  earth." 

The  German  government  does  not  recognize  tensile  tests  of  neat 
cement  mortar;  bat  for  1  to  3  sand  mortars  specifies  that  the  weight 
of  water  oaed  for  Portland  cement  shall  be  eqnal  to  10  per  cent,  of 
the  total  weight  of  the  sand  and  cement. 

The  French  Commission  gires  a  mlef  for  1  to  2,  1  to  3,  and 
1  to  6  mortars,  with  either  Portland  or  nataral  cement,  whioh  is 
eqsiraleDt  to  the  following  formnla: 

w  =  \WR  +  iS, 

ia  whidk  to  =  the   weight,  in   grammes,   of  water  required  f<Nr 
1,000  grammes  of  the  sand  and  cement; 
W  =  the  weight,  in  grammes,  of  water  required  to  re- 
dnce  1,000  grammes  of  neat  cement  to  plastio 
mortar  (see  g  104) ; 
It  =  the  ratio  of  the  weight  of  the  cement  to  the  weight 
of  the  sand  and  cement. 
For  a  1  to  3  mortar  the  preceding  formnla  gives  8.5  per  cent., 
which  seems  to  show  that  the  French  standard  reqaires  less  water 
than  the  German. 

The  cement  laboratory  of  the  city  of  Philadelphia  employs  the 
»boTe  formula,  but  Dses  60  for  the  constant  iDStead  of  4S.  For  a 
1  to  3  mortar,  the  Philadelphia  formula  gives  10  per  cent.,  which 
agrees  with  the  German  standard, 

106,  Mixing  the  Hortar.  The  sand  and  cement  shonld  be 
thoroughly  mixed  dry,  and  the  water  required  to  rednce  the  mass 
to  the  proper  consistency  shonld  be  added  all  at  once.     The  mixing 

•  The  Frenoli  GommlBeloD  TeoommeodB  dry  mortar  tor  tanslla  taets  oolj;  uid 
Also  Tooommends  that,  attor  an  Internatlooal  agreemeDt  to  that  elteot,  plaatla 
mortars  be  eraplOTdd  for  all  t«Bts  to  the  exolimlOD  of  dry  mortars. 

t  Carter  and  Oleaeler'a  CodcIhsIods  adopted  by  the  Frenah  Conunlsalon  la 
telerenoe  to  Teats  ot  Oementa,  p.  21. 


D.qilizMb,G00>^le 


72 


LIVE   AND   CEMENT. 


[chap,  riu 


shoald  be  prompt  and  thorough.  The  mass  shonld  not  be  dmply 
tnrned,  but  tbe  mortar  should  be  rubbed  agunst  the  top  of  th& 
Blate  or  glass  mixing-table  vith  a  trowel,  or  in  a  mortar  with  a 
pestle.  Insufficient  working  greatly  decreases  tbe  strength  of  tbft 
mortar— frequently  one  half.  The  inexperienced  operator  is  very 
liable  to  nse  too  mncfa  water  and  too  little  labor.  With  a  slow- 
Betting  cement  a  kilogramme  of  the  dry  materials  should  be  strongly 
and  rapidly  rubbed  for  not  less  than  5  minutes,  when  the  consist- 
ency should  be  such  that  it  will  not  be  changed  by  an  additional 
mixing  for  3  minutes. 

Usually  the  mortar  is  mixed  with  a  trowel  on  a  atone  slab;  but 
when  many  batches  are  required,  there  is  a  decided  advantage  in 
mixing  the  mortar  with  a  hoe  in  a  short  Y-shaped  trough  on  th» 
floor.  Various  machines  have  been  devised  with  wbich  to  mix  the 
mortar.  The  jig  mixer  *  is  an  apparatus  in  which  the  materials  ar& 
placed  in  a  covered  cup,  and  shaken  rapidly  up  and  down.  The 
Eaija  mixer  f  consists  of  a  cylindrical  pan  in  which  a  mixer 
formed   of   four   blades  revolves.     The- 

ir-^v — -:f- (  latter  seems  to  give  the  better  result^ 

j  bat  neither  ue  nsed  to  any  considerable 
I  extent. 

107.  The  Form  of  Briquette.    The 
'f  briquetterecommeaded  by  the  Committee 
/  of  the   American  Society  of   Civil  En- 
•  gineers,  Pig.  2,  is  the  form  ordinarily 
used  in  this  country  and  in   England. 
The  form   generally  employed   in  con- 
tinental Europe  is  somewhat  similar  to- 
the  above,  except  that  the  section  is  5- 
square  centimetres  (0.8  square  inch)  and 
the  reduction  to  prodnce  the  minimum 
section   is  by  very  much  more  abrupt 
cnrres.J     The  latter  form  gives  only  70 
to  80  per  cent,  ae  much  strength  as  the  former, 

■  For  llliiBtr&t«d  deearlptlan,  see  Trans.  Amer.  Soc.  ot  O.  E.,  vol.  zit.  p.  SOO-1. 

t  For  BiiUsh  torm,  see  Traas.  Am.  Soc.  ot  C.  E.,  vol.  xvll.  p.  333 ;  luid  lor  th» 
Amerloaii  torm,  see  catalogue  ot  Blahl^  Bros.  Teatlnt;  Machine  Co.,  Philsdelptila. 

t  For  an  elaborate  dlaansslon  ol  the  beat  torm  of  briquette,  see  Johnton'ft 
KateilaU  ot  Oonstmiition,  p.  tSS-SB. 


oiGoQi^lc 


ART.  4.]  TESTS  OF  CEKEKT.  7* 

The  moalds  are  made  of  brass  aDd  are  single  or  multiple,  the 
latter  being  preferred  where  a  great  nnmber  of  briqaettee  is  required, 
The  moolds  are  in  two  parts,  to  facilitate  lemoTol  from  the 
briqnette  withoat  breaking  it. 

108.  Konlding  the  Briquette.  Id  moalding  the  briquette  there 
are  two  general  methods  employed,  corresponding  to  the  two  stand- 
ard consiBtenciea  of  the  mortar. 

109.  Plaalic  Mortar.  The  rales  of  this  section  (109)  apply  to 
hand-moulding. 

The  Committee  of  the  American  Society  of  Civil  Engineers* 
recommendations  areas  foUowe:  "  The  moalds  while  being  charged 
shonld  be  laid  directly  on  glaas,  alate,  or  eome  non-absorbing- 
material.  The  mortar  should  be  firmly  pressed  into  the  monlda. 
with  a  trowel,  without  ramming,  and  struck  off  level.  The  moald- 
ing mast  be  completed  before  incipient  setting  begins.  As  soon  as. 
the  briquettes  are  hard  enoagh  to  bear  it,  they  should  be  taken 
frem  the  moalds  and  kept  covered  with  a  damp  cloth  until  they 
are  immersed." 

The  French  Commieaion  recommends  the  following  method;*' 
"  The  moalds  are  placed  npon  a  plate  of  marble  or  polished  met^ 
which  has  been  well  cleaned  and  labbed  with  an  oiled  cloth.  Six 
moulds  are  filled  from  each  ganging  if  the  cement  be  sluw-eetting, 
and  foar  if  it  be  quick-aetting.  Salficieat  material  is  at  once  placed 
in  each  mould  to  more  than  fill  it.  The  mortar  is  pressed  into  the 
moald  with  the  fingers  so  as  to  leave  no  voids,  and  the  side  of  the 
moald  tapped  several  times  with  the  trowel  to  assist  in  disengaging 
the  babbles  of  air.  The  excess  of  mortar  is  then  removed  by  slid- 
ing a  knife-blade  over  the  top  of  the  mould  so  as  to  prodnce  no 
compression  npon  the  mortar.  The  briquettes  are  removed  from 
the  mould  when  sufficiently  firm,  and  are  allowed  to  remain  tor  21 
bonrs  npon  the  plato  in  a  moist  atmosphere,  protected  from  currents 
of  air  or  the  direct  rays  of  the  sun,  and  at  a  nearly  constant  tem- 
perature of  15"*  to  18°  C.  (59°  to  ei-i"  F.)." 

110.  Various  machines  have  been  devised  for  moulding  bri- 
qnettee  of  plaatio  mortar,  but  none  are  used  to  any  considerablA 
extent,  t 

*  Cuter  uid  Oleoeler'B  OoaaluBlons  kdoptad  b7  the  Frenoh  Oammlselon  In 
refsreooe  to  Teats  ol  Oemeuts,  p.  33. 

t  Tor  HI  lUartmted  deMrlptlonotBuMU'slevermMhliu^iM  mane.  Amer.  Boo. 


ovGoQi^lc 


74  LIUE   AND   CEUBNT.  [CHAP.  III. 

In  Canada,  and  to  some  extent  io  England,  the  briquettes  are 
moalded  bj  applying  a  pressure  of  20  ponnds  per  sqaare  incb  on  tbe 
Bnrface  of  tbe  briquette.*  Some  adyocate  a  presaare  of  1,000  to 
1,500  ponnds  npon  the  upper  face  of  tbe  briqaette.| 

111.  Dry  Mortar.  The  rules  of  tbia  section  (111)  areforftond- 
moulding. 

Tbe  German  standard  rules  are:  \  "  On  a  meted  or  tbiok  glass 
plate  fire  sheets  of  blotting-paper  soaked  in  water  are  laid,  and  on 
these  are  placed  five  moulds  vetted  with  water.  250  grammes 
(8.76  oz.)  of  cement  and  750  grammes  (26.25  oz.)  of  standard  sand 
are  weighed,  and  thoroughly  mixed  dry  in  a  vessel.  Then  100 
cnbic  centimetres  (100  grammes  or  3.5  oz. )  of  f rosb  water  are  udded, 
and  the  whole  mass  thoroughly  mixed  for  five  minntee.  With  the 
mortar  so  obtained,  the  moulds  are  at  once  filled,  with  one  filling, 
so  high  as  to  be  rounded  on  top,. the  mortar  being  well  pressed  in. 
By  means  of  an  iron  trowel  5  to  8  oentimetree  (1.96  inches  to  3.14 
inches)  wide,  35  centimetres  (13.79  inches)  long,  luid  weighing 
about  250  grammes  (8.75  oz.),  the  projecting  mortar  is  pounded, 
first  gently  and  from  the  side,  then  harder  into  the  moulds,  until 
the  mortar  grows  elastic  and  water  flnahes  to  the  snrface.  A 
pounding  of  at  least  one  minute  is  absolutely  essential.  Au  addi- 
tional filling  and  pounding  in  of  the  mortar  u  not  admissible,  since 
the  test  pieces  of  the  same  cement  should  have  the  same  densities 
at  the  Afferent  testing  stations.  The  mass  projecting  over  the 
mould  is  now  cut  oS  with  a  knife,  and  the  surface  smoothed.  The 
mould  is  carefully  taken  off  and  the  test  piece  placed  in  a  box  lined 
irith  zinc,  which  is  to  be  provided  with  a  cover,  to  prevent  a  non- 
Duiform  drying  of  the  test  pieces  at  different  temperatures. 
Twenty-four  hours  after  being  made,  the  test  pieces  are  placed 
ander  water,  and  care  must  be  taken  that  they  remain  under  water 
during  the  whole  period  of  hardening." 

The  French  Commission  recommend  tbe  following  for  sand 


ot  0.  R,  vol.  nrll.  p.  Ml ;  ditto  of  JamleaoD'a  lever  macblDe,  see  The  Transit 
(Iowa  State  University),  December,  1B89,  or  Engineering  NeiB»,  voL  nv.  p.  138,  or 
Trans.  Amer.  Soo.  of  C.  E.,  vol.  uv.  p.  30a, 

■Trans.  Canadian 9oc.  of  O. E.,  vol, lx.p.U,  " Floal Beport Ol ths Oonimlttaa OB 
*  Standard  Uetbod  of  Testing  Cements." 

f  SpaldlDR's  Hydiaulio  dement,  p.  130. 

j  Eagineerina  Sewt.  vuL  xvL  c.  916. 


ovGoQi^lc 


ART,  4.]  TB8T8  OP  CEHEHT.  75 

raortara:  "  Sufficient  mortar  is  ganged  at  once  to  make  six 
briquettes,  reqairiog  350  grammea  of  cement  and  750  grammes  of 
normal  sand.  The  moald  is  placed  npon  a  metal  plate,  and  upon 
top  of  it  is  fitted  a  guide  having  the  same  section  as  the  mould  and 
a  height  of  125  millimetres  (5  inches).  180  grammes  of  the  mortar 
are  introdaced  and  roughly  distriboted  in  the  mould  and  guide  vith 
a  rod.  By  means  of  a  metallic  pestle  weighing  1  kilogramme,  and 
having  a  base  of  the  form  of  the  briquette  but  of  slightly  less 
dimensions,  the  mortar  is  pounded  softly  at  first,  then  stronger  and 
stronger  until  a  little  vater  escapes  under  the  bottom  of  the  mould. 
The  peetle  and  guide  are  thoD  removed  and  the  mortar  cut  off  level 
with  the  top  of  the  mould." 

Ilia.  TheB&bm6  hammer  apparatus  is  much  used,  particularly 
in  Germany.  It  consiats  of  an  arrangement  by  which  the  mortar 
is  compacted  in  the  mould  by  a  anccession  of  blows  of  a  hammer 
weighing  Z  kilogrammes  (4.4  pounds)  npon  a  plunger  sliding  in  a 
guide  placed  npon  top  of  the  mould.  The  machine  is  arranged  to 
lock  after  striking  150  blows.  A  high  degree  of  density  is  thna 
produced,  and  more  regular  results  are  obtained  than  by  hand. 
The  apparatus  is  alow.* 

The  Tetmajer  apparatus  f  is  simUar  in  character  to  the  B&bm6 
hammer.  "  It  consists  of  an  iron  rod  carrying  a  weight  upon  its 
lower  end,  which  is  raised  through  a  given  height  and  dropped  upon 
the  mortar  in  the  mould.  The  ram  weighs  3  kilogrammes.  This 
machine  is  used  in  the  Zurich  laboratory,  and  Prof.  Tetmajer  regu- 
lates the  number  of  blows  by  requiring  a  certain  amount  of  work 
to  be  done  upon  a  unit  volume  of  mortar, — 0.3  kilogrammetre  of 
work  per  gramme  of  dry  material  of  which  the  mortar  ia  composed. 
This  apparatus  is  anbject  to  the  same  limitations  in  practice  as  the 
Bdhme  hammer,  in  being  very  slow  in  use  and  somewhat  expensive 
in  first  cost." 

llli.  Storing  the  Briquettes.  It  is  asual  to  store  the  briquettes 
nnder  a  damp  cloth  or  in  a  moist  chamber  for  24  hoars,  and  then 
immerse  in  water  at  a  temperature  of  60°  to  65°  F.  For  one-day 
testa,  the  briquettes  are  removed  from  the  moulds  and  immersed  as 

*  For  an  llluBtrated  deaoHpUon,  see  En^ntermg  Uriel,  vol.  rflL  p.  300 ;  Tnna, 
Amer.  Boo.  ot  0.  E.,  vol.  zxi.  p.  34. 

-t  French  OommiMlon'e  Beport,  toL  L  p.  387. 


ovGoQi^lc 


76  LIME   AND    CEUEt^T.  [CHAP,  III. 

soon  as  they  have  begun  to  set.  The  volnma  of  the  water  shoald 
be  at  least  toar  times  the  volame  of  the  immersed  briquettes,  and 
the  vater  sboald  be  reDewed  every  seven  days. 

The  briquettes  shonld  be  labeled  or  nnmbered  to  preserve  their 
identity.  Keat-cement  briqnettCB  may  be  stamped  with  steel  dies, 
as  may  also  sand  briqaettes,  provided  a  thin  layer  of  neat  cement !» 
spread  over  one  end  in  which  to  stamp  the  number. 

lUc.  Agt  vhea  Tested.  Since  in  many  cases  it  is  impracticable 
to  extend  the  tests  over  a  longer  time,  it  has  become  customary  to- 
break  the  briquettes  at  one  and  seven  days.  This  practice,  together 
with  a  demand  for  high  tensile  strength,  has  led  mannfactnrers  to 
increase  the  proportion  of  lime  in  their  cements  to  the  highest 
possible  limit,  which  brings  them  near  the  danger-line  of  unsonnd- 
Dess.  A  high  strength  at  1  or  7  days  is  nsnally  followed  by  a 
decrease  in  strength  at  28  days.  Steadily  increasing  strength  at 
long  periods  ia  better  proof  of  good  quality  than  high  results  during 
the  first  few  days.  The  German  standard  test  recognizes  only 
breaks  at  28  days.  The  French  standard  permits,  for  slow-setting 
cements,  teste  at  7  and  38  days,  and  3  and  6  months,  and  1,  2, 
etc.,  years;  and  for  rapid-setting  cements,  from  3  to  24  hours  for 
neat  mortar  and  24  hoars  for  sand  mortars.  In  all  cases  the  time 
is  counted  from  the  instant  of  adding  the  water  when  mixing  the- 
briquette.  The  briquettes  should  be  tested  as  soon  as  taken  from 
the  water. 

llld.  The  Testing  Haohine.  There  are  two  types  in  common'  " 
nse.  In  one  the  weight  is  applied  by  a  stream  of  shot,  which  runs 
from  a  reservoir  into  a  pail  suspended  at  the  end  of  the  steelyard 
arm;  when  the  briquette  breaks  the  arm  falls,  automatically  cutting 
off  tbe  flow  of  shot.  In  the  other  type,  a  heavy  weight  is  slowly 
drawn  along  a  graduated  beam  by  a  cord  wound  on  a  wheel  turned 
by  the  operator.  The  first  is  made  by  Fairbanks  Scale  Co.,  and  tb» 
second  by  Biehle  Bros.,  and  also  by  Tinins  Olsen,  both  of  Phila- 
delphia. 

Fig.  3  represents  a  cement-testing  machine  which  can  b& 
made  by  an  ordinary  mechanic  at  an  expense  of  only  a  few 
dollars.  Athongh  it  does  not  have  the  conveniences  and  is  not 
as  accurate  as  the  more  elaborate  machines,  it  is  valuable  where 
tbe  quantity  of  work  will  not  warrant  a  more  expensive  one,  and 
in  many  oases  is  amply  sufficient.     It  was  devised  by  F.  W.  Bmca 


ovGoQi^lc 


ABT.  4.] 


TSSTB  OF  CBUENT. 


77 


for  nse  at  Fort  MarioD,  St.  Angaatine,  Fla.,  and  reported  to  the 
Engineering  News  (vol.  t.  pp.  194-96)  bj  Lieatenant  W.  M.  Black, 
U.  S.  A. 

The  machine  coDsiBta  easentiallj  of  a  connterpoiBed  wooden  lerer 
10  feet  long,  working  on  a  horizontal  pin  between  two  broad 
nprights  20  inches  from  one  end.  Along  the  top  of  the  long  arm 
ranB  a  grooved  wheel  carrjing  a  weight.  The  diGtaitces  from  the 
f  nlcmm  in  feet  and  inches  are  marked  on  the  sarface  of  the  lever. 
The  clamp  for  holding  the  hriqaette  for  tensile  teats  ia  suspended 
from  the  short  arm,  IS  inches  from  the  fnlcrnm.  Pressure  for 
shearing  and  compreBsive  Btresses  is  commnnicated  throngh  a  loose 
upright,  set  nnder  the  long  arm  at  any  desired  distance  (generally 
-fi  or  12  inches)  from  the  f  alcmm.  The  lower  clip  for  tensile  strains 
1  to  the  bed-plate.     On  this  plate  the  cnbe  to  be  crashed 


r-  B, 


rests  between  blocks  of  wood,  and  to  it  is  fastened  an  npright  with 
a  square  mortise  at  the  proper  height  for  blocks  to  be  sheared.  The 
rul  on  which  the  wheel  runs  is  a  piece  of  light  T-iroo  fastened  on 
lop  of  the  lever.  The  pin  is  iron  and  the  pin-boles  are  reinforced  by 
iron  waahers.  The  clampe  are  wood,  and  are  fastened  by  clevis 
joints  to  the  lever  arm  and  bed-plate  respectively.  When  great 
etreeses  are  desired,  extra  weights  are  hung  on  the  ead  of  the  long 
arm.  Pressores  of  3,000  pounds  have  been  developed  with  this 
machine. 

For  detailed  drawings  of  a  more  elaborate  home-made  cement- 
testing  machine,  see  Proceedings  Engineers*  Clnb  of  Philadelphia, 
Tol.  V.  p.  194,  or  Engins^ing  News,  vol.  it,  p.  310. 

III0,  The  Clips,  The  most  important  part  of  the  testing 
machine  are  the  clips,  by  means  of  which  the  stress  is  applied 
io  the  briquette.     1.  The  form   mnst  be  saoh  as  to  grasp  the 


ovGoQi^lc 


78  LIME   AND   CEUENT.  [CHAP.  HI. 

briqaeite  on  fonr  Bjmmetrical  sQrfaces.     3.  The  earfsce  of  con- 
tact mast  be  large  enongh  to  prevent  the 
0\  briquette  from  being  crashed  between  the 

J  points  of  contact,     3.  The  clip  mast  tnm 

vithont  appreciable  frictioQ  vhen   under 
^^  stresB.     4,  The  clip  must  not  spread  ap- 

I       I preciably  while  anbjectod  to  the  maximom 

load. 

The  form  of  clip  recommended  by  the 
Committee  of  the  American  Society  of 
Civil  Engineers  is  shown  in  Fig.  i.  This 
/-^  form  does  not  offer  snfficient  bearing  sar- 
face,  and  the  briquette  is  frequently  crashed 
at  the  point  of  contact.  The  difficulty  ia 
remedied  somewhat  by  the  use  of  rubber* 
tipped  clips. 

Whatever  the  form  of  the  machine  or 
clips,  great  care  should  be  taken  to  center 

□  II — I       the  briquette  in  the  machine. 
I  111/.  The  Speed.,    The  rate  at  which 
I     I       the  stress    is    applied   makes    a    material 
''— '       difference  in  the  strength.     The  following 

^°-  *■  data  are  given  by  H.  Faija,*  an  English 

authority,  as  showing  the  effect  of  a  variation  in  the  speed  of 
applying  the  stress: 

lute.  Teoaile  8tr«i«lli. 

100  pounds  Id  130  seoonda 400  pouods. 

100        '■         "    60       "  UB       " 

100        "        •■     80      "  480       " 

100       "       "    15      "  4M      " 

100        "        ..       1       ..  498       " 

The  French  and  German  standard  specifications  require  660 
pounds  per  minute.  The  American  Society  of  Civil  Engineers 
recommends  100  pounds  per  minute  for  strong  mixtures,  and  half 
this  speed  for  weak  mixtures.  The  Canadian  Society  of  Civil 
Eogineera  recommends  200  pounds  per  minute. 

111;.  Data  on  Tensile  Strength.     Owing  to  the  great  variation 

•  Tisns.  Amer.  8oo.  of  C.  E.,  vol.  rrli.  p.  9S7, 


ovGoQi^lc 


ABT,  4.]  TEST3   OF   CEMENT.  78fl 

in  the  manner  of  making  the  tests,  it  is  not  possible  to  j^ire  any  very 
Talaable  data  on  the  strength  that  good  cement  shonld  show.  In 
188fi  a  Committee  of  the  American  Society  of  Civil  Engineers 
recommended  the  values  given  in  Table  10  below.  At  least  the 
minimum  valnes  there  given  are  required  in  ordinary  specifications, 
and  the  maximum  valnes  are  sometimes  employed.     Many  of  the 

TABLE  la 
Tehtbilx  Stbenoth  of  Cemknt  Uobtabs. 


m    POUKDB  FU  84OIU  ImjH, 

ForUand. 

Katutal. 

Clear  Crment. 
1  day— 1  Lour,  or  until  aet,  in  idr,  tbe  remainder 

Kin. 
IW 
SCO 
SCO 
UO 

Hu. 

140 
560 
700 

800 

60 
100 
800 

80 
BO 
200 

Max. 

1  week— 1  day  In  dr,  the  remainder  of  the  time 

4  weeks— 1  day  in  air,  the  remainder  of  the  time 

1  veai^l  day  in  air,  the  rematoder  of  the  lime 

1  Part  Cmcbmt  to  1  Part  Sabd. 
1  week— 1  day  in  air,  the  remainder  of  the  time 

1  year— 1  day  in  air,  tbe  remainder  of  tbe  time 

1  Part  Ckmbbt  to  8  Pahta  8aot>. 
1  week— 1  day  in  air,  tbe  remainder  of  the  time 

80 
100 
200 

135 
300 
850 

4  weeks— 1  day  In  air,  the  remainder  of  the  time 

1  vear— 1  day  in  air,  tbe  remainder  of  tbe  time 

' 

tetter  cements  commonly  give  resalts  above  the  moximam  values 
in  the  table.  Natural  cement,  neat  plastic  mortar,  will  generally 
■how  50  to  75  ponnds  per  aqnare  inch  in  7  days,  and  100  to  SOO  in 


ovGoQi^lc 


"78J  LIMB  AND  CEMENT.  [cHAP.  IIL. 

28  days.  Good  Portland  cement,  neat  plastic  mortar,  vill  abov 
100  to  200  pounds  per  sqaare  inch  in  one  day,  100  to  600  in 
7  days,  and  600  to  800  in  28  days.  With  3  parts  sand,  Portland 
cement,  plastic  mortar,  will  give  at  least  100  ponnds  per  sqiiare 
inch  in  7  days,  and  200  in  28  days.  Of  coarse  the  strength  varies 
greatly  with  the  method  ol  testing.  In  consulting  aathoritiee  on 
this  subject,  it  shoald  be  borne  in  mind  that  the  strength  of  cement, 
particularly  Portland,  has  greatly  increased  in  the  past  10  years. 
The  specifications  should  be  drawn  to  correspond  with  the  personal 
eqnation  of  the  one  who  is  to  test  the  cement. 

For  various  specifications  for  tensile  strength,  see  Art.  5,  pages 
78C-78A,  particnlarly  Tables  10c  and  lOd,  pages  78/,  78j. 

For  additional  data  on  the  strength  of  mortars  composed  of 
different  proportions  of  cement  and  sand,  see  Fig.  5,  page  91. 

lllh.  EftUATlHO  THE  Eebults.  It  not  infrequently  occurs  that 
several  samples  of  cement  are  submitted,  and  it  is  required  to 
determine  which  is  the  most  economical.  One  may  be  high-priced  . 
and  have  great  strength;   another  may  show  great  strength  oeat 


TABLE  10a. 
BsnATiTB  EOoHOHT  OP  Ckmbmts  Tbstbd  Neat  at  T  Dats. 


.m™™. 

t™.  ».„„.. 

0...^ 

BlUTITI 

1 

1 

1 

1 

1 

i 

I 

j 

ill. 

1 

A 

M.O 

98.1 

638 

81. B 

$a.80 

100.0 

79.96 

B 

88.0 

95. 9 

771 

100.0 

3.B4 

98.8 

94.26 

0 

88.7 

96.6 

477 

61.9 

2.40 

96.8 

57.28 

D 

91.8 

100.0 

891 

60.7 

2.46 

98.8 

47.66 

B 

81.6 

88.8 

860 

86.6 

a.47 

»8.1 

70.79 

and   be  coarsely   ground.     If  tbe  cement  is   tested   neat,  then 
strength,  Gnenesa,  and  cost  should  be  considered ;  but  if  the  cement 


ovGoQi^lc 


ART.  S.]  SPECIFICATIONS  SOS,  CEMENT.  ISC 

IB  tested  with  tbe  proportiou  of  sand  naoall;  employed  in  pnustioe, 
then  only  strength  and  coet  need  to  be  considered. 

Table  10a  (page  78b)  shows  the  method  of  dedacing  the  relatirs 
cconom;  when  the  cement  ta  tested  neat;  and  Table  10^  shows  the 

t 

'  TABLE  It*. 

RKL&TITB  SoOHOlfT  OF  CBMBNTe  TZSTKD  WTtB  SaKD  AT  1  DATS. 


TDniLa 

v?r" 

CamtrtEaa. 

BaLtrm  Eoohokt. 

OMum. 

Ponwtopor 

B/tMtn. 

Cart  per 

IMatlTCL 

udBslSllM 
Co*. 

Buk. 

A 

168 

WA 

«3.80 

100.0 

SS.40 

B 

176 

100.0 

3.84 

08.3 

98.80 

0 

166 

M.8 

2.40 

95.8 

».S8 

D 

180 

76.7 

2.4D 

9S.8 

71.94 

E 

m 

76.7 

3.47 

98.1 

71.40 

method  when  tbe  cement  is  tested  with  sand.  The  data  ore  from 
.  -actaal  practice,  and  the  cements  are  the  same  in  both  tables. 
Resalts  similar  to  the  above  coald  be  deduced  for  any  other 
age;  the  circomstanoes  under  which  the  cement  is  to  be  asad 
shonld  detonnine  the  age  for  which  tbe  comparison  should  be 
made. 

The  ahoTe  method  of  equating  the  resnlts  gives  the  advantage 
^  a  cetnent  which  g^ns  its  strength  rapidly  and  which  is  liable  to 
be  nnsonnd.  Therefore  this  method  shonld  be  used  with  discretion, 
particularly  with  short- time  tests. 

Art.  5.  Specifications  foh  Ceuent. 

lilt.  Oement  is  eo  variable  in  quality  and  intrinsic  valne  that 
no  considerable  quantity  should  be  accepted  without  testing  it  to 
see  that  it  conforms  to  a  specified  standard.  A  careful  study  of 
Art.  4,  preceding,  will  enable  any  one  to  prepare  such  specifications 
as  will  suit  the  special  requirements,  and  also  give  the  iostmctions 


ovGoQi^lc 


?8<j  LIUB  AKD   CEMENT.  [CHAP.  III. 

neceaaary  for  applying  the  tests.     A  few  specifications  vill  be  given, 
to  setre  as  gnidee  in  preparing  others. 

SPBOIEIOATIOITS   FOB   QUAUTT. 

.lliy.  OSBKAK  POBTLAVD.  The  following  are  the  most  im- 
portant paragraphs  from  the  standard  specifications  of  the  German 
gOTernment  aa  given  in  the  official  circnlar  issned  hy  the  Jhtiniater- 
of  Pnblic  Worka  of  Prnssia  nnder  date  of  July  38, 1887  :* 

"  Timt  of  aetting.  Accordfog  to  Oke  purpoe  for  which  It  la  Intended, 
quick  or  ilow-MttlDg  Portland  cement  may  be  demanded.  Blow-aettlng  cements- 
are  tboee  that  wt  in  about  tvo  horns."  The  teat  U  made  at  deacrlbed  \\k 
%». 

"  Cantlant^  ^  FtrfuoM.  The  Tolume  of  Portland  cement  should  remain 
conatanL  The  declsiTe  test  of  this  should  be  that  a  cake  of  cement,  made  on  a. 
glass  piste,  protected  from  sudden  drying  and  placed  under  water  after  24 
hours,  should  show,  ereo  after  long  submersion,  no  signs  of  crumbling  or  of 
cracking  at  the  edges."     For  method  of  making  the  test,  see  §  93. 

"  Finentu  </  Grinding.  Portlaud  cement  must  be  ground  so  fine  that  no 
more  than  10  per  cent,  of  a  sample  shall  be  left  on  a  BJeve  of  900  meshes  per 
M^uare  centimetre  (6,800  per  square  Inch).  The  thickness  of  the  wins  of  the 
sieve  to  be  one-half  the  width  of  the  meshes."  Notice  that  a  store  having  90(^ 
neahes  per  square  centimetre  (5.BO0  per  sq.  la.)  Is  the  staadard,  although 
devea  of  5,000  meshes  per  square  centimetre  (89,000  per  sq.  in.)  are  frequently 
used. 

"  Ttet  of  Btrmgth.  The  binding  strength  of  Portland  cement  is  to  b» 
determined  hy  testing  a  mixture  of  cement  and  sand.  The  test  is  (o  l>e  con. 
ductad  for  tensile  and  compreBalve  strength  according  to  a  uniform  method, 
and  is  to  be  performed  upon  test  specimens  of  like  form,  like  cross  section,  and 
with  like  apparatus.  It  Is  recommended,  besides,  to  determine  the  strength  or 
neat  cement.  The  tests  for  tension  are  to  be  made  upon  briquettes  of  S  sq. 
cm.  (0.78  sq.  in.)  cron  section  at  the  place  of  rupture,  the  Icfits  f or  compressioo. 
upon  cubes  of  SO  sq.  cm.  (7.8  sq.  In,)  areft." 

"  TtntUt  and  CompreMtw  Strength.  Slow-setting  Portland  cement,  when, 
mixed  with  standard  sand  in  the  proportion  of  I  part  of  cement  to  S  of  sand, 
by  weight,  28  days  after  l>elng  mixed — one  day  In  air  and  37  In  water — must 
possess  a  tecdle  strength  of  not  less  than  16  kllog.  per  square  centimetre  (S!2& 
lbs.  per  square  inch),  nod  s  minimum  compreeaUe  strength  of  160  kllog.  per 
square  centimetre  (S,250  lbs.  persq.  In.).  Qnick-setting  cements  generally  show 
a  lower  strength  after  28  days  than  that  given  shove.  The  Ume  of  setting^ 
must,  therefore,  be  given  when  stating  figures  relative  to  strength."  The  test  is, 
made  as  described  In  the  second  paragraph  of  §111  or  the  first  paragraph  oC 
gill*. 

■  Translation  from  Trans.  Amer.  Soo.  ot  0.  E.,  voL  xa.  pp.  1A-3L 


ovGoQi^lc 


ART.  5.J  SPECIPICATIOSS  FOK  OEMSNT.  78« 

111k.  EXQUBH  PoRTtAlTD.  Ill  Great  Britain  tbere  are  no 
official  apecifications,  but  the  following  proposed  *  by  Mr.  Henry 
Faija  are  much  need: 

"  PitmiMi  to  be  Buch  tbBt  tbe  cement  will  all  pau  through  a  siere  haTlDg 
430  boliM  (30*)  to  the  square  Inch,  and  leave  onlj  10  per  cent  residue  when 
rifted  through  a  rieva  hnviug  2,500  holes  (50')  to  the  sqUKre  lach. 

"  Rcpanthn  or  OorUraetion,  A  pat  made  and  submlLted  to  mcdat  heat  and 
warm  water  at  a  temperature  of  100*  to  1 15*  F.,  ihall  show  do  lign  of  expaa- 
■lon  or  contraction  (blowing)  In  twenty-Four  boun, 

"  T»7itiU  Stnngih.  Brlquettei  of  iloiB-tetting  Portlnud,  which  have  been 
gauged,  treated,  and  teated  fu  the  prescribed  rononer,  to  cany  aa  average  ten- 
■ile  strain,  without  fracture,  of  at  least  17S  lbs.  per  sq.  in.  at  the  expiration  of 
8  dajs  from  gauging;  and  those  teated  at  the  uplraiiou  of  7  days,  to  show  ut 
Increaae  of  at  least  50  per  cent,  over  the  strength  of  those  at  S  days,  but  to 
carry  a  mlallnum  of  SOO  lbs.  per  sq.  In. 

"For guicktetting  Portland,  at  leut  1  TO  lbs.  p<>rsq.  In.  at  8  days,  and  an 
increase  at  7  day b  of  20  to  30  per  cent.,  but  a  minimum  of  400  lbs.  per  sq.  In. 
Very  high  tensile  strengths  at  early  dales  generally  Indicate  a  cement  verginff 
on  an  unsound  one." 

1111.  Fkehoh  FOBTlahs.  The  following  are  the  requirement* 
of  the  SerTicee  Maritimes  dee  Ponts  et  OhanSB6eB,f  and  are  fre- 
qnentl;  employed  in  France: 

"  J)muttg.  A  liter  measure  Is  looeely  filled  with  cement,  t^reviously 
acreened  through  a  sieve  of  180  mesbe*  to  the  linear  Inch,  and  weighed.  Thl» 
test  la  used  for  comparison  of  different  lots  of  the  same  cement,  the  weight  o( 
1  liter  of  which  must  exceed  a  certain  figure  determined  for  the  cement  la 
question.     No  general  requirement  as  to  density  Is  made." 

"  Chemteal  Cmnpotilioa.  Cement  containing  more  than  1  per  cent,  of  sul- 
pharic  anhydride  (=1.7  per  cent,  sulphate  of  lime)  Is  rejected,  while  that  con- 
taining more  than  4  per  cent,  of  oxide  of  Iron  Is  declared  suspicious.  Cement 
containing  lets  than  44  parts  of  silica  and  alumina  to  100  ot  lime  Is  also  con- 
sidered auspicious." 

3Vm«  tf  Setting.  The  test  for  time  ot  setting  Is  made  as  described  In  g  8S 
(page  58).  "  Cement  whlcli  begins  lo  set  In  leas  tUan  SO  minutes  or  seta  com- 
'  pleiely  In  less  than  8  hours  is  refused." 

"  Otnutaney  of  Vvlwne.  Pats  on  glass  are  Immersed  lo  f#a-ua(«-  kept 
at  a  temperature  of  GB*  to  6G*  F.,  and  examined  for  cracking  or  change  of 
form." 

"  TttuUe  BtrenglA.    The  amount  of  water  to  be  employed  is  determined  aa 

•  Trans.  Amer.  8oc.  ot  C.  E.,  toL  zvU.  p.  DSS ;  vol.  xuc.  (1S93)  p.  60. 
fOandlOt's  "OlmentsandChaiixHydraulloB,"  Paris,  1891,  pp.l5IMl. 


ovGoQi^lc 


78/ 


LIMB   AND   CEHKirr. 


LcHAP.  in. 


In  third  parsgTuph  of  g  lOS  (page  09).  The  briquettea  are  moulded  as  d«- 
•cribed  in  ia  the  third  pangiaph  of  g  109,  page  78. 

"  For  aeat  cemeDt,  the  teuile  strength  at  T  days  must  be  at  least  30  kllog. 
per  sq.  cm.  (2S<1  lbs.  per  sq.  in,);  at  28  dajs,  95  kilog.  per  «q.  cm.  (4ffT  Iba. 
per  sq.  in.);  at  12  weeks,  46  kllog.  per  sq.  cm.  (SS9  lbs.  per  sq.  in.).  The 
tenaile  strength  at  28  days  must  exceed  that  at  7  dajs  bj  at  least  S  Ulog.  per 
sq.  cm.  (71  lbs.  per  sq.  ia.).  The  tensile  alreiigth  at  12  weeks  must  be  greater 
than  that  at  28  dajv  uoleas  the  latter  shall  be  at  least  ESC  kilog.  per  sq.  cm. 
<781  Iba.  per  «q.  In.). 

"For  8  ports  crushed  quartz  to  1  part  cement,  with  13  per  cent,  water 
(moulded  as  described  in  the  third  paragraph  of  g  111],  the  tensile  strength 
must  be  at  T  days  at  least  8  kilog.  per  sq.  cm.  (Ill  lbs.  per  sq.  In.);  at  28  days 
«t  least  IS  kllog.  per  sq.  cm.  (318  lbs.  per  sq.  in.):  and  at  12  weeks,  IS  kilog. 
persq.  cm.  (258  lbs.  persq.  in.).  The  Strength  at  12  weeks  must  la  all  cases 
be  greater  than  that  at  38  days." 

111m.  American  Practice.  Tables  lOc  and  lOd  give  the  ayerage 
reqairemeats  for  fineneae  and  tensile  strength  of  Portland  and 
natnr&l  cements,  for  rarions  classes  of  work  in  the  United  States. 
These  Talaee  may  be  regarded  as  repreaeotatlre  of  the  average 
American  practice : 


TABLE  10c. 


AhKRIOAN  RDQOIRRtmHTS  B 


88XJ.  S.  A.  Engineers.. 
10  Cities 

ORailways. 

6  Bridges 

8  Aqueducts 

81  SpectflcatloDs 


Hast  Cement. 


A«e  when  Tsnad,  Dart. 


ovGoQi^lc 


ART.  5.] 


BPECIPICATION'8   FOE  CEMENT. 


78y 


24  U.  S.  A.  EDg1n««r8 , . 
lOCHIes 

4IUnwft7S 

2Bddgea. 

8  Aquedueto. 

01  SpeciflcatloDi. 


Ace  vlHii  Txtad.    Dkti. 


178 


n 


II  In.  f  BILASELFEU ;  Hatvsai  ASB  f  OETLAITO.  The  follow- 
ing IB  an  abstract  of  the  Bpecificationa  used  in  189?  by  tbe  Depart- 
ment of  Public  Works  of  the  City  of  Philadelphia.  Thes* 
Bpecificationa  are  inserted  aa  ahowing  the  extreme  of  American 
practice  in  the  high  degree  of  fineneas  and  great  strength  required. 
Compare  these  resolta  with  those  in  Tables  lOc  and  lOf^.  Tho 
Philadelphia  Bpecificationa  are  not  included  in  theae  tablea. 

NATDKAL    CEMENT. 

"  i^eeifie  Oravily.    Tbe  Bpeclflc  graTitf  shall  not  be  less  than  2.7. 

"  Fin^nau.  The  residue  shall  Dot  leave  more  Ibsn  2  per  cent  on  a  No.  GO 
•teTe,  nor  IS  od  a  No.  100  sieve,  nor  S5  on  a  No.  200  steve,  the  slevm  harln; 
2,400, 10,300,  ftod  85,700  meshes  per  square  Inch  and  the  diameter  of  tbe  wire 
being  0.00W,  0.004S,  sod  0.0020  of  ui  loch  respectlvel;. 

"  CoTutanry  of  Voivme.  Pals  ol  neat  cement  one  half  toch  thick  vitb 
thin  edges,  Immersed  In  water  after  haid  set,  shall  show  no  slgos  of  checUn; 
or  dMntegratlon. 

"  Time  <^  Batting.  It  shall  begin  to  set  in  not  less  tban  10  minntea,  and  set 
-  baid  In  less  than  30  minutes. 

"  Tatuila  BtrtngtA.  The  tensile  Urength  of  dry  mortar  [see  last  paragraplk 
of  %  lOS]  shall  not  be  lees  than  in  tbe  accompaDying  table : 


ovGoQi^lc 


LIHE   AlTD   OEUEMT. 


[chap.  in. 


PODHItt  PU  S4CAU  IKCH. 

Sew. 

*Qa2^ 

100 
200 
800 

38  d»y>  (1  day  In  »!r,  37  days  in  water) 

aoo 

POBTLAND   CEMENT. 

■'  Bpeeiflc  OravH]/.    The  specific  gravity  Bhall  not  be  le«  thui  8.0. 

"  FineMU.  The  residue  sball  not  be  more  than  1  per  cent,  on  a  No.  BOsieTC, 
10  on  a  No.  100  deve.  aod  80  on  a  No.  200  sieve. 

"  Conttaaei/  of  Volume.     Same  as  for  natural  cement  above. 

"  Tinu  of  Betting.  The  cement  shall  not  develop  initial  Kt  in  leu  than  80 
■nloutes. 

"  TeniHe  StrtngVi.  The  tensile  strength  of  dry  mortar  [see  last  paragragh 
■  «t  g  105]  shall  not  be  less  than  in  the  BccranpanylDg  table : 


Poems  piB  SqDABK  Ihcb. 

Nest. 

IQuwts. 

175 
800 
000 

2S  day*  (1  day  In  air,  37  days  in  walor) 

MO 

SPECIFIOATIOHS    FOB   DELIYEBT    AND   STOBAOE. 

lllo.  The  preceding  Bpecifications  preecribe  the  quality  of  the 
cement;  and  the  following  refer  to  the  quantity,  the  sampling,  and 
the  storage.  The  tests  onder  the  former  are  made  in  the  laboratory, 
those  under  the  latter  on  the  work. 

Paekage.    The  oeoient  shall  be  delivered  in  strong  barrels*  lined  with 

*  It  Is  enstomary  to  specify  that  the  eement,  partJeaUrly  Portland,  shall  be 
delivered  tn  barrals.  The  onl;  reason  tor  shipping  In  banela  Is  that  the  oement  I> 
abetter  protected  from  the  weather  In  barrels  than  In  bage.    The  ai^uments  in 


ovGoQi^lc 


,1^T.  5.]  SPECIFICATIONS  FOR   CEHENT.  78f 

'paper  so  a*  to  be  reAsoiubly  protected  from  tbe  air  and  dampneu.  Each 
packi^  ■ball  be  labeled  wltb  tbe  brand,  tbe  numufacturer'a  luune,  and  the 
.groM  weight. 

Weight  The  net  welgbt  of  a  bunel  of  cemeat  shall  be  uodarstood  to  be 
876  pnuQda  of  Ponlaod,  and  800  pounds  of  Eastern  natural  or  36S  pounds  of 
Wenera  nutural  [see  §  77,  page  04];  and  bags  shall  coutaiu  an  aliquot  part  of 
«  barrel.  A  variation  of  2  per  ceuL  is  allowable  in  the  weight  of  Individual 
parkageg.  Any  brokea  barrel  or  torn  bag  may  be  rejected  or  accepted  at  half 
Its  original  weight, — at  the  option  of  the  Inspector. 

Tine  of  Dttivery.  Tbe  Inspection  and  leMs  will  occupy  at  leaat  ten  *  days, 
«nd  the  Contractor  ahall  submit  tbe  cement  for  sampling  at  least  ten*  day* 
before  desiring  to  use  iL  Tbe  Inspeclor  shall  be  promptly  notified  upon  the 
receipt  of  each  shipment. 

Sampling.  The  cement  from  which  to  test  the  quality  ahall  be  selected  by 
tnklug,  from  the  Inierior  of  each  of  slif  well-distributed  barrels  or  bag!  In 
'S.ich  car-load,  auffldent  cement  to  make  from  five  to  ten  briquettes.  These 
■Isf  portions,  after  being  thrown  together  and  thoroughly , mixed,  will  be 
•ssumad  to  represent  ttie  average  of  the  whole  car-load. 

Storage.  All  cement  when  delivered  ahall  be  fully  protected  from  tbe 
weather  ;  nnd  shall  not  be  placed  upon  the  ground  without  proper  blocking 
under  it.  Accepted  cement  may  be  re-inspected  at  any  time  ;  and  if  found 
U>  be  damaged,  it  shall  be  rejected.  Any  cement  damaged  by  water  to  sucb 
«D  extent  as  to  show  upon  the  outside  of  the  barrel  will  be  rejected. 

Ijitptelioa  Mark*.  Cement  which  baa  been  accepted  may  be  so  labeled  by 
the  Inspector ;  and  the  Contractor  shall  preserve  these  labels  from  deface- 
ment and  ahall  prevent  their  imitation.  Rejected  cement  shall  be  so  marked ; 
and  tbe  Contractor  ahall  promptly  remove  such  cement. 

Baai0for  Bt^eeting.  Bach  shipment  of  cement  shall  be  tested  for  quandtj 
•ud  quality.  If  the  average  weight  of  the  barrels  or  bags  tested  is  less  than 
the  weight  specified,  a  corresponding  deduction  shall  be  made  in  the  price ; 
and  If  ten  per  cent,  falls  lo  conform  to  the  requiraments  for  quality,  the  entfra 

favor  of  ahlppinit  In  bags  are ;  1.  The  coat  Is  lees,  sinoe  the  cost  of  the  barrel  is 
«)lmlDated.  3.  The  oement  1b  more  eaaiiy  handled,  since  the  weight  of  a  unit  Is 
leee.  3,  la  oloth  bags  the  oement  Improvee  by  seasoning,  i.e..  the  contact  with 
the  air  hydrates  any  free  lime  due  to  Improper  chemical  aomblnatlon  or  Imperfeet 
ealoInatloD.  i.  The  praetloe  of  shipping  In  barrels  Is  only  a  survival  from  the  time 
when  the  best  oement  was  of  European  manufactore,  which  of  neoesslty  was 
shipped  In  barrels  because  of  the  exoeealve  moisture  In  the  holds  of  vassala,  S.  In 
Eumpe  Portland  cement  Is  usually  abippod  In  cotton-dnek  bags. 

*  For  Important  work  this  time  Is  nsnally  made  thirty  days. 

t  This  is  the  nnmber  epeolfied  by  the  Pennsylvania  Railroad,  a  rood  noted  for 
earetul  and  thorough  work.  It  Is  frequently  speolQed  that  ten  samples  shall  be 
taken;  and  In  Important  worklwhere  a  single  barrel  of  poor  oement  may  materially 
.■Seat  the  strength  of  tlia  work,  it  Is  sometlmea  speolQed  that  eaoh  and  every 
4)arral  shall  be  tested. 


ovGoQi^lc 


78;  LIME    AlfD   CEUENT.  [CHAP.  III. 

shipment  mftj  be  rejected.  Tbe  fkilnre  of  a  (hlpment  to  meet  the  speclflca- 
tioDS  for  quality  ma;  prohibit  further  um  of  that  brand  Od  the  work. 

Barrels  coDtalnlDg  a  Urge  proportion  of  lumps  Bhall  be  rejected. 

Spinal  to  Tett.  Tbe  Eagioeer  rewrrea  tbe  right  to  refuK  to  teat  tny^ 
bnnd  which  In  his  judgment  la  unsuitable  for  the  work,*  A  barrel  or  bag 
which  b  not  plainly  labeled  with  the  brand  and  maker's  name  shall  not  b« 
tested,  and  shall  be  immediately  removed. 


*  This  provision  Is  somettmss  Inserted  to  avoid  the  trouble  and  delay  of  teatlos 
aaj  brand  which  the  Engineer  Is  reasonably  oertaln  Is  nnflt  for  the  work  owing  Uk 
Its  genend  lepatation  tor  poor  quality  or  lack  of  uniformity. 


ovGoQi^lc 


CHAPTEB  in* 

BAND,  QRAY£L,  AND  BROKEN  STONE. 

112.  Sand  is  need  ia  making  mortar;  and  gravel,  or  sand  and 
broken  stone,  io  making  concrete.  The  qualities  of  the  sand  and 
brokea  Btone  have  an  important  effect  upon  the  strength  and  cost 
of  the  mortar  and  the  concrete.  The  effect  of  the  variation  in  these 
materials  is  generally  overlooked,  even  though  the  cement  is  subject 
to  rigid  specifications. 

AnT.  1.     Sand. 

lis.  Sand  is  mixed  vith  lime  or  cement  to  rednce  the  cost  of 
the  mortar;  and  is  added  to  lime  also  to  prevent  the  cracking  which 
would  occur  if  lime  were  used  alone.  Any  material  may  be  used  to 
dilute  the  mortar,  provided  it  has  no  effect  upon  the  durability  of 
the  cementing  material  and  is  not  itself  liable  to  decay.  Pulverized 
Btone,  powdered  brick,  slag,  or  co&l  cinders  may  be  used ;  but 
natural  sand  is  by  far  the  most  common,  although  fine  crushed 
stone,  or  "stone  screenings,"  are  sometimes  employed  and  are  in 
some  respects  better  than  natural  sand. 

In  testing  cement  a  standard  natural  sand  or  crushed  quartz  ia 
employed;  but  in  the  execution  of  actual  work  usually  local  natural 
Band  must  be  employed  for  economic  reasons.  Before  commencing 
any  considerable  work,  eH  available  natnral  sands  and  possible  sub- 
stitnteB  should  be  examined  to  determine  their  values  for  use  in 
mortar. 

114.  SxannTBS  fob  Good  Sard.  To  be  sniteble  for  use  in 
morter,  the  sand  shonld  be  sharp,  clean,  and  coarse ;  and  the  gnuns 
should  be  composed  of  durable  minerals,  and  the  size  of  the  grains 
should  be  such  as  to  give  a  minimum  of  voids,  i.t.,  luterstieeB 
between  the  grains. 

The  usual  specifications  are  simply :  "  The  sand  shall  be  sharp, 
clean,  and  coarse." 

114a.  Snrabilitj.    As  a  rule  ocean  and  lake  sands  are  more 


ovGoQi^lc 


"Vgfr  SAJITD.  [chap.  IIIO. 

durable  than  glacial  sands.  The  latter  are  rock  meal  gronnd  in  the 
.geological  mill,  and  nsnally  consist  of  silica  with  a  considerable  ad- 
mixture of  mica,  hornblende,  feldspar,  carbonate  of  lime,  etc.  The 
silica  is  hard  and  durable ;  but  the  mica,  hornblende,  feldspar,  and 
carbonate  of  lime  are  Boft  and  friable,  and  are  easily  decomposed 
bj  the  gases  of  the  atmosphere  and  the  acids'of  rain-water.  The 
lake  and  ocean  sands  are  older  geologically  ;  and  therefore  ore 
usually  nearly  pure  quartz,  since  the  action  of  the  elements  has 
eliminated  the  softer  and  more  easily  decomposed  constituents. 
Some  ocean  sands  are  nearly  pure  carbonate  of  lime,  which  is  soft 
and  friable,  and  are  therefore  entirely  unfit  for  nse  in  mortar. 
These  are  known  as  calcareous  sands. 

The  glacial  sands  frequently  contain  so  large  a  proportion  of 
Boft  and  easily  decomposed  constituents  as  to  render  them  unfit  for 
use  in  exposed  work,  as  for  example  in  cement  sidewalks.  Instead 
■of  constructing  exposed  work  with  poor  drift  sand,  it  is  better  either 
to  ship  natural  silica  sand  a  considerable  distance  or  to  secure 
'Crushed  quartz.  Gmshed  granite  is  frequently  used  instead  of  sand 
in  cement  sidewalk  construction;  but  granit«  frequently  contains 
mica,  hornblende,  and  feldspar  which  render  it  nnanitable  for  this 
kind  of  work. 

However,  as  a  rule  the  physical  condition  of  the  sand  is  of  more 
importance  than  its  chemical  composition. 

114d.  Sharpness.  Sharp  sand,  i.e.,  sand  with  angnlar  grains, 
is  preferred  to  that  with  rounded  grains  because  (1)  the  angular 
grains  are  roagher  and  therefore  the  cement  will  adhere  better;  and 
(3)  the  angnlar  grains  offer  greater  resistance  to  moving  one  on  the 
•other  under  compression.  On  the  other  hand,  the  sharper  the  sand 
the  greater  the  proportion  of  the  iuterstices  between  the  grains 
(compare  line  4  of  Table  10^;,  page  79t,  with  the  preceding  lines  of 
the  table);  and  oonseqnently  the  greater  the  amount  of  cement 
required  to  produce  a  given  strength  or  density.  But  a  high 
degree  of  sharpness  is  more  important  than  a  small  per  cent,  of 
yoids. 

The  sharpneBB  of  sand  can  be  determined  approximately  by 
rubbing  a  few  grains  in  the  hand,  or  by  cmahing  it  near  the  ear 
and  noting  it  a  grating  sound  is  produced;  but  an  examination 
through  a  small  lens  is  better.  Sharp  sand  is  often  difficult  to 
obt«n,  and  the  requirement  that  "  the  sand  shall  be  sharp"  is 
practically  a  dead  letter  in  most  specifications. 


ovGoQi^lc 


AKI.  1.]  CLSANH£B6.  79* 

114c.  OlMumvij.  Cleao  eaad  a  neceesary  for  the  atroogert 
mortar,  sioce  an  eorelop  of  loam  or  orgftoic  matter  about  the  sand 
gruDB  will  prevent  the  adherence  of  the  cement.  The  cleanneBa  of 
«and  may  be  judged  by  preaaing  it  together  in  the  hand  while  it  ii 
'damp;  if  the  sand  sticks  together  when  the  pressare  is  removed,  it 
U  entirely  unfit  for  mortar  parposes.  The  cleanness  may  also  be 
tested  by  robbing  a  little  of  the  dry  sand  in  the  palm  of  the  hand; 
if  the  huid  is  nearly  or  quite  clean  after  throwing  the  sand  oat,  it 
IB  probably  clean  enough  for  mortar.  The  cleanness  of  the  sand 
may  be  tested  qnantitatirely  by  agitating  a  qnantlty  of  sand  with 
water  in  a  graduated  glass  flask;  after  allowing  the  mixture  to 
settle,  the  amonnt  of  precipitate  and  of  sabd  may  be  re^  from  the 
padnation.  Care  shonld  be  taken  that  the  precipitate  has  folly 
settled,  dnce  it  will  condense  considerably  after  its  upper  surface  is 
clearly  marked. 

Sand  is  sometimes  washed.  This  may  be  done  by  placing  it  on 
«  wire  screen  and  playing  upon  it  with  a  hose;  or  by  placing  it  in 
An  inclined  revolving  screen  and  drenching  with  water.  When 
only  comparatively  small  qnantities  of  clean  sand  are  reqnired,  it 
«au  be  washed  by  shoveliog  into  the  npper  end  of  an  inclined 
:  Y-shaped  trough  and  playing  upon  it  with  a  hose,  the  clay  and 
lighter  organic  matter  floating  away  and  leaving  the  clean  sand  in 
the  lower  portion  of  the  trough,  from  which  it  can  be  drawn  off  by 
removing  for  a  short  time  plugs  in  the  sides  of  the  trough.  Sand 
■can  be  washed  fairly  cleaa  by  this  method  at  an  expense  of  about 
10  cents  per  cubic  yard  exolasive  of  the  cost  of  the  water.  For  a 
sketch  and  deacription  of  an  elaborate  machine  for  washing  sand 
by  paddles  revolving  in  a  box,  see  Engineering  Newt,  vol.  ili. 
IMge  111  (Feb.  16,  1899).  By  this  method  the  cost  of  thoroughly 
washing  dirty  sand  is  about  15  cents  per  cubic  yard. 

Although  it  is  cnstomary  to  require  that  only  dean  sand  shall 
1m  used  in  making  mortar,  a  small  quantity  of  very  finely  powdered 
-clay  will  not  materially  decrease  the  strength  of  the  mortar.  In 
some  instances  clay  to  the  amount  of  10  per  cent,  of  the  sand  seems 
not  to  decrease  the  strength  of  the  mortar.*  Mortar  containing 
^nsiderable  clay  is  much  more  dense,  plastic,  and  water-tight;  and 
it  occasionally  convenient  for  plastering  surfaces  and  stopping  leaky 
joints.     Such  mortar  is  not  affected  by  the  presence  of  water. 


ovGoQi^lc 


"iQd  SAVD.  [OHAP.  ino. 

In  cDgiaeeriag  literatare  but  lew  definite  specifications  for  the 
cleanneBB  of  sand  can  be  foand,  a  diligent  search  revealing  only  tho 
foUowing:  For  bridge  vork  on  the  New  York  Central  and  Uadsoa 
Biver  R.  B.,  the  specifications  required  that  the  sand  shall  be  bo 
clean  as  not  to  soil  white  paperirhea  rnbbed  on  it.  For  the  retain- 
ing walls  on  the  Chicago  Sanitarj  Canal,  the  snapended  matter 
when  shaken  with  water  was  limited  to  0.5  per  cent.  For  the  dam. 
on  the  Monongahela  Hirer,  built  under  the  direction  of  the 
U.  S.  A.  engineera,  the  snBpeoded  matter  was  limited  to  1  per 
cent.  For  the  dam  at  Portage,  N.  Y.,  bnilt  by  the  Stat«  Engineer, 
the  "  aggregate  of  the  impurities  "  was  limited  to  5  to  8  per  cent. 
The  contamination  permissible  ia  any  particular  case  depends  upon 
the  cleannees  of  the  sand  aTsilable  and  upon  the  difficulty  of 
obtaining  perfectly  clean  sand.  Sand  employed  in  masoniy  con- 
Btmction  frequently  contains  5,  and  sometimes  10,  per  cent,  of 
suspended  matter. 

Hid.  Fineness.  Coarse  sand  is  preferable  to  fine,  since  (1)  the 
former  has  leas  sarface  to  be  covered  and  hence  requires  leas 
cement;  and  (2)  coarse  sand  requires  loss  labor  to  fill  the  interstices 
with  the  cement.  The  sand  should  be  screeued  to  remove  the 
pebbles,  the  fiueaeas  of  the  screen  depending  upon  the  kind  of  work 
in  which  the  mortar  is  to  be  used.  The  coaner  the  sand  the 
better,  even  if  it  may  properly  be  designated  fine  gravel,  provided 
the  diameter  of  the  largest  pebble  is  not  too  nearly  equal  to  tho 
thickness  of  the  mortar  joint. 

Table  IO0  gives  the  results  of  a  series  of  esperiments  to  deter- 
mine the  effect  of  the  size  of  grains  of  sand  upon  the  teoBile 
strength  of  cement  mortar.  The  briquettes  were  all  made  at  the 
same  time  by  the  same  person  from  the  same  cement  and  sand,  the 
only  difference  being  in  the  fineneaa  of  the  sand.  The  table  clearly 
shows  that  coarse  sand  is  better  than  fine.  Notice  that  the  results 
in  line  4  of  the  table  are  lai^r  than  those  in  line  3.  This  is 
probably  due  to  the  tact  that  the  sand  for  line  4  has  a  greater  range 
of  sisee  and  consequently  fewer  voids.  If  this  explanation  ia  true, 
then  since  the  sand  in  each  line  of  the  lower  half  of  the  table  has 
greater  variety  of  sizes  than  those  ia  the  upper  half,  the  ooarse  sand 
is  relatively  better  than  appears  from  Table  IO0. 

Table  10/  shows  the  fineness  of  nstnral  sands  employed  in 

actual  oonstruotioD ;  and  as  the  sands  were  to  alt  appearances  of 

-  the  same  character,  this  table  also  shows  at  least  approximately  tho 


ovGoQi^lc 


or  FnfRKBsa  ot  Sans  upok  thx  Tekulb  Stbehoth  or  1 : 2 
Ckukt  Hortab. 


TsmiLB 

Si»inrrH 

a  ttmna  na  mtoi 

LUniCB, 

Bd. 

Bull  UDOBT  awmMK 

^""" 

TDftylu 

IMo. 

SUoa. 

a  Km. 

11  Km. 

No.    4  Mid  No.    8 

248 

442 

SS9 

.70 

0«0 

■■      8    •'    "     W 

m 

846 

478 

613 

673 

"    18     *'    "     » 

186 

aeo 

818 

897 

89a 

■'    80     "    "      SO 

SU 

381 

em 

403 

440 

■'    80     "     "     80 

149 

306 

388 

376 

818 

"    60    *•     "     76 

isa 

S14 

360 

276 

806 

'■    76    "    "   100 

98 

IDS 

311 

306 

368 

Puaing  No.  100 

98 

1S5 

101 

330 

371 

ravumm. 

3 

r- 

Pw  Otnt.  bj  weight,  oaii^t 

on  One  Mo. 

Pn 

0 

a 

M 

ai 

10 

16 

ao 

«0 

9 

TB 

iw 

100. 

h 

1 

30 

11 

8 

2 

700 

3 

0 

39 

20 

18 

10 

13 

6 

1 

447 

0 

33 

31 

11 

17 

30 

8 

1 

870 

0 

18 

15 

10 

19 

88 

6 

1 

841 

0 

9 

10 

6 

11 

45 

16 

1 

883 

0 

18 

16 

7 

8 

88 

16 

1 

809 

0 

0 

0 

0 

1 

6 

60 

38 

3 

248 

0 

0 

0 

0 

0 

0 

0 

6 

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SCO 

0 

0 

0 

8- 

8 

16 

4S 

80 

6 

189 

jvGooi^le 


79/  BAKD.  [chap.  Ilia. 

«fFect  of  fineneas  npoD  tensile  strength.  This  table  agrees  irith 
the  preceding  in  showing  that  the  coarser  sand  makes  the  stronger 
mortar.     This  oonol[ision  is  perfectly  general. 

If  the  Toids  are  filled  vith  cement,  uniform  coarse  grains  giT» 
greater  strength  than  coarse  and  fine  mixed ;  or,  in  other  words, 
for  rich  mortar  coarse  grains  are  more  important  thau  small  voids. 
Bnt  if  the  voids  are  not  filled,  then  coarse  and  fine  sand  mixed  give 
greater  strength  than  uniform  coarse  grains]  or,  in  other  words, 
for  lean  mortar  a  small  proportion  of  voids  is  more  important  than 
cnarse  grains.* 

As  a  rule,  the  sand  ordinarily  employed  in  making  cement 
mortar  is  much  too  fine  to  give  maiimnm  Btrength  or  to  permit 
the  use  of  a  minimum  amonnt  of  cement.  For  example,  the  sanda 
in  lines  13  and  14  of  Table  lOjr  (page  7di)  are  mnch  used  in  actual 
work,  and  have  approximately  the  same  degree  of  fineness  as  th& 
sands  in  the  last  three  lines  of  Table  10/,  which  give  a  moch  weaker 
mortar  than  the  preceding  sands  of  Table  10/. 

1140.  Specifications  seldom  contain  any  nnmerioal  reqairement 
for  the  finonees  of  the  sand.  The  two  following  ore  all  that  can 
be  fonnd.  For  the  retuning-wall  maeoory  on  the  Chicago  Sanitary 
Canal  the  requirements  were  that  not  more  than  SO  per  cen/  ihalt 
pass  a  No.  50  sieve,  uid  not  more  than  12  per  cent,  shall  pass  a 
No.  80  sieve.  For  the  Portage  Dam  on  the  Oenesee  Biver,  bnili 
by  the  New  York  State  Engineer,  the  apecificatious  were  that  at 
least  75  per  cent,  should  pass  a  No.  30  sieve  and  be  canght  on  a  * 
No.  40. 

The  fineness  of  the  sand  employed  in  severd  noted  works  is  as 
follows,  the  larger  figures  being  the  nnmber  of  the  sieve,  and  the 
smaller  figures  preceding  the  nnmber  of  a  sieve  being  the  per  cent, 
retained  by  that  sieve,  and  the  small  number  after  the  last  sieve 
number  being  the  per  cent,  passing  that  sieve:  Poe  Lock, 
St.  Mary's  Fall  Canal,  *  20  "30  •"40";  concrete  for  pavement 
fonudations  in  the  City  of  Washington,  D.  C,  •  3 '  6 '  8  ■*  10  *  20  •• 
40'60»80';  Genesee  (N.  Y.)  Storage  Dam,  •20'30''60* 
100  •;  Rough  Biver  (Ky.)  Improvement,  "  30  "  30  "  fiO  ";  St.  Begis 
sand,  Soulanges  Canal,  Canada,  '*%0"30''fiO";  Grtiud  Coteau 


•Beport  of  Chief  of  BD^neera,  U.  B.  A.,  ISSS,  p.  3863,  or  Jour.  Wsat.  Boo.  of 
Eiigrs.,  vol.11,  p.  B19;  and  Beport  of  Opentloiu  of  tbe  EngUieeriitg  Department  ol 
the  DiMilot  of  Oolumbla,  1S9S.  p.  lU. 


ovGoQi^lc 


AKi.  1.]  VOIDS.  79J;- 

■and,*  Sonlanges  Guial,  Canada,  "  20  "  30  **  fiO  **.  Tables  10/  and- 
IC^  abow  the  fineoees  of  a  number  of  nataral  sands  employed  in 
actual  work. 

114/*.  Voids.  The  smaUer  the  proportioD  of  Toids,  i.e.,  the 
interstices  between  the  grains  of  the  sand,  the  less  the  amount  of 
oement  reqnired,  and  oonsequentl;  the  more  economical  the  saud. 

The  proportion  of  Toids  ma;  be  determined  by  filling  a  Tossel. 
irith  sand  and  then  determiniog  the  amount  of  water  that  can  ba 
pnt  into  the  reesel  with  the  sand.  This  qoantity  of  water  divided 
by  the  amoont  of  water  alone  which  the  Tesael  will  oontain  is  thd, 
proportion  of  Toids  in  the  sand.  The  qoantiUea  of  water  as  above- 
may  be  determined  by  Tolnmes  or  by  weight.  The  proportion  at 
voids  may  be  determined  for  the  sand  loose  or  rammed,  ttie  latter- 
being  the  more  appropriate,  since  the  mortar  is  either  oompreeaed 
or  rammed  when  naed.  In  either  case  it  is  more  accurate  to  drop- 
the  sand  throngh  the  water  than  to  pour  the  water  upon  the  aand» 
nnoe  with  the  lattw  method  it  is  difficult  to  eliminate  the  air- 
bobbles, — ^particularly  it  the  sand  be  first  rammed.  If  the  sand  iai 
dirty  and  tbe  water  is  ponred  upon  it,  there  is  liability  of  the  clay'a; 
being  washed  down  and  puddling  a  stratum  which  will  prevent  th» 
water  penetrating  to  the  bottom.  If  the  bubbles  are  not  excluded^ 
or  if  the  water  does  not  penetrate  to  the  bottom,  the  reenlt  obtained 
is  less  tiian  the  true  proportion  of  voids.  Again,  if  the  sand  ia 
dropped  throngh  a  considerable  depth  of  water,  there  is  liability 
that  the  sand  may  become  separated  into  strata  having  a  single  Biz» 
of  grains  in  each,  in  which  odse  the  voids  will  be  greater  than  if 
the  Beven^  sizes  were  thoroughly  mixed. 

The  per  cent,  of  voids  Tariee  with  the  moisture  of  the  sand. 
A  small  per  cent,  ot  moisture  has  a  surprisiag  effect  npon  the- 
volume  and  consequently  npon  the  per  oent.  of  voids.  For 
example,  fine  sand  containing  2  per  .cent,  of  moisture  uniformly 
distributed  has  nearly  20  per  cent,  greater  volume  than  the  Bam» 
sand  when  perfectly  dry.  This  effect  of  moisture  increases  with 
the  fineness  of  the  sand  and  decreases  with  tbe  amount  of  water 
present. 

114^.  Table  lOf?,  page  79t,  shows  the  voids  of  a  number  of  both 
artifici^  and  natural  sands.     An  examination  of  the  table  showa 

■A  1  to  9  mort&r  wttb  UiU  aond  mta  only  79  per  oenL  as  strong  ae  tba  pre- 
McUugi  and  with  a  1  to  S  moTtarotil7Tl  p«r  eent.—Truia.OaD.  Sod.  ol  0.  K,  vol.  is. 


ovGoQi^lc 


79A  BAKD.  [chap.  Ilia. 

that  the  voids  of  natnnl  sand  vhen  rammed  •my  bom  30  to  37 
per  cent.  Sands  Nob.  10,  11,  and  12  are  rtry  good;  bnt  Nob.  13 
and  14  are  very  poor.  All  five  are  freqaentlj  employed  in  actoal 
work.  Compare  the  flneneos  of  these  aanda  irith  those  in  Table 
10/,  page  79e. 

114A.  The  following  obserrattons  may  be  nsefnl  in  inveeti^ting 
the  Telative  merits  of  different  aands : 

The  prc^rtion  of  Toids  is  independent  of  the  size  of  the 
grains,  bnt  depends  npon  the  gradation  of  the  sizes;  and  vuriep 
with  the  form  of  the  grains  and  the  roaghneflB  of  the  snrfaoe.  A 
mass  <A  perfectly  smooth  spheres  of  uniform  size  wonld  have  the 
flame  proportion  of  voids,  whether  the  spheres  be  large  or  small. 
A  mass  ot  perfectly  smooth  spheres  packed  as  closely  as  possible 
wonld  have  26  per  cent,  of  voids;  bnt  if  the  spheres  are  packed  aa 
loosely  as  possible  the  voids  woald  be  48  per  cent.  A  promiscnons 
mass  of  bird-flhot  has  about  36  per  cent,  of  voida.  The  difference 
between  this  and  the  theoretical  minimum  per  cent,  for  perfectly 
emooth  spheres  is  due  to  the  variation  in  size,  to  roaghnesa  of  the 
flurface,  and  to  not  securing  in  all  parts  of  the  mass  the  arrangement 
of  the  shot  necessary  for  minimum  voids.  German  standard  aand 
has  gnuns  nearly  spherical  and  nearly  uniform  in  size,  having 
slightly  rough  surface,  and  has  41  per  cent,  voids  loose  (see  line  3, 
Table  10^).  The  difference  in  the  per  cent,  of  voids  between  this 
sand  and  a  mass  of  spheres  uniform  in  size  and  perfectly  spherical 
is  due  to  irregularitieB  in  form  and  to  roughness  of  surface  of  the 
sand  grains,  hnd  to  not  secnring  the  arrangement  of  the  grains 
necessary  for  minimum  voids.  Crushed  stone  retained  between  the 
same  sieves  as  German  standard  sand  has  65  per  cent,  of  voids  (see 
lines  1  to  3  of  Table  lOg),  the  excess  of  this  over  German  standard 
aand  being  due  to  the  rough  surfaces  and  sharp  corners  preventing 
the  grains  from  fitting  closely  together. 

If  the  mass  consists  of  a  mixture  ot  two  sizes  such  that  the 
smaller  grmns  can  occupy  the  voids  between  the  larger,  then  the 
proportion  of  voids  may  be  very  much  smaller  than  with  a  single 
size  of  grains.  For  this  reason  a  mixture  of  two  grades  of  sand  of 
widely  different  sizes  has  a  smaller  per  cent,  of  voids  than  any  one 
size  alone, — compare  lines  1  to  9  with  the  remainder  of  Table  10^. 

The  best  sand  is  that  which  has  graios  of  several  sizes  such  that 
the  smaller  grains  fit  into  the  voids  of  the  larger,  the  proportion  of 
any  particnlar  size  being  only  sufficient  to  fill  the  voids  between 


ovGoQi^lc 


AKT.  1.] 


I 

Z  i  ^ 
II 


mi 


SSo53StiS&S8i:S8S8£S8 


SSKSSSSSSSSS  : 


ss^sessssssK 


S3S7«S3S««3« 


ooosgaB-sB-ssg 


ssss^g^^'ssi 


°Si=3"K:8sS 


,41=. 
lull'"" 
iipi 

_|Sj.|.  .... 


ovGoQi^lc 


79;'  SAND.  [chap.  iiio. 

the  grains  of  the  next  larger  aize.  If  the  grains  are  spherical  and 
the  diameter  of  the  smaller  ia  about  one  fifth  of  the  diameter  of  the 
larger,  the  smaller  grains  irill  jnst  fit  into  the  interstice  between 
the  larger  ones.  The  smaller  the  voids  the  greater  the  economy, 
and  the  denser  and  stronger  the  mortar. 

The  finer  the  sand  the  more  nearly  nniform  the  size  of  the 
grains,  and  consequently  tha  greater  the  proportion  of  voids.  Also 
the  finer  the  saud  the  less  sharp  it  is,  and  consequently  the  greater 
the  surface  to  be  covered.  Therefore  a  coarse  sand  is  to  be  preferred 
to  a  very  fine  one — see  Tables  lOe  and  10/,  page  79e.  Further,  the 
advantage  of  coaree  sand  over  fine  increases  as  the  proportion  of 
cement  decreases,  since  vrith  the  smaller  proportions  of  cement  the 
voids  are  not  filled. 

114t.  Concluiion.  An  examination  of  the  preceding  data  shows 
,  that  very  fine  sand  makes  a  much  weaker  mortar  than  coarse  sand, 
and  also  that  natural  sands  vary  considerably  in  the  proportion  of 
voids  and  consequently  differ  in  the  amount  of  cement  required  to- 
prodnce  any  particular  strength.  Therefore  before  adopting  a  sand 
for  a  work  of  any  considerable  magnitude,  all  available  sands  should 
be  carefully  examined  with  reference  to  (1)  their  effects  npon  the 
strength  of  the  mortar,  (2)  their  per  cent,  of  voids  or  the  amoani 
of  cement  required  with  each,  and  (3)  their  cost.  If  mortar  of  any 
particular  strength  is  desired,  the  proportion  of  cement  shoald  be- 
adJQsted  according  to  the  fineness  and  voids  of  the  best  available 
sand. 

114y.  StoITE  SoSEEinveB.  The  finer  particles  screened  out  of 
cmshed  stone  are  sometimes  used  instead  of  sand.  For  ths 
physical  characteristics  of  stone  screenings  see  Nob.  16  and  17, 
P^e  79t. 

Experiments  show  that  sandstone  screenings  give  a  slightly 
stronger  mortar  than  natural  sand,  probably  because  of  the  greater 
sharpness  of  the  grains.  Crushed  limestone  usually  makes  a  con- 
siderably stronger  mortar,  in  both  tension  and  compression,  than 
natural  sand,  and  this  difference  seems  to  increase  with  the  age  of 
the  mortar.*  Part  of  the  greater  strength  is  unquestionably  due 
to  the  greater  sharpness  of  the  limestone  screenings,  and  the  part 

■  ADDual  Report  of  Obiet  of  EoglneerB,  U.  S.  A.,  18S3,  Port  3,  p.  3015 ;  do.  1S94, 
I>ut  4,  p.  2331;  do.  1B9S,  Fart  i,  p.  29G8;  Jour.  Weat.  Soo.  ot  Eugra.,  voL  ii,  pp.  394 
audUO. 


ovGoQi^lc 


AET.  2.]  QRATEL.  79ife 

that  increaaee  with  the  age  of  the  mortar  seems  to  be  due  to  some 
chemical  action  between  the  limestone  and  the  cement. 

114it.  Cost  and  Weight  of  Band.  The  price  of  reasonably  good 
sand  varies  from  40  cents  to  tl.60  per  yard,  according  to  locality. 

Sand  is  Bometimea  sold  by  the  ton.  It  weighs,  when  dry,  from 
80  to  115  poands  per  cnbic  foot  fsee  Table  lO^r,  page  79t),  or  aboat 
1  to  1^  tons  per  cabio  yard,  ' 

Abt.  2.    Gravel  and  Bbosen  Stoke. 

116.  The  term  gravel  is  sometimes  used  aa  meaning  a  miztnre 
of  coarse  pebbles  and  sand,  and  sometimes  as  meaning  pebbles  with-' 
ont  sand.  In  this  volume,  gravel  will  be  understood  as  a  miztare 
of  coarse  pebbles  and  sand. 

llfia.  Gravel  and  broken  stone  are  mixed  with  cement  mortar 
t«  make  an  artificial  stone  called  concrete  (Art.  2,  Chap.  IV),  The 
quality  of  the  concrete  varies  greatly  with  the  condition  of  the 
gravel  or  broken  stone,  but  unfortanately  too  little  attention  ig 
given  to  the  character  of  this  component. 

115£.  GkAvel.  To  be  suitable  for  use  in  making  concrete, 
gravel  sboald  be  clean,  and  it  should  be  composed  of  durable 
minerals,  and  the  size  of  the  pebbles  and  grains  should  be  sach  as 
to  give  minimum  voids. 

The  investigation  of  the  suitability  of  gravel  for  use  in  concrete 
is  essentially  the  same  as  that  of  sand,  which  has  been  fully  con- 
sidered in  the  preceding  article. 

The  physical  characteristics  of  pebbles  and  gravel  are  given  near 
the  foot  of  Table  lOA,  page  80.  Judging  from  the  little  data  that 
can  be  found  in  engineering  literature  and  from  all  the  information 
gathered  by  an  extensive  correspondence,  gravels  No.  16  and  Xo. 
17  of  the  table  are  representative  of  the  gravels  employed  in  actual 
work. 

Concerning  No.  18  notice  that  65  per  cent,  passed  a  Ko.  5 
screen;  and  therefore  this  mixture  could  more  properly  be  called 
gravelly  sand.  If  one  fifth  of  the  material  passing  the  No.  5  sieve 
be  omitted,  the  voids  of  the  remainder  will  be  only  15  per  cent, 
when  rammed ;  in  other  words,  if  one-tenth  of  this  gravel  were 
sifted  on  a  No.  5  sieve  and  that  portion  retained  on  the  sieve  were 
mixed  with  the  remainder  of  the  original,  the  voids  would  be 
reduced  to  15  per  cent.,  which  would  improve  the  qu^ity  of  the 


ovGoQi^lc 


791  BKOKEH  STONB.  [OHAP.  IlIO. 

gravel  for  making  concrete.     This  is  a  Talnable  hint  as  to  the  pos- 
sible advantage  of  sifting  «T«n  a  portion  of  the  gravel. 

115c.  BsoKZV  Stohx.  Any  bard  and  durable  stone  ia  saitable 
for  use  in  making  concrete.  It  is  usual  to  specify  that  the  stone 
for  concrete  shall  be  broken  to  pass,  every  way,  through  a  S-incb 
ring,  although  it  is  sometimes  broken  to  pass  a  1-incb  ring.  The 
stone  should  be  broken  small  enough  to  be  conveniently  bandied 
and  easily  incorporated  with  the  mortar.  The  finer  the  stone  is 
broken  the  greater  its  cost,  and  the  greater  the  surface  to  be  coated; 
and  consequently  the  greater  the  amount  of  cement  required. 
Approximately  cubical  pieces  are  preferable  to  long,  thin,  sj^intery 
fragments,  since  the  latter  are  liable  to  break  under  pressure  or 
while  being  rammed  into  place,  and  thus  leave  two  uncemented 
surfaces. 

116d.  Toidi.  The  proportion  of  voids,  i.e.,  interstices  between 
the  fragments,  may  be  determined  in  either  of  two  ways  as  follows : 

1.  The  voids  may  be  found  by  filling  a  vessel  with  the  aggregate, 
and  then  pouring  in  water  until  the  vessel  ia  full.  The  amount  of 
water  required  to  fill  the  voids  divided  by  the  amount  of  water 
alone  tbe  vessel  will  contain  la  the  proportion  of  voids  in  the 
aggregate.  The  amount  of  water  in  each  case  may  be  determined 
by  weight  or  by  volume. 

For  Borne  preoantlons  applicable  in  this  case,  particularly  in 
determining  the  voids  of  broken  stone  contuning  considerable  fine 
material,  see  g  114/.  If  the  material  is  porous,  it  is  beat  to  wet  it, 
80  as  to  determine  tbe  voids  eitfirior  to  the  fragments.  The  water 
absorbed  by  tbe  material  should  not  be  included  in  the  voids,  since 
when  the  concrete  is  mixed  the  E^gregate  is  usually  dampened, 
particularly  if  it  is  porous.  Of  course  in  wetting  the  aggregate 
before  determining  the  voids  no  loose  water  should  remain  in  the 
pile.  The  voids  may  be  determined  for  the  material  either  loose ' 
or  compacted.  The  proportion  of  the  voids  ia  found  to  determine 
the  amount  of  mortar  required  to  fill  the  voids  of  the  concrete  in 
place;  and  therefore  it  is  better  to  determine  the  voids  in  the  com- 
pacted mass,  since  the  concrete  is  usually  rammed  when  laid.  The 
•compacting  may  be  done  by  shaking  or  by  ramming,  the  latter 
.heing  the  better  since  it  more  nearly  agrees  with  the  conditions 
Tinder  which  the  concrete  is  used,  and  further  since  in  compacting 
by  shaking  tbe  smaller  pieces  work  to  tbe  bottom  and  the  latter  to 
the  top,  which  separation  increases  the  voids. 


ovGoQi^lc 


ART.  2.]  VOIDS.  79to 

This  method  usually  gives  results  slightly  too  Bmall,  owing  to 
the  difficulty  of  excliidiDg  all  the  air-bubbles.  However,  a  high 
degree  of  accuracy  can  not  be  expected,  since  the  material  is  neither 
uniform  in  composition  nor  uniformly  mixed. 

3.  To  find  the  voids  determine  the  specific  gravity  of  a  frag* 
ment  of  the  material  (§  7) ,  and  from  that  the  weight  of  a  unit  of 
Tolume  of  the  solid;  and  also  weigh  a  unit  of  volume  of  the  aggre- 
gate. The  difference  between  these  weights  divided  by  the  firat 
gives  the  proportion  of  voids. 

il5e.  Table  lOA,  page  80,  shows  the  per  cent,  of  voids  ia 
various  grades  of  broken  stones  used  in  making  concrete. 

The  per  cent,  of  voids  in  broken  stone  varies  with  the  hardness 
of  the  stone,  the  form  of  the  fragmente,  and  the  relative  propor- 
tions of  the  several  sizes  present.  The  last  is  the  most  important. 
If  broken  stone  passing  a  3j-inch  ring  and  not  a  |-inch  screen 
be  separated  into  three  sizes,  any  one  size  will  give  from  52  to  54 
per  cent,  of  voids  loose,  white  equal  parts  of  any  two  of  the  three 
sizes  will  give  48  to  50  per  cent.,  and  a  mixture  in  which  the 
volume  of  the  smallest  size  is  equal  to  the  sum  of  the  other  two 
gives  a  trifle  less  than  48  per  cent.  Hotico,  however,  that  un- 
screened crushed  stone  has  only  32  to  35  per  cent,  voids — see  lines 
7  and  11  of  Table  lOA.  This  is  a  very  excellent  reason  for  not 
screening  the  broken  stone  to  be  used  in  making  concrete. 

A  mass  of  pebbles  baa  only  about  three  fourths  as  many  voids 
as  a  mass  of  broken  etone  having  pieces  retained  between  the  same 
screens.  Notice,  however,  that  gravel,  i.e.  pebbles  and  sand,  has  a 
leas  proportion  of  voids  than  pebbles  alone. 

lis/.  Coat  and  Weight.  The  cost  of  breaking  stone  for  con- 
crete varies  from  fiO  to  75  cents  per  cubic  yard  according  to  kind 
of  stone  and  size  of  plant.*  The  original  cost  of  the  stone  and 
transportation  expenses  are  too  variable  to  attempt  to  generalize. 
Ordinarily  the  cost  of  broken  stone  is  not  more  than  tl.50  to  $2.00 
per  cubic  yard  f.  o.  b.  cars  at  destination. 

The  weight  of  broken  stone  varies  from  85  to  120  lbs.  per  cubio 
foot  (see  Table  lOh,  page  80) ;  or  about  3200  to  3200  pounds  per 
oabic  yard. 

*  ^r  addlUonal  dsta,  see  Bapplemeiital  Notes,  No.  5,  p.  (MS. 


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jvGooi^le 


FART  II. 

METHODS  OF  PREPARING  AND  USING  THE 
MATERIALS. 


CHAPTER  IV. 

HORTAB,  CONCRETE,  AND  ARTIFICIAL  STONE. 

Abt.  1.     MOBTAB. 

116.  Mortar  is  a  miztare  of  the  paete  of  cement  or  lime  vith 
sand.  Id  common  mortar,  the  cementing  sabfitanee  is  ordinary 
lime;  in  hydraulic  mortar,  it  is  hydraalio  cement. 

117.  COKKOV  Like  Kobtar.  Mortar  made  of  the'  paate  of 
«ommon  or  fat  lime  ia  extensirely  used  on  account  of  (1)  its  intrin- 
sic oheapnesB,  (2)  ita  great  economic  advantage  oving  to  ite  great 
increase  of  volume  in  slaking,  and  (3)  the  simplicity  attending  the 
mixing  of  the  mortar.  On  account  of  the  augmentation  of  volnme, 
the  paste  of  fat  lime  shrinks  in  hardening,  to  snch  an  extent  that 
it  can  not  be  employed  as  mortar  without  a  large  doee  of  sand. 

Ab  a  paste  of  common  lime  sets  or  hardens  very  slowly,  even  In 
the  open  air,  nnlees  it  he  sabdivided  into  small  particles  or  thin 
films,  it  is  important  that  the  volnme  of  lime  paste  in  common 
mortar  shonld  he  bat  slightly  in  excess  of  what  is  sufficient  to  coat 
all  the  grains  of  sand  and  to  fill  the  voids  between  them.  If  this 
limit  be  exceeded,  the  strength  of  the  mortar  will  be  impaired. 
With  most  sands  the  proper  proportions  will  be  from  S.5  to  3 
ToInmeB  of  sand  to  1  volume*<of  lime  paate.  Generally,  if  either 
less  or  more  sand  than  this  be  used,  the  mortar  will  be  injured, — 
in  the  former  case  from  excess  of  time  paste,  and  in  the  latter  from 

81 


ovGoQi^lc 


83  UOKTAR,  [chap.  IT. 

porosity.     Notice  that  the  yolnme  of  the  Tesulting  mortar  is  abonfe 
equal  to  the  volame  of  the  sand  alone. 

118.  The  ordinary  method  of  slaking  lime  coosistB  in  placing 
the  lamps  in  a  layer  6  or  8  inches  deep  in  either  a  vater-tight  box, 
or  a  basin  formed  in  the  sand  to  be  nsed  in  mixing  the  mortar,  and 
ponring  npon  the  Inmps  a  qnantity  of  water  %i  to  3  times  the 
Tolnme  of  the  lime. 

This  process  is  liable  to  great  abnse  at  the  hnnds  of  the  work> 
men.  They  are  apt  either  to  nse  too  mach  water,  which  reduces 
the  slaked  lime  to  a  semi-flnid  condition  and  thereby  injares  itg 
binding  qaalitiee;  or,  not  having  nsed  enongh  water  in  the  first 
place,  to  seek  to  remedy  the  error  by  adding  more  after  the  slaking 
has  well  progressed  and  a  portion  of  the  lime  is  already  rednced  to 
powder,  thns  snddeuly  depressing  the  teraperatnre  and  chilling  the 
lime,  which  renders  it  granalar  and  lumpy.  It  is  also  very  im- 
portant that  the  lime  should  not  be  stirred  while  slaking.  The 
essential  point  ia  to  secnre  the  redaction  of  all  the  lumps.  Cover- 
ing the  bed  of  lime  with  a  tarpanlin  or  with  a  layer  of  aand  retains 
the  heat  and  accelerates  the  slaking.  All  the  lime  neceasary  for 
any  required  qnantity  of  mortar  should  be  sl^ed  at  least  one  day 
before  it  is  incorporated  with  the  sand. 

After  the  lime  is  slaked  the  sand  is  spread  evenly  over  the  paste^ 
and  the  ingredients  are  thoroughly  mixed  with  a  shovel  or  hoe,  & 
little  water  being  added  occasionally  if  the  mortar  is  too  stiff. 

119.  Mortar  composed  of  common  lime  and  sand  is  not  St  for 
thick  walls,  becaase  it  depends  npon  the  slow  action  of  the  atmos- 
phere for  hardening  It;  and,  being  exclnded  from  the  air  by  tho 
sorronnding  masonry,  the  mortar  in  the  interior  of  the  mass 
hardens  only  after  the  lapse  of  years,  or  perhaps  never."  The 
mortar  of  cement,  if  of  good  quality,  seta  immediately;  and,  as  far 
aa  is  known,  continues  forever  to  harden  without  contact  with  the 
(ur.  Cement  mortar  is  the  only  material  whose  strength  increases 
with  age.  Owing  to  its  not  setting  when  excluded  from  the  air, 
common  lime  mortar  shonld  never  be  used  for  masonry  coostrnctioQ 
under  water,  or  in  soil  that  is  constantly  wet;  and,  owing  to  its 
weakness,  it  is  nnsnitable  for  structures  requiring  great  strength,  or 

•  Lime  mortar  taken  (rom  the  walls  olaocieiit  buildings  has  been  touod  to  bo- 
onlf  GO  to  80  per  aent.  saturated  with  carbonio  acid  otter  nearly  3,000  years  ol  ex- 
poanre.  Lime  mortar  3.000  jaars  old  has  been  found  la  aubterranean  vaalta,  In. 
«iaaUy  the  ooodlUou,  exoopt  tor  a  tbln  eruat  on  top,  at  freshly  mixed  mortar. 


ovGoQi^lc 


ART.  1.]  UBTEODS   OF   PROPOBTIONIKO.  S3- 

subject  to  shock.  Its  use  in  engineeriDg  masonry  has  been  aban- 
doned on  all  flrst-class  railroads.  Cement  iB  bo  cheap  that  it  coald 
pro&tablj  be  Bab8titnt«d  tor  lime  in  the  mortar  for  ordinary 
masonry. 

130.  Htdbaitlic  Like  Hoktab.  With  mortars  of  hydraalio 
lime  the  volume  of  sand  should  not  be  less  than  1.8  times  that  of 
the  lime  paste,  in  order  to  secure  the  best  results  regardless  of  cost. 
The  usual  proportions  are,  hovever,  for  ordinary  work,  the  same 
as  in  common  mortars,  care  being  taken  to  incorporate  sufficient 
paste  to  coat  all  the  grains  of  sand  and  to  fill  up  the  voids  between 
them. 

.  121.  Htssaitlic  Cekeh  Hoeiab.  Hydraulic  cement  mortar 
hardens  simultaneonsly  and  uniformly  throughout  the  maas,  and  if 
itbft  cement  is  good  continues  to  gain  in  hardness  with  age, — th& 
'  slov-setting  cements  for  a  longer  time  than  the  quick-setting.  For 
the  best  results  the  cement  paste  should  be  jnst  saSlcieut  to  coat 
.  the  grains  and  fill  the  voids  of  the  sand.  More  cement  than  this 
adds  to  the  cost  and  weakens  the  mortar  (see  §  100).  If  the  amoant 
of  cement  is  not  sufficient  to  coat  all  the  grains  and  fill  the  voids, 
the  mortar  will  be  weak  and  porous,  and  hence  will  not  be  darable. 
A  dense,  impervious  mortar  is  particularly  desirable  for  masonry 
exposed  to  sea-water,  to  exclude  the  water  from  the  interior  of  the 
mass  and  prevent  its  chemical  as  well  as  physical  action  apon  the 
cement. 

182.  Xethoda  of  Proportioning.  In  laboratory  work  the  propor- 
tions of  the  cement  and  sand  are  uniformly  determined  by  weigh- 
ing; but  there  is  no  uniform  practice  of  measuring  the  proportions 
on  the  work.  One  of  the  three  following  methods  is  generally 
employed. 

1.  By  Weight.  The  most  accurate  bnt  least  oommoa  method 
is  to  weigh  the  ingredients  for  each  batch.  This  method  is  incon- 
venient in  practice,  and  adds  somewhat  to  the  cost  of  the  work; 
and  therefore  occasionally  the  weight  of  a  unit  of  volume  of  the 
sand  and  of  the  cement  is  determined,  and  the  relative  volumes  of 
the  ingredients  are  fixed  accordingly,  the  actual  proportioning  being 
done  by  volumes.  Cement  is  bought  and  sold  by  weight,  and 
hence  it  is  very  appropriate  to  proportion  the  mcrtar  by  weight. 

2.  Packed  Cement  and  Loose  Sand.  A  commercial  barrel  of 
cement  is  mixed  with  one  or  more  barrels  of  loose  sand,  i.e.,  the 
proportioning  is  done  by  mixing  one  volnme  ot  packed  cement  with. 


ovGoQi^lc 


S4  MOBTAtt.  [chap.  it. 

one  or  more  Tolames  of  loose  Band.  This  method  ie  freqnentlj' 
oaed.  As  far  as  the  cement  is  concerned,  it  is  as  accurate  as  tbe 
first,  since  the  veight  and  volnme  of  a  barrel  of  cement  ma;  readil; 
be  known  when  only  whole  barrels  are  used, — as  is  nsnally  tbe  case. 
Hven  though  the  cement  is  received  in  bags,  the  barrel  of  packed 
cement  ia  still  a  ooDTenient  nnit,  for  an  integral  number  of  bags, 
usnally  three  or  four,  are  eqnal  in  weight  to  a  barrel.  As  far  as 
the  sand  is  concerned  this  method  is  not  as  accurate  aa  the  first. 
TFhe  weight  of  the  sand  is  affected  by  the  amount  of  moisture 
present;  but  a  small  amount  of  moisture  sfEects  the  Tolnme  in  a 
greater  proportion  than  the  weight.  For  example,  the  addition  of 
3  per  cent,  of  water  (by  weight)  thoroaghly  mixed  with  dry  sand 
increases  tbe  Tolume  of  the  sand  nearly  SO  per  cent.*  Therefore  if 
the  mortar  is  proportioned  by  Tolumes,  damp  sand  will  give  a  richer 
mortar  than  dry  sand.  The  effect  of  moisture  on  the  volume  ia 
greater  the  finer  the  sand,  and  decreases  as  the  amount  of  moistare 
inoreasee.  Measuring  the  sand  by  volumes  is  inaccurate  also  owing 
to  the  packing  of  the  sand. 

Except  for  the  inaccuraci^  in  measuring  the  sand,  tbia  method 
gives  practically  the  same  results  for  Portland  as  the  first  method, 
since  ordinarily  a  unit  of  volume  of  packed  cement  and  of  sand 
weighs  substantially  the  same;  viz.,  100  pounds  per  cubic  foot. 
Since  natural  cement  when  packed  in  barrels  nsn^ly  weighs  about 
75  pounds  per  cubic  foot,  a  mortar  of  1  part  natural  cement  to 
1  part  sand  by  weight  is  equivalent  to  IJ  parts  cement  to  1  part 
«and  by  Tolumea  of  packed  cement  and  loose  sand. 

3.  Loose  Cement  and  Loose  Sand.  A  volume  of  host  cement  is 
mixed  with  one  or  more  volumes  of  loose  sand.  The  actual  propor- 
tioning is  usually  done  by  emptying  a  bag  or  fractional  part  of  a 
barrel  of  cement  into  a  wheelbarrow,  and  filling  one  or  more  wheel- 
barrows equally  full  of  sand.  As  far  as  the  sand  is  concerned,  this 
method  is  as  inaccurate  as  the  second ;  and  it  is  also  subject  to  great 
Tariationa  owing  to  differences  in  specific  gravity,  fineness  and 
packing  of  the  cement.  Even  though  inaccurate,  it  is  very  fre- 
quently employed.  It  is  the  most  convenient  method  when  the 
cement  is  shipped  in  bulk, — which  is  only  rarely. 

Occasionally  the  actual  proportioning  is  done  by  throwing  into 

•  Foret,  Ohiet  o(  Laboratorr  Ponts  et  CbausB^eB,  In  Engineering  Nttot,  vol. 
xxTll.  p.  810.  For  BimlUr  data  B«e  Beport  at  Chief  ol  Engineers,  U.  8.  A.,  1S9B, 
P.298S. 


ovGoQi^lc 


ABT.  1.]  mSINQ   THZ   UOBTA.B.  85 

the  mortor-box  one  shoveUtil  of  cement  to  one  or  more  ahoveUnla 
of  aand.     This  is  rery  crnde,  and  should  never  be  permitted. 

Since  a  commercial  barrel  of  Portland  nill  make  1.1  to  1.4 
barrels  if  measured  loose,  a  mortar  composed  of  1  part  Portland 
cement  to  1  part  sand,  by  weight,  is  equivalent  to  0,7  to  0.8  parts 
«ement  to  1  part  sand  by  Tolnmes  of  loose  cement  and  loose  sand; 
and  a  mortar  composed  of  1  part  nataral  cement  to  1  part  aand, 
by  weight,  is  equivalent  to  O.SO  to  0.75  parts  cement  to  1  part  of 
Band  by  volames  of  loose  cement  and  loose  sand. 

122a.  For  a  tabular  statement  incidentally  showing  the  relatire 
omonntB  of  cement  required  by  the  three  methods  of  proportioning, 
see  Table  11,  page  88. 

138.  Proportions  in  Praotiee.  The  proportions  commonly  used 
in  practice  are:  for  Portland  cement,  1  TOlame  of  cement  to  2  or  3 
Tolnmes  of  sand;  and  for  natural  cement,  1  volume  of  cement  to  1 
or  2  Tolnmes  of  sand.  The  specifications  are  usually  defective  in 
not  defining  vhich  method  is  to  be  employed  in  proportioning. 
This  is  a  matter  of  great  importance.  Compared  with  the  second 
method  of  proportioning  in  1 122,  the  third  requires  for  Portland 
only  0.7  to  0.8  as  much  cement,  and  for  natural  cement  only  0.1 
to  0.5  as  much. 

134.  *^^^Tlg  the  Hortar.  When  the  mortar  is  required  in  small 
quantities,  as  for  use  in  ordinary  masonry,  it  is  mixed  as  follows: 
Aboat  half  the  sand  to  be  nsed  in  a  batch  of  mortar  is  spread  evenly 
over  the. bed  of  the  mortar-box,  then  the  dry  cement  is  spread 
evenly  over  tbe  sand,  and  finally  the  remainder  of  the  aand  is 
spread  on  top.  The  sand  and  cement  are  then  mixed  with  a  hoe 
or  by  turning  and  Te-taining  with  a  shovel.  Tbe  misiug.can  he 
done  more  economically  with  a  shovel  than  with  a  hoe;  but  the 
eftectiveneas  of  the  shovel  varies  greatly  with  the  manner  of  using 
it.  It  is  not  sufficient  to  simply  turn  tbe  mass;  but  the  sand  and 
cement  should  be  allowed  to  run  off  from  tbe  shovel  in  such  a 
manner  as  to  thoroughly  mix  them.  Owing  to  the  difficulty  of 
getting  laborers  to  do  this,  the  hoe  is  sometimes  prescribed.  If 
ekiUfuUy  done,  twice  taming  with  a  shovel  will  thoroughly  mix 
the  dry  ingredients;  although  four  turnings  are  sometimes  specified, 
and  occasionally  as  high  as  six  (see  g  260).  It  is  very  important 
that  the  sand  and  cement  be  thoroughly  mixed.  When  thoroughly 
mixed  it  will  have  a  uniform  color. 

Tbe  dampness  of  tbe  sand  is  a  matter  of  some  importance.     It 


ovGoQi^lc 


¥6  itosTAS.  [chap.  IV. 

the  sand  U  yarj  damp  vhen  it  is  mixed  with  the  cement,  anfficieat. 
moistare  may  be  given  oS  to  cause  the  cement  to  set  partially^ 
which  may  materially  decrease  its  strength.  This  ie  particnlarly 
noticeable  with  qnick-settiog  cementB. 

The  dry  mixture  is  then  shoveled  to  one  end  of  the  box,  and 
water  is  poured  into  the  other.  The  sand  and  cement  are  then 
drawn  down  with  a  hoe,  small  qaantities  at  a  time,  and  mixed  with 
water  nntil  enough  has  been  added  to  make  a  stiff  paste.  The 
mortar  shonld  be  vigoroasly  worked  to  insnre  a  uniform  product. 
When  the  mortar  is  of  the  proper  plasticity  the  hoe  should  be  clean 
when  drawn  out  of  it,  or  at  most  hut  very  little  mortar  shonld  stick 
to  the  hoe. 

Cements  vary  greatly  in  their  capacity  for  water  (see  §  104),  the- 
naturals  requiring  more  than  the  Portlands,  and  the  fresh-ground 
more  than  the  stale.  An  excess  of  water  is  better  than  a  deficiency, 
particularly  with  a  quick-setting  cement,  as  its  capacity  for  com- 
bining with  water  is  very  great ;  and  farther  an  excess  la  better  tlian 
a  deficiency,  owing  to  the  possibility  of  the  water  evaporating 
before  it  has  oombined  with  the  cement.  On  the  other  hand,  an 
excess  of  water  makes  a  porous  and  weak  mortar.  If  the  mortar  is 
stiff,  the  brick  or  stone  should  be  dampened  before  laying;  else  tho 
brick  will  absorb  the  water  from  the  mortar  before  it  can  set,  and 
thus  destroy  the  adherence  of  the  mortar.  In  hot  dry  weather,  the 
mortar  in  the  box  and  also  in  the  wall  should  be  shielded  from  the 
direct  rays  of  the  sun. 

When  mortar  is  required  in  considerable  quantities,  as  in  making 
concrete,  it  is  usually  mixed  by  machinery  (see  §  156n). 

125.  Qboitt.  This  is  merely  a  thin  or  liquid  mortar  of  lime  or 
cement.  The  interior  of  a  w^l  is  sometimes  laid  up  dry,  and  the 
grout,  which  is  poured  on  top  of  the  wall,  is  expected  to  find  ita 
way  downwards  and  fill  all  voids,  thus  making  a  solid  mass  of  the 
wall.  Qront  should  never  be  used  when  it  can  he  avoided.  It 
made  thin,  it  is  poroos  and  weak;  and  if  made  thick,  it  fills  only 
the  upper  portions  of  the  wall.  To  get  the  greatest  strength,  the 
mortar  should  have  only  enongh  water  to  make  a  stiff  paste — the 
less  water  the  better. 

126.  Data  fos  Estihates.  The  following  will  be  found  use- 
ful in  estimating  the  amounts  of  the  different  ingredients  necessary 
to  produce  any  required  quantity  of  mortar: 

Lima  weighs  about  330  pounds  per  barrel.     One  barrel  of  lima 


ovGoQi^lc 


ART.  1,]  DATA    FOR  ESTIMATES.  S7 

-vill  make  abont  %i  barrels  (0.3  ca.  yd.)  of  stiff  lime  paste.  Ooe 
barrel  of  lime  paste  and  three  barrels  of  sand  will  make  abont 
three  barrels  (0.4  ca.  yd.)  of  good  lime  mortar.  One  barrel  of 
nnalaked  lime  will  make  aboat  6.75  barrels  (0.95  en.  yd.)  of  1 
to  3  mortar. 

Portland  cement  weighs  370  to  380  pounds  per  barrel  net  (see 
§  77,  page  54).  The  capacity  of  a  Portland  cement  barrel  Taries 
from  3.20  to  3.75  ca.  ft.,  the  aven^  being  3.49*  or  practically 
3.50  en.  ft.  A  barrel  of  Portland  will  make  from  1.1  to  1.4  bar- 
rels if  measnred  loose.  A  cubic  foot  of  packed  Portland  cement 
(105  ponnds)  and  aboat  0.33  en.  ft.  of  water  will  make  1  en.  ft.  of 
■Stiff  paste;  and  a  cubic  foot  of  loose  cement  (gently  shaken  down 
bat  not  compressed)  will  make  abont  0.8  ca.  ft.  of  stiff  paste.' 

Natural  cement  weighs  from  865  to  300  pounds  per  barrel  net 
(see  §  77,  page  54).  The  capacity  of  a  natural  cement  barrel  varies 
from  3.37  to  3.80  ca.  ft.,  the  average  being  3.52,*  or  practically 
3.50  en.  ft.  A  barrel  of  natural  cement  will  make  from  1.33  to 
1.50  barrels  if  measnred  loose.  Volame  for  volnme,  natural 
cement  will  make  abont  the  same  amonnt  of  paBt«  as  Portland;  or 
a  cable  foot  of  packed  natnral  cement  (75  pounds)  sod  abont  0.45 
CO.  ft.  of  water  will  make  1  en.  ft.  of  stiff  paste,  and  a  cable  foot 
of  loose  cement  (gently  shaken  down,  but  not  compressed)  will 
maKe  abont  0.8  ou.  ft.  of  stiff  paste. 

128.  Quantities  for  a  Yard  of  Mortar,  Table  11,  page  88, 
shows  the  approximate  quantities  of  cement  and  sand  required  for 
■a  cubio  yard  of  mortar  by  the  three  methods  of  proportioning 
described  in  §  122.  The  table  is  based  upon  actual  tests  made  by 
mixing  3^  cubio  feet  of  the  several  mortars;  f  but  at  best  such  date 
-can  be  only  approximate,  since  so  much  depends  upon  the  specifio 
gravity,  fineness,  compactness,  etc.,  of  the  cement;  upon  the  fine- 
ness, hamidity,  sharpness,  compactness,  etc.,  of  the  sand;  and 
npon  the  amoont  of  water  used  in  mixing.  The  sand  employed  in 
-deducing  Table  11  contained  37  per  cent,  of  voids  when  measured 
loose;  and  the  plasticity  of  the  mortar  was  each  that  moiatnre 
flashed  to  the  sarface  when  the  mortar  was  stmok  with  the  baok 
-of  the  shovel  Qsed  in  mixing. 

The  Tolnme  of  the  resulting  mortar  is  always  less  than  the  sum 
*  Tbb  Tbchkooiufh,  UnlTeratt;  of  lUlnoia,  No.  II,  p.  101. 
t  Bf  L.  a  Bablii,  Aulstuit  U.  S.  Englneer—Me  Baport  ol  Ohlsf  of 

>D.aA.,  ia»t.p.383e. 


ovGoQi^lc 


[chap.  it. 


3    S    S    S    S 


jvGooi^le 


Data  tor  bsthiates. 


TABLE  13. 
Amovst  or  HoRTAB  beiiiiikbd  fob  a  Cdbio  Tabd  ot  Habohbt. 


^o.■ 

DBKnoFTloii  or  HuontT. 

Hoaru. 

Mla. 

Hu. 

0.08 
0.00 
0.10 
0.25 
0.85 

0.S8 
O.SO 
0.13 
0.20 

Brickwork,— UADcUrd  rize(g  266)  uid  i"      jolata 

rtof"  .... 

rtoj""    .... 

CoDcrete-sM  Tablea  ISd  and  18«.  pagM  llSf,  IISA. 

0.1» 
0.8S 
0.40 

10 

large  stoaes,  rough  bammsr  dreaaed 

8quared.alone  masonry,— 18"  couraea  and  I"  jdots. . . . 
ir      ■•      "    ■•     "    .... 

0.80 
O.IS 
0.26 

of  the  TolnmeB  of  the  cement  and  sand,  or  of  the  paste  snd  sand, 
becaase  part  of  the  paste  enters  the  Toids  of  the  sand;  but  the 
Tolnme  of  the  mortar  is  always  greater  than  the  snm  of  the  Tolames 
of  the  paste  and  the  solids  in  the  sand,  becaase  of  imperfect  mixing 
and  also  becanse  the  paste  coats  the  grains  of  sand  and  thereby 
increases  their  size  and  consequently  the  Tolnme  of  the  interBtices 
betveen  them.  This  increase  in  Tolnme  varies  with  the  dampness 
and  compactness  of  the  mortar.  For  example,  the  volume  of  a 
rather  dry  mortar  with  cement  paste  equal  to  the  voids,  when 
compacted  enough  to  exclnde  great  voids,  was  136  per  cent,  of  the 
BQm  of  the  volumes  of  the  paste  and  solids  of  the  sand ;  and  the 
same  mortar  when  rammed  had  a  volume  of  102  to  104  per  cent. 
If  the  paste  is  more  than  equal  to  the  voids,  the  per  cent,  of  in- 
crease is  less;  and  if  the  paste  is  not  equal  to  the  voids,  the  per  cent, 
of  increase  is  more.  The  excess  of  the  volume  of  the  mortar  over 
that  of  the  sand  increases  with  the  fineness  of  the  sand  and  with 
the  amount  of  mortar  used  in  mixing. 

129.  Hortar  for  a  Yard  of  Xaionry.    Table  13,  page  89,  gives 


ovGoQi^lc 


■flO  UOUTAB.  [CHAP.  IV. 

data  ooDcemiag  the  amoatit  of  mortar  required  per  cubic  jard  for 
the  different  classcB  of  masoniy,  extracted  from  sncceeding  pages 
of  this  Tolame;  and  are  collected  here  for  greater  cooTenienoe  in 
making  estimates. 

130.  STBEiroTE  OF  KoBiAK.  The  Btrength  of  mortar  ia 
dependent  upon  the  strength  of  the  cementing  material,  upon  the 
strength  of  the  sand,  and  npon  the  adhesion  of  the  former  to  the 
latter.  The  kind  and  amount  of  strength  required  of  mortar 
depends  npon  the  kind  and  purpose  of  the  maeonry.  If  the  blocks 
are  large  aad  well  dressed,  and  if  the  masonry  is  subject  to  com- 
pression only,  the  mortar  needs  only  hardness  or  the  property  of 
resisting  compression ;  hard  sharp  grains  of  sand  with  comparatively 
little  cementing  material  woald  satisfy  this  requirement  fairly  well. 
If  the  blocks  are  small  and  irregular,  the  mortar  should  have  the 
capacity  of  adhering  to  the  surfaces  of  the  stones  or  bricks,  so  as  to 
prevent  their  displacemeDt ;  in  this  case  a  mortar  ricti  in  a  good 
cementing  material  should  be  used.  If  the  masonry  is  liable  to  be 
enbject  to  lateral  or  oblique  forces,  the  mortar  should  possess  both 
adhesion  and  cohesion. 

131.  Tensile  Strength.  Fig.  5  shovs  the  effect  of  time  upon 
the  strength  of  various  mortars.  The  diagram  represents  the 
average  results  of  a  great  nnmber  of  experiments  made  in  connec- 
tioQ  with  actual  practice.  Eesnlts  which  were  nniformly  extremely 
high  or  low  as  compared  with  other  experiments  were  exclnded  on 
the  assnmption  that  the  difference  was  dae  to  the  method  of  monld- 
ing  and  testing.  Since  the  individual  v&lnes  plotted  were  them- 
selves means,  there  were  no  very  erratic  results,  and  consequently 
the  lines  are  quite  reliable.  There  were  fewer  experiments  for  the 
larger  proportions  of  sand  to  cement,  and  hence  the  curves  are  less 
accurate  the  larger  the  proportion  of  sand. 

The  line  for  the  strength  of  lime  mortar  probably  represents  the 
nuudmnm  value  that  can  be  obtained  by  exposing  the  mortar  freely 
to  the  air  in  small  briquettes.     This  line  is  not  well  determined. 

Unusually  hard-burned  Portland  cements  when  tested  neat 
will  show  a  greater  strength  than  that  given  in  the  diagrams. 
Very  fine  cement  when  mixed  with  sand  will  show  greater  strength 
ihan  that  given  by  Fig.  5.  Ag^n,  the  diagram  shows  neat  cement, 
both  Portland  and  natural,  stronger  than  any  proportion  of  sand, 
while  frequently  neat  cement  mortar  is  not  as  strong  as  a  mortar 
■composed  of  one  part  sand  and  one  part  cement — particularly  at 


ovGoQi^lc 


•.  1.] 


TENSILE   8TRENOTH. 


91 


"the  greater  agee.  However,  notwithetaading  these  exceptions,  it 
is  b^ieved  that  the  resnlts  represent  fair  average  practice.  The 
proportions  of  sand  to  cement  were  determined  by  weight. 

132.  The  reenlta  in  Fig.  5  are  tabulated  in  another  form  in 
,  to  show  the  effect  of  varying  the  proportions  of  the  sand 


«nd  cement,  and  also  to  show  the  relative  strength  of  natural  and 
Portland  cement  mortars  at  different  ages.  The  curves  of  Fig,  6 
are  especially  nsefnl  in  discussing  the  question  of  the  relative 
eoonomy  of  Portland  and  natural  cement  (g  136).  Por  example, 
assnme  that  we  desire  to  know  the  strength  of  a  1  to  2  natursj 
cement  mortar  a  year  old,  and  also  the  proportions  ot  a  Portland 
cement  mortar  of  equal  strength.     At  the  bottom  of  the  lover 


ovGoQi^lc 


92  MORTAB.  [OHAP.  IT.   ■ 

right-haud  dugrun  of  Fig.  6  find  the  proportion  of  sand  in  thd 
mortar,  which  in  this  case  is  2 ;  follow  th«  correeponding  line  np 
ootil  it  iDtflreects  the  "  natural "  line.  The  elevation  of  this  in- 
tersection above  the  biee,  as  read  from  the  figure  at  the  side  of 
the  diagram,  b  the  strength  of  the  specified  mixture,  which  in  this 


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Parts  dand  to  I  Part  Cement   by  ]A/eight 


oaae  ia  aboat  350  ponnds  per  sqnare  inch.  The  second  part  of  the- 
problem  then  is  to  detennine  the  proportions  of  a  Portland  cement 
mortar  which  will  have  a  strength  of  250  ponnda  per  square  inch. 
Find  the  250  point  on  the  Bcale  at  'the  side  of  the  diagram,  and 
imagine  a  horizontal  line  paaaing  tbroogh  this  point  and  intersect* 


ovGoQi^lc 


ART,  1.]  COHPRESSIVE   8TKEK0TB.  93 

ing  the  "  Portland  "  line;  from  tbia  point  of  inteTsection  draw  a 
Tertical  line  to  the  base  of  the  diagram,  and  thia  point  of  intersec- 
tion gives  the  required  number  of  volames  of  sand  to  one  Tolnme  of 
cement,  which  ii^  this  case  is  5.5.  Therefore  a  1  to  2  natural 
mortsr  a  year  old  has  a  strength  of  250  pounds  per  square  inch,  and 
is  then  eqniralent  to  a  1  to  5.5  Portland  mortar, 

183.  Compreuive  Strenifth.  But  few  experiments  have  been 
made  npon  the  compreBsive  strength  of  mortar.  An  examination 
of  the  results  of  about  sixty  experiments  made  with  the  Watertown 
testing-machine  seems  to  show  that  the  compressive  strength  of 
mortar,  as  determined  by  testing  cubes,  is  from  8  to  10  times  the 
tenule  strength  of  the  same  mortar  at  the  same  age.  This  ratio 
increases  with  the  age  of  the  mortar  and  with  the  proportion  of 
•and.  The  standard  German  specifications  require  that  the  com- 
pressive strength  of  cement  mortar  shall  be  at  least  10  times  the 
tensile  strength. 

Data  determined  by  submitting  ou.fes  of  mortar  to  a  compreesive 
stress  are  of  little  or  no  value  as  showing  Xbe  strength  of  mortar 
when  employed  in  thin  layers,  as  in  the  joints  of  masonry.  The 
strength  per  anit  of  bed  area  increases  rapidly  as  the  thickness  of 
tiie  test  specimen  decreases,  but  no  experiments  have  ever  been 
made  to  determine  the  law  of  this  increase  for  mortar, 

134.  Adhesive  Strength.  Unfortunately  very  few  experimeDta 
have  been  made  on  the  adhesive  strength  of  mortars,  i.e.,  the 
power  with  which  mortars  stick  to  brick,  stone,  etc.  It  is  com- 
monly assnmed  that,  after  the  lapse  of  a  moderate  time,  the 
adhesive  and  cohesive  strengths  of  cement  mortars  are  about  eqnal, 
and  that  in  old  work  the  former  esoeeds  the  latter.  Modem 
experiments,  however,  fail  to  establish  the  truth  of  this  assumption, 
and  indicate  rather  that  the  adhesion  of  mortar  to  brick  or  stone  ia 
much  less,  during  the  first  few  months,  than  its  tensile  strength; 
and  also  that  the  relation  between  the  adhesive  strength  and 
cohesive  strength  (the  resistance  of  the  mortar  to  pulling  asunder) 
is  very  obscure.  The  adhesion  of  mortars  to  brick  or  stone  varies 
greatly  with  the  different  varieties  of  these  materials,  and  particu- 
larly with  their  porosity.  The  adhesion  also  varies  with  the  quality 
of  the  cement,  the  character,  grain,  and  quantity  of  the  sand,  the 
amoant  of  water  used  in  tempering,  the  amount  of  moisture  in  the 
stone  or  brick,  and  the  age  of  the  mortar.  Some  cements  which 
exhibit  high  tensile  strength  give  low  values  for  adhesion;  and  ooa- 


ovGoQi^lc 


[CUAP,  IV. 


TABLE  18. 

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D.qilizMb,G00>^le 


ART.  1.]  COST   OP    UORTAR.  95 

Tersolj,  cements  which  are  apparently  poor  when  tested  for  cobeeiOQ, 
show  excellent  adbeeive  qaalities. 

The  table  *  on  the  preceding  page  givea  all  the  reliable  data 
known.  A  comparieon  of  the  table  with  the  diagram  on  page  92 
ehows  that  the  adhesion  of  a  mortar  ia  far  leas  than  its  tendle 
strength  at  the  same  age,  bnt  faila  to  ahow  any  definite  relation 
between  the  two.  In  the  experiments  by  Dr.  B5hme  at  the  Boyal 
Testing  Laboratory  at  Berlin  the  mortar  waa  made  with  standard 
qaartz  sand,  and  the  tensile  strength  of  the  mortar  and  its  adheaion 
to  common  brick  were  determined  separately.  By  comparing  the 
tensile  and  adhesive  strengths  at  the  same  ages,  it  was  fonnd  that 
the  former  was  always  abont  ten  times  greater  than  the  latter  when 
the  mortar  consisted  of  one  part  of  cement  to  three  or  fonr  parts 
of  sand,  and  from  six  to  eight  times  greater  when  the  cement  waa 
nsed  neat  or  with  one  or  two  parts  of  sand.  In  the  experiments 
made  by  Prof.  Warren,  of  Sydney  UniTereity,  New  Sonth  Wales, 
tbe  tensile  strength  of  neat  Portland  cement  mortar  waa  three  and 
a  half  times  ite  adhesion  to  brick.  The  result  of  twelve  thousand 
epecial  testa  by  Mr.  Mann  was  that  pnre  Portland  cement  of  425 
pounds  tensile  and  5,640  pounds  compressive  strength  pe'rsqnara 
inch  has  bnt  60  to  80  pounds  adhesion  to  limestone,  and  that  the 
ratio  of  tenaila  to  adhesive  strength  varies  from  5  te  1  to  9  to  1. 

135.  Cost  or  Uobtas.  Knowing  the  price  of  the  materials  it 
is  very  easy,  by  the  nse  of  Table  11,  page  88,  to  compute  the  cost 
of  the  ingredients  required  for  a  cubic  yard  of  mortar.  The 
expense  for  labor  is  quite  variable,  depending  upon  tbe  distance  the 
materials  must  be  moved,  the  qnantity  mixed  at  a  time,  etc.  As  a 
rough  approximation  it  may  be  assumed  that  a  common  laborer  can 
n^ix  3  jarda  f  er  day,  at  a  cost  of,  say,  50  cents  per  cubic  yard.  If 
the  mixing  is  done  by  machinery,  the  cost  may  be  as  low  as  25 
cents  per  cabic  yard.  The  cost  of  a  cubic  yard  of  mortar  composed 
of  1  part  Portland  cement  and  2  parts  sand,  both  by  weight  ia 
then  ahont  as  follows : 

Cemeat 3.80  bbls.  (see  page  88)  @  S8.00  =  $8.40 

Sand 0.78CU.  yd.  (seepage 88j  igi     .60  =      .89 

LatMr,  handling  msterial«  and  mlziog i  day®  (l.fK)  =       .60 

Talalco*tofi  eubie  yard  of  mortar  =  19.29 


ovGoQi^lc 


96  HOBIAB.  [CHA.F.  17. 

136.  Hatnral  vs.  Fortland  Cement  HorUr.  It  is  sometimes  a 
qaestion  whether  Portland  or  nataral  cement  Bhoald  be  osed.  If 
a  qnick-setttng  cement  ig  reqaired,  then  natnral  cement  is  to  be 
preferred,  since  as  a  rale  the  natural  c«menta  are  quicker  setting, 
although  there  are  many  and  marked  exceptions  to  this  role.  Other 
things  being  the  same,  a  slow-setting  cement  is  preferable,  since 


■  k' 
\^ 
t' 

fltrftt  SatHt  ra  /  Atrr  Cement  by  Weight 
Flo.  Ta,— Cost  of  OENEtrr  Mobtib. 

it  is  not  so  liable  to  set  before  reaching  its  place  in  the  wall.  This 
is  an  important  item,  since  with  a  quick-setting  cement  any  slight 
delay  may  necessitate  the  throwing  away  of  a  boifal  of  mortar 
or  the  remoTal  of  a  atone  to  scrape  oat  the  partially-set  mortar. 

Generally,  however,  this  qaestion  shoald  be  decided  npon 
economical  gronnds,  which  makes  it  a  question  of  relative  strength 
and  relative  prices.  The  tensile  strength  of  natnral  and  Portland 
cement  mortars  is  shown  in  Fig.  6,  page  93,  The  cost  of  mortar 
of  Tarions  proportions  of  sand  may  be  computed  as  in  the  preceding 
flection;  but  as  the  cost  of  labor  is  uncertain  and  ig  sabstantially 
the  same  for  both  kinds  of  mortar,  it  is  sufficient  to  deal  with  the 
cost  of  the  materials  only.  Assuming  Portland  cement  to  cost  13 
per  barrel,  natural  (1  per  barrel,  and  sand  50  cents  per  cubic  yard, 
and  using  Table  II,  page  86,  the  cost  of  the  materials  in  a  onbiA 
yard  of  mortar  is  as  in  Fig.  7a. 


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'.  1.]  HATCRAL  VS.    PORTLAND   CEMENT  UORTAS. 


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Cost  of  tlortar  in  DoUara  per  Cubic  Yard 
Wia.  75.— RcATm  Ecohoht  or  Natdbu,  ahq  Pdbtumd  CramrrH. 


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ovGoQi^lc 


'  98  M0RT4E.  [CHAP,  IT- 

By  plotting  the  strength  of  Portland  and  tiatnral  cement  mortar 
6  months  old  and  the  coet  of  a  yard  of  mortar  as  given  in  Fig.  loy 
Fig.  7b  is  obtained,  which  ehovs  the  relation  hetween  the  strength 
at  6  months  and  the  coat  of  the  mortar  made  of  the  two  kinds  of 
cement.  Kotice  that  for  any  tensile  strength  under  abont  370 
ponnde  per  square  inch,  either  natnral  or  Portland  cement  may  be 
need,  bnt  that  the  former  is  the  cheaper.  In  other  words,  Fig.  7^' 
shows  that  if  a  strength  of  abont  370  poands  per  sqnare  inch  at 
6  months  is  sufficient,  nataral  cement  is  the  cheaper.  Nearly  all 
carefnlly  condncted  testa  of  the  strength  of  cement  mortar  6 
months  old  or  over  give  a  aimilar  resnlt,  except  that  the  above- 
limit  ifl  nsnally  between  300  and  350  pounds.  A  considerable 
change  in  prices  does  not  materially  alter  the  resnit,  and  hence  the 
conclnsion  may  be  drawn  that  if  a  strength  of  300  to  350  pounds- 
per  square  inch  at  6  months  is  sufficient,  nataral  cement  is  more 
economical  than  Portland.  Incidentally  Fig.  7c,  page  97,  shows 
the  same  relation.  However,  in  this  connection  it  should  not  be 
forgotten  that  other  considerations  than  strength  and  coat  may 
govern  the  choice  of  a  cement;  for  example,  aniformity  of  prodnct^ 
rapidity  of  set,  and  sonndnesa  are  of  equal  or  greater  importance 
than  strength  and  cost. 

Mortar  made  of  two  brands  of  Portland  or  nataral  cement  will 
differ  considerably  in  economic  values,  and  hence  to  be  of  the 
highest  value  the  above  comparison  should  be  made  between  the 
most  economical  Portland  and  the  most  economical  natnral  cement, 
as  determined  by  the  method  described  in  §  lllA. 

Short-time  tests  do  not  warrant  any  general  conclnsion  as  to  the 
relative  economy  of  nataral  and  Portland  cements,  since  the 
strength  at  short  times  varies  greatly  with  the  activity  of  the 
cement.  For  example,  the  two  apper  diagrams  of  Fig.  6,  page 
93,  when  plotted  as  in  Fig.  7&  show  Portland  to  be  the  more 
economical,  while  other  similar  experiments  show  nataral  cement  to 
be  the  more  economical. 

137.  Economic  Proportion  of  Sand.  Fig.  7c,  page  97,  ehowa 
the  ratio  of  strength  to  cost  for  different  proportions  of  sand,  for 
both  Portland  and  nataral  cement;  in  other  words.  Fig.  7c  shows. 
the  tensile  strength  in  poands  per  square  inch  for  each  dollar  of  the 
cost  of  a  cubic  yard  of  mortar.  For  example,  if  a  nataral  cement 
mortar  at  6  months  has  a  tensile  strength  of  280  pannda  per  squarfr 
inch,  and  costs  t3.95  per  yard,  the  strength  per  dollar  is:  380  •{- 


ovGoQi^lc 


ART.  1.]  EFFECT  OP    RE-TEMPEBIHO.  ^9 

2,95  =  94.9  pounds  per  square  inch.  In  this  way  Fig.  7c  waa 
oonBtnicted,  aaing  the  cost  of  mortar  as  given  in  Fig.  la  and  the 
strength  as  determined  by  L.  C.  Sabin  in  connection  with  the  con- 
strnotiAn  of  the  Poe  lock  on  the  St.  Mary's  Falls  Canal.*  Accord- 
ing to  this  diagram  the  most  economic  mortar,  either  natural  or 
Portland,  conaists  of  3  parts  sand  to  1  part  cement,  by  weight. 

A  atndy  of  the  resnlta  of  other  eiperimenta  shows  that  the  above 
coQclnsiona  are  not  general.  The  maximom  ratio  aa  above  is 
different  for  different  ages  for  the  same  cement,  and. at  the  same 
age  is  different  for  different  cements.  The  above  ratio  varies  (1) 
with  the  activity  of  the  cement,  which  determines  the  strength 
neat  at  different  ages;  (3)  with  the  fineness,  which  determines  the 
sand-carrying  power  of  the  cement;  (3)  with  the  fineness  of  the 
sand,  which  determines  the  surface  to  be  covered  by  the  cement; 
and  (4)  with  the  cost  of  the  cement  and  the  sand.  If  the  strength 
of  any  particular  cement  with  the  various  proportions  of  sand  ia 
known  for  a  particalar  age,  and  the  price  of  the  cement  and  sand 
also  is  known,  the  most  economic  propertion  of  sand  can  be  com- 
puted as  above.  To  determine  the  most  eoonomio  mortar,  the 
most  economic  cement  should  be  selected  as  described  in  §  lllA, 
and  then  be  mixed  with  the  most  economical  proportion  of  sand  as 
,,-  above. 

Strictly,  the  maximum  ratio  of  strength  to  cost  determined  as 
above  ia  not  necessarily  the  most  economical  mortar.  The  work  in 
band  may  not  require  a  mortar  as  strong  as  that  giving  the  maxi- 
mum patio  of  strength  to  cost,  in  which  case  a  mortar  having  a 
smaller  proportion  of  cement  may  be  used;  and  similarly,  if  the 
work  requires  a  mortar  stronger  than  that  giving  the  maximum 
ratio  of  strength  and  cost,  then  a  mortar  must  be  used  which  con- 
tains a  greater  proportion  of  cement. 

1S8.  Effect  O?  Hl-TBUMEnro.  Frequently,  in  practice, 
cement  mortar  which  has  taken  an  initial  set,  is  re-mixed  and  used. 
Masons  generally  claim  that  re-tempering,  i.e.,  adding  water  and 
re-mixing,  is  beneficial;  while  engineers  and  architects  usually 
specify  that  mortar  which  has  taken  an  initial  set  shall  not  be  need. 

Be-tempering  makes  the  mortar  slightly  less  "short"  or 
"brash,"  that  is,  a  little  more  plastic  and  easy  to  handle.  Be- 
tempering  also  increases  the  time  of  set,  the  increase  being  very 

•  Baport  of  Chlet  of  Eagluaere,  U.  S.  A.,  1B93,  page  3019,  Table  L 


ovGoQi^lc 


1°  !>-''. 

^Ts ......  ^f.'  fj^  ^-  ■ 

100  KOBTAR.  [chap.  IV. 

different  for  different  cements.  Bat  on  the  other  hand,  re-temper- 
ing Ttsnally  weakens  &  cement  mortar,  A  qnick-settiog  natDral 
cement  Bometimee  loses  30  or  40  per  cent,  of  ita  strength  b;  being 
re-tempered  after  standing  20  minntes,  and  70  or  80  per  cent,  by 
being  re-tempered  after  standing  1  hour.  With  slow-setting 
cements,  particnlarly  Portlands,  the  loss  hj  re-tempering  immedi- 
ately after  initial  set  (§  84)  is  not  material.  A  mortar  which  has 
been  insnfiiciently  worked  is  sometimes  made  appreciably  stronger 
by  re-tempering,  the  additional  labor  in  re-mixing  more  than  com- 
pensating for  the  loss  caused  by  breaking  the  set. 

The  loBsof  strength  by  re-tempering  is  greater  for  qnick-setting 
than  for  slow-setting  cement,  and  greater  for  neat  than  for  sand 
mortar,  and  greater  with  fine  sand  than  with  coarse.  The  loss 
increases  with  the  amonnt  of  set.  If  mortar  is  to  stand  a  consider- 
able time,  the  injaiy  will  be  less  if  it  is  re-tempered  several  times 

'  daring  the  interval  than  if  it  is  allowed  to  stand  nndistnrbed  to  the 
end  of  the  time  and  is  then  re-mized.  Re-tempered  mortar  shrinks 
more  in  setting  than  ordinaiy  mortar.  This  fact  sometimes 
accounts  for  the  cracks  which  frequently  appear  npon  a  troweled 
surface. 

The  only  safe  mle  for  practical  work  is  to  require  the  mortar 
•to  be  thoroughly  mixed,  and  then  not  permit  any  to  be  used  which 
lias  taken  an  initial  set  (§  84).  This  rule  should  be  more 
atrennoDsly  innsted  upon  with  natural  than  with  Portland  cements, 

-and  more  with  qnick-setting  than  with  slow-setting  varieties. 

139.  Lna  WITH  Cekeft.  Cement  mortar  before  it  begins  to 
aet  has  no  cohesive  or  adhesive  properties,  and  is  what  the  maeoo 

-calls  "  poor,"  "short,"  "brash  ";  and  conseqnently  is  difficnlt  to 
use.  It  will  not  stick  to  the  edge  of  the  brick  or  stone  already  laid 
sufficiently  to  give  mortar  with  which  to  strike  the  joint.  The 
addition  of  a  small  per  cent,  of  lime  paste  makes  the  mortar  ' '  fat  '* 
or  "  rich,"  and  more  pleasant  to  work.  The  substitution  of  10  to 
20  per  cent,  of  lime  paste  for  an  equal  volume  of  the  cement  paste 
does  not  materially  decrease  the  strength  of  the  mortar,  and 
frequently  the  addition  of  this  amount  of  lime  slightly  increases  its 
strength.  In  all  cases  the  substitution  of  10  to  20  per  cent,  of  lime 
decreases  the  cost  more  rapidly  than  the  strength,  and  hence  is 

'  economical;  but  the  snbstitation  of  more  than  about  20  per  cent, 
decreases  the  strength  more  rapidly  than  the  cost,  and  hence  is  not 

•  Monomioal.     The  economy  of  using  lime  with  cement  is,  of  coutse, 


ovGoQi^lc 


ART.  1.]  HORTAB   lUPERTIODS  TO  WATER.  *     101 

greater  with  Portlaad  thao  with  n&tural  cement  owing  to  the 
greater  cost  of  the  former. 

If  the  mortar  is  porone,  i.e.,  if  the  voids  of  the  sand  are  not 
filled  with  cement,  the  addition  of  lime  will  make  the  mortar  more 
dense  and  plastic,  and  will  also  increase  its  strength  and  cost.  The 
increase  in  strength  is  not  proportional  to  the  increaae  in  cost,  hat 
the  increased  plasticity  and  density  jastify  the  increased  cost — the 
former  adds  to  the  ease  of  using  the  mortar,  and  the  latter  to  its 
dnrability. 

The  addition  of  lime  does  not  materially  aSect  the  time  of  set, 
«nd  nsoally  slightly  increases  it. 

It  has  long  been  an  American  practice  to  reinforce  lime  mortar 
by  the  addition  of  hydraulic  cement.  The  mortar  for  the 
"ordinary  brickwork"  of  the  United  States  pnblic  hnildings  is 
composed  of  "  one  fourth  cement,  one  half  sand,  and  one  fourth 
lime."  The  cement  adds  somewhat  to  the  strength  of  the  mortar, 
bnt  not  proportionally  to  the  increase  in  the  cost  of  the  mortar. 

140.  XOSTAS  iKFEBTloirs  TO  Wateb.  Nearly  every  failnre 
«f  masonry  is  due  to  the  dis integration  of  the  mortar  in  the  ontside 
of  the  joints.  Ordinary  mortar — either  lime  or  cement — absorbs 
water  freely,  common  lime  mortar  absorbing  from  50  to  60  per  cent. 
of  its  own  weight,  and  the  beet  Portland  cement  mortar  from  10 
to  20  per  cent. ;  and  conseqnently  the;  disintegrate  under  the 
action  of  frost.  Mortar  may  be  made  practically  non-absorbent 
by  the  addition  of  alnm  and  potash  soap.  One  per  cent.,  by 
weight,  of  powdered  alnm  is  added  to  the  dry  cement  and  sand,  and 
thoroQghly  mixed;  and  about  one  per  cent,  of  any  potash  soap 
{ordinary  soft^eoap  made  from  wood  ashes  is  very  good)  is  dissolved 
in  the  water  nsed  in  making  the  mortar.  The  alum  and  soap  com- 
bine, and  form  oompoonds  of  alnmina  and  the  fatty  acids,  which 
are  insoluble  in  water.  These  compounds  are  not  acted  npon  by 
the  carbonic  acid  of  the  air,  and  add  considerably  to  the  early 
Btrengtb  of  ihe  mortar,  and  somewhat  to  its  nltimate  strength. 

With  lime  mortar,  the  alnm  and  soap  has  a  slight  disadvantage 
in  that  the  oompounds  which  render  the  mortar  impervious  to  water 
also  prevent  the  air  from  coming  in  contact  with  the  lime,  and 
conseqnently  prevent  the  setting  of  the  mortar.  On  the  other 
han^,  the  alum  and  soap  compounds  add  considerably  to  both  the 
early  and  the  nltimate  strength  of  the  mortar. 

This  method  of  rendering  mortar  impervious  is  an  application 


ovGoQi^lc 


103  MORTAR,  [nHAP.  IT. 

of  the  principle  of  Sylvesier's  method  of  repelling  moietute  from 
external  walls  by  applying  alam  and  soap  washes  alternately  on  the 
outside  of  the  wall  (see  §  363).  The  same  principle  is  applied  in 
McMnrtrie's  artificial  stone  (see  g  162).  The  alam  and  soap  are 
easily  need,  and  do  not  add  greatly  to  the  cost  of  the  mortar.  The 
mixture  conld  be  advantageonsly  used  in  plastering,  and  in  both 
cement  and  lime  mortars  of  ontside  walls  or  masonry  in  damp 
places.  It  has  been  very  Bnccessfnlly  used  in  the  plastering  of 
cellar  and  basement  walls.  It  should  be  employed  in  all  mortar 
need  for  pointing  (§  204). 

The  addition  of  a  small  amount  of  very  finely  powdered  clay 
(§  114c)  decreases  the  permeability  of  mortar;  but  since  clay  absorh» 
and  parts  with  water  with  the  changing  seasons,  the  use  of  clay  ia 
not  efficient  in  preventing  disintegration  by  freezing  and  thawing. 

141.  Fbeeziho  or  Uobtab.  The  freezing  of  mortar  before  it 
has  set  has  two  effects:  (1)  the  low  temperature  retards  the  setting 
and  hardening  action;  and  (3)  the  expansive  force  of  the  freezing 
water  tends  to  destroy  the  cohesive  strength  of  the  mortar. 

142.  Effect  on  Lime  Mortar.  The  freezing  of  lime  mortar 
retards  the  evaporation  of  the  water,  and  consequently  delays  the 
combination  of  the  lime  with  the  carbonic  gas  of  the  atmosphere. 
The  expansive  action  of  the  freezing  water  is  not  very  serious  upon 
lime  mortar,  since  it  hardens  so  slowly.  Consequently  lime  mortar 
is  not  seriously  injured  by  freezing,  provided  it  remains  frozen 
nntil  fully  set.  Alternate  freezing  and  thawing  somewhat  damages 
its  adhesive  and  cohesive  strength.  However,  even  if  the  strength 
of  the  mortar  were  not  materially  affected  by  freezing  and  thawing, 
it  is  not  permissible  to  lay  masonry  during  freezing  weather;  for 
example,  if  the  mortar  in  a  thin  wall  freezes  before  setting  and 
afterwards  thaws  on  one  side  only,  the  wall  may  settle  injariously. 

When  masonry  is  to  be  laid  in  lime  mortar  during  freezing 
weather,  frequently  the  mortar  is  mixed  with  a  minimum  of  water 
and  then  thinned  to  the  proper  consistency  by  adding  hot  water 
just  before  using.  This  is  nndesirable  practice  (see  §  118).  When 
the  very  best  results  are  sought,  the  brick  or  stone  should  be 
warmed — enough  to  thaw  off  any  ice  upon  the  surface  is  sufficient 
' — before  being  laid.  They  may  be  warmed  either  by  laying  them 
on  a  tomace,  or  by  suspending  them  over  a  slow  fire,  or  by  w-^ting 
with  hot  water,  or  by  blowing  steam  throagh  a  hose  against  them. 

143.  Effect  OS  Cement  Hortar.    Owing  to  the  retardation  of  the 


ovGoQi^lc 


ABT.  I.]  EFPECT  OF  FfiEEZlKQ.  103 

low  temperatare,  the  settiDg  and  hardening  may  be  so  delayed  that 
the  water  may  be  dried  ont  of  the  mortar  and  not  leave  enongh  for 
the  chemical  action  of  hardening;  and  consequently  the  mortar  will 
he  weak  and  cmmhly.  This  wonld  be  anbatantially  the  same  as 
aaing  mortar  with  a  dry  porons  brick.  Whether  the  water  evapo- 
rates to  an  iDJnrions  extent  or  not  depends  npon  the  hamiditj  of 
the  air,  the  temperature  of  the  mortar,  the  activity  of  the  cement, 
«nd  the  extent  of  the  exposed  anrface  of  the  mortar.  The  mortar 
in  the  interior  of  the  wall  is  not  likely  to  be  injured  by  the  loss  of 
water  while  frozen;  but  the  edges  of  the  joints  are  often  thus  seri- 
•onsly  iujured.  In  the  latter  case  the  damage  may  bo  fnlly  repaired 
by  pointing  the  masonry  (§  304)  after  the  mortar  has  fnlly  set. 

On  the  other  hand  when  the  cement  has  partially  set,  if  the 
expansive  force  of  the  freezing  water  is  greater  than  the  cohesive 
strength  of  the  mortar,  then  the  bond  of  the  mortar  is  broken,  and 
on  thawing  ont  the  mortar  will  crumble.  Whether  this  action  will 
take  place  or  not  will  depend  chiefly  npon  the  Btreugth  and  activity 
of  the  cement,  upon  its  hardness  at  the  time  of  freezing,  aud  upon 
the  amount  of  free  water  present.  The  relative  effects  of  these 
several  elements  is  not  known  certainly;  but  it  has  been  proven 
conclusively  that  for  the  best  results  the  following  precautions 
shonld  he  observed:  1.  Use  a  qnick-aetting  cement.  3.  Make  the 
mortar  richer  than  for  ordinary  temperatures.  3.  Use  the  mini- 
mum quantity  of  water  in  mixing  the  mortar.  4.  Prevent  freezing 
as  long  as  possible. 

There  are  various  ways  of  preventing  freezing:  1.  Cover  the 
masonry  with  tarpaulin,  straw,  manure,  etc.  2.  Warm  the  stone 
and  the  togredients  of  the  mortar.  Heating  the  ingredients  is  not 
of  much  advantage,  particularly  with  Portland  cement.  3.  Instead 
of  trying  to  maintain  a  temperature  above  the  freezing  point  of 
fresh  water,  add  salt  to  the  water  to  prevent  its  freezing.  The 
usual  mle  for  adding  salt  is:  "Dissolve  1  pound  of  salt  in  18 
gallons  of  water  when  the  temperature  is  at  33°  Fahr.,  and  add 
3  ounces  of  salt  for  every  3°  of  lower  temperature."  The  above 
rule  gives  a  alight  excess  of  salt.  The  following  rnle  is  soientifically 
correct  and  easier  remembered:  "  Add  one  per  cent,  of  salt  for  each 
Fahrenheit  degree  below  freezing."  Apparently  salt  slightly 
decreases  the  strength  of  cement  mortar  setting  in  air,  and  slightly 
increases  the  strength  when  setting  in  water.* 
'  •  Beport  of  Clael  of  Engliieera,  U.  B.  A.,  189S,  pp.  2963-71,  301S.  ' 


ovGoQi^lc 


104  HOBTAB.  [chap.  IV. 

Alternate  freezing  txti  thawing  is  more  damaging  than  contin- 
QOBB  freezing,  since  with  the  former  the  bond  may  be  repeatedly 
broken;  and  the  damage  dne  to  sncceaBive  disturbance  increases 
with  the  nnmber. 

144.  Practice  has  abown  that  Portland  cement  mortar  of  th» 
nsnal  proportions  laid  in  the  ordinary  way  is  not  materially  injured 
by  alternate  freezing  or  thawing,  or  by  a  temperature  of  10°  to 
15"  F.  below  freezing,  except  perhaps  at  the  exposed  edges  of  thfr 
joints.  Under  the  same  conditions  natural  cement  mortar  is  liable 
to  be  materially  damaged. 

By  the  use  of  salt,  even  in  less  proportions  than  specified  above^ 
or  by  warming  the  materials,  masonry  may  be  safely  laid  with. 
Portland  at  a  temperature  of  0°  P. ;  and  the  same  may  nanally  b& 
done  with  natural  cement,  -although  it  will  ordinarily  be  necessary 
to  re-point  the  masonry  in  the  spring.  Warming  the  materials  is 
not  as  efTective  as  using  salt. 

14fi.  CHAHeE  07  VoLVU  IK  SsTmre.  The  Committee  of  th» 
American  Society  of  Civil  Engineers  draw  the  following  oonoln- 
sions:*  1.  Cement  mortars  hardeniug  in  air  diminish  in  linear 
dimensions,  at  least  to  the  end  of  twelve  weeks,  and  in  most  oase» 
progresdvely.  3.  Cement  mortars  hardening  in  water  increase  ia 
like  manner,  but  to  a  leas  degree.  3.  The  contractions  and  expan- 
«ions  are  greatest  in  neat  cement  mortars.  4.  The  quick-setting 
cements  show  greater  expansions  and  contractions  than  the  slow- 
setting  cements.  5.  The  changes  are  less  in  mortars  containing- 
sand.  6.  The  changes  are  less  in  water  than  in  air.  7.  The  con- 
traction at  the  end  of  twelve  weeks  is  as  follows:  for  neat  cement 
mortar,  0.14  to  0.33  per  cent. ;  for  a  mortar  composed  of  1  part 
cement  and  1  part  sand,  0.08  to  0.17  per  cent.  8.  The  expansion, 
at  the  end  of  twelve  weeks  is  as  follows:  for  neat  cement,  0.04  to> 
0.35  per  cent. ;  for  1  part  cement  and  1  part  sand,  0.0  to  0.08  per 
cent.  9.  The  contraction  or  expansion  is  essentially  the  same  m 
all  directions. 

146.  Elabticitt,  Cohprebbioit,  ash  Set  op  Hobiak.  For 
data  on  elasticity  see  page  14.  The  evidence  is  so  conflicting  that 
it  is  impossible  to  determine  the  coefficient  of  compression  and  of 

•  Bee  the  "  Report  ot  Progreas  at  the  Oommittee  on  the  OompraBalve  Strei^th  of 
Cemente  and  the  Oompreasion  ot  Hortare  aod  Settlement  of  Maaourj,"  in  the 
Tr&nsaoUoiiB  ot  that  Sooiety,  vol.  xvU.  pp.  3IS-3T ;  also  s  similar  report  In  vol.  zri 
pp.  717-33. 


ovGoQi^lc 


ART.  1.]    ELASTICITY,  COUPRGBSIOST,  AKD   SET   OF  VOBTAB.  105> 

Bet  of  mortar,  even  tipproziniat«ly.  For  mach  valoable  data  on. 
this  and  related  sabjecta,  see  tho  "  Report  of  Progress  of  the  Com- 
mittee  od  the  GompressiTe  Strength  of  CemeDta  and  the  Compres- 
sionof  Mortars  and  Settlement  of  Masonry,"  in  the  Transactiods  of 
the  American  Society  of  Civil  Engineers,  vol.  xti.  pp.  ?17-33„ 
Tol.  xvii.  pp.  213-17,  and  also  vol.  zriii.  pp.  2S4r-80.  The  aeverai 
annnal  reports  of  tests  made  with  thB  United  States  GoTemment 
teating-nuichiue  at  Watertown  contain  valuable  data — particnlarljr 
the  report  for  1884,  pp.  69-247 — bearing  indirectly  npon  this  and 
related  Babjecte;  bat  since  some  of  the  details  of  the  eiperimenta 
are  wanting,  and  since  the  fnndamental  principles  are  not  well 
enough  anderatood  to  carry  ont  intelligentlj  a  series  of  experimentB, 
it  is  impossible  to  draw  any  v^aable  ooBolosionB  from  the  data. 


ovGoQi^lc 


[chap.  it.  ' 


ABT.  2.    CONCBETB. 

147.  Concrete  consists  of  mortar  in  which  is  embedded  small 
pieces  of  some  hard  material.  The  mortar  is  often  referred  to  oa 
the  matrix;  and  the  embedded  fragments,  as  the  aggregate.  Ood* 
«rete  is  a  epeoies  of  artificial  stone.  It  is  sometimee  called  b4toQ, 
the  French  eqaivaleht  of  concrete. 

"  Concrete  is  admirably  adapted  to  a  Tariety  of  moat  importast 
Qses.  For  fonndatioos  in  damp  and  yielding  soils  and  for  snbter- 
ranean  and  submarine  masonry,  under  almost  every  combination  of 
circnmstancee  likely  to  be  met  with  in  practice,  it  is  superior  to 
brick  masonry  in  strength,  hardneBs,  and  dnrability;  is  more 
economical;  and  in  some  cases  is  a  safe  snbstitnte  for  the  best 
natural  stone,  while  it  is  almost  always  preferable  to  the  poorer 
varieties.  For  submarine  masonry,  concrete  poBsesaeB  the  advan- 
tage that  it  can  be  laid,  under  certain  precautions,  withont  ezhaast- 
ing  the  water  and  without  the  use  of  a  diving-bell  or  submarine 
armor.  On  account  of  its  continuity  and  its  impermeability  to 
water,  it  is  an  excellent  material  to  form  a  substratum  in  soils 
infested  with  springa;  for  sewers  and  conduits;  for  basement  and 
sustaining  walls;  for  columns,  piers,  and  abutments;  for  the 
hearting  and  backing  of  walls  faced  with  bricks,  rubble,  or  ashlar 
work;  for  pavements  in  areas,  basements,  sidewalks,  and  cellars; 
for  the  walls  and  floors  of  cisterns,  vaalts,  etc.  Groined  and 
vaulted  arches,  and  even  entire  bridges,  dweiUng-hoases,  and  fac- 
tories, in  single  monolithic  masses,  with  saitable  ornamentatioD, 
have  been  constructed  of  this  material  alone." 

Concrete  ia  rapidly  coming  into  use  in  all  .kinds  of  engineering 
constructions.  It  enables  the  engineer  to  build  his  su pc I'S t rue t lire 
on  a  monolith  as  long,  aa  wide,  and  as  deep  iis  he  may  think  best, 
which  can  not  fail  in  parts,  but,  if  rightly  proportioned,  must  go 
«11  together — if  it  fulls  at  all. 

148.  The  Xobtab.  The  matrix  may  be  either  lime  or  cement 
mortar,  but  is  usually  the  latter.  The  term  concrete  is  almost 
universally  nnderstood  to  be  cement  mortar  with  pebbles  or  broken 
stone  embedded  in  it.  Lime  mortar  is  wholly  unfit  for  use  in  large 
masses  of  concrete  since  it  does  not  set  when  excluded  from  the  air 
(see  §  119). 


ovGoQi^lc 


^RT.  3.]  THE  A08RE0ATE.  107 

The  cement  mortar  may  be  made  as  already  described  in  Art.  1 
preceding. 

149.  Thx  Aooee&atz.  The  aggregate  may  cooBist  of  small 
pieces  of  any  hard  material,  as  pebbles,  broken  stone,  broken  brick, 
shells,  slag,  coke,  etc.  It  is  added  to  the  mortar  to  rednoe  the 
cost,  and  withio  limits  also  adds  to  the  strength  of  the  coDcrete. 
Ordinarily  either  broken  stone  or  gravel  is  nsed.  Coke  or  blast- 
farnace  slag  is  nsed  when  a  light  and  not  strong  concrete  is  desired, 
se  for  the  fonndation  of  a  pavement  on  a  bridge  or  for  the  fioon 
of  a  tall  building.  Of  course  a  soft  porons  aggregate  makes  a  weak 
concrete. 

What«Ter  the  aggregate  it  should  be  free  from  dust,  loam,  or 
any  weak  material.  The  pieces  shonld  be  of  graduated  sizes,  so 
that  the  smaller  shall  fit  into  the  voids  between  the  larger.  When 
this  condition  is  satisfied  less  cement  will  be  required  and  conae- 
<]Qently  the  cost  of  the  concrete  will  be  lees,  and  at  the  same  time 
ita  strength  will  he  greater.  Other  things  being  eqnal,  the  rongfaer 
the  snrfaces  of  the  fragments  the  better  the  cement  adheres,  and 
consequently  the  stronger  the  concrete. 

160.  It  is  sometimes  specified  that  the  broken  stone  to  he  nsed 
in  making  concrete  shall  be  screened  to  practically  an  nniform  size; 
bnt  this  is  nnwise  for  three  reasons;  viz.:  1.  With  graded  sizes  the 
smaller  pieces  fit  into  the  spaces  between  the  larger,  and  conse- 
quently less  mortar  is  required  to  fill  the  spaces  between  the 
fragments  of  the  stone.  Therefore  the  unscreened  broken  stone  is 
more  economical  than  screened  broken  stone.  3.  A  concrete  con- 
tuning  the  smaller  fragments  of  broken  stone  is  stronger  than 
thongh  they  were  replaced  with  cement  and  sand.  Experiments 
shoir  that  sandstone  screenings  give  a  considerably  stronger  mortar 
than  natural  sand  of  eqnal  fineness,  and  that  limestone  screenings 
make  stronger  mortar  than  sandstone  screenings,  the  latter  giving 
from  10  to  50  per  cent,  stronger  mortar  than  natural  sand.* 
Hence,  reasoning  by  analogy,  we  may  oonclade  that  including  the 
finer  particles  of  broken  stone  will  make  a  stronger  concrete  than 
replacing  them  with  mortar  made  of  natural  sand.  Farther, 
experiments  show  that  a  concrete  containing  a  considerable  propor- 

•ADUiua  Beport  ot  Ohlel  of  En^naera,  U.  S.  A.,  189S,  Fart  3,  p.  SOIB;  do.  IBM, 
Part  i,p.a8U;  do.  JBSB,  Put  4,  p.  3959 ;  Jour.  West.  Boo.  ol  Sng^,  vol.  U.  pp.  3U 
and  400. 


ovGoQi^lc 


108  CONCEBTE.  [CHAP.  IT. 

tioa  of  brokeo  atone  is  itronger  than  the  mortar  ^one  (see  the  second 
and  third  paragrapha  of  g  153).  Since  the  mortar  alone  ia  -weaker 
than  the  concrete,  the  leas  the  proportion  of  mortar  the  strontrer  the 
concrete,  provided  the  roids  of  the  aggregate  are  filled;  and  ther^ 
fore  concrete  made  of  broken  stone  of  graded  aizes  is  atronger  than 
that  made  of  practically  one  size  of  broken  stone.  3.  A  aingle  size 
of  broken  atone  has  a  greater  tendency  to  form  archea  while  being 
rammed  into  place,  than  atone  of  graded  aizea. 

Therefore  concrete  mode  with  acreened  atone  ia  more  ezpenaive 
and  more  liable  to  arch  in  being  tamped  into  place,  and  is  leas  denae 
and  weaker  than  concrete  made  with  anacreened  stone. 

In  short,  screening  the  atone  to  nearly  one  size  is  not  only  a 
needless  expense,  bnt  ia  also  a  positive  detriment. 

The  dnat  ahonld  be  removed,  aince  it  baa  no  atrengtb  of  itself 
and  adda  greatly  to  the  surface  to  be  coated,  and  also  prevents  the 
oontact  of  the  cement  and  the  body  of  the  broken  atone.  Particles 
of  the  size  of  aand  grains  may  be  allowed  to  remain  if  not  too  fine 
nor  in  excess.  The  small  particles  of  broken  atone  shoald  be 
removed  if  to  do  so  redacea  the  proportion  of  voida  (g§  115d,  115e). 

161.  Oravel  n.  Broken  Stone.  Often  there  is  debate  as  to  the 
relative  merits  of  gravel  and  broken  atone  oa  the  aggregate  for  con- 
crete ;  bnt  when  compared  npon  the  same  basis  there  is  no  room  for 
doubt. 

In  the  preceding  section  it  was  shown  that  finely  crashed  stone 
gave  greater  tensile  and  compressive  strengths  than  equal  propor^ 
tiona  of  sand;  and  hence  reaaoning  by  analogy,  the  conclaaioa  is 
that  concrete  composed  of  broken  atone  ia  atronger  than  that  con- 
taining an  equal  proportion  of  gravel.  Thia  element  of  strength  is 
dne  to  the  fact  that  the  cement  adheres  more  closely  to  the  rongh 
snrfaces  of  the  angalar  fr^menta  of  broken  stone  than  to  the 
smooth  surface  of  the  rounded  pebbles. 

Again,  part  of  the  resiataDce  of  concrete  to  crushing  ia  dne  to 
the  frictional  resistance  of  one  piece  of  ^gregate  to  moving  on 
another;  and  consequently  for  this  reason  broken  stone  ia  better 
than  gisvel.  It  is  well  known  that  broken  atone  makes  better 
macadam  than  gravel,  aince  the  rounded  pebbles  are  more  easily 
displaced  than  the  angular  fragments  of  broken  stone.  Concrete 
differs  from  macadam  only  in  the  use  of  a  better  binding  material : 
and  the  greater  the  frictional  resistance  between  the  particles  the 
stronger  the  mass  or  the  less  the  cement  required. 


ovGoQi^lc 


IRT.  2.]  THBOBY  0»  THE   PE0P0BTI0H8.  109 

A  Beriea  of  experiments*  m&de  bj  the  City  of  Washington, 
D.  C,  to  determine  the  relative  valne  of  broken  atone  and  gravel 
for  concrete,  vhich  are  enmrnarized  in  §  157^,  P&ge  112r,  gives  the 
following  reaolts: 


Stbbnoth  of  QiuTaL  Cohcbbtb  ih  txbkb 

or  BitoEBM  Stohb  Cow 

Fonuini  CnONT 

10  days.                              88  per  cent. 

76  per  cent. 

45     ■'                                 78   "      '■ 

91    "      ■■ 

8momh».                      96  "     " 

119  "     " 

6     "                            48  "     '■ 

78  '■     ■' 

1  yew.                             88   "      " 

108  ■•     " 

JfM»                   68  "     " 

98  "     ■' 

Each  reealt  is  the  mean  for  two  1-foot  cnbes,  except  tbat  the  valnes 
for  a  year  are  the  means  for  five  cnbes.  Kotice  that  the  gravel 
coocrete  is  relatively  weaker  for  the  earlier  ages,  owing  probably  to 
the  greater  internal  friction  of  the  broken-stone  concrete. 

In  a  BericB  of  forty-eight  French  expert m eels,  f  the  crashing 
strength  of  gravel  concrete  with  Portland  cement  is  only  79  per 
cent.  OB  great  as  that  of  brokea-stone  concrete.  The  grarel  had  40 
per  cent,  of  voids,  while  the  broken  stone  had  47  per  cent.,  which 
favored  the  gravel  concrete  (see  §  154).  The  resalta  of  these  test» 
are  shown  graphically  in  Fig.  8,  page  112a. 

153.  Since  frequently  gravel  is  cheaper  than  broken  stone,  » 
mixture  of  broken  stone  and  gravel  may  make  s  more  efficient  con- 
crete than  either  alone,  {.  e.,  may  give  greater  strength  for  the  same 
coat,  or  give  leas  cost  for  the  same  strength. 

153.  Thzobt  of  tee  Fsopoetiokb.  The  voids  in  the  aggre- 
gate should  always  be  filled  with  mortar.  If  there  is  not  enough 
mortar  to  fill  the  voids,  tbe  concrete  will  be  weak  and  porona.  On. 
the  other  hand,  more  mortar  than  enongh  to  fill  the  voids  of  the 
aggregate  increases  the  cost  of  the  concrete  and  also  decreases  its- 
strength.  The'  decrease  in  strength  dne  to  an  excess  of  mortar  is 
nsnally  greater  than  wonld  be  prodnced  by  aubstitnting  the  same 
amount  of  aggregate,  since  ordinarily  the  sand  and  the  aggregate 
have  approximately  the  same  per  cent,  of  voids,  while  the  sand  has 
the  greater,  and  also  the  smoother,  surface. 


ovGoQi^lc 


110  CONCKBTB.  [chap.  IT. 

A  correctly  proportioned  concrete  is  always  stronger  than  the 
mortar  alone.  For  example.  Table  13a  *  shows  thajt  a  concrete 
containing  a  oonaiderable  proportion  of  pebbles  is  stronger  than  the 
mortar  alone — compare  lines  2,  5,  and  8  with  the  preceding  line  of 
each  gronp,  reepectirely.  The  reeults  are  for  grarel  concrete,  and 
they  wonld  be  more  striking  tor  broken-stone  concrete,  since  the 
cement  adheres  better  to  broken  stone  than  to  either  sand  or 
grarel. 

TABLE  18a. 
KxLATivs  Stbrksth  or  Hortab  aso  Qrayml  Coxcbxtc 


Tbibothb 

■  niUTKKJ). 

Bar.  No. 

Froport.0.-. 

c™b^«™.gth. 

Cnoaot. 

Bud. 

PebblM. 

tbkt  of  tlie  MorMr. 

1 

2 

0 

8  1S8 

100  per  cent. 

8 

3783 

136  "     " 

9 

a  414 

136  ■'     " 

I 

8 

0 

1406 

ITO  POT  oanl. 

B 

1661 

114  "     " 

S.6 

1084 

10»  "     " 

1 

4 

0 

1068   " 

100  percent 

S 

1391 

131   "     " 

8.5 

laai 

lU  *■     " 

The  average  strength  of  twenty-fonr  cnbes  ranging  from  6  to 
16  inches  on  a  side,  made  nnder  the  direction  of  Gen.  Q.  A.  Oill- 
more,t  and  composed  of  1  volame  of  cement,  3  volumes  of  sand, 
and  6  volumes  of  broken  stone,  was  15  per  cent,  more  than  that  of 
corresponding  cnbes  made  of  the  mortar  alone.  In  another  series 
of  the  same  experimeQtB,J  the  average  strength  of  eight  cubes  of 

*  Dr.  B.  Dyeberhoff,  a  0«rmau  aathorlty,  as  qooted  In  "  Der  Portland  Cemaut 
nnd  seina  Anvrendaagen  Im  Bauwasaa."  p.  90. 

f  IToteB  on  the  OompresalTe  BeslBtanoe  ol  Preeatonee,  Brlok  Flars,  Hydnulio 
Cement,  Kortar,  and  Ooneretee,  Q.  A.  Glllmore.  John  Wiley  A  Bona,  New  Tork, 
188S,  pp.  lST-10  and  14S-U. 

}  Ibid.,  pp.  141-43. 


ovGoQi^lc 


THEOBT  OF  THB  PH0P0BTI0H8. 


Ill 


AST.  2.] 

concrete  oompoeed  of  1  pftrt  cement,  1^  parta  aand,  uid  6  pHti 
broken  stone  was  9fi  per  cent,  of  that  of  corresponding  cnbes  of  the 
mortar  slone,  which  is  interesting  ss  showing  that  a  lean  concrete 
is  nearly  as  strong  as  a  veiy  rich  mortar, 

A  correctly  proportioned  concrete  is  also  stronger  than  either  a 
richer  or  a  leaner  mixture — see  Table  13t,  page  113/. 

164.  For  the  strongeet  and  densest  concrete,  the  voids  of  the 
aggregate  shoald  be  filled  with  a  rich  strong  mortar;  bnt  if  a 
oheaper  concrete  ia  desired,  fill  the  roida  of  the  aggregate  with  sand 
and  odd  as  mach  cement  as  the  cost  will  justify.  In  other  words, 
to  make  a  cheap  concrete,  nse  as  lean  a  mortar  as  the  cironmstanoea 
warrant,  but  nse  enough  of  it  to  fill  the  Toida  of  the  oggr^ate. 
Sand  is  so  cheap  that  there  is  no  appreciable  saTing  by  omitting  it; 
and  the  use  of  it  makes  the  concrete  more  dense. 

The  strength  cf  a  concrete  varies  nearly  with  the  amount  and 
strengUi  of  the  cement  used,  provided  the  mortar  is  not  more  than 
enoagh  to  fill  the  voids.  Table  13d  shows  the  strength  of  con- 
crete in  terms  of  the  cement  employed.  The  data  from  which 
TABLE  IW. 

BZIATION  BBTWEEN  THE  CbUSHINO  STXBKQTE  OF  CONCBRTK  ABD  THB 

Phopoetion  of  Ckmkmt. 
Hoitai  Equal  to  the  Tolda  Id  ilie  Aggregate. 


R- 

VolunH  Loom. 

C-JS""' 

iSK'SSSS. 

OOMDt. 

Sud. 

keCaal. 

RolMiTe. 

AcnuU. 

TheoretlMl. 

RelMln. 

0.00 

1.00 

4.467 

6,000 

1.00 

8 

0.88 

0.67 

8.781 

8,800 

0.68 

0.8S 

O.SO 

2.M8 

8,800 

0.80 

o.ao 

0.40 

a,oio 

8,000 

0.40 

0.17 

0.S8 

1,796 

1.600 

0.88 

0.14 

0.28 

1,885 

1.400 

0.88 

this  table  was  made  are  the  same  as  those  summarized  in  Table 
13/,  page  llZq.  The  actnal  crashing  strengths  were  plotted,  and  it 
was  fonnd  that  they  conld  be  reasonably  well  represented  by  a  right 
line  paning  through  the  origin  of  co-ordinates.  The  values  for  this 
average  line  are  shown  in  next  to  the  last  oolnmn  of  Table  IRA. 


ovGoQi^lc 


l\Sa  CONCRETE,  [chap.  IT. 

Theae  ezperimeDte  seem  to  prove  that  the  strength  of  concrete 
Taries  as  tbe  qnaotit;  ot  cement,  provided  the  voids  are  filled  with 
mortar.     The  same  conclneioa  is  proved  by  the  data  snnunarized 


Portland  Cemeni -Barrels  per  Cubic  Yard 

no.  8.— KiLmoR  nrmni  tbi  BTRuraTD  or  the  Cohckiti  ihd  tbi  Ahddht  of  CncrK 

in  Fig.  8,  The  diagram  presents  the  reaalta  of  forty-eight  experi- 
ments oa  4-inch  cabes.*  Each  point  represents  two  experiments, 
the  age  of  the  mortar  in  one  being  7  days  and  in  the  other  28  days. 
The  points  with  one  circle  aronnd  them  represent  the  strength  of 
broken-stone  concrete,  and  tbe  points  with  two  circles  gravel  con- 
crete. Both  the  sand  and  the  gravel  employed  in  these  experiments 
were  very  coarse,  and  conseqaently  the  amount  of  cement  per  cabic 
yard  is  nnnsnally  great. 

155.  When  mortar  is  mixed  with  broken  stone,  the  film  ot 
mortar  sarronnding  each  fragment  increases  tbe  volume  of  the 
resnlting  concrete.  Table  13c,  page  ll%b,  gives  the  reanlt  of  fifteen 
experiments  to  determine  this  increase  in  volume.     The  mortar  was 

*  Oandlot'a  CemeDts  ot  Cbaux  HydrauUques,  pp.  340-U. 


ovGoQi^lc 


AET,  2.]  THBOBT   OP   THB   PBOPORTIOHS.  112S 

moderately  diy,  and  the  conciete  was  qaite  dry,  tnoistnre  flushing 
to  the  surface  only  after  vigorous  tamping.  The  broken  stone  vu 
No.  10  of  Table  lOh,  page  80,  and  contained  28  per  cent,  of  roidf 
when  rammed. 

Line  4  of  Table  13c  shows  that  if  the  mortar  is  eqnal  to  the 
voids,  the  rolnme  of  the  rammed  concrete  is  7^  per  cent,  more  than 
the  Tolnme  of  the  rammed  broken  stone  alone.  Possibly  part  of 
TABLE  IBe. 

Ikcbkabk  of  Voluue  by  Uixiho  Hortab  witk  Bbokkb  Stone. 


E«r.No. 

Tolums  of  Hortar  in 
t*rm«  or  the  Voids  tn 
the  Broken  Stone.- 

Volume  ot  Rain  Died  ■ 

TolcOinlheRMiiined 

70  per  cent 

105.0  per  cent 

16.8  percent 

aO   ■'      ■■ 

106.5  "      " 

13.3   ■•       " 

90  "      " 

108. S  "      " 

9.5  "      " 

100  "      " 

107.5  '■      " 

7.0  "      " 

110  "      " 

109.0  •■      •■ 

4.9  "      " 

130  "      " 

UO.S  '•     •• 

8.8  "      " 

180  "      " 

iia.6  "    •■ 

1.2  '•      '• 

8 

140  '■      " 

114.0  '■      ■' 

0.0  "     •■ 

)  of  Tolnme  was  due  to  imperfect  mixing,  altboagh  it 
was  believed  that  the  mass  was  perfectly  mixed.  The  table  also 
shows  that  the  voids  in  this  concrete  are  eqnal  to  7  per  cent,  of  its 
volume;  in  other  words,  even  though  the  volume  of  the  mortar  is 
equal  to  the  volume  of  the  voids,  the  voids  are  not  filled.  Appar- 
ently the  voids  can  be  entirely  filled  with  this  grade  of  mortar  only 
when  the  mortar  is  abont  40  per  cent,  in  excess  of  the  voids. 

The  increase  in  volume  in  Table  ISc  may  be  regarded  as  the 
maximum,  since  the  mortar  was  qaite  dry  and  the  stone  unscreened. 
With  moderately  wet  mortar  and  the  same  atone,  the  increase  in 
Tolnme  was  only  abont  half  that  in  the  table;  and  with  moist 
mortar  and  atone  ranging  between  3  inches  and  1  inch,  there  was 
no  appreciable  increase  of  volume.  With  pebbles  the  increase  is 
only  about  two  thirds  that  with  broken  stone  of  the  same  size. 
With  fine  gravel  (So.  18,  page  80)  the  per  cent,  of  increase  was 
considerably  greater  than  in  Table  13c;  with  mortar  equal  to  150 
per  cent,  of  the  voids,  it  was  possible  to  fill  oaly  about  5  to  7  per 


ovGoQi^lc 


1130  COHCBSTB.  [OHA.P.  IT. 

cent,  of  the  Toida.  The  mortar  used  in  Table  13c  vaa  1  Tolnme  of 
cement  to  2  Tolamea  of  sand,  both  measured  loose;  bat  with  richer 
mortan  the  inoraaee  in  volume  was  a  little  less,  and  with  leaner 
mortars  a  little  more.  Theee  differencee  are  so  sniall  that  they  may 
be  disregraded. 

Notice  that  the  voids  io  Table  13c  are  for  the  vet  concrete. 
When  the  concrete  has  dried  oat  the  voids  will  be  more;  since 
ordinarily  all  the  water  employed  in  making  the  concrete  does  not 
enter  into  chemical  combination  with  the  cement,  and  coneeqaently 
when  the  concrete  dries  ont  the  space  occupied  by  the  free  water  ia 
empty. 

156.  Kethods  of  Determining  the  Proportions.  There  are  two 
methods  of  fixing  the  proportions  for  a  concrete;  viz.:  1.  adjiut 
the  proportions  so  that  tbe  Toids  of  the  aggregate  shall  be  filled 
with  mortar,  and  the  voids  of  the  sand  with  cement  paste;  or,  %, 
fix  tbe  proportions  witbont  reference  to  the  voids  in  the  materials. 
These  two  methods  will  be  considered  in  order. 

156a.  With  Reference  to  Ike  Voidt.  To  find  the  correct  prc- 
portions  for  a  concrete,  first  determine  the  per  cent,  of  voids  in  the 
rammed  aggregate  (§  llbd).  Next  determine  the  voids  in  the 
sand.  Then  use  that  proportion  of  cement  which  will  fill  the  voids 
of  the  sand  with  cement  paste  (see  g  126).  The  amount  of  mortar 
to  be  used  depends  upon  the  per  cent,  of  voids  in  the  aggregate  and 
tbe  density  desired  iu  the  concrete  (see  Table  13c,  page  113d). 

The  det^ls  of  the  method  of  determining  the  amount  of  mortar 
and  of  cement  will  be  illustrated  by  the  following  example.  Assume 
the  aggregate  to  be  broken  stone,  unscreened  except  to  remove  the 
dust,  containing  38  per  cent,  of  voids  when  rammed  (see  No.  10, 
Table  lOA,  page  80).  Also  assome  that  a  concrete  tA  maximum 
density  ia  desired ;  and  that  therefore  the  mortar  should  be  equal 
to  about  140  per  coat,  of  tbe  voids  (see  Table  13c,  page  llZb).  The 
aggregate  compaote  5  per  cent,  in  ramming  (No.  10,  Table  lOA), 
and  therefore  a  yard  of  loose  material  will  equal  0.95  of  a  yard 
rammed.  Adding  mortar  eqnal  to  140  per  cent,  of  tbe  voids 
increases  the  volume  to  about  114  percent.  (Table  13c);  and  there- 
fore adding  the  mortar  will  increase  the  volume  of  the  ramn^ed 
aggregate  to  0.95  X  1.14  =  1.08  cu.  yd.,  which  is  the  volume  of 
concrete  produced  by  a  yard  of  loose  aggregate.  To  produce  a  yard 
of  concrete  will  therefore  require  1  -f-  1.08  =  0.93  on.  yd.  of  loose 
broken  stone.    Since  the  mortar  is  to  be  eqnal  to  140  per  oent.  of 


ovGoQi^lc 


ABT.  2.]     HETHODS  OF  DETZBUININO 'THE  PBOPOBTIOIT&.  HZd 

the  voids,  a  yard  of  ooaorete  will  reqaire  1.40  x  0.38  =  0.S9  co. 
yd.  of  mortar.  ABsnine  the  rammed  eand  to  contain  37  per  oent. 
of  Toida  (see  Table  lOjr,  page  79i).  Therefore  to  fill  the  voids  of 
the  sand  vith  cement  paate  will  require  3?  per  cent,  as  much 
packed  cement  m  loose  aand;  or  in  other  words,  the  proportions  of 
the  mortar  sbonld  be  abont  1  votome  paclced  cement  to  2^  Tolumee 
loose  sand.  Interpolating  from  Table  11,  page  88,  ve  aee  that  to 
produce  a  yard  of  this  mortar  will  reqaire  abont  2.40  bbl.  of  Port- 
land cement  and  0.79  en,  yd.  of  sand.  Gonsequentlj  a  yard  of  the 
concrete  will  require  0.S9  X  3.40  =  0.94  bbl.  of  Portluid  cement, 
and  0.39  X  0.79  =  0.31  en.  yd.  of  aand.  The  quantities  for  a 
eobic  yard  of  the  rammed  concrete  are:  0.94  bbl.  of  packed  Fort- 
land  cement,  0.31  co.  yd.  of  loose  sand,  and  0.93  co.  yd,  of  loose 
brokea  stone;  and  since  1  bbl.  =  0.13  en.  yd.,  the  proportions 
are:  1  volnme  ot  packed  Portland  cement,  S^  Tolnmea  of  looee 
sand,  and  7^  volnmes  of  loose  broken  stone. 

156d.  Without  Raference  to  the  Voids.  tJsaally  the  proportions 
of  a  concrete  are  fixed  withoat  any  reference  to  the  method  to  be 
employed  in  measuring  the  cement,  and  also  without  reference  to 
the  voids  in  the  sand  and  in  the  aggregate.  The  proportiona  are 
nanally  atated  in  Tolomee,  that  of  the  cement  being  the  unit.  For 
example,  a  concrete  is  described  as  being  1  part  cement,  2  parts 
eand,  and  4  parts  broken  stone. 

This  method  is  inexact,  in  the  first  place,  since  it  does  not  state 
the  degree  of  compactueas  of  the  cement.  If  the  unit  of  cement  is 
a  commercial  barrel  of  packed  cement,  the  resulting  concrete  will 
be  much  richer  than  if  the  cement  were  measared  loose  (see  §  126). 
In  the  second  place,  this  method,  in  name  and  naoatly  in  fact, 
takes  no  account  of  the  proportion  of  voids  in  either  the  sand  or 
the  aggregate.  If  the  stone  is  screened  to  practically  one  size,  it 
may  have  4fi  to  $0  per  cent,  of  voids  when  rammed;  but  if  it  is 
unscreened  except  to  remove  the  dust,  it  may  have  only  30  per 
cent,  of  voids  (see  Table  lOh,  page  80). 

Ifi6c.  To  explain  the  method  of  testing  whether  or  not  the  voids 
are  filled  in  a  concrete  described  in  the  above  form,  take  the  com- 
mon proportions:  I  volume  cement,  2  volomes  sand,  and  4  volumes 
broken  stone.  If  the  cement  is  measured  by  volumes  loose,  as  is 
usually  the  case,  1  volume  of  dry  cement  will  make  abont  0.8  of  a 
volame  of  paste.  If  the  sand  is  the  best,  it  wHl  probably  have 
about  30  per  cent,  of  voids  when  rammed  (see  Table  lO^r,  page  79t) ; 


ovGoQi^lc 


llZe  COITCRETE.  [chap.  IT. 

and  hflDce  the  2  Tolames  of  BBnd  Trill  contain  about  0.6  of  a  volame 
of  Toids.  Tbe  cement  is  then  S6  per  cent,  more  than  eaongb  to 
fill  the  Yoida  of  the  sand.  Tbe  cement  and  sand  \Tben  rammed 
will  make  3  -|-  (0.8  —  0.6)  =  2.2  +  volnmea  of  mortar.*  If  the 
broken  atone  is  nnscreeiied,  it  will  probably  have  aboat  30  per  cenL 
Toide  when  rammed  (aee  Table  lOA,  page  80);  and  hence  the  4 
Tolnmee  of  stone  will  contain  1.2  Tolnmes  of  voids.  The  excess  of 
mortar  is  then  2.2  — 1.2  =  1.0  nnits,  or  83  per  cent,  more  than 
enongh  to  fill  the  voids  of  the  broken  stone.  Tbe  mortar  and  the 
broken  stone  will  make  4  +  (2.2  —  1.2)  =:  5.0  +  Tolnmes  of 
rammed  concrete. f 

For  the  materials  assamed,  the  preceding  proportions  are  very 
uneconomical,  since  there  is  25  per  cent,  more  cement  than  the 
voids  in  the  sand  and  83  per  cent,  more  mortar  than  the  voids  in 
the  broken  stone.  The  possible  saving  in  cement  may  be  compated 
as  follows :  25  per  cent,  of  the  cement  coald  be  omitted  in  making 
the  mortar.  The  mortar  woald  then  be  3  volnmes,  of  which  0.8 
of  a  volume,  or  40  per  cent.,  is  in  excess  of  the  voids  in  the  aggre- 
gate. The  omission  of  this  snrplas  mortar  is  equivalent  to  omitting 
0.40  X  0.75  =  30  per  cent,  of  the  original  cement.  The  total 
snrplas  of  cement  is  then  25  -)-  30  =  55  per  cent.  It  the  above 
proportions  were  intended  to  give  a  conoreta  of  mazimnm  density, 
then  the  mortar  employed  shoald  be  about  40  per  cent,  in  excess 
of  the  void  (§  155).  In  this  case,  the  surplus  mortar  wonld  be 
(2.0  —  1.40  X  1.2)  =  0.32  volumes,  or  16  per  cent,  of  the  total 
mortar;  and  the  snrpli^s  cement  in  this  mortar  wonld  be  (0.75x0.16) 
=  12  per  cent.  Therefore  the  total  snrplas  cement  is  25  4- 12  = 
37  per  cent.     Even  in  this  case  the  proportions  are  uneconomical. 

166d.  The  above  example  shows  bow  extravagant  the  above 
proportions  are  with  tbe  beet  grades  of  sand  and  broken  stone.  If 
the  sand  has  37^  per  cent,  of  voids  and  the  broken  stone  40  per 
cent.,  then  with  the  preceding  proportions  there  will  be  practically 
no  surplus  cement,  and  there  will  be  an  excess  of  mortar  of  aboat 
25  per  cent.  In  other  words,  with  coarse  sand  and  screened  stone, 
tbe  voids  of  the  sand  will  be  filled  with  cement  paste,  and  the  voids 

•  The  mortar  whan  rammed  will  make  from  3  to  4  per  cent,  mora  volume  ttian 
the  Bum  ol  tbe  sand  and  the  exoasa  ot  the  pftate  (aae  the  laat  paragraph  ol  %  138, 
page  87). 

t  The  Tolume  ot  tbe  oonuFets  will  be  ellghtl;  more  than  6.0  units,  slnoe  some 
sand  will  remain  twtweeii  the  tragmohts  of  stone,  and  thereby  Inoreaaa  the  Tolams 
(see  Table  13o,  page  113b.) 


ovGoQi^lc 


ABT.  2,]  DA.TA.   FOB  ESTIUATES.  113/ 

of  the  broken  stone  will  be  filled  with  mortar.  However,  it  ia 
«X06edi&glf  uneconomical  to  nse  a  very  poroQB  aggregate  and 
attempt  to  make  a  very  dense  concrete. 

The  above  comparisoDs  show  how  anscientific  it  is  to  proportion 
concrete  regardless  of  the  condition  of  the  materials  to  be  need. 

166s.  Occasionally  specifications  state  the  qnality  of  the  mortar 
to  be  nsed,  and  require  the  mortar  and  the  aggregate  to  be  so  pro- 
portioned that  the  mortar  shall  at  least  be  eqnal  to  the  voids  in  the 
aggregate.  Under  this  method  of  procedure,  to  gnard  against  lack 
of  aniformity  in  the  aggregate,  imperfect  mixing,  and  insafQcient 
tamping,  it  is  cnatomary  to  require  more  than  enough  mortar  to 
fill  the  voids,  this  excess  varying  from  0  to  50  percent.,  but  usnally 
being  from  15  to  25.  Apparently  15  per  cent,  ii  frequently  nsed 
in  Grermany.* 

Xotice  that  this  method  is  an  approxiinatJon  to  that  discussed 
In  %  156(1  preceding. 

166/.  Data  for  Eitimatei.  Table  13d  and  Table  13e,  pages 
112jr  and  112A,  give  the  quantities  of  cement,  sand,  and  broken  stone 
required  to  make  a  cubic  yard  of  concrete,  for  the  two  methods  of 
proportioning  described  in  §  156a  and  §  156J,  respectively.  Each 
table  gives  the  quantities  for  unscreened  and  also  for  screened 
broken  stone;  and  Table  IZd  gives  also  the  quantities  of  cement 
and  gravel  required  for  a  cubic  yard  of  concrete. 

The  barrel  of  cement  in  both  tables  is  the  commercial  barrel  (^ 
packed  cement. 

166g.  Table  ISd  is  recommended  for  general  use.  The  first  line 
gives  a  concrete  of  the  maximum  density  and  maximum  strength, 
i.e.,  the  quantity  of  mortar  is  snflScient  to  fill  the  voids  (see  g  155); 
and  the  successive  lines  give  concretes  of  decreasing  density  and 
strength.  The  third  and  subsequent  lines  give  concretes  containing 
mortar  equal  to  the  voids,  the  mortar  in  the  third  line  being  1  tp  3j 
in  the  fourth  1  to  i,  etc. 

The  qnantilies  were  computed  aa  described  in  g  156a,  and  were 
afterwards  checked  by  making  6-inch  cabes  of  concrete.  While 
the  results  are  only  approximate  for  any  particular  case,  it  is 
believed  that  they  represent  average  conditions  with  reasonable 
accuracy. 

The  quantities  in  the  table  are  for  stone  nniform  in  qnality,  and 

*  Der  FortUnd  Oement  uod  selno  Annendnngea  im  BauireHeD,  pp.  IM  uid  US. 


jvGooi^le 


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jvGooi^le 


ART.  3.] 


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jvGooi^le 


iiai  coucsBTB.  [chap.  IV, 

for  concrete  thoroaghlj  and  Tigoronaly  r&mmed;  aad  if  it  is  desired 
certainl;  to  secare  the  deaseet  coacrebe,  it  might  he  wise  to  iDcreaae 
somewhat  the  cement  and  sand  given  in  the  first  line  of  Table  13d, 
The  per  cent,  of  increase  should  vaiy  with  the  circnniBtances  of  the 
case  iu  hand  (see  §  156e). 

The  proportions  of  the  concretes  can  be  determined  b;  remem- 
bering that  a  barrel  of  cement  is  eqnaltoO.lScn.  yd.  For  example, 
for  ansoreened  broken  stone  and  Portland  cement,  the  0.94  bbl.  of 
cement  iseqaal  to  0.1^  ca.  jd.;  and  the  proportions  are:  1  volame 
of  packed  cement,  %.5  volames  of  loose  sand,  and  7.5  volames  of 
loose  nnscreened  broken  stone.  It  it  be  assamed  that  a  barrel  of 
packed  cement  will  make  1.25  barrels  when  measured  loose  (see 
g  126),  the  above  proportions  become:  1  volame  loose  cement, 
2,0  Tolnmes  loose  sand,  and  6.0  rolnmes  loose  nnsoreened  broken 
stone. 

1S6A.  Table  13e  is  given  for  use  in  determining  the  ingredients 
required  for  a  concrete  designed  in  the  ordinary  way — see  §  156d. 
The  quantities  were  computed  sabHtantially  as  illustrated  in  156<;. 
This  table  is  not  as  accnrate  as  Table  13d,  and  besides  many  of  the 
proportions  are  uneconomical  (see  the  second  paragraph  of  §  156c), 

156i.  Froportione  from  Practice.  While  a  statement  of  the 
proportions  ased  in  practice  may  be  of  interest,  it  can  not  be  of  any 
great  value  since  it  is  impracticable,  if  not  impossible,  to  describe 
fully  the  circumstances  and  limitations  under  which  the  work  was 
done.  Farther  the  specifications  and  records  from  which  such  data 
must  be  drawn  are  frequently  very  indefinite.  It  is  believed  that 
the  following  examples  are  as  accnrate  as  it  is  possible  or  practicable 
to  make  them,  and  also  that  they  are  representative  of  the  best 
American  practice. 

For  foundations  for  pavements:  1  volume  otnaiureU  cement, 
2  volumes  of  sand,  and  i  or  5,  and  occasionally  6,  volnmes  of  broken 
stone;  or  1  volume  of  Portland  cement,  3  volumes  of  sand,  and  6 
or  7  volumes  of  broken  stone.  Occasionally  gravel  is  specified,  and 
more  rarely  gravel  and  broken  stone  mixed. 

For  foundations  and  minor  railroad  work:  1  volume  of  natnral 
cement,  2  volnmes  of  sand,  and  2  to  6,  nsnally  i  or  5,  parts  of 
broken  stone.     See  also  pages  532  and  535. 

For  important  bridge  and  tnnnel  work:  1  part  of  Portland 
cement,  3  parts  of  sand,  and  4  or  5  parta  of  broken  stone. 


ovGoQi^lc 


AKT.  3.]  PEOPOEnONS  FHOM    FRACTICB.  112/ 

For  ateel'grill^e  foundationB :  1  part  Portland  cement,  1  part 
aand,  and  2  parts  broken  stoae. 

For  the  Melan  steel  and  coocrete  constmction  the  usual  pro- 
portions are:  1  Tolnme  of  Portland  cement,  2j  Tolnmes  of  aand, 
fi  Tolnmea  of  broken  stone. 

For  the  retaining  valU  o;i  the  Chicago  Sanitary  Canal :  1  part 
natural  cement,  1^  parta  sand,  and  4  parts  unscreened  limestone. 

For  the  dams,  locks,  etc.,  on  the  Illinois  and  HissiBsippi  Canal: 
1  volume  of  loose  Portland  cement,  8  Tolnmes  of  gravel  and  broken 
■tone;  or  1  volame  loose  natural  cement  and  5  volnmes  gravel  and 
broken  stone. 

For  the  Poe  Lock  of  the  St.  Mary's  Fall  Cuial:  1  part  nataral 
cement,  1^  parts  of  sand,  and  4  parts  of  sandstone  broken  to  pass 
a  Si'inch  ring  and  not  a  f-inch  screen.  The  broken  stone  had  46 
per  cent,  voidaloose  and  38  when  rammed. 

In  harbor  improTements  the  proportions  of  concrete  range  from 
the  richest  (used  to  resist  the  violent  action'  of  iravea  and  ice)  to 
the  very  lowest  (used  for  filling  in  cribwork).  At  Buffalo,  N.  Y., 
an  extensive  breakwater  built  in  1890  by  the  TI.  8.  A.  engineers, 
consistbd  of  concrete  blocks  on  the  faces  and  a  backing  of  coucrete 
deposited  in  place.  Portland  was  used  for  the  blocks  and  natural 
for  the  backing,  the  proportions  being:  1  volume  cement,  3  aand, 
and  8^  of  broken  stone  and  pebbles  mixed  in  equal  parts. 

For  the  concrete  blocks  used  in  constructing  the  Mississippi 
Jetties  the  proportions  were:  1  part  Portland  cement,  1  part  sand, 
1  part  gravel,  and  5  parts  broken  stone. 

For  incidental  information  concerning  proportions  need  in  prac- 
tice, see  Cost  of  Concrete,  §  158a,  page  llSi;. 

156y.  Watxs  Requiees.  There  is  a  considerable  diversity  of 
opinion  among  engineers  as  to  tlie  amount  of  water  to  be  used  in 
makiog  concrete.  According  to  one  extreme,  the  amount  of  water 
should  be  snch  that  the  concrete  will  quake  when  tamped ;  or  in 
other  words,  it  should  have  the  consistency  of  liver  or  jelly. 
Aocording  to  the  other  extreme,  the  concrete  sbonld  be  mixed  so 
dry  that  when  thoroughly  tamped  moisture  jnst  finshes  to  the  sur- 
face. The  advocates  of  wet  mixture  claim  that  it  makes  the 
stronger  and  more  dense  concrete;  while  the  advocates  of  dry  mix- 
ture claim  the  qtposite.  The  difference  in  practice  is  not  as  great 
aa  in  theory;  the  apparent  difference  is  chiefly  due  to  difference* 
in  condition. 


ovGoQi^lc 


llSJt  CONCEKTB.  [chap.  IV. 

It  is  nnqnefltionably  trn«  that  diy  miitnrea  of  neat  oement,  and 
also  of  cement  and  sand,  are  stronger  than  wet  miztDies,  prorided 
the  amonat  of  water  is  enfficient  for  the  crystallization  of  the 
cement.  It  is  also  certainly  true  that  in  even  a  dry  mortar  or  con- 
crete, the  water  is  considerably  in  excess  of  that  necessary  for  the 
crystallization  of  the  cement,  this  excess  increasing  with  the  amonnt 
of  sand  and  aggregate.  Of  conrse  the  excess  water  is  an  element 
of  weakness.  Bat  the  amonnt  of  water  to  be  nsed  in  making  con- 
crete is  nsnally  a  qnestion  of  expediency  and  cost,  and  not  a  qnee- 
tion  of  the  greatest  attainable  strength  regardless  of  expense. 

1.  Dry  mistares  set  more  qnickly  and  gain  strength  more 
rapidly  than  wet  ones;  and  therefore  if  quick  set  and  early  strength 
are  desired,  dry  concrete  shoald  be  preferred.  2.  Wet  concrete 
contains  a  great  number  of  invisible  pores,  while  dry  concrete  is 
liable  to  contaio  a  considerable  nnmber  of  visible  voids;  and  for' 
this  reason  there  is  liability  that  wet  concrete  will  be  pronounced 
the  more  dense,  even  though  both  have  the  same  density.  3.  Wet 
concrete  Is  more  easily  mixed ;  and  therefore  if  the  concrete  is  mixed 
by  band  and  the  supervision  is  insufficient  or  the  labor  is  careless, 
or  if  the  machine  by  which  it  is  mixed  is  inefficient,  wet  mixtures 
are  to  be  preferred.  4.  Wet  mixtures  can  be  compacted  into  place 
with  less  eSort  than  dry;  but  on  the  other  hand  tbe  excess  of  water 
makes  the  mass  more  porous  than  though  tbe  concrete  had  been 
mixed  dry  and  thoroughly  compacted  by  ramming.  Dry  con- 
crete must  be  compacted  by  ramming,  or  it  will  be  weak  and 
porous;  therefore  if  the  concrete  can  not  be  rammed  into  place,  it 
should  be  mixed  wet  and  then  the  weight  of  the  stones  will  bury 
themselves  in  the  mortar,  and  the  mortar  will  flow  into  the  voids. 
5.  A  rich  concrete  can  be  compacted  much  easier  than  a  lean  one, 
owing  to  the  lubricating  effect  of  the  mortar;  vid  hence  rich  con- 
cretes can  be  mixed  dryer  than  lean  ones.  The  quaking  of  concrete 
frequently  is  due  more  to  an  excess  of  mortar  than  to  an  excess  of 
water.  6.  Lean  concretes  should  be  mixed  dry,  since  if  wet  the 
cement  will  find  its  way  to  the  bottom  of  the  layer  and  destroy  the 
uniformity  of  the  mixture.  7.  Machine-made  concrete  may  be 
mixed  dryer  than  hand*made,  owing  to  the  more  thorough  incor- 
poration of  the  ingredients.  8.  Gravel  oonorete  can  be  more  easily 
compacted  than  broken  stone,  and  hence  may  be  mixed  dryer. 
Cement  and  sand  alone  is  more  easily  compacted  than  when  mixed 
with  ooaiur  material,  particularly  broken  stone;  and  therefore 


ovGoQi^lc 


ABT.  2.]  WATKB  KBQUIBED.  IIZI 

mortar  to  be  depoaited  in  moaa  should  be  mixed  diyer  than  concrete. 
9.  In  mixing  dry  b;  band  there  is  a  tendency  for  the  cement  to  ball 
np,  or  form  nodnles  of  neat  cement,  vhile  in  mixing  wet  this  does 
not  occur.  10.  If  wet  oonorete  is  deposited  in  a  wood  form,  there 
is  liability  of  the  water  exuding  between  the  planking  and  carrying 
away  part  of  the  cement  and  thns  weakening  the  face — which  should 
be  the  strongest  part  of  the  mass. 

The  conclnsion  is  that  sometimes  wet  concrete  must  be  used 
regardless  of  any  qnestion  of  strength  and  cost;  while  with  thorongh 
mixiog  and  vigoroas  ramming,  dry  concrete  is  strongest  bnt  also 
most  ezpeosiTe  to  mix  and  lay. 

IMk.  The  following  experiments  are  the  only  ones  of  any  im- 
portance made  to  determine  the  relative  strength  of  wet  and  di; 
concretes.  The  mean  crashing  strength  of  fonr  handred  and 
ninety-six  1-foot  cnbes  *  made  with  mortar  as  "  dry  as  damp  earth  '* 
was  11  per  cent,  stronger  than  cnbes  made  with  mortar  of  the 
"ordinary  consistency  nsed  by  the  average  mason,"  and  13  per 
cent,  stronger  than  cnbes  that  "  qnaked  like  liver  nnder  moderate 
ramming."  The  oabes  were  made  of  five  brands  of  Portland 
cement,  with  broken  stone  and  five  proportions  of  sand  varying 
from  1  to  1  to  1  to  6;  half  the  oabes  had  a  little  more  mortar  than 
enoDgh  to  fill  the  voids,  while  the  other  half  had  only  about  80  per 
cent,  as  mncb  mortar  as  voids.  One  quarter  of  the  cnbes  were 
stored  in  water,  one  quarter  in  a  cellar,  one  quarter  under  a  wet 
cloth,  and  one  quarter  in  the  open  air;  and  all  were  broken  when 
approximately  Z  years  old.  The  diSerenoe  in  the  amonnt  of  mortar 
made  no  appreciable  diSerenoe  in  the  strength. 

The  mean  of  twelve  cubes  of  dry  concrete  was  61  per  cent, 
stronger  than  corresponding  cubes  of  quaking  concrete,  f 

A  few  minor  experiments  have  been  found  confirming  the  above, 
and  none  have  been  found  that  contradict  them. 

1661.  I'he  amount  of  water  required  to  prodnoe  any  puiicnlar 
plasticity  varies  so  greatly  with  the  proportions  of  the  ingredients, 
the  kind  and  fineness  of  the  cement,  the  dampness  of  the  sand,  the 
kind  of  aggregate,  etc.,  that  it  is  scarcely  possible  to  give  any  valu- 
able general  data.  The  water  varies  from  10  to  40  pounds  per  cubic 
foot  of  concrete.    The  only  general  rule  that  can  be  given  is  that  for 

•  Geo.  W.  Batter,  1b  Beport  oC  the  Mew  York  BUto  Engtneer  lor  1807,  pp.  ttS-IM, 
pKrtlcalarir  Table  ^,  page  89S. 
t  Feret,  Xnginmring  Uttot,  voL  zxrll,  p.  Sll, 


ovGoQi^lc 


llZm.  OOUCSFtTE.  [chap.  IV. 

dry  concrate  the  aggregate  ahonld  be  wet  but  hare  no  free  water  la 
the  heap;  and  that  the  mortar  shoold  be  damp  enongh  to  show 
water  only  when  it  is  thorongfaly  rammed,  or  so  that  water  will 
flush  to  the  surface  when  it  is  tightly  squeezed  for  a  coDsiderahle 
time  in  the  hand. 

In  the  experiments  referred  to  in  the  first  paragraph  of  the 
preceding  section,  the  average  quantity  of  water  for  the  different 
grades  of  dry  mortar  was  19. S  Iba.  per  en.  ft.,  and  for  the  plastic 
21.1,  and  for  the  wet  HZ. 5,  the  sand  being  reasonably  dry. 

166m.  Xiznre.— The  value  of  the  concrete  depends  greatly 
upon  the  thoronghsess  of  the  mixing.  Every  grain  of  sand  and 
every  frt^^ent  of  a^regate  should  have  cement  adhering  to  every 
point  of  its  surface.  Thorough  mixing  should  cause  the  cement 
not  only  to  adhere  to  all  the  surfaces,  hut  should  force  it  into 
intimate  contact  at  every  point.  It  is  possible  to  increase  the 
strength  of  really  good  concrete  100  per  cent,  by  prolonged  tritura- 
tion and  rubbing  together  of  its  constituents.  The  longer  and  more 
thorough  the  mixing  the  better,  provided  the  time  does  not  trench 
upon  the  time  of  set  or  the  working  does  not  break  and  pulverize 
the  angles  of  the  stone.  Uniformity  of  the  mixtare  ia  as  important 
as  intimacy  of  contact  between  the  ingredients.  Of  coarse  tborongh- 
ness  of  mixing  adds  to  the  cost,  and  it  may  be  wiser  to  nae  more 
cement,  or  more  concrete,  and  less  labor. 

Concrete  may  he  mixed  by  hand  or  by  machinery.  The  latter 
is  the  better;  since  the  work  is  more  quickly  and  more  thoroughly 
done,  and  since  ordinarily  the  ingredients  are  brought  into  more 
intimate  contact.  Machine  mixing  is  frequently  specified.  If  any 
considerable  quantity  is  required,  machine  mixing  is  the  cheaper, 
ordinarily  costing  oi^y  about  half  as  much  ae  hand  mixing. 

Ifi6n.  Hand  Kxing.  The  sand  and  aggregate  are  usually 
measured  in  wheelbarrows,  the  quantity  being  adjusted  for  a  bag 
or  barrel  of  cement.  The  dry  cement  and  sand  are  mixed  as 
described  in  the  first  paragraph  of  g  124  (page  85),  which  see. 
The  proper  quantity  of  water  is  then  added,  preferably  with  a 
spray  to  secure  greater  uniformity  and  prevent  the  washing  away 
of  the  cement.  The  mass  should  he  agmn  turned  until  it  is  of 
uniform  consistency.  The  broken  stone,  having  previously  been 
sprinkled  but  having  no  free  water  in  the  heap,  is  then  added.  The 
whole  is  then  tamed  antil  every  fragment  is  oorered  with  cement. 
Specifioationa  nsoally  require  ooncret*  to  be  turned  at  least  foar 


ovGoQi^lc 


AHT.  2.]  HIXIMG.  UZn 

times,  and  freqnently  six.  The  concrete  appe&rs  wetter  eoob  time 
it  is  tnrned,  and  should  appear  too  dry  antil  the  very  lost. 

If  gravel  is  used  iostead  of  broken  stone,  the  mixing  is  done  as 
described  for  cement  and  sand. 

Ififto.  Haohine  Kizin^.  A  variety  of  concrete-mixing  maobines 
are  in  nae.  Some  forms  are  intermittent  and  some  continuous  in 
their  Action.  Some  of  the  latter  automatically  measnre  the  in- 
gredients, A  simple  variety  of  the  former  oonsists  of  a  cubical  box 
revolved  slowly  about  a  diagonal  axis.  The  dry  materials  are 
inserted  through  a  door,  and  the  water  is  admitted  through  the 
axis  daring  the  process  of  mixing,  Sight  or  ten  revolutions  are 
sometimes  specified;  but  eighteen  or  twenty  are  more  frequently 
specified  and  give  a  mnch  better  concrete.  Sometimes  an  inclined 
cylinder  or  long  box  revolving  abont  the  long  axis  is  employed. 
Another  form  consiata  of  a  vertical  box  having  a  series  of  inclined 
shelves  projecting  alternately  from  opposite  sides,  the  materials 
being  thrown  in  at  the  top  and  becoming  mixed  by  falling  succes- 
sively from  the  inclined  shelves.  A  modification  of  thta  form  sub- 
stitutes rods  for  the  shelves,  the  mixing  being  accomplisbed  by  the 
ingredients  in  their  descent  striking  the  rods.  Still  another  type 
form  consists  of  a  spiral  conveyor  or  a  bladed  screw-shaft  revolving 
in  a  trough  in  which  the  materials  are  thrown.  All  of  these  forms, 
and  also  modifications  of  them,  are  to  be  had  on  the  market.. 

166p.  Latdto.  Aftermixing,  the  concrete  is  conveyed  in  wheel- 
barrows or  in  buckets  swung  from  a  crane,  deposited  in  layers  6  to 
8  inches  thick,  and  compacted  by  ramming.  In  dumping,  the  mass 
sbonld  not  be  allowed  to  fall  from  any  considerable  height,  as  doing 
80  separates  the  ingredients.  If  in  handling,  the  larger  fragments 
become  separated,  they  should  be  returned  and  be  worked  into  the 
mass  with  the  edge' of  a  shovel. 

The  rammer  aaually  employed  consists  of  a  block  of  iron  having 
a  face  6  to  8  inches  square  and  weighing  anything  up  to  30  or  40 
pounds.  The  face  of  the  rammer  is  sometimes  corrugated,  to  keep 
the  surface  of  the  layer  rough  and  thus  aSord  a  better  bond  with 
the  next,  and  also  to  transfer  the  compacting  effect  of  the  blow  to 
the  bottom  of  the  layer.  The  tamping  should  be  vigorous  enoogh 
to  thoroaghly  compact  the  mass;  bnt  too  severe  or  too  long-con- 
tinned  ponnding  injarea  the  strength  of  the  concrete  by  forcing  the 
broken  stone  to  the  bottom  of  the  layer,  or  by  disturbing  the 
incipient  set  of  the  cement. 


ovGoQi^lc 


112o  COKCKETE.  [CHAP.  IT, 

When  one  layer  is  laid  on  another  already  portiallf  eet,  the 
entire  sarface  of  the  latter  should  be  thoroughly  wet;  bnt  water 
Bhonld  not  stand  in  paddlee.  In  case  the  first  layer  is  fully  set,  it 
is  wise  to  sweep  the  sarface  with  neat  oement  paste  to  make  sure 
that  the  two  layers  adhere  firmly.  If  the  sand  or  gravel  contains 
any  appreciable  clay  and  the  concrete  is  mixed  vet,  clay  is  liable  to 
be  fiashed  to  the  snrface  and  prevent  the  adherence  of  the  next 
layer;  therefore  under  these  conditions  particnlar  care  shoald  be 
given  to  secure  a  good  union  between  the  layers.  After  the  con- 
crete is  in  place  it  should  be  protected  from  the  snn,  and  not  be 
disturbed  by  walking  apon  it  until  fnlly  set:  this  limit  shonld  be 
at  least  13  hours  and  is  frequently  specified  as  4  or  5  days. 

169q.  Bepoiiting  Concrete  under  Water.  In  laying  ooocrete 
nnder  water,  an  essential  requisite  is  that  the  materials  shall  not 
fall  from  any  height,  but  be  deposited  in  the  allotted  place  in  a 
compact  mass;  otherwise  the  cement  will  be  separated  from  the 
other  ingredients  and  tbe  strength  of  the  work  be  serioasly  im- 
paired. If  the  concrete  is  allowed  to  fall  through  the  water,  its 
ingredients  will  be  deposited  in  a  series,  the  heaviest — the  atone — 
at  the  bottom  and  the  lightest — the  oement — at  the  top,  a  fall  of 
even  a  few  feet  causing  an  appreciable  separation.  Of  coarse  con- 
crete should  not  be  used  in  running  water,  as  the  cement  would  be 
washed  out. 

A  common  method  of  depoeiting  concrete  under  water  is  to 
place  it  in  a  V-shaped  box  of  wood  or  plate-iron,  which  is  lowered 
to  the  bottem  by  a  crane.  The  box  is  so  constructed  that,  on 
reaching  the  bottem,  a  pin  may  be  drawn  out  by  a  string  reaching 
to  the  surface,  thus  permitting  one  of  the  sloping  sides  to  swing 
open  and  allowing  the  concrete  to  fall  out.  The  box  is  then  raised 
to  be  refilled.  It  usually  has  a  lid.  Concrete  nnder  water  should 
not  be  rammed;  bnt,  if  necessary,  may  be  leveled  by  a  rake  or 
other  suitable  tool  immediately  after  being  deposited. 

A  long  box  or  tnbe,  called  a  trhnie,  is  also  sometimes  used.  It 
oonsists  of  a  tnbe  open  at  top  and  bottom,  boilt  in  detachable  sec- 
tions BO  that.the  length  may  be  adjusted  to  the  depth  of  water. 
The  tnbe  is  suspended  from  a  crane,  or  movable  frame  running  on  a 
track,  by  which  it  is  moved  aboat  as  the  work  progresses.  The 
upper  end  is  hopper-shaped,  and  is  kept  above  the  water;  the  lower 
end  leats  against  the  bottom.  Tbe  trSmie  is  filled  in  the  beginning 
by  placing  the  lower  end  in  a  box  with  a  mnvuble  bottom,  filling 


ovGoQi^lc 


ABT.  2  ]  BTBENGTH,  112^ 

the  tabe,  levering  all  to  the  bottom,  and  then  detaching  the 
bottom  of  the  box.  The  tabe  is  kept  fall  of  boncrete,  as  the  mass 
issoee  from  the  bottom  more  is  thrown  in  at  the  top. 

Concrete  has  also  been  BnGcessfnll;  deposited  ander  water  hj 
enoloeing  it  in  paper  bags,  and  levering  or  sliding  them  down  a 
chate  into  place.  The  bags  get  wet  and  the  pressiin  of  the  con- 
crete soon  bursts  them,  thns  alloviag  the  concrete  to  nnite  into  a 
solid  mass.  Concrete  is  also  sometimes  deposited  nnder  vater  b; 
enclosing  it  in  open-cloth  bags,  the  cement  oozing  throngh  the 
meshes  snflQcientl;  to  nnite  the  whole  into  a  single  mass. 

When  concrete  is  deposited  in  vater,  a  pnlpy  gelatinous  flnid  i» 
washed  from  the  cement  and  rises  to  the  surface.  This  oaosee  tho 
water  to  assume  a  milky  hue;  hence  the  term  Untance,  which 
French  engineers  apply  to  this  substance.  It  is  more  abundant  ia 
salt  water  than  in  fresh  water.  It  sets  totj  slovlj,  and  sometimes 
scarcely  at  all,  and  its  interposition  between  the  layers  of  concrete 
forma  strata  of  separation.  The  proportion  of  laitance  is  greatly 
diminished  by  using  large  immerBing  boxes,  or  a  tr6m!e,  or  paper 
or  cloth  bags. 

167.  Stbevoth.  The  strength  of  concrete  depends  upon  the 
kind  and  amoant  of  cement,  and  upon  the  kind,  size,  and  strength 
of  the  ballast.  Mortar  adheres  to  broken  stone  better  than  to 
pebbles,  and  therefore  concrete  containing  the  former  is  stronger 
.  than  that  containing  the  latter  (see  g  151).  If  the  sizes  of  the  indi- 
Tidoal  pieces  of  the  ballast  are  so  adjusted  that  the  smaller  fit  into 
the  interstices  of  the  larger,  successively,  then  the  cementing 
material  will  act  to  the  best  advantage  and  consequently  the  con- 
crete wUl  be  stronger.  Bamming  the  concrete  after  it  is  in  place 
brings  the  pieces  of  aggregate  into  closer  contact,  and  conseqneutly 
makes  it  stronger.  The  strength  of  concrete  also  depends  somewhat 
cpon  the  strength  of  the  ballast,  but  chiefly  upon  the  adhesion  o£ 
the  cement  to  the  ballast. 

There  are  comparatively  few  experiments  upon  the  strength) 
of  concrete  in  which  the  data  was  complete  enough  to  make  the- 
reaalts  of  any  considerable  value. 

167a.  Compressive  Strength.  In  a  series  of  experiments  made 
by  Geo.  W.  Bafter*  to  determine  the  crashing  strength  of  concrete, 
three  varieties  of  Portland  cement  were  used,  all  of  which  wer& 

*  Baport  ot  tlie  Kew  ToA  state  EnglnMr.  IBST,  pp.  STS-tfO. 


ovGoQi^lc 


1127 


[chap.  it. 


eqnal  to  the  maximnm  both  neat  and  with  sand  in  Table  10,  pag« 
78a.  The  sand  was  pore,  clean,  sharp  silica,  containing  33  per 
cent,  of  voids.  The  aggregate  was  sandstone  broken  to  pass  a 
S-inch  ring,  having  37  per  cent,  voids  when  tamped.  In  half  the 
blocks  the  mortar  was  a  little  more  than  enongh  to  fill  the  Toida; 
and  in  the  other  half  the  mortar  was  equal  to  about  80  per  cent,  of 
the  voids.     The  mortar  was  mixed  as  "  irj  as  damp  earth." 

The  test  specimens  were  1-foot  oabee,  and  were  stored  nnder 
water  for  fonr  months  and  then  bnried  in  sand.     The  age  when 
tested  ranged  from  550  to  650  days,  the  average  being  abont  600. 
The  cnbes  were  crnsbed  on  the  U.  S.  Watertown  Arsenal  testing- 
machine.     The  means  are  shown  in  Table  13/.     The  individoal 
molts  agreed  well  among  tbemflelves. 
TABLE  18/. 
Orubbirc  Strehotb  op  PoB-n.uiD  ConcKEXX. 
Toida  of  broken  (tone  praclfcally  filled  wlih  morui^-we  the  lest. 

Age  wben  tsated  eOO  dajs. 


Bw.Ho. 

or   HOBTAR. 

Nn. 

Cmmanm 

«.»™. 

Cement. 

Sud. 

''■?^S' 

)l».per«i.lD. 

ton,  per  1.  ft. 

1 

4.467 

833 

3 

8,781 

«ia 

8 

2,558 

181 

4 

3,018 

HI 

B 

1.706 

129 

A 

1.865 

«8 

The  cubes  snmmarized  in  Table  13/  were  stored  nnder  water. 
Companion  blocks  stored  in  a  cool  cellar  gave  83  per  cent,  as  much 
strength;  those  fally  exposed  to  the  weather,  81  per  cent.;  and 
those  covered  with  barlap  and  wetted  several  timee  a  daj  for  abont 
three  months  and  afterwards  exposed  to  the  weather,  80  per  cent. 

The  cubes  of  Table  13/  were  mixed  as  "  dry  as  damp  earth." 
Companion  blocks  of  which  the  mortar  was  mixed  to  the  "  ordinary 
consistency  nsed  by  the  average  mason,"  gave  90  per  cent,  as  mnoh 
strength ;  and  those  mixed  to  "  qnake  like  liver  nnder  moderate 
ramming,"  88  per  cent. 


ovGoQi^lc 


ART.  2.]  COUFBESSITE  STRKKOTH.  112r 

167b.  Table  13^  ebovs  the  results  of  a  aeries  of  experimenti 
made  by  A.  W.  Dow,  Inspector  of  Asphalt  and  Cement,  Washing* 
ton,  D.  C* 

TABLE  1^. 
CKUSRins  Strbhoth  or  Coscretr  ik  Poukim  fbb  BquAUR  Ihoh. 


''™!r?^.'?.s:sssr' 

,..S;s.„. 

AOB  or  Cum  wan  Bbour. 

^; 

Hortu-. 

AatrvpiH.  la 
Sliax  from 
«J*"  lo  A". 

± 

Fn 

Cent. 

mi«d 

wUh 
Mortar 

DV* 

4t 

DTI 

.U 

Ho*. 

Tmt, 

Cemwt 

8ud. 

Broken 

QnTsl. 

1 

a 

3 

a 
a 
a 

3 

a 

3 
3 

a 
a 
a 

e 
e" 

6t 

s 

4 

6 
«• 

et 

8 
4 

e 

8 
3 
Port 

e 

8 
3 

iimlCe 
4B.S 
49.7 
89,6 
29.8 
8ft.5 
87.8 

u<iCe 
4S.8 
4B.7 
S9.B 
39.8 
80. B 
87.8 

nent. 
.  88.9 
88,9 
96.a 
120.1 
107.0 

100. e 

meot. 
68.0 
88.0 
.06.2 
130.1 
107.0 
100.8 

328 

689 

876 
096 

T06 

OlS 

4 

B 

87 
108 

421 
804 

861 
693 

844 
683 

788 
841 

7 

908 

1,700 

3.360 
1,680 

3.680 

2,610 

i.sai 

1.84(1 
8.O70 

8,060 

D 
10 
11 
13 

«04 
960 

1.680 
1.860 

3.700 

a.8ao 

3.760 
3.840 

tTbrMtourttwordliuuTitoiM,  01 


I  fourtb  gnnollihlc 


The  Btrength  of  the  cement  is  shown  in  Table  13A.  Notioe  that 
the  Portland  cement  did  not  gain  strength  proportionally  as  fast  u 
the  natural  cement;  for  example,  the  Portland  mortar  in  line  4  is 
two  aod  two-thirds  times  as  strong  as  the  preceding  natnral-oement 
mortar,  while  that  in  line  13  is  not  qaite  as  strong  as  the  natnral- 
oement  mortar  immediately  preceding. 


ovGoQi^lc 


[chap,  it. 


TxaanM  STBaHOTH 


TABLE  18%. 

or  Cbhkht  dbed  ni  Taslb  18;. 


B*v.No. 

iMWEnlMTBD. 

PunaSTunuw 

''°*^«»T. 

VMbXM. 

POHlMd. 

ld.y. 

Ijow. 

M 

180 

441 

889 

IS8 

827 

414 

486 

la 

Tbo  fineneaa  of  the  Band  WM  asfoUows:*  'S"  6'-*  S"  10"20" 
40' 60»  80"  100"  and  contained  44.1  per  cent,  of  Toids.  With 
the  nataral  cement  the  vater  naed  was  0.317  on.  ft.  (20  Iba.)  per 
en.  ft.  of  rammed  concrete,  and  with  Portland  cement  0.^  on.  ft. 
(12  lbs.) — in  both  cases  inclndtng  the  moigtare  in  the  aand.f 

The  broken  stone  vaa  gneiss  broken  to  pass  a  S^-inch  ring,  none 
pasaing  a  No.  10  sieve,  the  voids  for  each  partionlar  concrete  being 
as  stated  in  Table  13^.  The  gravel  was  clean  qnartz  passing  a 
l^-inoh  ring  and  only  3  per  cent,  passing  a  No.  10  ring,  and  had 
39  per  cent,  of  voids.  The  per  cent,  of  voids  in  the  aggregate  filled 
with  mortar  is  stated  in  Table  13^.  Each  resnlt  in  the  table  is  the 
mean  of  two  cabea,  except  those  for  one  year,  which  are  the  mean 
of  five.  Owing  to  the  friction  of  the  press  with  which  the  tests 
were  made,  the  reenlts  are  3  to  8  per  cent,  too  high. 

*167c.  Table  13i  shows  the  relative  strength  of  rich  and  lean 

*For  azpl&nftUoa  oE  the  nomanolature,  see  the  seooDd  paragraph  off  Hit. 
t  The  Hud  oontklned  iA  per  cent,  of  water,  whlah  inareased  the  volama  of  Uie 
Mnd  ud  made  Uie  mortar  eUghtlT  rloher  than  aa  stated. 


ovGoQi^lc 


r.2.] 


COKPBBBSITE   STfiENOTH. 


TABLS  IK 
Rblatitb  Btbckoth  op  Rich  and  Lsak  Cohoketm. 


o™.„b™™. 

^No. 

OWMnt. 

Bud. 

ODdWeak. 

VourW««h«L 

8W110. 

^r 

B«UlJ*& 

^■r 

BelMln. 

Portbmd  Mod-oement 

1 

H 

S 

413 

0.77 

400 

0.68 

4 

449 

0.S8 

«79 

0.03 

** 

SS6 

1.00 

741 

1.00 

1 

s 

4 

81S 

0.«1 

441 

0.60 

0 

87S 

0.68 

477 

0.64 

6  . 

031 

1.00 

<89 

1.00 

1 

8 

S 

144 

0.6* 

274 

0.85 

e 

110 

0.C3 

182 

0.07 

7 

210 

1.00 

823 

1.00 

EngUib  Portluid  cement 

10 

1 

9 

S 

494 

0.60 

S66 

0.81 

11 

8 

Sll 

0.76 

065 

0.80 

12 

4 

810 

1.00 

818 

0.88 

18 

S 

S81 

0.71 

680 

0.07 

U 

« 

600 

0.61 

8S8 

1.00 

» 

1 

8 

8 

888 

.300 

0.68 

4 
B 

e 

Gwnuin 

868 
S8« 
86? 

PortUnd  cenwnt 

B 
8 

708 
738 

jvGooi^le 


112h  concrete.  [chap,  it, 

concretes.*  The  water  waa  equal  to  20  per  cent,  of  the  weight  of 
the  cement  and  the  sand.  The  teat  specimens  for  the  Portland 
saud-cement  were  9  inches  square  and  13  inches  high,  and  for  the 
remainder  12-inch  cubes.  All  were  crashed  between  sheets  of  rubber 
(see  §  12,  page  9).  Each  Talae  in  the  table  is  the  resnlt  for  a  single 
cube.  Table  13i  is  Talnable  chiefly  as  shoving  the  relative  strength 
of  rich  and  lean  concretes.  The  table  shows  that  a  moderately  lean 
concrete  ia  stronger  than  a  very  rich  one,  which  is  in  accordance 
with  the  conclnsion  from  Table  13a,  page  110,  that  a  concrete  is 
stronger  than  the  mortar  alone.  Table  13i  also  shows  that  the 
strength  of  the  concrete  increases  with  the  richness  of  the  mortar, 
which  agrees  with  Table  13d,  page  111,  and  Fig.  8,  page  112a. 

167d.  For  data  on  the  crnshiDg  strength  of  grairil  concrete,  see 
Table  13a,  page  110. 

For  data  on  the  cmahing  strength  of  gravel  and  broken-stone 
oomoretes  approximately  17  days  old,  see  Fig.  8,  pape  1  I2a. 

Ibte.  The  strength  of  concrete  made  of  coke  does  not  increase 
with  age  owing  to  the  soft  and  friable  nature  of  the  aggregate. 
Apparently  the  maximum  strength*  of  1  volame  loose  cement, 
3  Tolnmes  sand,  and  6  volumes  crushed  coke  is  abont  600  to  700  lbs. 
persq.  in.  with  Portland,  and  about  300  to  360  with  natural  cement. 

107/.  Transverse  Strength.  Table  13^,  pagellSv,  is  a  summary 
of  191  tests  OQ  concrete  bars  30  inches  long  and  1  inches  sqaare.f 
The  cement  stood  49?  lbs.  per  sq.  in.  neat  at  7  days,  and  309  lbs. 
with  3  parts  sand  at  i  weeks.  In  most  of  the  bars  the  mortar  waa 
made  of  pulverized  sandstODC,  altboagh  in  some  cases  river  and  pit 
sands  were  used.  The  aggregate  was  generally  broken  sandstone, 
but  gravel  and  broken  whtnatoue  were  also  used.  "  In  each  case 
the  voids  io  the  '  sand '  were  filled  with  cement,  and  those  in  the 
aggregate  with  mortar." 

The  results  are  tabulated  in  the  order  of  the  ratio  of  the  cement 
to  the  total  sand  and  aggregate.  Kotioe  that  the  resnlts  in  the  last 
line  are  proportionally  higher  than  those  in  the  remainder  of  the 
table.  This  difference  is  probably  due  to  the  fact  that  the  apeci- 
mena  for  the  first  four  liuea  were  made  with  natural  sand  and 
atone,  while  in  those  for  the  last  line  only  crashed  sandstone  was 
nsed  for  both  the  sand  and  the  aggregate. 

*  W.  B.  Andaraaii,  Btndent  Can.  8oo.  C.  E.,  In  Truis.  Cu.  Boo.  0.  B..  voL  xUL, 
Portl. 

t  A.  F.  Bnioa,  In  Proa,  ot  Inst,  ot  O.  E.  (LoDdon),  toL  oxlll,  pp.  Sll-M. 


ovGoQi^lc 


ABT.  %.]  TBAKSTBBSB  STRENOTH. 


TiBLB  18^. 
lIoDin.TJ8  or  RuFTUSK  ov  PoBTLAND  Co\cRKTB  Barb,  Pomme  pkk 


A..  ,.w.,„  .„».«. 

r- 

0^. 

s... 

^ 

■ 

' 

• 

a 

,. 

a 

" 

2 

03 

145 

SIS 

266 

801 

303 

820 

84 

87 

m 

166 

104 

268 

280 

200 

S 

8S 

13D 

176 

101 

3U 

214 

3* 

81 

ISO 

IS6 

m 

100 

210 

8 

87 

118 

1S4 

187 

sie 

248 

2S3 

157^.  In  connection  with  the  constniction  of  the  Poe  Lock  of 
the  St.  Mary's  Falls  Canal  *  a  series  of  one  hundred  and  forty-Mf  en 
oonorete  beams  10  inches  square  were  tested.  The  experiments 
were  very  carefully  conducted,  bnt  there  were  bo  many  rariables 
that  it  is  impossible  to  draw  any  general  conclnsions  therefrom. 
The  beams  made  with  Portland  cement  were  tested  when  about  19 
months  old  and  those  with  natural  cement  when  about  13  months. 

157A.  Weisht  of  Cohohztx.  The  weight  of  concrete  varies 
with  the  materiulH  and  the  proportions,  and  with  the  amount  of 
Tsmming.  Tho  weight  varies  from  130  to  160  Ibe.  per  ou.  ft.,  bnt 
is  nsuaily  from  140  to  160.  The  differeoce  in  weight  of  the  con- 
crete due  to  the  aggregate  and  to  the  ramming  is  greater  than  that 
dae  to  the  difference  in  weight  between  Portland  and  natural 
cement.  The  maximum  difference  between  Portland  and  natnral 
concrete,  due  to  the  greater  weight  of  Portland  cement,  is  4  or 
5  lbs.  per  cubic  foot.  Concrete  made  of  blaat-fnmaoe  slag  weighs 
from  110  to  130  lbs.  per  cubic  foot;  and  that  made  of  coke  from 
80  to  90  lbs.  per  en.  ft. 

168a.  Cost  or  Cohcbste.  The  cost  of  concrete  varies  greatly 
with  the  materials,  the  proportions,  the  cost  of  material  and  labor, 
etc. 

The  following  is  the  analyeis  of  the  compoeition  and  cost  of  the 
concrete  employed  for  the  foundations  of  tbe  sea-wall  at  Lovell's 
Island,  Boston  Harbor:  f 

*  Report  ol  Ohlst  or  Engineen,  V.  B.  A.,  1896.    Part  4,  pp.  393a-SI. 

t  Oompiled  trora  (MUmore's  Limea,  HydmaUa  CemeiiU  uid  Hort&re,  p.  347. 


ovGoQi^lc 


2tt  ooncebh.  ,  [oHAP.  it. 

Cement,  O.SS  bbl 0.13  cu.  yd.  ®91M  =  913a 

Band 0.35  cu.  jd.  ®      TO  17 

Gimvel O.WciLyd.  ®      27  U 


Total 


Labor,  maklog mortar O.OSdajr*  ®  1  30  =  08 

L*bor,  mmklngcoDcraW. 0.11  dmyl  ®  IM  18 

Labor,  trangporllug  conorelA 0.08  dajl  @  1  90  OS 

Labor,  packing  oodgtMa 0.08  daya  %  120  01 

mallabor 0.28  daya  88 

Toola,  Implemanta,  etc 11 

3t>lal  cm(  1  «u.  yd.cfeonortU.in  place fS  11 

Th«  pTDportiona  for  this  concrete  were  1  cement,  3  nnd,  and 
i  gnvel.  It  was  niiuinalljr  cheap,  owing  parti;  to  th^  use  of 
pebbles  inetead  of  broken  stone.  If  the  latter  had  been  naed,  it 
would  hare  ooet  probably  4  to  6  times  as  mnoh  as  the  gravel.  The 
amonat  of  labor  required  was  also  nnnsnall;  amall,  this  item  idone 
being  frequently  6  to  8  times  as  much  as  in  this  case. 

The  following  ia  the  aQalysis  *  of  the  coat  of  nearly  10,000  yards 
of  concrete  as  laid  for  the  fonndstions  of  a  blast-fnraaoe  plant  near 
Troy,  N.  Y.,  in  1886.  The  conditions  were  unusually  farorabla 
for  oheap  work.  The  concrete  consisted  of  1  Tolnme  of  packed 
cement  to  7  of  sand,  gravel,  and  broken  stone. 

Oemeat,  1.28  bbl O.I8cu.7d.  ®  |1  00  =  <!  28 

Sand 0.10     "  ®   0  80=       08 

Gravel O.M     "  «   0  80=       11 

BnAeaatone 0.74     "  @   141=    104 

Total  mat«rUiU 1.88     "  =  (3  41 

Labor,  handltng  cement 0.03  dajr 

"      unloading  stone 0.14    " 

"       mixing 0.86    " 

"      auperlotendence 0.01    " 

Totallabor 1.02    "  =    I  0» 

roMeiMto/aouNifanliifwnergCa,  injiau =$8  59 


*  Tnna.  Am.  Boo.  ol  0.  E.,  toL  xr.  p.  8TS. 


® 

100  = 

« 

100  = 

« 

100  = 

® 

»01  = 

jvGooi^le 


ART.  2.]  .  COBT  OF  COXCBETE.  112x 

Th«  followiog  IB  the  cost  of  the  concrete  used  in  the  constrno- 
tion  of  HiUnd  Avenue  reservoir,  Pittsburg,  Penn.*  The  stone  wm 
hroken  so  as  to  pass  through  a  ii^-incfa  ring.  The  mortar  was 
1  part  Roaendale  natural  cement  to  2  parta  Band.  The  concrete 
Tras  1  part  mortar  to  2^  of  atone.  The  concrete  wae  mixed  by  hand. 
Common  laborers  received  tl.26  per  day,  and  foremen  t2.60.  Tbs 
contract  price, was  t6.00  per  yard. 

Quairytog  alone ^OiS 

TraDsponlng  stone SO 

Breaking  stoae SO 

Cement®  9L8S  perbbl 1  80 

Ssod,  cost  of  digging 10 

Water 00 

lAbor,  mlKlugand  laylog 10 

IncideutaU 00 

Total  eott  ptr  eiibie  pard,  inplac* (4  00 

The  following  is  the  cost  of  concrete  in  the  foundations  of  an 
electric  power-house  at  Pittsburg,  Pa.,  in  ISM.f  The  proportions 
were  1  volume  of  pocked  cement,  3  volumes  of  sand,  and  5  volumes 
of  broken  atone.  The  cost  of  labor  was  abnormally  high.  The  day 
was  ten  working  hours. 

Portland  cement  l.SSbbl O.lTcu.yd.  ®t3.(IO  98.88 

8«Dd 0.00     "  ®    1.80  0.«S 

Broken  atone 0.90     "  ®    1,30  1.13 

Lftbor O.ftldsr  ®    1.70  1.09 

SuperlDteodence 0.07  "  (Q  8.00  0.21 

Total  cMl  per  ev.j/d.,  inplaea 10  00 

The  following  is  the  cost  of  constructing  the  concrete  letaia- 
ing  wall  on  the  Chicago  Sanitary  Canal.];  Tlie  average  height  of 
the  wall  was  10  ft.  iu  Sec.  11,  and  33  ft.  in  Sec.  15.  The  thickness 
on  top  was  6  ft.,  and  at  the  bottom  it  waa  equal  to  half  the  height* 
The  atone  was  taken  from  the  adjacent  canal  excavstiou.  The  body 
of  the  wall  was  made  with  natural  cement,  bat  the  coping  and 
facing,  each  3  inches  thick,  were  made  with  Portland  cement. 

*  Emlle  Low  In  SnginMrijig  NeiB»,  vol.  illl.  p.  fl,  S3. 

t  E.  T.  Ohibu  in  The  Polyleehaie,  Benaselaer  FolTteobnla  Inatltate,  toL,  vlL 
p.l«E. 

X  lonr.  WMt.  Soo.  ta  Bng^,  tOL  lU.  pp.  1810.83. 


ovGoQi^lc 


112y  CONCBBTB,  [chap.  IT. 

The  proportions  wen  1  Tolnme  of  cement,  H  Tolnmes  of  sand,  and 
4  Tolnmee  of  nnacreened  limestone.  The  oost  of  plant  employed  in 
Sec.  11  was  t9,600,  and  in  Sec.  15  was  125,420.  The  contract 
price  for  the  ooncrete  in  Sec  14  was  12.74,  and  in  Sec.  15  (3.40 
per  OB.  jA. 

bbor.gmeral 90.078  *    (0.083 

onthewaU 108  -IIU 

mlzliig  concrete 131  .2S0 

pUdng  Hud  remorlDg  forma ISO  .143 

tnnqxtrtlDg  matori&li 143  .081 

quaiTTlaf  stooe. SOS  .370 

cnuhing  none. 078  .138 

7b<al  fir  tabor $0.I»7B       $1,074 

MalerUl,  cement,  natural  ®90.6SperbU.      0.868  .930 

■■      PorlUiidig)»3.35  "      "            .800  .180 

aand ® fl.8apeTcn.7d.    .460  .476 

ntal  for  maUrialt fl.6SS  |1.086 

Uftcblnery,  cost  of  opentiDg 407  .06? 

Total  oott  parol,  yd. (8.010  (8.337 

For  additional  data  concerning  the  cost  of  ooncrete,  see 
§g  233-34,  page  157. 

166b.  The  following  items  relate  only  to  the  labor  of  making 
ooncrete. 

Table  13i  gives  the  details  cf  the  cost  per  cnbic  yard  of  the 
labor  reqaired  in  mixing  and  laying  coacrete  for  the  Buffalo,  ^.  Y., 
breakwater,  constmcted  in  1867-89.  The  data  were  commnaicated 
by  Capt.  F.  A.  Mahan,  Corpa  of  Engineers,  U.  S.  A.,  who  had 
charge  of  the  work.  The  total  amount  of  concrete  laid  was  14,587 
on.  yds.  The  conditions  nnder  which  the  work  was  done  yaried 
considerably  from  year  to  year.* 

Table  13m  gives  the  details  of  the  labor  required  in  mixing  and 
laying  concrete  in  the  oonstrnotion  of  the  Boyd*s  Corner  dam.f 

■  Tbe  work  U  folly  deeoribed  In  Beport  or  Oblel  ol  EnglDeere,  IT.  a  A.,  tor  1B90, 
pp.  3808-36. 

t  From  KD  MoODDt  of  the  ooiuitruotloii  o(  the  Boyd's  Oomer  dam  on  the  Croton 
Blver  near  New  York  CUty,  by  J.  Jtmet  B.  Oroee,  In  Traaa.  Am.  Boo.  ot  O.  E.,  toL 

iu.p.8ea. 


ovGoQi^lc 


ABT.  S.]  COST  OF   CONCBETE. 

TABLE  ISk. 
Ck>BT  OF  Hixnro  akd  Li.Tnia  Corobsth. 


TramporliDg  cement  from  alore-houw. . 

UsBSuring  cement 

Hiilog  cement  paste 

Meuurtng  aand  and  pebbles 

Ueuuring  broken  stone 

Mixing  concrete 

TruiBportlng  concrete 

Spreading  &nd  Tsraming  concrete 

Placing  forms 

Building  temponuT  rallwaj 

Tofal  lidor  per  eu.  yd 


.  tl.7»0  $3.098 11.538 


TABLE  13m. 
Labob  Rbqtjired  in  Mixraa  juis  LiTma  Cosobstr. 


hjjnn  PBO  Cowo  Ti«D. 

Hew  ToA  Stonce  BeBarrolr. 

Bt.  Louis  BeMTTolr. 

SSil^"J 

.£f2l,'?i. 

% 

IP 

111 

All  WOTk  on  lerel 

HSS^"^^;;;;;; 

[..» 

;..» 

O.ISR 
OUG 

if 

1 

i 

can 

O.OST 

om 

fo.wi 

O.OtG 
0.U& 

0.(r» 

'i:i 

^s 

(.». 

jvGooi^le 


llSo  CONOBBTB.  [chap.  IT, 

I681;.  The  coat  of  mixing  and  laying  6  inclies  of  concrete  for  a 
pavement  foandation  is  about  7  cents  per  acj.  yd.,  for  1  part  cement, 
2  partB  sand,  and  i  parte  broken  stone,  turned  six  times — ezclasiTe 
of  casting  into  place.  With  gravel  inBtead  of  broken  stone,  the  cost 
is  about  6  cents  per  sq.  yd. ;  and  with  fonr  turnings  instead  of  six, 
the  cost  is  about  half  a  cent  less  than  the  prices  above. 

1BB(J.  Economio  Concrete.  The  relative  economy  of  natural  and 
Portland  cement  mortars  can  be  investigated  as  explained  in 
§§  136,  137. 

The  relative  strengths  of  gravel  and  of  broken>stone  concretes 
are  stated  in  the  last  two  paragraphs  of  g  151.  The  relative 
economy  of  concrete  made  with  broken  stone  and  gravel  will  vary 
with  the  cost  of  each;  bnt  aa  a  role,  when  gravel  costs  less  than  80 
per  cent,  of  that  of  broken  stone,  gravel  is  more  economical. 

The  strengths  of  both  broken-stone  and  gravel  concretes  are 
given  in  Table  13y,  page  I13r,  for  both  natural  and  Portland 
cements  at  diSereut  ages.  A  study  of  these  results  shows  that  the 
relative  strength  of  natural  and  Portland  concrete  is  different  at 
different  ages.  For  example,  taking  averages  for  10  days,  the 
Portland  concrete  was  &  times  as  strong  as  the  natural  concrete; 
while  at  a  year  the  Portland  concrete  was  only  3  times  as  strong  as 
the  natural  concrete.  At  45  days  and  also  at  6  mouths,  the  Port- 
land concrete  was  i  times  stronger  than  the  natural  concrete;  and 
at  3  months  5  times  as  strong.  Taking  averages  for  like  dates 
and  compositions,  the  Portland  cement  concrete  was  3.7  times 
as  strong  as  natural  cement  concrete.  With  the  data  in  Table  13d 
or  13e,  puge  llSjr  or  112/<i,  it  is  easy  to  compute  the  cost  of  each 
kind  of  concrete,  ii  the  cost  of  a  cubic  yard  of  Portland  cement 
coniTete  J"  more  llian  3,7  times  that  of  a  cubic  yard  of  natural 
cement  concrete,  then  the  latter  is  on  the  average  the  more  econom- 
ical; but  if  Llie  Portland  cement  concre^  costs  less  than  3.7  times 
thut  of  the  natural  cement  concrete,  then  the  former  is  on  the 
average  the  more  economical.  Of  course  the  relative  cost  will  vary 
with  the  condition  of  the  cement  market  and  with  the  locality. 

198s.  The  following  example,  from  actual  practice,  illnstratee 
the  possibilities  in  the  way  of  combinations  between  Portland  and 
natural  cements,  and  gravel  and  broken  stone.  The  specifications 
called  for  a  concrete  composed  of  1  volume  of  natural  cement, 
2  volnmes  of  sand,  and  i  volumes  of  screened  broken  stone.  The 
contractor  found  that  at  current  prices  a  concrete  composed  of 
1  volume  of  Portland  cement  and  9  Totames  of  gravel  would  cost 


ovGoQi^lc 


AKT.  3.]  ARTIFICIAL   STONE.  113ft 

aixmt  the  eame  as  the  concrete  specified.  A  teet  of  the  strength  of 
the  two  oonontes  showed  that  at  a  week  the  Fortlaad-graTel  con- 
crete was  1.6S  timet  as  strong  as  the  ostoral  cement  and  broken- 
stone  oonorete ;  and  at  a  month  1.S9  times  as  strong.  Therefore  th« 
Fortland-grarel  concrete  was  the  more  economical,  and  was  nied. 

Abt.  3.  Artificial  Stoke. 

169.  Several  kinds  of  artificial  atone  have  come  into  nse  within 
the  last  tventj-fire  years  tor  architeGtDi:&I  and  artistic  purposes,  and 
ior  the  pavements  of  cellars,  for  footpaths,  areas,  and  other  locali- 
ties not  subjected  to  the  tread  of  heavy  animals.  They  are  all  a 
-combination  of  hydraolio  cement  and  sand,  pebbles,  etc.  Some  of 
them  possess  very  connderable  merit,  and  are  of  valne  in  districtfi 
"Where  dnrable  and  cheap  bailding-stone  is  not  supplied  by  nature. 

The  strength  and  hardness  of  all  varieties  of  artificial  stone  vary 
directly  with  the  ultimate  strength  and  hardness  attainable  by  the 
hydraulic  ingredients  employed.  An  obvious  means  of  improving 
the  quality  of  the  stone,  therefore,  is  the  employment  of  the  highest 
grades  of  cement. 

160.  K^TOl-CoiOBET.  As  made  by  its  inventor,  Goignet,  of 
Paris,  its  asosl  ingredients  are :  Portland  cement,  silioeons  hydraulic 
lime  (like  that  obtuned  at  Toil,  France),  and  dean  sand,  mixed 
tc^ether  with  a  little  fresh  water.  The  proportions  are  varied  con- 
siderably for  diflerent  kinds  of  work.  The  dry  ingredients  are  first 
thoroughly  mixed  by  hand,  and  again  in  a  mill  after  moistening 
them  very  slightly  with  clean  water.  Moulds  are  then  filled  with 
the  mixture,  which  is  compacted  by  ramming.  The  pecnliaritiea 
of  this  stone  result  from  (1)  the  small  quantity  of  water  Qsed  in  its 
manufacture,  (2)  a  jadicloas  choice  of  the  qufdities  and  proportions 
-of  the  ingredients,  and  (3)  the  thoroughness  with  which  the  mixing 
^is  done.  It  Is  nothing  more  tiian  hydraulic  concrete,  from  which 
the  coarse  fragments  have  been  omitted,  and  upon  which  have  been 
conferred  all  the  advantages  to  be  derived  from  their  thorongh 
manipulation.  It  is  used  in  France  to  a  considerable  extent  in 
-constructing  the  walls  of  honses,  and  in  repairing  masonry, — as 
bridge  piers,  culverts,  etc. 

In  this  country  a  mixture  of  either  natural  or  Portland  cement 
and  sand  is  frequently,  but  improperly,  called  B6ton-Coignet. 

161.  FOETLAKS  BtOBI.  .This  is  a  mixture  of  Portland  cement 
jmd  sand,  or  sand  and  gravel,  compacted  into  form  by  tamping. 


ovGoQi^lc 


114  ARTIFICIAL  8T0NB.  [OHAP.  IV. 

When  properly  made  it  posaesseB  the  eaeential  reqaiBitea  of  atreDgtb 
and  hardness  in  a  degree  proportionate  to  the  ralae  of  the  cement 
employed.  The  proportions  of  1  measnre  of  dry  cement  to  2  or  3}- 
measnres  of  sand  will  answer  for  most  purposes.  The  manipulation 
should  be  prolonged  and  thorough  to  insure  the  production  of  a. 
homogeneous  atone.  It  is  much  used  for  flagging,  for  which  pur- 
pose the  surface  layer,  to  the  thickness  of  about  half  an  inch,  may 
advantageously  bs  composed  of  1  measure  of  cement  to  1^  or  1}  of 
sand.  ' 

162.  HcHtTBTBiE  fiTOiTE.  This  stone  consiata  eesentially  of  the 
Portland  stone  described  above,  in  the  pores  of  which  are  formed 
compounds  of  alumina  with  the  fatty  acids  by  the  double  decom- 
position of  alum  and  a  potash  soap  (see  §  140,  page  101).  Thefl& 
compounds  are  insoluble  in  water,  are  not  acted  upon  by  the  car- 
bonic acid  of  the  air,  and  add  conaiderably  to  the  early  strength  of 
the  stone  and  somewhat  to  its  ultimate  strength. 

The  peculiar  merit  of  this  stone  is  that  its  power  of  absorbing 
water  la  decreased  by  the  ube  of  the  alum  and  the  soap.  All  mot- 
tars  and  most  of  the  artificial  stones  absorb  water  freely,— porous 
mortar  from  50  to  60  per  cent,  of  its  own  weight  and  the  best  Port- 
land from  10  to  20  per  cent, — and  consequently  they  disintegrate 
rapidly  under  the  action  of  frost.  The  absorbed  water  also  disBolves 
the  salts  of  magnesia,  lime,  soda,  and  potash  (of  all  of  which  thero 
is  always  more  or  less  in  cement),  and  on  evaporating  leaves  a  white 
efflorescence  on  the  surface,  which  injures  the  appearance  of  the 
wall.  For  these  reasons  the  ordinary  artificial  stones  are  in  dis- 
repute for  architectural  purposes.  The  absorptive  power  of  the  Mc- 
Murtrie  stone  la  about  twice  that  of  granite,  about  equal  to  that  of 
•  the  best  limestones,  and  about  one  tenth  or  less  of  that  of  the  best 
sandstones.  It  has  been  used  in  Washington,  D.  C,  to  a  limited 
extent,  the  window  trimmings  of  the  National  Museum  and  also  the 
fronts  of  a  few  stores  and  dwellings  being  of  this  stone.  It  appears 
to  have  given  entire  satisfaction. 

163.  Fbeab  Stohe.  Thisiscomposedof  siliceous  sand  and  good 
Portland  cement,  to  which  gum  shellac  is  added.  The  composition 
used  by  the  inventor  was  1  measure  of  cement  and  2J  measures  of 
sand  moistened  with  an  alkaline  solution  of  shellac  of  sufficient 
strength  to  furnish  an  ounce  of  the  shellac  to  a  cubic  foot  of  stone. 
The  shellac  adds  to  the  early  strength  of  the  stone  ;  but  it  is  not 
certain  that  it  adds  to  the  nltimate  strength,  nor  is  it  certain  that 


ovGoQi^lc 


AST.  3.]  SOKSL  8T0NB.  116 

the  sbeUac  may  not  decay  and   ultimately  prove  an   element  of 


When  mixed,  it  is  rammed  into  wooden  monlds,  and  after  setting 
is  laid  away  to  eeaeon, — which  reqaires  several  months  for  best 
resalts.  It  was  mnch  nsed  in  architectural  work  in  the  West  a  few 
years  ago,  bat  did  not  gire  satiBtaction. 

164.  BUraoME  8to>x.  This  is  made  by  forming  in  the  in- 
terstices of  sand,  gravel,  or  any  pnlverized  stone  a  hard  and 
insolnble  cementing  substance,  by  the  natural  decomposition  of 
two  chemical  componnde  in  solution.  Sand  and  the  silicate  of 
Boda  are  mixed  in  the  proportion  of  a  gallon  of  the  latter  to  a 
bnshel  of  the  former  and  rammed  into  moulds,  or  it  may  be 
rolled  into  elabe  for  footpaths,  etc.  At  this  stage  of  the  process 
the  blocks  or  slabs  may  be  easily  cut  into  any  desired  form.  They 
are  then  immereed,  under  pressure,  in  a  hot  eolution  of  chloride  of 
calcium,  after  which  they  are  thoroughly  drenched  with  cold  water 
— for  a  longer  or  shorter  period,  according  to  their  sizo— to  wash 
out  the  chloride  of  sodium  formed  during  the  operation.  In 
England  grindstones  are  frequently  made  by  this  proceaE. 

165.  SOESL  BtOHB.  Some  years  ago,  K.  Sorel,  a  French  6hemist> 
discovered  that  the  oxychloride  of  magnednm  possessed  hydraulic 
energy  in  a  remarkable  degree.  This  cement  is  the  basis  of  the 
Sorel  stone.  It  is  formed  by  adding  a  solution  of  chloride  of  mag- 
nesium, of  the  proper  strength  and  in  the  proper  proportions,  to 
the  oxide  of  magneaium.  The  strength  of  this  stone,  as  well  as  its 
hardness,  exceeds  that  of  any  other  artificial  stone  yet  produced, 
and  may,  when  desirable,  be  made  equal  to  that  of  the  natural 
stone  which  furnishes  the  powder  or  sand  used  in  its  fabricatioa- 
The  process  is  patented,  and  is  used  mainly  in  making  emery-wheels. 
By  incorporating  large  pebbles  and  cobble-stones  in  the  mixture 
the  stone  can  be  .made  quite  cheaply,  and  is  therefore  suitftble  fot 
fonndatioos  and  plain  masslTe  walls. 


ovGoQi^lc 


OHAPTEE  V. 
QUARRYING, 

166.  This  is  so  lai^  a.  sabject  that  it  caiiQot  be  more  than  en- 
tered upon  here  ;  for  greater  detail,  see  treatises  on  Qnarrying,  Eock- 
bloBting,  and  Tunneling, 

167.  Soubcsb  of  BuILDDTO  Btohes.  The  bowlders,  which  are 
scattered  promiscuonsly  over  the  surface  of  the  ground  and  also 
frequently  buried  in  it,  furnish  an  eicellent  building  stone  for  massive 
structures  where  strength  is  essential.  They  are  usually  of  tough 
granite  or  of  a  slaty  strnctnre,  and  are  difficult  to  work.  Sometimes 
they  have  a  cleavage  plane  or  rift,  along  which  they  may  be  split. 
They  can  be  broken  into  irregular  pieces  by  building  a  fire  about 
them,  and  drenching  them  while  hot  with  water,  or  they  may  be 
broken  by  explosives. 

Of  oourse  by  far  the  greater  quantity  of  stone  is  taken  directiy 
from  quarries.  All  building-stone  deposits  have  usually  a  certain 
amount  of  covering,  consisting  either  of  a  portion  of  the  same  de- 
posit, which  has  been  disintegrated  by  atmospheric  influences,  or  of  a 
later  deposit.  This  covering  is  called  the  "cap-rock"  or  "strip- 
ping," In  opening  the  quarry,  the  solid  portions  of  cap-rock  are 
liroken  op  by  blasting,  and  the  whole  is  cart«d  out  of  the  way.  After 
asufficientspaceisstripped,  the  next  Btep  necessary,  when  the  quarry 
rock  does  not  stand  out  in  clifFa,  is  to  excavate  a  narrow  space  on 
one  side  for  a  quarry  face,  either  by  blasting  or  by  some  of  the 
methods  to  be  described  presently. 

168.  Kethods  of  flUABBTino.  After  a  considerable  area  has 
thus  been  laid  bare,  the  stone  is  quarried  in  one  of  three  ways, 

169.  J.  By  Hand  Tools.  When  the  stone  is  thin-bedded,  it  may 
be  quarried  by  hand-tools  alone.  The  principal  tools  are  pick,  crow- 
bar, drill,  hammer,  wedge,  and  plug  and  fenthers.  The  layers  are 
forced  apart  by  the  crow-bar  or  wedges.     The  flat  pieces  are  broken 

jip  with  the  hammer  or  by  drilling  holes  for  the  plug  and  feathers. 

lis 


ovGoQi^lc 


>  QUARBYINO  BY  BXPL08IVI8.  IIT 

The  plug  ii  a  narrow  wedge  with  pluie  tocee;  the  feathers  are 
wedges  ^t  od  one  side  and  roanded  on  the  other  (Fig.  S5,  page  128). 
When  a  plug  is  placed  between  two  feathers,  the  three  will  slip  into 
a  cylindrical  hole  ;  if  the  plug  is  then  driven,  it  exerts  a  great  force. 
If  these  plugs  and  feathers  are  placed  a  few  inches  apart  in  a  row, 
and  all  driven  at  the  same  time,  the  stone  will  be  cracked  along  the 
line  of  the  holes,  even  though  it  be  comparatively  thick. 

The  drill  used  to  cut  the  holes  for  the  plug  and  feathers  is  a  bar 
of  steel  furnished  with  a  wide  edge  sharpened  to  a  blunt  angle  and 
hardened.  It  is  operated  by  one  man,  who  holds  the  drill  with  one 
hand  and  drives  it  vrith  a  hammer  in  the  other,  rotating  the  drill 
between  blows.     The  holes  are  usually  from  |  to  }  of  an  inch  in 


Sandstonee  and  lunestones  occnrring  in  layers  thin  enough  to 
be  quarried  as  above  are  usually  of  inferior  quality,  suitable  only 
for  slope  walls,  paving,  riprap,  concrete,  etc. 

170.  //.  By  Exploalvea.  Generally,  the  cheapest  method  of 
qoarrying  small  blocks  is  by  the  use  of  ezplosiveB.  However,  ex- 
plosives are  used  mainly  for  detaching  large  blocks,  which  are  after- 
wards worked  up  by  means  of  wedges.  In  this  method  of  quarry- 
ing, drill-boles  are  put  down  to  the  depth  to  which  the  rock  is  to. 
be  split,  and  the  requisite  amount  of  powder  or  other  explosive  put 
in,  covered  with  sand,  and  fired  by  a  fuse.  Sometimes  numerous 
charges  in  a  line  of  drill-holes  are  fired  simultaneously  by  means  of 
electricity. 

Quick-acting  explosives,  like  dynamite,  have  a  tendency  to  shatter 
the  stone  and  break  it  in  many  directions,  the  texture  being  affected 
by  the  sudden  explosion  in  the  same  manner  as  by  the  blow  of  a 
Irammer.  Coarse  gunpowder  is  generally  preferred  for  quarrying 
stone.  Light  charges  of  powder  lightly  covered  with  sand  are  better 
than  heavy  charges  tightly  tamped  ;  *  and  experience  goes  to  show 
that  better  work  is  done  by  repeated  light  bUiste  in  the  same  hole, 
than  by  a  single  heavy  blast.  By  means  of  light  charges  often  re- 
peated, a  mass  of  rock  may  be  detached  without  being  broken  up, 
which  would  be  badly  shattered  by  a  single  charge  strong  anough  to 
detach  It. 

In  each  locality  the  atrncture  of  the  rock   must  be  carefully 

*  For  an  utlcle  ihowlog  tbat  »n  aiz-apaoe  Bboold  be  left  betneea  Ui*  explodr* 
and  tbe  tanqilDg,  we  Siigineering  jVhut,  vol.  xviii.  p.  S83. 


ovGoQi^lc 


118  QUABBTUra.  [chap.  V, 

studied  with  a  view  to  take  advantage  of  the  cleavage  plaiies  and 
Datura)  joints.  For  quarrying  each  class  of  rocks  there  is  a  charac- 
teristic method  employed,  which  is,  however,  varied  in  detail  in 
different  quarries.  The  minor  details  of  qnarry  methods  are  as 
various  as  the  differences  existing  in  the  textures,  structaree, 
and  modes  of  occurrence  of  the  rocks  quarried.  Much  depends 
upon  how  the  hlast  is  made.  The  direction  ia  which  the  rock  is 
most  liahle  to  break  depends  upon  the  structure  of  the  rock  and 
the  shape  of  the  drill-hole.  Even  such  an  apparently  unimportant 
matter  as  the  form  of  the  bottom  of  the  drill-hole  into  which  the 
explosive  is  put  has  a  very  marked  effect.  If  bored  with  a  hand- 
drill,  the  hole  is  generally  triangular  at  the  bottom,  and  a  blast  in 
snch  a  hole  will  break  the  rock  in  three  directions.  In  some  qnar* 
Ties  the  lines  of  fracture  are  made  to  follow  predetermined  directions 
by  putting  the  charge  of  powder  into  canistors  of  special  forms.* 

171.  Drills.  The  holes  are  bored  by  jumpers,  chnrn-drills,  or 
machine-drUIs.  The  first  is  a  drill  similar  to  the  one  need  for  drill- 
ing  holes  for  plugs  and  feathers  (§  169),  except  that  it  is  larger  and 
longer.  It  is  usually  held  by  one  man,  who  rotates  it  between  the 
alternating  blows  from  hammers  in  the  hands  of  two  other  men. 
Chum-drills  are  long,  heavy  drills,  usually  6  to  8  feet  in  length. 
They  are  raised  by  the  workmen,  let  fall,  caught  on  the  rebound, 
raised  and  rotated  a  little,  and  then  dropped  again,  thus  cutting 
a  hole  without  being  driven  by  the  hammer.  They  are  more  eco- 
nomical than  jumpers,  especially  for  deep  holes,  as  they  cut  faster 
and  make  larger  holes  than  hand-drills. 

172.  Machine  rock-drills  bore  much  more  rapidly  than  hand- 
drills,  and  also  more  economically,  provided  the  work  is  of  sufBcient 
magnitude  to  justify  the  preliminary  outlay.  They  drill  in  any 
direction,  and  can  often  be  used  in  boring  holes  so  located  that  they 
could  not  be  bored  by  hand.  They  are  worked  either  by  steam 
directly,  or  by  air  compressed  by  steam  or  water-power  and  stored 
in  a  tank  called  a  receiver  and  thence  led  to  the  drills  through  iron 
pipes. 

A  variety  of  rock-drilling  machines  has  been  invented,  f  but 
they  can  be  grouped  in  two  classes,  viz.,  percussion-drills  and  rotat- 
ing drills.     The  method  of  action  of  the  percussion-drill  is  the  same 


ovGoQi^lc 


QD4HKYISU   BY   EXPLOSIVES.  119 

aa  that  of  the  churn-drill  already  described.  The  usual  form  ia 
that  of  a  cylinder,  in  which  a  piaton  ia  moved  by  Btoam  or  com- 
pressed air,  and  the  drill  is  attached  to  this  pieton  bo  as  to  make  a 
stroke  with  every  complete  movement  of  the  piston.  An  aatomatio 
device  cansea  it  to  rotate  slightly  at  each  stroke. 

173.  In  the  rotating  drills,  the  drill -rod  is  a  Jong  tube,  revolving 
about  its  axis.  The  end  of  the  tnbe — hardened  so  as  to  form  an 
annular  cutting  edge — is  kept  in  contact  with  the  rock,  and  by  its 
rotation  cuts  in  it  a  cylindrical  hole,  generally  with  a  solid  core  in 
the  center.  The  drill-rod  is  fed  forward,  or  into  the  hole,  as  the 
■drilling  proceeds.  The  dibria  is  removed  from  the  hole  by  a  con- 
stant stream  of  water  which  is  forced  to  the  bottom  of  the  hole 
through  the  hollow  drill-rod,  and  which  carries  the  dibris  up 
through  the  narrow  apace  between  the  outside  of  the  drill-rod  and 
the  sides  of  the  hole. 

The  diamond  drill  is  the  only  form  of  rotary  rock-drill  ezten- 
aively  used  in  this  conntry.  The  tube  has  a  head  at  its  lower  end, 
in  which  are  set  a  number  of  carbons  or  black  diamonds.  The 
diamonds  usually  project  slightly  beyond  the  circumference  of  the 
head,  which  is  perforated  to  permit  the  ingress  and  egress  of  the 
"water  used  in  removing  the  debris  from  the  hole  and  at  the  same 
time  prevent  the  head  from  binding  in  the  hole.  When  it  ia  desir- 
able to  know  the  precise  nature  and  stratification  of  tho  rock  pene- 
trated, the  catting  points  are  bo  arranged  aa  to  cut  an  annular  groove 
in  the  rock,  leaving  a  solid  coro,  which  is  broken  off  and  lifted  out 
whenever  the  head  is  brought  up.  Where  it  is  not  desired  to  pre- 
serve the  core  intact,  a  solid  boring-bit  is  used  instead  of  the  core- 
bit.    They  are  made  of  any  size  np  to  15  inchea  in  diameter. 

174.  Explosives.*  The  principal  explosivea  are  gunpowder, 
nitro-glycerine,  and  dynamite.  Only  a  coarse-grained  and  cheap 
variety  of  the  first  is  used  in  quarrying,  the  others  being  too  sudden 
and  too  strong  in  their  action. 

The  pressure  exerted  by  gunpowdpr  when  fired  in  a  confined 
fipace  depends  upon  the  relative  weight  and  quality  of  powder  used, 
and  upon  the  space  occupied  by  the  gases  evolved.  The  absolute 
force  of  gunpowder,  the  force  which  it  exerts  when  it  exactly  fills 
the  space  in  which  it  ia  confined,  has  never  been  satiBfactorily  ascer- 

*  *  Taimollng,'' 


jvGooi^le 


120  QUA&BYINO.  [chap.  V. 

tallied.  It  has  been  vftrtoasly  eetiinated  &t  from  15,000  to  1,500,000 
poandB  per  square  inch.  ExperimentB  by  Gen.  Sodman  ahow  that 
for  the  powder  used  in  gunnery  the  absolute  force  of  explosion  i& 
at  least  300,000  pounds  per  sqiiare  inch.  "  In  ordinary  quarrying^ 
a  cubic  yard  of  solid  rock  in  place  (or  about  1.9  cubic  yards  piled, 
up  after  being  quarried)  requires  from  i  to  }  pound  of  powder. 
In  very  refractory  rock,  lying  badly  for  quarrying,  a  solid  yard  may 
Irequire  from  1  to  2  poands.  In  some  of  the  moat  aucceEsful  great- 
blasts  for  the  Holyhead  Breakwater,  Wales,  (where  several  thou- 
sands of  poands  of  powder  were  exploded,  usually  by  galvanism,  at 
a  single  shot,)  from  2  to  4  cubic  yards  (solid)  were  loosened  per 
pound  of  powder ;  but  in  many  instances  not  more  than  1  to  I^ 
yards.  Tnnnels  and  shafts  require  2  to  6  pounds  per  solid  yard,. 
usually  3  to  5  pounds.  Soft,  partially  decomposed  rock  frequently 
requires  more  than  harder  ones."  * 

The  explosion  of  the  powder  splits  and  loosens  a  mass  of  rook 
whose. volume  is  approximately  proportional  to  the  cube  of  the  Una 
of  least  resisloTicei^thai  is,  of  the  shortest  distance  from  the  charga 
to  the  surface  of  the  rock, — and  may  be  roughly  estimated  at  ttoic& 
that  cube ;  but  this  proportion  varies  much  in  different  cases.  Thd 
ordinary  mle  for  the  weight  of  powder  in  small  blasts  is 

PowDBB,  inpounds,  =  (Lute  op  Eesistance,  in  feet,)'  -*-  32. 

Powder  is  sold  in  kegs  of  25  lbs.,  costing  about  $2.00  to  t2.2& 
per  keg,  exclusive  of  freight, — which  is  very  high,  owing  to  the  lisk^ 

176.  Most  of  the  explosives  which  of  late  years  have  been  tak- 
ing the  place  of  gunpowder  consist  of  a  powdered  substance,  partly- 
saturated  with  nitro-glycerine — afuid  produced  by  mixing  glycerine 
with  nitrio  and  sulphuric  acids.  ,  Nitro-glycerine,  and  the  powders. 
containing  it,  are  always  exploded  by  means  of  sharp  percussion, 
which  is  applied  by  means  of  a  cap  and  fuse.  The  cap  is  a  hollow 
copper  cylinder,  about  i  inch  in  diameter  and  an  inch  or  two  in 
length,  containing  a  cement  .composed  of  fulminate  of  mercnry  and. 
some  inert  substance.  The  cap  is  called  single-force,  double-force, 
etc,  according  to  the  amount  of  explosive  it  contains. 

The  principal  advantages  of  nitro-glycerine  as  an  explosive  con- 
sist (I)  in  its  instantAneoua  development  of  force,  due  to  the  fact 
that,  pound  for  pound,  it  produces  at  least  three  and  a  half  times. 
*  Tnntwlne's  Englueer's  PocKet-book. 


ovGoQi^lc 


QUARRTING  BY  BXPL06ITES.  12X. 

as  much  goe,  and  twice  as  much  beat,  as  gaupowder ;  and  (2)  in  ita 
high  specific  graTity,  irhich  permits  the  use  of  small  drill-holeB. 

Nitro-gljcerine  is  rarely  used  in  the  liquid  state  in  ordinary 
qnarrjing  or  blastings  owing  to  the  liability  of  explosion  through 
accidental  percussion,  and  owing  to  its  liability  to  leakage.  It  ex- 
plodes 80  suddenly  that  very  little  tamping  is  required,  the  mer& 
weight  of  moist  sand,  earth,  or  water  being  sufficient.  This  fact^ 
and  the  additional  one  that  Ditro-gljcerine  is  uuaffected  by  immer- 
sion in  water  and  is  heavier  than  water,  render  it  particularly  suit- 
able (or  sub-aqueous  work,  or  for  holes  containing  water.  If  th» 
rock  is  seamy,  the  nitro-glycenne  must  be  confined  in  water-tight 
casings.  Such  casings,  however,  necessarily  leave  some  spaces  be- 
tween the  rock  and  the  explosive,  which  diminishes  the  effect  of  the 
latter.  The  liquid  condition  of  nitro-glycerine  is  oseful  in  causing 
it  to  fill  the  drill-hole  completely,  so  that  there  are  no  empty  spaces 
in  it  to  waste  the  force  of  the  explosion.  On  the  other  hand,  the 
liquid  form  is  a  disadvantage,  because  when  thus  used  in  seamy 
rock  without  a  containing  vessel  portions  of  the  nitro-glycerine  leak 
away  and  remain  unexploded  and  unsuspected,  and  may  cause  aoci~ 
dental  explosion  at  a  future  time. 

The  price  of  nitro-glycerine  is  from  50  to  60  cents  per  quart. 

176.  Dynamite  is  the  name  given  to  any  explosive  vhich  con- 
tains nitro-glycerine  mixed  with  a  granular  absorbent.  If  the 
absorbcot  is  inert,  the  mixture  is  called  true  dynamiie;  if  the 
absorbent  itself  contains  explosive  substances,  the  mixture  is  called 
false  dynamite.  The  absorbent,  by  its  granular  and  compressible 
condition,  acts  as  a  cushion  to  the  oitro-glycerine,  and  protects  it 
from  percussion  and  from  the  consequent  danger  of  explosion,  bat 
does  not  diminish  its  power  when  exploded.'  \itro-glycerine 
undergoes  no  change  in  composition  by  being  absorbed ;  and  it 
then  freezes,  burns,  explodes,  etc.,  under  the  same  conditions  as 
to  pressure,  temperature,  etc.,  as  when  in  the  liquid  form.  The 
cuahiouing  effect  of  the  absorbent  merely  renders  it  more  difiQcult 
to  bring  about  sufficient  percussive  pressure  to  cause  explosion. 
The  absorption  of  the  nitro-glycerine  in  dynamite  renders  the  lat- 
ter available  in  horizontal  holes  or  in  holes  drilled  npward.  True- 
dynamite  loses  only  a  very  small  percentage  of  ita  explosive  power 
when  saturated  wiUi  water,  but  is  then  much  more  diMcult  to  ex- 
plode. 


ovGoQi^lc 


322  QLARKTIXO.  [CHAP.  V. 

True  dynamites  must  contaia  at  least  50  per  cent,  of  uitro- 
f^ljcerine,  otherwise  the  latter  will  be  too  completely  cushioned 
by  the  absorbent,  and  the  powder  will  be  too  difficult  to  explode. 
False  dynamitee,  on  the  contrary,  may  contain  as  small  a  percentage 
of  nitro-glycerine  aa  may  be  desired,  gome  containing  as  little  as  15 
per  cent.  The  added  explosive  substances  in  the  false  dynamites 
generally  contain  large  quantities  of  oxygen,  which  are  liberated 
upon  explosion,  and  aid  in  effecting  the  complete  combuation  of 
any  noxious  gases  arising  from  the  nitro-glycerine.  The  false  are 
generally  inferior  to  the  trne  dynamites,  since  the  bulk  of  the 
iormer  is  increased  in  a  higher  ratio  than  the  power;  and  as  the 
cost  of  the  work  is  laigely  dependent  upon  the  size  of  the  drill- 
faolee,  there  is  no  economic  gain. 

Dynamites  which  contain  large  percentages  of  nitro-glycerine 
explode  with  great  suddenness,  tending  to  break  the  rock  into 
small  fragments.  They  are  most  useful  in  blasting  very  hard  rock. 
In  such  rock  dynamite  containing  75  per  cent,  of  nitro-glycerine 
is  roughly  estimated  to  hare  about  6  times  the  force  of  an  equal 
weight  of  gunpowder  ;  but  in  soft  rock  or  clay  its  power,  at  equal 
cost,  is  inferior  to  that  of  common  gunpowder,  because  its  action 
is  akin  to  a  sudden  blow,  rather  than  to  a  continued  push.  F'^r 
«oft  or  decompoaed  rocks,  sand,  and  earth,  the  lower  grades  -:* 
ilynamite,  or  those  containing  a  smaljer  percentage  of  nitro-glyceh 
ine,  are  more  suitable.  They  explode  -with  less  suddenness,  and 
their  tendency  is  rather  to  upheave  large  masses  of  rock  than  to 
splinter  email  masses. 

"Judgment  must  be  exercised  as  to  the  grade  and  quantity  of 
explosive  to  be  used  in  any  given  case.  Where  it  is  not  objection- 
able to  break  the  rock  into  small  pieces,  or  where  it  is  desired  to  do 
BO  for  convenience  of  removal,  the  higher  shattering  grades  are  use- 
ful. Where  it  is  desired  to  get  the  rock  out  in  large  masses,  as  in 
quarrying,  the  lower  grades  are  preferable.  For  very  difficult  work 
in  hard  rock,  and  for  submarine  blasting,  the  highest  grades,  con- 
taining 70  to  75  per  Cent,  of  nitro-glycerine,  are  used.  A  small 
<charge  docs  the  same  execntion  as  a  larger  charge  of  lower  grade, 
and  of  course  does  not  require  the  drilling  of  so  large  a  hole.  In 
submarine  work  their  sharp  explosion  is  not  deadened  by  the 
water.  For  general  railroad  work,  ordinary  tunneling,  mining  of 
ores,  etc.,  the  average  grade,  containing  40  per  cent,  of  nitro-glycer* 


ovGoQi^lc 


NITBO-GLTOEBIKB  EXPL08ITE8.  133 

ine,  is  used  ;  (or' quarrying,  35  per  cent.;  for  blnetiog  stumps,  trees, 
piles,  etc.,  30  per  cent;  for  sand  and  earth,  15  per  cent." 

177.  A  great  variety  of  dynainiteB  is  made.  £aoh  manufactarer 
usually  makes  a  number  of  grades,  containing  different  percentages 
of  nitro-glycerine,  and  gives  to  his  powder  some  fanciful  name. 
Dynamite  is  sold  in  cylindrical,  paper-co^^red  cartridges,  from  ^  of 
an  incli  to  3  inches  in  diameter,  and  6  to  8  inches  long,  or  longer, 
which  are  packed  in  boxes  containing  25  or  50  pounds  each.  They 
are  furnished,  to  order,  of  any  required  size.  The  price  per  pound 
ranges  from  15  cents  for  15  per  cent,  nitro-glycerine  to  50  cents  for 
75  per  cent,  nitro-glycerine. 

Table  14  (page  124)  gives  the  names  of  all  the  explosives  con- 
taining nitro-glycerine,  with  the  per  cent  in  each  case.* 

178.  HI'  By  Cbanseling  and  Wodging,  By  channeling  is  meant 
the  process  of  cutting  long  narrow  channels  in  rock  to  free  the  sides 
of  large  blocks  of  atone.  Quite  a  large  number  of  machines  have 
been  invented  for  doing  this  work,  all  of  which  make  the  channels 
by  one  form  or  the  other  of  the  machine  drills  already  described 
{see  the  second  paragraph  of  §  Y!%).  The  machines  are  mounted 
upon  a  track  on  the  bed  of  the  quarry,  and  can  be  moved  forward 
«8  the  work  progresses.  If  the  rock  is  in  layers,  it  is  only  necessary 
to  cut  the  channels  part  way  through  the  layer,  when  the  block  can 
be  detached  with  wedges,  the  groove  guiding  the  fracture.  If  the 
rock  is  not  in  layers,  after  the  necessary  channels  have  been  cnt 
«round  the  block,  it  is  necessary  to  under-cut  the  block  in  order  to 
release  it.  This  is  accomplished  by  drilling  a  series  of  holes  along 
the  bottom,  which  process  Is  called  "gadding"  by  quarry-men.  The 
block  is  then  split  from  its  bed  by  means  of  wedges.  The  method 
■of  channeling  and  wedging  is  much  employed  in  quarrying  marble, 
the  massive  limestones,  and  the  thick-bedded  sandstones.  The 
method  is  very  economical  and  expeditious,  except  in  granite  and 
the  hardest  sandstones.  For  illustrations  of  the  two  principal  chan- 
neling machines  and  also  quarries  being  worked  by  this  method,  see 
Report  on  the  Quarry  Industry,  pp.  44-52,  in  Vol.  X.  ex  the  Tenth 
"Census  of  the  United  States. 

•  W.  C,  Foster,  In  Engineering  Aew,  vol.  ili.  p.  2H.  For  a  Ust  o(  all  the  eiplo- 
tUvea  employed  as  h\aal\ng  attenta,  together  with  a  description  at  their  composition 
and  references  to  the  llteraturo  of  each,  see  Englsitering  A'aet,  vol.  xlx.  pp.  S33-31, 
«Dd  vol.  xz.  pp,  8-10. 


ovGoQi^lc 


[chap.  t. 


TABLE  14. 
ZdR  or  X^PLoama  conrAiHiiia  NmuMn-TCBBnn. 


Ammonia  powder.. . 
AjbeMoa  powder. . . . 
Atlu  powder,  A 

::     ::  2+- 


"   B+ 

'■   E 

"      F+ 

Brady's  dynamite. 

Brain's  powder 

Co  Ionia  powder 

Dualln  (Dinmar's) 

Dynamite  (Nobel's,  Eieael- 
guhr  dynamite), 

Old  No.  1 
Old  No.  3 
Old  No.  " 

£leclrlc  powder 

Explosive  gelatine 

PordtB.  a  grades 

Fulgurite  (Holid) 

(liquid) 

Gelatine  dynamite,  A 

No.  1. 


QeUtine  c 


iploslve  d< 


Qdlgnlte 

Oiant  powder.  No.  1 . 
"        ■'  New"    1. 


■    (Nobel's)! 


Glyxoline 

HecU  powder.  No,  IXX. 

Oun  Sawdust 

'■      No.  IX..... 


Herculee  powder.  No.  IZX 


Horsley's    powder    (■ 

TarieUes) 

Jud«oD  Giant  Pt>wder,No.2 
Judsou  powder,  FFF. 

FF 

F 

UUP 

Litbofracteur 

Metalllue  Nltroleum 

Uica  powder.  Mo.  1., 

"    a 

Miners'  Powder  Co.  "a  Dy- 

uamite 

Nepluue  powder 

Nitro  Tolnol 

Norrbin  &  OblsaoD's  pow> 

Poniopollte 

Porlleia  Nitroleum. . . 

Bendrock 

Sebastin,  No.  I 

■'    S 

Selenitic  powder 

Vifioriteiif.'s)".!;'.".!! 
I  Vitrlle,  No.  1 


S  10  C 

sa 


48.& 


ovGoQi^lc 


CHAPTER  VL 
stone  outtinq. 

Art.  1.  Tools. 

179.  In  order  to  describe  intelligibly  the  varions  methods  of 
preparing  stonea  for  use  in  masonry,  it  will  be  necessary  to  begin 
Tith  a  description  of  the  tools  used  in  stoue-catting,  ae  the  names 
«f  many  kinds  of  dressed  stones  are  directly  derived  from  those  of 
the  tools  used  in  dressing  them. 

With  a  view  to  securing  uniformity  in  the  nomenclature  of 
building  stones  and  of  stone  masonry,  a  committee  of  the  American 
Society  of  Civil  Engineers  prepared  a  classification  and  recommended 
that  all  specifications  should  be  made  in  accordance  therewith.  The 
old  nomenclature  was  very  unsystematic  and  objectionable  on  many 
grounds.  The  new  system  is  good  in  itself,  is  recommended  by  the^ 
most  eminent  authority,  has  been  quite  generally  adopted  by  en- 
gineers, and  should  therefore  be  strictly  adhered  to.  The  following 
description  of  the  Itand  tooh  used  in  stone  cutting  is  from  the 
report  of  the  American  Society's  committee.* 

180.  Hass  Toolb.  "The  Double  Face  Hammer,  Pig.  9,  is  a 
heavy  tool  weighing  from  20 
to  30  ponnds,  used  for  roagh- 
1y  shaping  stones  as  they 
■come  from  the  quarry  and 
for  knocking  off  projections. 
This  is  used  only  for  the  fio-  b.— doiibl«  Fiat  HAMim. 
roughest  work. 

"The  Face  Hammer,  Fig.  10,  has  one  blunt  and  one  cutting 
end,  and  Is  used  for  the  same 
purpose  as  the   double  face 
hammer  where  less  weight  is  ( 
required.     The   cutting  end 
is  used  for  roughly  squaring 

stones,  preparatory  to  the  use  fio.  id.— Face  Ruaan. 

•of  finer  tools. 

•  Tnns.  Am.  Soo.  of  C.  E.,  voU  tL  pp.  297-801 


ovGoQi^lc 


126  STONE   CUTTING.  [CHAP.   VI. 

"The  Cavil,  Fig.  11,  lias  one  blunt  and  one  pyramidal,  or 
,. — T-r~^^^^  pointed,  end,  and  weighs  from  15  to  20  pounds. 
'J|__LL--^^  It  ie  used  in  quarries  for  rooghly  shaping  stone 

^r ^i-*,^^^  for  transportation. 

'I — "^        The  rick.  Fig.  12,  somewhat  resembles  the 

Tia.  11.— Civn.  pi^k  Used  in  digging,  and  is  used  for  rough  dress- 
ing, mostly  on  limestone  and  sandstone.  Its  length  varies  from 
l.*^  to  Zi  inches,  the  thickness 
at  the  eye  being  about 
inches. 

"The  Ax,  or  Pean  ffam-\ 
mer,  Fig.  13,  has  two  opposite  jOr  t 
cutting  edges.     It  is  used   for  \ 
making  drafts  around  the  arris, 
or  edge,  of  stones,  and  in  re-  1 
ducing    faces,    and    sometimes  '"■ "-— P>ot 

joints,  to  a  level.  Its  length  is  about  10  iuches,  and  the  cutting 
edge  about  4  inches.  It  is  used  after 
the  point  and  before  the  patent  ham* 


"The  Tooth  Ax,  Fig.  U,  is  like 
Fio.  IS.— Ax.  the  as,  except  that  its  cutting  edges 

are  divided  into  teeth,  the  number  of  which  varies  with  the  kind 
of  work  required.     This  tool 
is   not  used   in  granite    and 
gneiss  cutting. 

"The  Bush  Hammer, 
Fig.  15,  is  a  square  prism  of 
steel  whose  ends  are  cut  into 
a  number  of  pyramidal  points.  Pro.  m.-TootbAi. 

The  length  of  the  hammer  ia  from  4  to  8  inches,  and  the  cutting 

face  from  2  to  4  inches  square. 

The  points  vary  in  number  and 
in  size  with  the  work  to  be  done. 
One    end    is    sometimes    made 
■  ^r-l  with  a  cutting  edge  like  that  of 
Fro.  IB.— BtiBB  HinaB.  t)^e  ^X. 

"  The  Crandall,  Fig.  16,  is  a  malleable-iroB  bar  abont  two  feet 


ovGoQi^lc 


f 


FiQ.  IS.— Cruoili. 


ART.  1.]  T00L8,  137 

long,  slightly  flattened  at  one  cod.     In  this  end  ia  a  slot  3  inches 

longand  finchwide.  Throughthia         r~'~^ — 

slot  are  passed  ten  double-headed   , 

points   of  i-inch  square   Bteel,    9  I 

inches  long,   which  are    held   in  "I 

place  by  a  key. 

"The  Patent  Hammer,  Fig. 
17,  18  a  double-headed  tool  bo 
formed  as  to  hold  at  each  end  a  set  of  wide  thin  chisels.     The  tool 

f-  ^m  is  in  two  parts,  which  are  held  to- 

uWJ gether  by  the  bolts  which  hold  tho 
pi^3 '  chiBels.  Lateral  motion  is  prevented 
^^,  by  four  guards  on  one  of  the  pieces. 

fm.it.— PiramHAiuEK.  The    tool     without    the    teeth     is 

fiiXSJXl^  inches.    The  teeth  are  3^  inches  wide.    Their  thickness 
varies  from  ^  to  ^  of  an   inch.      This  tool  is       _.  ^ 
used  for  giving  a  finish  to  the  surface  of  stones.     JbW  1        .  ..  ..-^ 

"The  Hand  Hammer,  Fig.   18,  weighing   '*U-\J 
from  3  to  5  pounds,  is  used   in  drilling  holes,  Fia.  is.— Hahd  hihhba. 
ai)d  in  pointing  and  chiseling  the  harder  rocks. 

"The  Mallei,  Fig.  19,  is  used  whei-e  the  softer  limestones  and 
—  sandstones  are  to  be  cut. 

I     r'     1     fl     n  "  '^^^  Pitching  Chisel,  Fig.  30, 

V        J     fl     11     is  OBually  of  li-inch  octagonal  steel, 
^ —       "^    ^      spread  on   the   cutting   edge  to  a 
pS^i^o     rectangle  of  i  X  3^  inches.      It  is 
Fi8. 11.— HiLUT.  cmmi.     used  to  make  a  well-defined  edge  to 

the  face  of  a  stone,  a  line  being  marked  on  the  joint  surface  to 
which  the  chisel  is  applied  and  the  portion  of  the  stone  outside  of 
the  line  broken  oS  by  a  blow  with  the  hand-hammer  on  the  head 
of  the  chisel. 

"The  Point,  Fig.  21,  is  made  of  round  or  octagonal  rods  of 
steel,  from  i  inch  to  1  inch  in  diameter.     It  is  made  about  19 
inches  long,  with  one  end  bronght  to  a  point. 
It  is  used  until  its  length  is  reduced  to  about  C(  J> 


inches.     It  is  employed  for  dressing  off  the  (J 
irregular  surface  of  stones,  either  for  a  perma- 
nent finish  or  preparatory  to  the  use  of  the  ax.         ^'-  *•■— Po""- 
According  to  the  hardness  of  the  stone,  either  the  haud-hamn 
or  the  mallet  is  used  with  it. 


ovGoQi^lc 


STONE  ODTTINO. 


[chap.  VI. 

"  The  Chisel,  Fig.  32,  of  round  etee]  of  ^  to  j  inch  in  diameter 

^_^___^__^^  and  about  10  inches  long,  with  one  end  brought 

C(  "1  to  a  cutting  edge  from  i  inch  to  2  inches 

-..  ~.^  wide,  is  used  for  cutting  drafts  or  margins  on 

the  &ce  of  Btonee. 

Fra  tt-CmMu  "The  Tooth  Chisel,  Fig.  33,  is  the  same 

as  the  chisel,  except  that  the  cutting  edge  is  divided  into  teeth. 

It  is  used  only  on  mar-  ^ ■ 

bles  and  sandstones.        ^^i  '  -      t 

"The  Splitting   CH. 
Chisel,  Fig.  34,  is  used 
chiefly  on  the  softer,  Toorac 

stratified  stones,  and  sometimes  on  fine  architectural  carvings  in 
granite. 

"The  Plug,  a  truncated  wedge  of  steel,  and  the  Feathers  of 
'half-round  malleable  iron.  Fig.  25,  are  used  for  splitting  unstrati- 
■  fled  stone.     A  row  of  holes  is  made  with  the  DriU,  Fig.  26,  on  the 


Pig  a.  '*'■  *■— Dwu*. 

line  OD  which  the  fracture  is  to  be  made ;  In  ench  of  these  holes 
two  feathers  are  inserted,  and  the  plugs  lightly  driven  in  between 
them.  The  plugs  are  then  gradually  driven  home  by  light  blows 
•of  the  hand  hitmmer  on  each  in  snccession  until  the  stone  splits." 

181.  BUCHIBE  Tools.  In  all  large  stone-yards  machines  are 
used  to  prepare  the  stone.  There  is  great  variety  in  their  form, 
but  since  the  surface  never  takes  its  name  from  the  tool  which 
forms  it,  it  will  be  neither  necessary  nor  profitable  to  attempt  a  de- 
scription of  individual  machines.  They  include  stone-saws,  ston&- 
ontters,  stone-planers,  stone-grinders,  and  stone-polishers. 

The  saws  may  be  either  drag,  circular,  or  band  saws  ;  the  cut- 
ting may  be  done  by  sand  and  water  fed  into  the  kerf,  or  by  carbons 
or  black  diamonds.  Several  saws  are  often  mounted  side  by  side  and 
operated  by  the  same  power. 

The  term  ".stone-cutter"  is  oaoally  applied  to  the  machine  which 


D.qitizeabyG00l^lc 


ABT.  3.]  HBTHOD  OF  FORMING   SCBFACES.  199 

sttackB  the  rough  stone  and  reduces  the  inequalitieB  somewhat. 
After  this  treatment  the  stone  goes  id  Bucceseion  to  the  atooe- 
planer,  stone-grinder,  and  Btone-polieher. 

Those  stones  which  are  homogeneous,  strong  and  tough,  and 
•comparativeiy  free  from  grit  or  hard  spots,  cau  be  worked  by  ma- 
chines which  resemble  those  used  for  iron ;  but  the  harder,  more 
brittle  stones  require  a  mode  of  attack  more  nearly  resembling  that 
employed  in  dressing  stone  bj  hand.  Stone-ontters  and  stone- 
planers  employing  both  forms  of  attack  are  made. 

Stone-grinders  and  stone-polisbers  differ  only  in  the  degree  of 
fineness  of  the  surface  produced.  They  are  sometimes  called  "  rub- 
bing-machines." Essentially  they  consist  of  a  large  iron  plate  re- 
Tolving  in  a  horizontal  plane,  the  stone  being  laid  npon  it  and  braced 
to  prevent  its  sliding.  The  abradent  is  sand,  which  is  abundantly 
supplied  to  the  surface  of  the  revolving  disk.  A  small  stream  of 
water  works  the  sand  under  the  stone  and  also  carries  away  the 
44bris. 

ABT.  3.   UffTHOD  OF  FOHUIXa  THE  ScBFACES. 

182.  It  is  important  that  the  engineer  should  understand  the 
methods  employed  by  the  stone-cutter  in  bringing  atones  to  any  re- 
quired form.  The  surfaces  moat  frequently  required  in  stone  cutting 
are  plane,  cylindrical,  warped,  helicoidal,  conical,  spherical,  and 
sometimes  irregular  snrfacea. 

183.  PtUtS  SntTACEB.  In  squaring  up  a  rough  stone,  the  first 
thing  the  stone-cutter  does  is  to  draw  a  line,  with  iron  ore  or  black 
lead ,  on  the  edges  of  the  stone,  to  indicate  as  nearly  as  possible  the 
required  plane  surface.  Then  with  the  hammer  and  the  pitching- 
tool  he  pitches  off  all  debris  or  waste  material  above  the  lines, 
thereby  reducing  the  surface  approximately  to  a  plane.  With  a 
chisel  he  then  cnta  a  draft  around  the 
edges  of  this  surface,  /.  e.,  he  forms  nar- 
row plane  surfaces  along  the  edges  of  the 
stone.  To  tell  when  the  drafts  are  in  | 
the  same  plane,  he  uses  two  straight- 
edges having  parallel  sides  and  equal 
■widths.     See  Fig.  27.     The  projections  '^■*'- 

on  the  aartace  are  then  removed  by  the  pitching  chisel  or  the  point, 
antil  the  straight-edge  will  just  touch  the  drafta  and  the  inter- 
mediate surface  when  applied  across  the  stone  in  any  direction. 


ovGoQi^lc 


180  eroNE  ccrnNO.  [chap.  vt. 

The  surface  is  oBoally  left  a  little  "  slack,"  t.  e.,  concave,  tf'  stlov 
room  for  the  mortarj  however,  the  snrtiioe  Bbould  be  but  a  verf 
little  concave. 

The  surface  is  then  flmsbed  with  the  ax,  patent  hammer,  bnu 
hammer,  etc,  according  to  the  degree  of  smoothness  reqaired. 

181.  To  form  a  second  plane  sujface  at  right  angles  to  the  first 
one,  the  workman  draws  a  line  oa  the  out  face  to  form  the  inters 
^section  of  the  two  planes  ;  he  also  draws  a  line  on  the  ends  of  th» 
stone  approximately  in  the  reqaired  plane.  With  the  ax  or  tha 
chisel  he  then  cuts  a  draft  at  each  end  of  the  atone  until  a  steel 
square  fits  the  angle.  He  then  joins  these  drafts  by  two  others  afe 
right  angles  to  tfaem,  and  brings  the  whole  surface  to  the  samfr 
plane.     The  other  faces  may  be  formed  in  the  same  way. 

It  the  surfaces  are  not  at  right  angles  to  each  other,  a  berel  i> 
tued  instead  of  a  square,  the  same  general  method  being  pursued. 

186,  CnnnisiOAi  BVBFAOBS.  These  may  be  either  concave  or 
oonvez..  The  former  are  frequently  required,  as  in  arches;  and  th» 
latter  sometimes,  as  in  the  outer  end  of  the  face-stones  of  an  arch. 
The  stone  is  first  reduced  to  a  paralellopipedon,  after  which  the 
onrved  surface  is  produced  in  either  of  two  ways :  (1)  by  cutting; 
a  oircular  draft  on  the  two  ends  and  applying  a  straight-edfi^e  along 
the  rectilinear  elements  (Fig.  !28);  or  (3)  by  cutting  a  draft  along 
the  line  of  intersection  of  the  plane  and  cylindrical  surface,  and 
^)plying  a  carved  templet  to  the  reqaired  surface  (Fig.  : 


186.  ConcAL  SlTBTAOBB  may  be  formed  by  a  process  very  sindlar 
to  the  first  one  given  above  for  cylindrical  surfaces.  Such  surfaces 
are  seldom  used. 

187.  S?KSSlOAi  fluKFAOXB  are  sometimes  employed,  as  in  domes. 
They  are  formed  by  essentially  the  same  general  method  as  cylin* 
drioal  surfaces. 

188.  Wab?BO  Bvbfaobs.    Under  this  head  are  included  what 


ovGoQi^lc 


ART.  3.J  1IBTH0D3  OF   PINI3HIN0  SUBFACEB.  181 

the  Btone-catters  call  "  twiBted  earfaoeB,  "  beliooidal  eurfaces,  sud 
the  general  warped  surface.     None    of 
these  are  common  in  ordinary  stone-work. 

The  method    of    forming  a    anrtace 
equally  twinted  right  and  left  will  be  de- 
scribed ;  by  obvious  modiflcatione  the  same  L 
method  can  be  applied  to  secure  other  j: 
forms.     Two  twist  rules  are  required,  the 
angle  between  the  upper  and  lower  edges  ^'-  "'■ 

being  half  of  the  required  twist.  Draf  ta  are  then  cut  in  the  eoda  of 
the  stone  antil  the  tops  of  the  twist  rules,  when  applied  as  in  Fig. 
30,  are  in  a  plane.  The  remainder  of  the  projecting  face  ia  remored 
until  a  straight-edge,  when  applied  parallel  to  the  edge  of  the  stoD«^ 
will  just  touch  the  end  drafts  and  the  intermediate  surface. 

If  the  surface  is  to  be  twisted  at  only  one  end,  a  parallel  rulo 
and  a  twist  rule  are  used. 

166.  Kunre  THX  SR&VlXOa.  The  method  of  making  work- 
ing drawings  for  constructions  in  stone  will  appear  in  subsequent 
chapters,  in  connection  with  the  study  of  the  structures  them- 
Gelves;  but  for  detailed  instructioss,  see  the  text-books  on  Store- 
otomy  or  Stone  Gutting. 

Aet.  3.  Methods  of  PoiiSFtiio  thb  Suefacm.* 

190.  "All  stones  used  in  building  are  divided  into  three  clasBei^ 
according  to  the  finish  of  the  surface;  rjz.  : 

I.  Bough  stones  that  are  used  as  they  come  iroai  the  quarry. 

II.  Stones  roughly  squared  and  dressed.  ■ 

III.  Stones  accurately  squared  and  finely  dressed. 

"In  practice,  the  line  of  separation  between  them  isnotTery 
distinctly  msrlced,  but  one  class  gradually  merges  into  the  next. 

191.  I.  "UHBauAKED  STons.  This  class  covers  all  stones 
which  are  used  as  they  come  from  the  quarry,  without  other 
preparation  than  the  removal  of  very  acute  angles  and  excessive  pro- 
jections from  the  general  figure.  The  t«rm  'backing,' which  ia 
frequently  applied  to  this  class  of  stone,  is  inappropriate,  as  it  prop- 
erly designates  material  used  in  a  certain  relative  position  in  a  wall, 
whereas  stones  of  this  kind  may  be  used  in  any  position. 

192.  n.  "Sqdased  Stoheb.     This  class  covers  all  stones  that 

■This  Biticle  la  taken  from  the  report  of  tile  committee  o(  tbe  Amerfcaii  Bodttf 
«f  CiTil  Eogtneera  previously  referred  to. 

D.qitizeabvG00l^lc 


139 


BTONB  cirmso.  [chap,  vl 

are  roughly  squared  and  roughly  dressed  on  beds  and  joints.  The 
dressing  is  usually  done  with  the  face  hammer  or  ai,  or  in  soft 
stones  with  the  tooth  hammer.  In  gneiss  it  may  sometimes  be 
necessary  to  use  the  point.  The  distinction  between  this  class  and 
the  third  lies  iu  the  degree  of  closeness  of  the  joints.  Where  the 
dressing  on  the  joints  is  such  that  the  distance  between  the  general 
planes  of  the  surfaces  of  adjoining  stones  is  one  half  inch  or  more^ 
the  stones  properly  belong  to  this  class, 

"Three  subdivisions  of  this  class  may  be  made,  depending  OD 
the  character  of  the  face  of  the  stones: 

"  (n)  Quarry-faced  stones  are  those  whose  faces  are  left  «n- 
tonched  as  they  come  from  the  quarry. 

"  {b)  Fitch-faced  stones  are  those  on  which  the  arris  is  clearly 
defined  by  a  line  beyond  which  the  rock  is  cut  away  by  the  pitching 
'Chisel,  so  as  to  give  edges  that  are  approKimatelj  true, 

"  (c)  Drafted  Btonei  are  those  on  which  the  face  is  surrounded  by 
a  chisel  draft,  the  space  inside  the  draft  being  left  rough.  Ordi- 
narily, however,  this  is  done  only  on  stones  in  which  the  cutting  of 
the  joints  is  such  as  to  exclude  tliem  from  this  class. 

"  In  ordering  stones  of  this  daes  the  specifications  should  always 
etate  the  width  of  the  bed  and  end  joints  which  are  expected,  and 
also  how  far  the  surface  of  the  face  may  project  beyond  the  plane 
of  the  edge.  In  practice,  the  projection  varies  between  1  inch  and 
6  inches.  It  should  also  be  specified  whether  or  not  the  faces  are  to 
be  drafted. 

193.  IIL  "  Cut  STOITXS.  This  class  covers  all  squared  stones 
with  smoothly-dressed  beds  and  joints.  As  a  rule,  all  the  edges  of 
cut  stones  are  drafted,  and  between  the  drafts  the  stone  is  smoothly 
dressed.  The  face,  however,  is  often  left  rough  where  construction 
is  massive. 

"  In  architecture  there  are  a  gr^t  many  ways  in  which  the  faces 
of  cut  stone  may  be  dressed. 


but  the  following  are  those 
that  will  usually  be  met  in 
engineering  work; 

"  Rough-pointed.    When  it 
is  necessary  to  remove  an  inch 
Fw.  M.-BOTBH-wni«D.  or  more  from  the  face  of  a 

le,  it  ifl  done  by  the  pick  or  heavy  point  until  the  projectiona 


ovGoQi^lc 


ART.  3.]  METHODS  OF   TINISHINO  SUBFACES, 


vary  from  ^  inch  to  1  inch.     The  atone  is  then  said  to  be  rough- 
pointed  (Fig.  31).     In  areesing 


Fio.  Si.^FiKi-roiiiTm. 


limestone    and     granite,    this 
operation  precedes  all  otliers. 

"Fine-pointed.  (Fig.  32). 
If  a  smoother  finish  is  desired, 
rongh  pointing  ie  followed  by 
fine  pointing,  which  is  done 
with  a  fine  point.  Fine  point- 
ing is  used  only  where  the  finish  made  by  it  is  to  be  final,  and  never 
as  a  preparation  for  a  final  finish  by  another  tool. 

"  Crandalled.  This  is  only  a  speedy  method  of  pointing,  the 
effect  being  the  same  as  fine  pointing,  except  that  the  dots  on  the 
stone  are  more  regular.  Tlie  variations  of  level  are  about  i  inch, 
and  the  rows  are  made  parallel.  When  other  rows  at  right  angles 
to  the  first  are  introduced,  the  stone  is  said  to  be  cross-crandaUed. 
Fig.  33. 


T\a.  33.— CB1HD1U.CD.  Fia. 

"  Axed,  or  Pean-hammered,  and  Patent-hammered.  These  two 
vary  only  in  the  degree  of  smoothness  of  the  surface  which  is  pro- 
duced. The  number  of  blades  in  a  patent  hammer  varies  from  6  to 
12  to  the  inch;  and  in  precise  specifications  the  number  of  cuts  to 
the  inch  must  be  stated,  such  as  6-ctit,  8-cut,  10-cut,  12-cut.  The 
effect  of  axing  is  to  cover  the  surface  with  chisel  marks,  which  are 
made  parallel  as  far  as  practicable.     Fig.  34.     Axing  is  a  final  finish, 

"Tooth-azed.  The  tooth-ax  is  practically  a  nnmber  of  points, 
and  it  leaves  the  surface  of  a  stone  in  the  same  condition  as  fine 
pointing.  It  is  usually,  however,  only  a  preparation  for  buiih-liam- 
muring,  and  the  work  is  then  done  without  regard  to  effect  so  long 
as  the  surface  of  the  stone  is  sufficiently  leveled. 

"  BuBb-hammered.     The  roughnesscsof  a  stone  are  pounded  off  by 


ovGoQi^lc 


STONE  CUmNG.  [CHAP.  71. 


the  bnsh  hammer,  and  the  Btone  is  then   eaid   to  be  'bushed.' 
This  kind  of  finiah  ia  dtiQgeroas 


Fra.  n.— BcBs-n. 


OD  sandstooe,  as  experience  has 
ahowD  that  sandstoDe  thus  treated 
IB  Tery  apt  to  scale.  In  dreeaing 
limestone  which  ia  to  have  a  buah- 
hammered  finish,  the  usual  se- 
qaence  of  operation  ie  (1)  rough- 
pointing,  (3)  tooth-azing,  and  (3) 
boab-hammering.     Fig.  35. 

"  Rubbed.  In  dressing  sandstone  and  marble,  it  ia  reij  common 
to  give  the  stone  a  plane  aurface  at  once 
by  the  use  of  the  atone-aaw  [§  181].  Any 
roughnesaea  left  by  the  saw  are  removed 
by  rubbing  with  grit  or  sandstone  [§  181]. 
Such  atones,  therefore,  have  no  margins. 
They  are  frequently  used  in  architecture 
forstriog-coursGS,  lint^la,  door-jambs, etc.;  fi«-  w— bdsbr>. 

and  they  ai-e  also  well  adapted  for  use  in  facing  the  walls  of  lock- 
chambers  and  in  other  localitiea  where  a  stone  surface  ia  liable  to  be 
rubbed  by  veBsela  or  other  moving  bodiee.     Fig.  36. 

"  Diamond  Panels.  Sometimea  the  apace  between  the  mai^ns 
ia  sunk  immediately  adjoining  them  and 
then  riaea  gradually  until  the  four  planea 
form  an  apex  at  the  middle  of  the  panel. 
In  general,  such  panels  are  called  diamond 
panels,  and  the  one  just  deacribed,  Fig. 
37,  ia  called  a  sunk  diamoiid  panel. 
When  the  surface  of  the  atone  riaea  grad- 
ually from  the  inner  linee  of  the  margins 
to  the  middle  of  the  panel,  it  is  called  a 
Both  kinds  of  finish  are  common  on  bridge 
The  detoila  of  this  method  should  be 


.— DUMOND  PaNCL. 


raised  diamond  panel, 
quoins  and  similar  work, 
given  in  the  specifications." 


ovGoQi^lc 


CHAPTER  VII. 

STONE  MA80NBT. 

Iv  preparing  Bpecificatione,  it  is  Dot  safe  to  depend  alone  upoo 
ft  he  tenne  in  common  use  to  designate  the  varioas  Glasses  of  masonry; 
but  every  specification  should  contain  an  accurate  description  of  the 
character  and  quality  of  the  work  dsBired.  Whenever  practicable, 
samples  of  each  kind  of  cutting  and  masonry  should  be  prepared 
.beforehand,  and  be  exhibited  to  the  pereous  who  propose  to  under- 
take  the  work. 

194.  SBTDimon  of  Fabts  of  thx  Wau,.*  Face,  the  front 
.snrface  of  a  wall;  back,  the  inside  surface. 

Facing,  the  stone  which  forms  the  face  or  outside  of  the  wall. 
Backing,  the  stone  which  forms  the  back  of  the  wall.  Filling,  the 
•interior  of  the  wall. 

Batter,     The  slope  of  the  surface  of  the  wall. 

Course.     A  horizontal  layer  of  stone  in  the  wall. 

Joints.  The  mortar-layer  hetween  the  atonu.  The  horizontal 
joints  are  called  hed-Joinls  or  simply  beds;  the  vertical  joints  are 
.sometimes  called  the  builds.  Usually  the  horizontal  joints  are 
called  beds,  and  the  vertical  ones  joints. 

Coping.     A  course  of  stone  on  the  top  of  the  wall  to  protect  it. 

Pointing.  A  better  quality  of  mortar  put  in  the  face  of  the 
joints  to  help  them  to  resist  weathering. 

Bond.     The  arrangement  of  stones  in  adjacent  courses  (§  303). 

Stretcher.  A  stone  whose  greatest  dimension  lies  parallel  to  the 
Jaoe  of  the  wall. 

Header.  A  stone  whose  greatest  dimenaon  liee  perpendicnlw 
to  the  face  of  the  wall. 

Quoin.  A  comer-stone.  A  quoin  is  a  header  for  one  face  and  a 
stretcher  for  the  other. 

Dowels.  Straight  bars  of  iron  which  enter  a  hole  in  the  upper 
side  of  one  stone  and  also  a  hole  in  the  lower  side  of  the  stone  next 
aboye. 

Cramps.    Bars  of  iron  having  the  ends  turned  at  right  angles  to 

*The  deflnlttonsln  this  ch&pUr  ve  In  Bccordance irith  the  recommendatloDH  of 

'the  CommlttM  of  tbe  AmerlcAo  Society  of  CItU  Eoglneen  previooBl;  referred  to, 

.  and  contocm  to-  Uw  best  pracUoe.    Uiif  ortDiuitel;  they  are  not  anlvenwU;  adopted. 


jvGooi^le 


136  STOyE   MASONRY.  [CHAP.  VII. 

to  the  body  of  the  bar,  which  enter  holes  in  the  upper  aide  of  ad- 
jacent stones. 

19fi.  Defihiiiorb  or  Kims  of  Haboitbt.  Stone  masonry  is 
olaaaified  (1)  according  to  the  degree  of  fiuiah  of  the  face  of  the 
stones,  as  quarry-faced,  pitch-faced,  pointed,  hnsh-hammered,  etc. ; 
(2)  according  to  whether  the  horizontal  joints  are  more  or  less  con- 
tinuous, as  range,  broken  range,  and  random;  and  (3)  according 
to  the  care  employed  in  dressing  the  beds  and  joints,  as  ashlar, 
squared-stone,  and  rubble. 

196.  Quarry-faced  Masonry.  That  in 
which  the  face  of  the  stone  is  left  as  it 
comes  from  the  quarry.     Fig.  38. 

Pitch-faced  Masonry.    That  in  which 

the  face  edges  of  the  beds  are  pitched  to- 

a  right  line.     Fig.  39. 

no.  as.  FM.M.  Cuts/one  Masonry.    That  in  which 

the  face  of  the  stone  is  finished  by  one  of  the  methods  described  in 

g§  190-193. 

197.  Range.  Masonry  in  which  a  course  is  of  the  same  thick- 
ness throughout.     Fig.  10. 

Broken  Range.  Masonry  in  which  a  course  is  not  continnous 
throughout.     Fig.  41, 

Random,    Masonry  which  is  not  laid  in  courses  at  all.   Fig.  43. 


'  l'  l'  l' 

^FT^ 

1    1     1     1 

V  1 1  ^  1  h 

1     1       1 

1   '1-"— ^^i^ 

1    1     1    1 

1    1    1 

H        r"-^ 

Fia.  40.— RiNOB, 


Fia.  41.— Bbokih  Rimqi.  Fib.  4^.— Bani 


Any  one  of  these  three  terms  may  be  employed  to  designate  the 
coursing  of  either  ashlar  {§  196)  or  sqnare-stone  masonry  (§  197), 
but  can  not  be  applied  to  rubble  (g  198). 

198.  Ashlar.  Cut-stone  masonry,  or  masonry  composed  of  any 
of  the  various  kinds  of  cat-stone  mentioned  in  g  193.  According 
to  the  Keport  of  the  Committee  of  the  American  Society  of  Civil 
Engineers,  "  when  the  dressing  of  the  joints  is  snch  that  the  dis- 
tance between  the  general  planes  of  the  surfaces  of  adjoining  stones 
is  one  half  inch  or  less,  the  masonry  belongs  to  this  class."     From 


ovGoQi^lc 


DEFINITIONS   OF    KINDS   OF   UABONRT.  137 

its  derivatioD  ashlar  apparently  meaos  large,  square  blocks;  bnt 
practice  seems  to  have  made  it  synooymous  with  "  cnt-stone,"  and 
this  secondary  meaning  has  been  retained  for  convenience.  The 
coursing  of  ashlar  is  dcBcribed  by  prefixing  range,  broken  range, 
or  random ;  and  the  finiah  of  the  face  la  described  by  prefixing  th« 
name  of  the  cat-atone  (see  g§  190-93)  of  which  the  masonry  la 
composed. 

Small  Aaltlar.  Cnt-atone  masonry  in  which  the  stones  are  loaa 
than  one  foot  thick.     The  term  is  not  often  nsed. 

Rough  Ashlar,  A  term  sometimes  given  to  aqn&red-atone 
masonry  (g  197),  either  qnarry-faced  or  pitch-faced,  when  laid  aa 
range-work;  bnt  it  is  more  logical  and  more  expressive  to  call  snch 
work  range  sqnared-stone  masonry. 

Dimension  Stones.  Cut-stones,  all  of  whose  dimensions  have 
been  fixed  in  advance.  "If  the  specifications  for  ashlar  masonry 
are  so  written  as  to  prescribe  the  dimensions  to  be  need,  it  will  not 
be  necessary  to  make  a  new  class  for  masonry  composed  of  aach 
atones." 

Squared-ttone  Masonry.  Work  in  which  the  stones  are  roughly 
squared  and  roughly  dressed  on  beds  and  joints  (§  193).  The 
distinction  between  aqaared-stone  masonry  and  ashlar  (g  196) 
lies  in  the  degree  of  closeness  of  the  joints.  According  to  the 
Eeport  of  the  Committee  of  the  American  Society  of  Civil  Engineers, 
"  when  the  dressing  on  the  joints  is  such  that  the  distance  between 
the  general  planes  of  the  snrfoce  of  adjoining  stones  is  one  half  inch 
or  more,  the  atones  properly  belong  to  this  class;"  nevertheless, 
euch  masonry  is  often  classed  as  ashlar  or  cut-atone  masonry. 

Rubble  Masonry.  Masonry  composed  of  nnsqnared  stone 
(§  191). 

Uncoursed  Rubble.     Masonry  composed  of   unsquared  stones 
laid   withoDt  any   at- 
tempt   at    regular 
conrsea.     Pig.  43. 

Coursed  Rubble. 
"Cnsqnared-stone  ma- 
sonry which  is  leveled 
off  at  specified  heif  hta 
to   an   approximately 

horizontal  surface.  It  may  be  speoified  that  the  stone  shall  be  rough- 
ly shaped  with  the  hammer,  so  as  to  fit  approximately.     Fig.  j14. 


ovGoQi^lc 


138  STONK  UASOKHT.  [CMAP.  TU. 

199.  QXXBBAL  Rinis.  Baokine  gives  the  following  roles  to  be 
oboerred  in  the  bnilding  of  all  claesee  of  stone  musonry: 

"  L  Bnild  the  masonry,  as  far  as  possible,  in  a  series  of  coarses, 
perpendionlar,  or  as  nearly  so  as  possible,  to  the  direction  of  the 
presBOre  which  they  have  to  bear;  and  by  breaking  joints  avoid  all 
long  continnoDS  joints  parallel  to  that  pressure. 

"  II.  Use  the  largest  stones  for  the  foundation  course. 

"  III.  Lay  all  stones  which  consist  of  layers  in  such  a  manner  that 
the  principal  preasure  which  they  have  to  bear  shall  act  in  a  direction 
perpendicular,  or  as  nearly  so  as  possible,  to  the  direction  of  the 
layers.  This  is  called  laying  the  stone  on  its  natural  bed,  and  is  of 
primary  importance  for  strength  and  durability. 

"  IV.  Moisten  the  surface  of  dry  and  porous  stones  before  bed- 
ding them,  in  order  that  the  mortar  may  not  be  dried  too  fast  and 
reduced  to  powder  by  the  stone  absorbing  its  moisture. 

"V.  Fill  every  part  of  erery  joint,  and  all  spaces  between  the 
-gtones,  with  mortar,  taking  care  at  the  same  time  that  such  spaces 
shall  be  as  small  as  possible." 

Another  and  very  important  rule  is:  the  rougher  the  stones,  the 
better  the  mortar  should  be.  The  principal  object  of  the  mortar  is 
-to  equalize  the  pressure;  and  the  more  nearly  the  stones  are  reduced 
to  closely  fitting  surfaces,  the  less  important  is  the  mortar.  Not 
infrequently  this  rule  is  exactly  reversed;  i.  e.,  the  finer  the, dressing, 
-the  better  the  quality  of  the  mortar  nsed, 

200.  A"<"»*  Kabovst.  For  definitions  of  this  class  of  masonry 
-and  its  subdiTision,  see  §  196. 

The  strength  of  a  mass  of  ashlar  masonry  depends  upon  the 
eize  of  the  blocks  in  each  course,  upon  the  accuracy  of  the  dressing, 
«nd  upon  the  bond. 

In  order  that  the  stones  may  not  be  liable  to  be  broken  across, 
1L0  soft  stone,  such  as  the  weaker  kinds  of  sandstone  and  granular 
iimestone,  should  have  a  length  greater  than  3  times  its  depth;  bnt 
~in  harder  materials,  the  length  may  be  4  or  5  times  the  depth.  The 
breadth  in  soft  materials  may  range  from  1^  to  2  times  the  depth ; 
■in  hard  materials,  it  may  be  3  times  the  depth. 

201.  DrMung.  The  closeness  with  which  stones  fit  is  depend- 
ent solely  upon  the  accuracy  with  which  the  surfaces  in  contact  are 
wrought,  or  dreseed,  and  is  of  special  importance  in  the  case  of 
^bed-jointa.    Ifaqyiiui  of  the  sorface  projeots  beyond  the  plans 


ovGoQi^lc 


■    AaHLAE  MA80NBT.  139 

lit  the  chiBel-draf  t,  that  projecting  part  will  have  to  bear  an  nadne 
share  of  the  pressure,  the  joint  will  gape  at  the  edges, — conBtitnting 
what  ifi  called  an  open  joint, — and  the  whole  will  be  wanting  in 
«tability.  On  the  other  hand,  if  the  surface  of  the  bed  is  concave, 
having  been  dressed  down  below  the  plane  of  the  chisel-draft,  the 
pressure  is  concentrated  on  the  edges  of  the  stone,  to  the  risk  of 
splitting  them  off.  Such  joints  are  said  to  hejluthed.  They  are 
more  difficult  of  detection,  after  the  masonry  has  been  built,  than 
open  joints ;  and  are  often  executed  by  design,  in  order  to  give  a 
nest  appearance  to  the  face  of  the  building.  Their  occurrence 
must  therefore  be  guarded  against  by  careful  inspection  daring 
the  progress  of  the  stone  cutting. 

Great  smoothness  is  not  desirable  in  the  joints  of  ashlar  masonry 
intended  for  strength  and  stability ;  for  a  moderate  degree  of  rough- 
ness adds  at  once  to  the  resistance  to  displacement  by  sliding,  and 
to  the  adhesion  of  the  mortar.  When  the  stone  has  been  dressed 
ao  that  all  the  small  ridgea  and  projecting  points  on  its  surface  are 
reduced  nearly  to  a  plane,  the  pressure  is  distributed  nearly  nni- 
iormly,  for  the  mortar  serves  to  transmit  the  pressure  to  the  small 
depressions.  Each  stone  should  first  be  fitted  into  its  place  dry, 
in  order  that  any  inaccnraey  of  figure  may  be  discovered  and  cor- 
rected by  the  stone-cutter  before  it  is  finally  laid  in  mortar  and 
settled  in  its  bed. 

The  thickness  of  mortar  in  the  joints  of  the  very  test  ashlar 
masonry — for  example,  the  United  States  post-office  and  custom- 
house  buildings  in  the  principal  cities — is  about  i  of  an  inch  ;  in 
flrat^^lass  railroad  masonry — for  example,  important  bridge  piera 
and  abutments,  and  large  arches — the  joints  are  from  i  to  f 
of  an  inch.  No  catting  should  be  allowed  after  the  stone 
has  been  set  in  mortar,  for  fear  of  breaking  the  adhesion  of  the 
mortar. 

A  ohiBel-diatt  1 J  or  2  inches  wide  is  usually  cut  at  each  exterior 
comer. 

202.  Bond.  No  side- joint  of  any  course  should  be  directly  above 
a  side-joint  in  the  course  below  ;  but  the  stones  should  overlap,  or 
break  joint,  to  an  extent  of  from  1  to  IJ  times  the  depth  of  the 
coarse.  This  is  called  the  bond  of  the  masonry.  The  effect  is  that 
©ach  stone  is  sapported  by  at  least  two  stones  of  the  course  below,  and 
asBists  in  supporting  at  least  two  stones  of  the  course  above.     The 


ovGoQi^lc 


140  STONE   MASONRY.  [CHAP.  VII. 

object  Ts  twofold  ;  first,  to  distribute  the  pressure,  so  that  inequali- 
tieBof  loud  on  the  upper  part  of  the  structure  (or  of  resistance  at 
the  fonndation)  may  be  traasmitted  to  and  spread  over  an  increas- 
ing ar«a  of  bed  in  proceeding  downwards  (or  upwards) ;  and  second, 
to  tie  the  building  together,  t.  e.,  to  give  it  a  sort  of  tenacity,  both 
lengthwise  and  from  face  to  back,  by  means  of  the  friction  of  the 
stones  where  they  overlap. 

The  strongest  bond  is  that  in  which  each  course  at  the  face  of 
the  structure  contains  a  header  and  a  stretclier  alternately,  the 
enter  end  of  each  header  resting  on  the  middle  of  a  stretcher  of 
the  coarse  below,  so  that  rather  more  than  one  third  of  the  area  of 
the  face  consists  of  ends  of  headers.  This,  proportion  may  be 
deviated  from  when  circnmstancea  require  it,  but  in  every  case  it 
is  advisable  that  the  ends  of  headers  should  not  form  less  than  one 
fourth  of  the  whole  area  of  the  face  of  the  structure.  A  header 
should  extend  entirely  through  the  wall,  and  shonld  be  over  the 
middle  of  the  stretcher  in  the  course  below. 

A  trick  of  masons  is  to  use  "  blind-headers,"  or  short  stones  that 
look  like  headers  on  the  outside  but  do  not  go  deeper  into  the  wall 
than  the  adjacent  stretchers.  When  a  conree  has  been  put  on  top 
of  these,  they  are  completely  covered  up ;  and,  if  not  suspected, 
the  fraud  will  never  be  discovered  unless  the  weakness  of  the  wall 
reveals  it. 

Where  very  great  resistance  to  displacement  of  the  nuksonry  is 
required  (as  in  the  upper  courses  of  bridge  piers,  or  over  openings, 
or  where  new  masonry  is  joined  to  old,  or  where  there  is  danger  of 
unequal  settlement),  the  bond  is  strengthened  by  dowels  or  by 
'  ciamp-irons  (§  195)  of,  say,  l^inch  ronnd  iron  set  with  cement 
mortar. 

203.  Baoking.  Ashlar  is  usually  backed  with  rubble  masonry 
(g  213),  which  in  such  caaes  is  specified  as  coursed  mbble.  Special 
care  should  be  taken  to  secure  a  good  bond  between  the  rubble 
backing  and  the  ashlar  facing.  Two  stretchers  of  the  ashlar  fac- 
ing having  the  same  width  should  not  be  placed  one  immediately 
above  the  other.  The  proportion  and  length  of  the  headers  in 
the  rubble  backing  should  be  the  same  as  in  the  ashlar  facing.  The 
"  tails  "  of  the  headers,  or  the  parts  which  extend  into  the  rubble 
backing,  may  be  left  rough  at  the  back  and  sides;  bat  their  upper 
and  lower  beda  should  be  dressed  to  the  geoeral  plane  of  Uie  bed  of 


ovGoQi^lc 


ABHLA.B   HASOKRT.  141 

the  conrse.     These  "  tails"  may  taper  slightly  in  breadth,  but  should, 
not  taper  in  depth. 

The  backing  should  be  carried  up  at  the  same  time  with  the 
£tce-work,  and  in  courses  of  the  same  depth;  and  the  bed  of  each 
coarse  sbonld  be  carefully  built  to  the  same  plane  vith  that  of  the 
ashlar  facing.  The  rear  face  of  the  backing  should  be  lined  to  a 
jair  surface. 

204.  Pointing.  In  laying  masonry  of  any  character,  whether 
with  common  or  hydraulic  mortar,  the  exposed  edges  of  the  joints 
will  naturally  be  deficient  in  density  and  hardnese.  The  mortar  in 
the  joints  near  the  surface  is  especially  subject  to  dislodgment, 
since  the  contraction  and  expansion  of  the  masonry  is  liable  either 
to  separate  the  stone  from  the  masonry  or  to  crack  the  mortar  in 
the  joint,  thus  permitting  the  entrance  of  rain-water,  which,  freezing, 
forces  the  mortar  from  the  joints.  Therefore  it  is  usual,  after  the 
niasonry  is  laid,  to  refill  the  joints  aa  compactly  as  possible,  to  the 
depth  of  nt  least  half  an  inch,  with  mortar  prepared  especially  for 
this  purpose.     This  operation  is  called  pointing. 

The  very  best  cement  mortar  should  be  used  tor  pointing,  as  the 
best  becomes  dislodged  all  too  soon.  Clear  Portland  cement  mor- 
tar is  the  bent,  although  1  volume  of  cement  to  1  of  sand  is  fre- 
quently used  in  flrst-ckss  work.  The  mortar,  when  ready  for  use, 
should  be  rather  incohercntnndquitedoficiont  in  plasticity.  ■  Before 
applying  the  pointing,  the  joint  should  be  well  cleansed  by  scrap- 
ing and  brushing  out  the  loose  matter,  and  then  be  well  moistened. 
01  course,  the  cleansing  out  of  the  joints  can  be  most  easily  done 
while  the  mortar  is  now  and  soft.  The  depth  to  which  the  mortar 
shall  bo  dug  out  is  not  often  specified ;  it  is  usually  cleaned  out 
about  half  an  inch  deep,  but  should  be  at  least  an  inch.  In  the 
Brooklyn  bridge  piers  the  joints  were  cleared  IJ  inches  deep. 

The  mortar  is  applied  with  a  mason's  trowel,  and  the  joint  well 
calked  with  a  calking  iron  and  hammer.  In  the  very  best  work, 
the  joint  is  also  rubbed  smooth  with  a  steel  polishing  tool.  Walla 
shontd  not  be  allowed  to  dry  too  rapidly  after  pointing ;  therefore, 
pointing  in  hot  weather  should  be  avoided. 

205.  Amount  of  Hortar.  The  amount  of  mortar  required  for 
ashlar  masonry  varies  with  the  size  of  the  blocks,  and  also  with 
the  closeness  of  the  dressing.  With  f-  to  i-ioch  joints  and  12-  to 
^O-inch  conraes,  there  will  be  about  2  cubic  feet  of  mortar  per 


ovGoQi^lc 


143  STONE  UABONRT.  [CHAP.  Tll- 

oobic  yard;  with  larger  blocks  and  cloaer  joints,  i.  e.,  in  the  best 
masonry,  there  will  he  abont  1  cubic  foot  of  mortar  per  yard  ot 
masonry.  Laid  in  1  to  2  mortar,  ordinary  ashlar  will  reqnire  i  to- 
i  of  a  barrel  of  cement  per  cnbio  yard  of  masonry. 

For  the  qnantities  of  cement  and  sand  required  for  a  cobic  yard 
of  mortar  of  different  compositions,  see  page  88. 

306.  When  Employed.  Ashlar  masoniy  is  nsed  for  piers,  abut- 
ments, arches,  and  parapets  of  bridges;  for  hydranlio  worksj  for 
facing-qnoins,  and  string  courses;  for  the  coping  of  inferior  kinda 
of  masonry  and  of  brick  work;  and,  in  general,  for  works  in  which 
great  strength  and  stability  are  required. 

207.  Specifloatioas  foi  Aahlai.  The  specifications  for  ashlar,. 
or  "  fiist-daaa  masonry  "  as  employed  on  the  railroads,  are  abont 
as  follows ;  * 

A«hlftr  Bball  coaatet  of  range  pitch-faced  muoniy.  The  stone  (hftll  be  of 
durable  quality:  aad  shall  be  fr«e  from  seami,  poirdar  crack*,  diTS,  flawi,  or 
other  Imperfections. 

All  foundation  counei  iball  be  laid  with  ulecied,  luge,  flat  stones  not  less. 

than  1  Inches  In  thickness,  nor  of  leas  superficial  surface  than  fifteen  (IS) 

square  feet. 

The  coutses  shall  be  not  less  than Inches  thick  nor  more  than  — 

Inches.^  The  courses  shall  be  continuous  around  and  through  the  wall ;  andi 
no  course  shall  be  thicker  than  the  one  below  It,  except  that  the  footing- 
course  may  be  thinner  than  the  one  next  above.  Stretchers  shall  be  st  least 
twice  as  wide  as  thick,  and  at  least  four  times  as  long  as  thick.  Headers  thtiX 
be,  for  at  least  three  fourths  of  their  length,  not  less  than  twice  as  wide  at  . 
thick;  tad  shall  extend  entirely  through  the  wall,  or  have  a  length  not  less 
than  five  times  the  thickness  of  the  course.  The  masourr  shall  consist  of 
headers  and  stretchers  alternating;  at  least  one  third  %  of  the  face  of  the  wall 
shall  consist  of  headers.  Stretchers  of  the  some  width  shall  not  be  placed 
immediately  one  above  Ihe  other ;  but  this  shall  not  apply  to  the  ends  of 
stretchetB  where  headers  come  centrally  between  stretchers.  Every  header 
shall  be  Immediately  over  a  stretcher  of  the  course  next  below.  Joints  on  tbo 
face  of  the  wall  shall  be  broken  at  least  three  quarters  of  the  thickness  of  tb» 

The  beds  and  the  vertical  joints  for  IS  inches  back  from  the  face  of  the 
wall  shall  be  dressed,  before  being  brought  io  the  wall,  so  as  to  form  mortar 

■  For  oompleta  speciflcotions  tor  railroad  and  also  other  kinds  of  masonry,  see 
Appendix  I.  page  529. 

t  Frequently  12;  sometimes  18. 

j  The  conrses  of  the  olasees  of  moaonry  referred  to  above  nsnally  range  from 
U  to  30  inohea ;  but,  of  course,  may  vary  according  to  the  cironmstoncaa,  and  for 
some  purposes  may  be  as  low  as  10  iDohes. 

I  Cntten  specfflad  as  one  fourth. 


ovGoQi^lc 


BQtJABE-STOHSD  UASOHBY.  IJS'- 

Joints  Dot  less  than  one  quattei  inch  nor  mora  than  one  halt  Incli  In  thlckneat. 
All  aloaea  shall  be  laid  on  tha  natural  bed.  No  part  of  a  stone  shall  extend 
beyond  the  back  edge  of  the  under  bed.  All  corueia  and  batter  lines  shall 
have  a  neat  chisel-draft  one  and  one  half  Inches  wide  on  each  face.  The  pn>- 
Jecllons  of  the  rock- face  must  not  exceed  four  inches  beyond  the  draft-lines ; 
and  In  tunnel  dde-walls,  the  projectloo  must  not  exceed  two  Inches.  Th* 
face-edge  of  the  Joint  shall  be  pitched  to  a  straight  Ibe. 

The  backing  shall  consist  of  stone  of  the  same  thickness  as  the  correspond- 
ing face  stone.  .  When  walls  exceed  four  feet  In  thickness,  there  shall  be  aa 
many  headers  of  the  same  size  In  the  back  of  the  wall  as  in  the  face,  so  ar- 
ranged that  a  header  In  the  rear  of  the  wall  shall  be  between  two  headers  in 
the  front.  Tbe  backing  shall  be  so  laid  as  to  leaTe  no  spaces  between  the 
■tones  over  six  Inches  wide,  wblch  spaces  shall  be  filled  with  spalls  set  In 
cement  mortar.    Ho  spalls  shall  be  allowed  In  the  bed  joints. 

The  coping  shall  be  formed  of  large  flat  stones,  which  shall  extend  entirely 
aoroas  the  wall  when  tbe  same  Is  not  more  than  six  feet  wide.  The  steps  of 
irlng  walls  shall  be  capped  with  stone  covering  the  entire  step  and  extending 
under  the  step  next  above  at  least  twelve  Inches.  Coping  and  step  stones  shall 
be  at  least  twelve  Inches  thick,  and  have  such  projections  as  tbe  engineer  may 
direct  [neually  8  to  6  Inches].  The  tops  and  faces  of  copings  and  step  atones 
shall  be  bush- hammered,  and  their  Joints  and  beds  cat  to  one  quarter  Inch 
throughout. 

208.  BaiTAXXB^Ton  Xasohbt.  For  deflnitiotu  of  this  olaai  of 
maaoury  and  its  anbdiriBioiiB,  eee  §  197.  Tbe  distinction  b«tween 
Bqnarad-atoue  masonry  and  ashlar  Iie«  in  the  d«^pree  of  closeness  of 
the  joints.  According  to  the  Report  of  the  Committee  of  the 
American  Society  of  CItU  Engineers,  "  when  the  dressing  on  the 
joints  is  such  that  the  distance  between  the  general  planes  of  tbe 
surfaces  of  adjoining  stones  is  one  half  inch  or  more,  the  stones 
properly  belong  to  this  doss ; "  howerer,  snch  masonry  is  frequently 
classed  as  ashlar  or  cat-stone  masonry. 

Sqnared-stone  masonry  is  asually  quarry  •faced,  random- work, 
although  pitch-faced  range-work  is  not  ancommon.  Tbe  qnoins 
and  the  sides  of  openings  are  nsiially  rednoed  to  a  rongb-smooth 
sarface  with  the  face-hammer,  the  ordinary  ax,  or  the  tooth-ax. 
This  work  is  a  necessity  where  door  or  window  frames  are  inserted; 
and  it  greatly  improves  the  general  effect  of  the  wall,  if  nsed 
wherever  a  corner  is  tamed, 

209.  Sqnared-stone  masonry  is  distingnished,  on  the  one  hand, 
from  ashlar  in  having  less  accarately  dressed  beds  and  joints,  and,  on 
the  other  band,  from  mbble  in  being  more  oarefnily  constrncted. 
Id  ordinary  practice,  tbe  field  covered  by  this  class  is  not  very 
definite.     The  speoiflcationB  for  "  second-class  masoniy"  as  nsed 


ovGoQi^lc 


144  STONE    UASONRY.  [CHAP,  VII. 

on  Tailroads  nsnally  conform  to  the  above  deBcripUon  of  qnarrj-faced, 
range  eqnared-stone  maaonrj ;  but  sometimes  this  grade  of  masonry 
is  designated  "  superior  rabble.  '* 

210.  Amoimt  of  Mortal  Beqaired.  The  amount  of  mortar 
required  for  squared-stoue  masonry  varies  with  the  size  of  the 
atones  and  with  the  quality  of  the  masonry;  as  a  rough  average, 
one  sixth  to  one  quarter  of  the  mass  is  mortar.  When  laid  in  1  to 
3  mortar,  squared-stone  masonry  will  require  ^  to  J  of  a  barrel  of 
cement  per  cubic  yard  of  masonry. 

'For  quantities  of  cemeut  and  sand  required  for  mortars  of 
Tarions  compositions,  see  the  table  on  page  88. 

211.  Baoking  and  Foiating.  The  statements  Goncomiog  the 
backing  and  pointing  of  ashlar  (§§  203  and  204)  apply  flubstautJally 
to  Bqnared-Btone  masonry.  As  the  joints  of  squared-stone  masonry 
are  thicker  than  those  of  ashlar,  the  pointing  should  be  done  pro- 
portionally more  carefully;  while  as  a  rule  it  is  done  much  more 
careleesly.  The  mortar  is  often  thrown  into  the  joint  with  a 
trowel,  and  then  trimmed  top  and  bottom  to  give  the  appearance 
of  a  thinner  joint.  Such  work  ia  called  ribbon  pointing.  Trimming 
the  pointing  adds  to  the  appearance  bat  not  to  the  durability. 
When  not  trimmed  it  is  called  dashed  poiating. 

212.  Specifications  for  Squared-stone  Hasonry.  Squared-stone 
masonry  is  employed  for  the  piers  and  abutmects  of  lighter  bridges, 
for  small  arches,  for  box-cnlverts,  for  basement  walls,  etc.  The 
specifications  are  about  as  follows:  * 

The  stones  shall  be  of  durable  quality;  and  shall  be  free  from  seams, 
powder  crackB,  drjs,  or  other  imperfections. 

The  couraea  shall  be  not  lesa  than  10  Incheii  thlelc. 

Btretchers  sfaall  be  at  least  twice  as  wide  as  thick,  aod  at  least  four  times  as 
long  as  thick.  Headers  shall  be  at  least  five  times  as  long  as  thick,  and  at  least 
as  wide  at  thick.  There  shall  be  at  least  one  header  lo  three  atretchen.  Joints 
on  the  face  shall  be  broken  at  least  8  Inches. 

Tbe  beds  and  verltcal  joints  for  8  Inches  back  from  the  face  of  the  wall 
■hall  be  dressed  to  make  jointB  one  half  to  one  inch  thick.  Tbe  front  edge  of 
the  joint  shall  be  pitched  10  a  straight  line.  AU  comers  and  balter-ltnes  shall 
be  bammer-dressed. 

Tbe  backing  shall  constat  of  atones  not  less  In  thickness  than  the  facing. 
At  least  one  half  of  the  backing  shall  be  stone*  containing  3  cubic  teeU 
The  backing  shall  be  laid  in  full  mortar  beds;  and  the  vertical  Joints  shall 

«  Appendix]^ 


ovGoQi^lc 


BUBBLE  MASONET.  US 

also  be  filled  with  mortar.    Tbe  epacea  between  the  Isrge  itones  HhaU  be  filled 
with  spalla  Bet  Id  mortar. 

The  coping  absll  be  fonaed  of  large  flat  Btonea  of  such  tblckneas  aa  ths 
«ii|;ineer  may  direct,  but  in  no  case  to  be  less  than  eight  inches  (8").  The 
upper  surface  of  tbe  coping  Hliall  be  bush- hammered,  and  the  Joints  and  I>eda 
shall  be  drened  to  one  lialf  an  inch  (1")  throughout.  Eacb  atone  must  extend 
•ntireiy  across llie  wall  when  the  wall  is  not  mora  than  four  feet  (4)  thick. 

213.  BUBBIB  HaboveT.  For  defiaitioDs  connected  with  tliis 
'class  of  masonry,  see  §  198. 

The  BtoneB  used  for  rubble  masonry  sbonld  be  prepared  by 
eimply  knocking  off  all  tbe  weak  angles  of  the  block.  It  Bbonldbe 
cleansed  from  duat,  etc.,  and  moistened,  before  being  placed  on  its 
bed.  This  bed  is  prepared  by  spreading  over  the  top  of  the  lower 
course  an  ample  quantity  of  good,  ordinary-tempered  mortar  in 
which  tbe  stone  is  firmly  embedded.  The  vertical  joints  should  be 
carefully  filled  with  mortar.  The  interstices  between  the  larger 
masses  of  stone  are  filled  by  thmsting  small  fragments  or  chippings 
■of  stooe  into  the  mortar.  In  heavy  walla  of  rubble  masonry,  the 
precaution  should  be  obeerred  to  give  tbe  stones  the  same  position 
in  the  masonry  that  they  had  in  the  qoarry,  t.  e.,  to  lay  them  on 
their  "natural  bed,"  since  stone  offers  more  resistance  topressnre 
in  a  direction  perpendicular  to  the  quarry-bed  than  in  any  other. 
Tbe  directions  of  the  laminee  in  stratified  stones  show  tbe  position 
of  the  quarry-bed. 

To  connoct  the  parts  well  together  and  to  strengthen  the  weak 
points,  Ihroughs  or  binders  should  be  used  in  all  tbe  courses,  and 
the  angles  should  be  constructed  of  cut  or  hammered  stono. 

When  carefully  exocntod  with  good  mortar,  rubtjle  possesses  all  the 
strength  and  durability  required  in  strnctures  of  an  ordinary  char- 
acter, and  is  much  less  expensive  than  ashlar.  The  difbcnity  le  in 
getting  it  well  executed.  The  most  common  defects  are  (1)  not  bring- 
ing tbe  stones  to  an  even  bearing;  (3)  leaving  large  vertical  openings 
between  the  several  stones;  (3)  laying  up  a  considerable  height  of 
tbe  wall  dry,  with  only  a  little  mortar  on  the  face  and  back,  and 
then  pouring  mortar  on  the  top  of  the  wall;  (4)  using  insuEBcient 
cement,  or  that  of  a  poor  qnality.  The  last  defect  is  usually  obviated 
by  furnishing  the  cement  to  the  contractor ;  and  the  second  and 
third  defects  may  be  detected  by  probing  the  vertical  joints  with  a 
«mall  steel  rod.    In  order  to  seonre  good  mbble,  great  skill  and 


ovGoQi^lc 


146  STONE  UASO^TBT.  [CRAP.  TO. 

oare  are  required  on  the  part  of  the  mason,  and  constant  vatchial- 
ness  on  the  psrt  of  the  inspector. 

A  very  stable  wall  can  be  built  of  rubble  masonry  without  any 
dressing,  except  a  draft  on  the  quoins  by  which  to  plumb  the  cor- 
Dere  and  carry  them  up  neatly,  and  a  few  strokes  of  the  hammer  to 
spall  off  any  projections  or  surplus  stone.  This  style  of  work  ia 
not  generally  advisable,  as  very  few  mechanics  can  be  relied  upon  to 
take  the  proper  amount  of  care  in  leveling  up  the  beda  and  filling 
the  joints;  and  as  a  coneequence,  one  small  stone  may  jar  loose  and 
&11  oat,  resulting  probably  in  the  downfall  of  a  considerable  part  of 
the  wall.  Some  of  the  naturally  bedded  stones  are  so  smooth  and 
oniform  as  to  need  no  dressing  or  spalling  up;  a  wall  of  such  stones 
ia  very  economical,  since  there  is  no  expense  of  cutting  and  no  time 
U  lost  in  hunting  for  the  right  stone,  and  yet  strong,  massive  work 
is  assured.  However,  many  of  the  naturally  bedded  stones  have 
inequalities  on  their  surfaces,  and  in  order  to  keep  them  level  in  the 
course  it  becomes  necessary  to  raise  one  comer  by  placing  spalls  or 
chips  of  stone  under  the  bed,  and  to  fill  the  vacant  spaces  well  and 
full  with  mortar.  It  is  just  here  that  the  disadvantage  of  this  styl& 
of  work  btKJomes  apparent.  Unless  the  mason  places  these  spalls  so 
that  the  stone  rests  firmly,  i.  e.,  does  not  rock,  it  will  work  loose, 
particularly  if  the  strnctnre  is  subject  to  shock,  as  the  walls  of 
cattle- guards,  etc  Unless  these  spalls  are  also  distributed  so  as  to 
support  all  parts  of  the  stone,  it  is  liable  to  be  broken  by  the  weight 
above  it  A  few  such  instances  in  the  same  work  may  occasion  con- 
siderable disaster. 

One  of  the  tricks  of  masons  is  to  put  "  nigger-heads"  (stones 
from  which  the 'natural  rounded  surface  has  not  l»en  taken  off) 
into  the  interior  of  the  wall. 

214.  Rubble  masonry  is  Bomctimes  laid  without  any  mortar,  as 
in  slope  walls  (%  316),  paving  (§  219),  etc.,  in  which  case  it  iscalled 
dry  rubble;  but  as  such  work  is  much  more  frequently  designated 
BB  slope-wall  masonry  and  stone-paving,  it  is  better  to  reserve  the 
term  rubble  for  undressed  stone  laid  in  mortar.  Occasionally  box 
culverts  are  built  of  the  so-called  dry  rubble;  but  as  such  construc- 
tion is  not  to  be  commended,  there  is  no  need  of  a  term  to  desig- 
nate that  kind  of  masonry. 

21fi.  Amount  of  Hortai  Bequired.  If  rubble  masonry  is  com- 
posed of  small  and  irregular  stones,  about  one  third  of  the  mass 


ovGoQi^lc 


BCBBLB  HASOKBT.  14T 

vill  consist  of  mortar;  if  the  stonea  are  larger  and  more  regular, 
one  fifth  to  one  quarter  will  be  mortar.  I^id  in  1  to  2  mortar, 
ordinary  rubble  requiree  from  one  half  to  one  barrel  of  cement  per 
cubic  yard  of  masonry. 

For  the  amount  of  cement  and  sand  required  for  mortar  of  Ta- 
rionB  compositions,  see  the  table  on  page  88. 

216.  When  Smployed.  Bubble  masonryof  the  quality  described 
•bore  is  frequently  employed  for  the  emalleat  sizes  of  bridge  abut- 
ments, small  arch  culverts,  box  and  open  cnlverts,  foundations  of 
buildings,  etc.,  and  for  backing  for  ashlar  maaonry  (§  300). 

217.  Bpecifloationi  for  Subble  Kwonry.*  The  following  re- 
qnirements,  if  properly  complied  with,  will  secure  what  is  generally 
known  among  railroad  engineers  as  superior  rubble. 

Rubble  masoDTy  sball  consist  of  couned  rubble  of  good  qualtty  laid  In 
cement  mortar.  No  slone  shall  be  leas  than  alx  lnches(6")  in  thlckuesB,  unleaa 
otherwise  directed  by  the  eagineer.  No  slone  sbbll  measure  teas  tbau  twelve 
Inches  (12")  in  ila  least  horizontal  dlmeQalon,  or  leas  than  its  thickness.  At 
least  one  fourth  oC  the  stone  In  the  faCe  aball  be  headers,  evenly  dlatrlbnted 
throughout  the  wall.  The  atones  shall  be  roughly  squared  on  joints,  beds,  and 
faces,  laid  so  as  to  break  Joints  and  in  full  mortar  beds.  All  vertical  spaces 
•hall  be  flusbed  with  g9od  cement  mortar  and  then  be  packed  full  with  spalls. 
No  spalls  will  be  allowed  In  the  beds.  Selected  atones  shall  be  used  at  all 
angles,  and  alkali  be  neatly  pitched  to  true  Hues  and  laid  on  hammer-dressed 
beds;  draft  llnea  may  be  required  at  the  more  prominent  angles. 

The  top  of  parapet  walls,  piers,  and  abutments  shall  be  capped  with  stonea 
extending  entirely  acrf'BS  the  wall,  and  having  a  front  and  end  projectton  of 
not  less  than  four  Inches  (4").  Coping  stones  shall  be  neatly  squared,  and  laid 
with  joints  of  less  than  one  half  Inch  (f ).  The  steps  of  wlug-walls  shall  be 
capped  with  stone  covering  the  entire  step,  and  extending  at  least  six  Inches 
(ff)  into  the  wall.  Coping  and  step  stones  shall  be  roughly  hammer- dressed 
on  top,  their  outer  faces  pitched  to  true  lines,  and  be  of  such  thickness  (not 
less  than  six  Inches)  and  have  sucii  projections  as  the  eti^neer  may  direct. 

' '  The  specifications  for  rubble  maaonry  will  apply  to  rubble  maaoury  laid 
■iry,  except  as  to  the  use  of  tlie  mortar  (see  ^  314)." 

218.  Slo?e-wail  MauiteT,  A  slope-Wall  is  a  thin  layer  of 
masonry  nsed  to  preserve  the  slopes  of  embankments,  excavations, 
canals,  river  banks,  etc.,  from  rain,  waves,  weather,  etc  Theusnal 
Bpecificationa  are  as  follows: — 

The  stones  must  reach  entirely  through  the  wall,  and  be  not  leas  thao  four 
inches  (4")  thick  and  twelve  inches  (12")  long.  They  must  be  laid  with  brakes 
joiniK;  and  the  joints  must  be  as  close  and  free  from  spalls  as  possible. 

•*  For  complete  speciflcatlona  for  masom^  for  varioaa  purposes,  see  Appendix  I. 


ovGoQi^lc 


148  STONE    HABONRT.  [CHAP,  VII. 

216.  8T0>z  Pati>0.  Stone  paving  is  naed  for  the  inverts  of  arch 
caiverta,  for  protecting  the  lower  end  of  archea  from  nndcrmining, 
and  for  fonndationa  of  box  culverta  and  emaU  archeB.  It  is  nBoallf 
classed  iw  dry  rubble  masonry,  although  it  is  occasionally  laid  with 
cement  mortar.     The  asual  specifications  are  about  as  follows  : 

Stone  paving  shall  be  made  of  flat  stones  from  eight  laches  (8")  to  fifteen 
inches  (tS"}  In  depth,  «et  on  edge,  closely  laid  sud  well  bedded  in  the  soil,  and 
shall  present  an  even  lop  surface. 

320.  BtnULP.  Kiprsp  is  stone  laid,  without  mortar,  about  the 
base  of  piers,  abntmentB,  etc,  to  prevent  scour,  and  on  banks  to 
prevent  wash.  When  used  for  the  protection  of  piers,  the  stones 
are  dumped  in  promiscuously,  their  size  depending  upon  the 
material  at  hand  and  the  velocity  of  the  current;  stones  of  15  to 
25  cubic  feet  each  are  frequently  employed.  When  used  for  the 
protection  of  banks,  the  riprap  is  laid  by  hand  to  a  uniform  thick- 
ness. 

231.  STBBSaTH  OF  Stohe  Xasohbt.  The  results  obtained  by 
testing  small  specimens  of  stone  (see  §  14)  are  useful  in  determine 
ing  the  relative  strength  of  different  kinds  of  stone,  but  are  of  no 
Tftlue  in  determining  the  ultimate  strength  of  the  same  stone  when 
-built  into  a  masonry  structure.  The  strength  of  a  mass  of  masonry 
depends  upon  the  strength  of  the  stone,  the  size  of  the  blocks,  the 
accuracy  of  the  dressing,  the  proportion  of  headers  to  stretchers, 
and  the  strength  of  the  mortar.  A  variation  in  any  one  of  these 
items  may  greatly  change  the  strength  of  the  masonry. 

The  importance  of  the  mortar  as  affecting  the  strength  of 
masonry  to  resist  direct  compression  is  generally  overlooked.  The 
mortar  acts  as  a  cushion  (g  13)  between  the  blocks  of  stone,  and  if 
it  has  ineuflBcient  strength  it  will  be  squeezed  out  laterally,  pro- 
ducing a  tensile  strain  in  the  stone;  weak  mortar  thus  causes  the 
stone  to  fail  by  tension  instead  of  by  compression.  No  experiments 
have  ever  been  made  upon  the  strength  of  stone  masonry  under  the 
conditions  actually  occurring  in  masonry  structures,  owing  to  the 
lack  of  a  testing-machine  of  sufBcient  strength.  Experiments 
made  upon  brick  piers  (g  246)  12  inches  square  and  from  2  to  10 
feet  high,  laid  in  mortar  composed  of  1  volume  Portland  cement 
and  2  sand,  show  that  the  strength  per  sqaare  inch  of  the  masonry 
is  only  about  one  sixth  of  the  strength  of  the  brick.  An  increase 
i.ot  50  per  cent,  in  the  strength  of  the  brick  produced  no  appreciable 


ovGoQi^lc 


BTRENOTH  OF  STONB  MA80NBT.  149 

«ffect  on  the  atrength  of  the  masonry;  bat  the  substitution  of 
cement  mortar  (1  Portland  and  2  sand)  for  lime  mortar  (1  lime  and 
3  sand)  increased  the  strength  of  the  masonry  70  per  cent.  The 
method  of  failure  of  these  piers  indicates  that  the  mortar  squeezed 
out  of  the  joints  and  caused  the  brick  to  fail  by  tension.  Since  the 
mortar  is  the  weakest  element,  the  less  mortar  used  the  stronger  the 
vail;  therefore  the  thinner  the  joints  and  the  larger  the  blocks,  the 
stronger  the  masonry,  provided  the  surfaces  of  the  stones  do  not 
come  in  contact. 

It  is  generally  stated  that  the  working  strain  or  stone  masonry 
should  not  exceed  one  twentieth  to  one  tenth  of  the  atrength  of  the 
stone;  but  it  is  clear,  from  the  experiments  on  the  brick  piers  re- 
ferred to  above,  that  the  strength  of  the  masonry  depends  upon  the 
strength  of  the  stone  only  in  a  remote  degree.  Id  a  general  way  it 
may  be  said  that  the  results  obtained  by  testing  small  cubes  may 
vary  50  per  cent,  from  each  other  (or  say  35  per  cent,  from  the 
mean)  owing  to  undetected  difierences  in  the  material,  cutting,  and 
manner  of  applying  the  pressure.  Experiments  also  show  that 
stones  crack  at  about  half  of  their  ultimate  crnshing  strength. 
Bence,  when  the  greatest  care  possible  is  exercised  in  selecting  and 
bedding  the  stone,  the  safe  working  strength  of  the  stone  alonfr 
should  not  be  regarded  as  more  than  three  eighths  of  the  ultimate 
strength.  A  further  allowance,  depending  apon  the  kind  of  atruo- 
tnre,  the  quality  of  mortar,  the  closeness  of  the  joints,  etc.,  should 
be  made  to  insure  safety.  Experiments  upon  even  comparatively 
large  monoliths  give  but  little  indication  of  the  strength  of  masonry. 
The  only  practicable  way  of  determining  the  actual  strength  of 
masonry  is  to  note  the  loads  carried  by  existing  structures.  How- 
ever, this  method  of  investigation  will  ^ve  only  the  load  which  doea 
not  crush  the  masonry,  since  probably  no  structure  ever  failed  owing 
to  the  crnshing  of  the  masonry.  After  an  extensive  correspondence 
and  a  thorough  search  through  engineering  literature,  the  following 
list  ia  given  as  showing  the  maximum  pressure  to  which  the  several 
classes  of  masonry  have  been  subjected. 

223.  Pressure  Allowed.  Early  builders  used  much  more  ma^ 
sive  masonry,  proportional  to  the  load  to  be  carried,  than  is  cus- 
tomary at  present.  Experience  and  experiments  have  shown  that 
such  great  strength  is  unnecessary.  The  load  on  the  monolithio 
piers  supporting  the  large  churches  in  Europe  does  not  exceed  3tf 


ovGoQi^lc 


150  STONE   MASONRY.  [cHAP.  V]}. 

toQs  per  sq.  ft.  (420  lbs.  per  eq.  iD.)>*  <>■'  &boat  one  thirtieth  of  the 
nitiniate  strength  of  the  stone  alone.  The  etone-arch  bridge  of  140 
ft,  span  at  Pont-j-Prydd,  over  the  Taff,  in  Wales,  erected  in  1750, 
is  sapposed  to  have  a  pressure  of  72  tons  per  sq.  ft.  (1,000  lbs.  per 
sq.  in.)  on  hard  limestone  rubble  masonry  laid  in  lime  mortar.f 
Rennie  subjected  good  hard  limestone  rubble  in  columns  4  feet 
square  to  22  tons  per  sq.  ft,  (300  lbs.  per  sq.  in-)4  "^h^  granite  piers 
of  the  Saltaeh  Bridge  eustaln  a  pressure  of  9  tons  per  sq.  ft.  (125 
lbs.  per  sq.  in,). 

The  Doaximum  pressure  on  the  granite  masonry  of  the  towers  of 
the  Brooklyn  Bridge  isabout  28(  tons  per  sq.  ft.  (about  400  lbs.  per 
sq.  in.).  The  maximum  pressure  oq  the  limestone  masoury  of  this 
bridge  is  about  10  tone  per  sq.  ft  (125  lbs.  per  sq.  in,).  The  face 
atones  ranged  in  cubical  contents  from  1(  to  5  cubic  yards;  the 
atones  of  the  granite  backing  averaged  about  1^  en,  yds.,  and  of  the 
'imestone  about  IJ-  cu,  yds,  per  piece.  The  mortar  was  1  volume 
of  Bosendale  cement  and  3  of  sand.  The  stones  were  rough-axed, 
or  pointed  to  ^inch  bed-joints  and  |-inch  vertical  face-joints.g 
These  towers  are  very  fine  examples  of  the  mason's  art. 

In  the  Rookery  Building,  Chicago,  granite  columns  nbout  S  feet 
square  sustain  30  tons  per  sq.  ft.  without  any  signs  of  weakness. 

In  the  Washington  Monument,  Washington,  D.  C,  the  normal 
pressure  on  the  lower  joint  of  the  walls  of  the  shaft  is  20.2  tons 
per  sq.  ft,  (280  lbs.  per  sq.  in.),  and  the  maximum  pressure  brought 
upon  any  joint  under  the  antion  of  the  wind  is  S5.4  tons  per  sq.  ft 
(350  lbs.  per  sq.  in.).| 

The  pressure  on  the  limestone  piers  of  the  St  Louis  Bridge  was, 
before  completion,  38  tons  per  sq.  ft.  (527  lbs.  per  sq.  in.);  and  after 
completion  the  pressure  was  19  tons  per  sq.  ft.  (273  lbs.  persq.  in.) 
on  the  piers  and  15  tons  per  sq.  ft.  ( I  !I8  lbs.  per  sq.  in. )  on  the  abut- 
ments.^ 

The  limestone  masonry  in  the  towers  of  the  Niagara  Suspension 

*  Id  this  connection  It  Is  convenleDt  to  remember  that  1  ton  per  oqnare  foot  la 
•qalnJent  neerl;  to  14  (exaoUj  13. SB)  ponnda  per  sqo&re  incb. 
f  The  TeabDOKrapb,  Unlvereity  of  IlUnols,  No,  7,  p.  27. 
t  Proo.  loat  of  0.  E.,  vol.  i.  p.  Sll. 

I F.  CoUlngwood,  aaat.  engineer,  In  Trans.  Am.  Boo.  of  C.  E. 
I  Bepoit  of  OoL  T.  L.  Caa«j,  V.  S.  A,,  engineer  Id  charge. 
\  Hlatonr  of  St.  Louis  Bridge,  pp.  870-71. 


ovGoQi^lc 


VBASVBEMEirC   OF    UABONBT.  151 

Bridge  failed  under  36  toos  per  Bq.  ft.,  and  were  taken  down, — ^how- 
ever, the  masonry  was  not  well  executed.* 

At  the  South  Street  Bridge,  Philadelphia,  the  pressure  on  the 
limestone  rubble  masonr;  in  the  pnenmatic  piles  is  15.7  tons  per 
8q.  ft.  (220  lbs.  per  sq.  in. )  at  the  bottom  and  13  tons  per  sq.  It  at 
the  top.  "This  is  uDusnall;  heary,  but  there  are  do  signs  of  weak- 
ness, "f  The  maximum  pressure  on  the  rubble  masonry  (laid  in 
cement  mortar)  of  some  of  the  large  masonry  dams  is  from  11  to  14 
toua  per  sq.  ft.  (154  to  195  lbs.  per  sq.  in.).  The  Quaker  Bridge 
Dam  is  designed  for  a  maximum  pressure  of  16f  tons  per  sq.  ft. 
(230  lbs.  per  sq.  m.)  on  massire  rubble  masonry  in  best  hydranlio 
cement  mortar.  I 

223.  Bafb  FramTe,  In  the  light  of  the  preceding  examples 
it  may  be  assumed  that  the  safe  load  for  the  diflereat  classes  of 
jnasonry  is  about  as  follows,  provided  each  is  the  best  of  its  chias : 

Concrete S  to  10  toni  per  square  foot. 

Rubble lOtolO    •'     " 

Squared  itoae, 18  to  80    "     "        "       " 

Limeetone  ashlar,     ....  SO  to  29    "     "        "       " 

Qnolte  ashlar, 80    "     "       "       " 

824.  IfunrsncnrT  or  Huovbt.  The  method  of  determining 
the  quantity  of  masonry  in  a  strncture  is  frequently  governed  by 
trade  rules  or  local  custom,  and  these  vary  greatly  with  locality, 
Kasons  have  voluminous  and  arbitrary  rules  for  the  measurement 
of  masonry;  for  example,  the  masons  and  stone-cutters  of  Boston 
at  one  time  adopted  a  code  of  thirty-six  complicated  rules  for  the 
measurement  of  hammer-dressed  granite.  As  an  example  of  the 
indefinitenees  and  arbitrariness  of  all  such  rules,  we  quote  the  follow- 
ing, which  are  said  to  be  customary  in  Pennsylvania :  "  All  open- 
ings less  than  3  feet  vide  are  counted  solid.  All  openings  more 
than  3  feet  wide  are  taken  out,  but  18  inches  is  added  to  the 
running  measurement  for  every  jamb  built.  Arches  are  counted 
solid  from  the  spring  of  the  arch,  and  nothing  allowed  for  arching. 
The  comers  of  buildings  are  measured  twice.  Pillars  lees  than  3  feet 
square  are  counted  on  three  sides  as  lineal  measurement,  multiplied 
by  the  fourth  side  aud  depth;  if  more  than  3  feet,  the  two  opposite 

•  Trans.  Am.  Soc.  of  C.  E.,  vol.  z*U.  pp.  aM-LL  i  Ibid.,  tAiO-pfi.  SOB-ft. 

t  Slnfftatrrbv  ^f*"!  voL  xlz.  p.  TB. 


ovGoQi^lc 


15S  erONB  MABONBT.  [cHAP.  VII. 

Bides  are  taken;  to  each  side  18  inches  for  each  jamb  is  added  to- 
lineal  measurement  thereof;  the  whole  multiplied  by  the  smaller  side- 
and  multiplied  by  the  depth." 

A  well-eetablished  custom  has  all  the  force  of  law,  unless  dua 
notice  is  given  to  the  contrary.  The  more  definite,  and  therefore- 
better,  method  ia  to  measure  the  exact  solid  contents  of  the  masonry, 
and  pay  accordingly.  In  "  net  meaenrement"  all  openings  are  de- 
ducted; in  "gross  measurement"  no  openings  are  deducted. 

The  quantity  of  masonry  is  usually  expressed  in  cubic  yards. 
The  perch  is  oocasiooally  employed  for  this  purpose;  but  since  the^ 
supposed  contents  of  a  peich  vary  from  16  to  25  cubic  feet,  the  term 
is  very  properly  falling  into  disuse.  The  contents  of  a  maaonry 
structure  are  obtained  by  measuring  to  the  neat  lines  of  the  design. 
If  a  wall  ia  built  thicker  than  specified,  uo  allowance  is  made  for  the- 
masoQry  outside  of  the  limiting  lines  of  the  design;  but  if  the- 
masonry  does  not  extend  to  the  neat  lines,  a  deduction  is  made  for- 
the  amount  it  falls  short.  Of  course  a  reasonable  working  allow- 
ance must  be  made  when  determining  whether  the  dimensions  of 
the  masonry  meet  the  specifications  or  not. 

Id  engineering  construction  it  is  a  nearly  uniform  custom  Uy 
measure  ^I  masonry  in  cubic  yards;  but  in  architectural  construc- 
tion it  is  customary  to  measure  water  tables,  string-courses,  etc., 
by  the  lineal  foot,  and  window-silla,  lintels,  etc.,  by  the  square  foot. 
In  engineering,  all  dressed  or  cut-stone  work,  such  as  copings,  bridge- 
seats,  cornices,  water-tables,  etc,  is  paid  for  in  cubic  yards,  with 
an  additional  price  per  square  foot  for  the  surfaces  that  are  dressed, 
cut,  or  bush- hammered. 

226.  Clasaifloation  of  Sailroad  Sasonry.  The  stone  masonry 
required  in  the  construction  of  a  railroad  is  usually  classified  about, 
as  follows:  first-class  masonry,  second-class  masonry,  rubble  masonry 
(sometimes  called  third-class  masonry,  §  309),  rubble  maaonry  laid 
dry  (§  214),  stone  paving,  slope-waits,  and  riprap.  Firet-class  ma- 
sonry is  equivalent  to  ashlar  (§§  200-7) ;  thia  head  generally  includes- 
bridge  abutments  and  piers  of  the  lai^r  class,  and  arch  culverts  of 
greater  span  than  10  feet.  Sometimes  second-class  masonry  is  speci- 
fied aaaquared-atone  maaonry  (§§308-12),  and  aometimes  as  superior 
rubble  (§§  313-17);  it  is  used  in  less  important  structures  than  first- 
olass  masonry. 

Frequently  specifications  recognize  also  the  following  classifica- 


ovGoQi^lc 


BSnUATES   OF  COST.  Ids' 

tioD  :  first-class  arch  masonr;,  second^cIasB  arch  masonry,  first-claas 
bridge-pier  masonry,  seoond-class  bridge-pier  masonry,  and  pedestal 
masonrj.  The  quality  of  work  thus  specified  is  the  same  as  for  firat- 
clase  and  second-class  masonry  respectively,  the  only  difference 
being  peculiar  to  the  form  of  the  masonry  etructare,  as  will  be  dis- 
cussed in  succeeding  chapters.  The  specifications  foreacbstmctnre^ 
should  give  the  quantities  of  each  kind  of  masonry. 

For  complete  specifications  for  railroad  masonry,  see  Appendix  L 

S26.  ESTDUTU  OF  Cora  07  HuOHBT.  The  following  estimateB- 
of  the  cost  of  masonry,  from  Trautwine's  Engineer's  Pocket-book,* 
ftre  pronounced  by  experts  to  be  as  accurate  as  such  averages  can 
be  stated,  since  every  item  is  liable  to  great  variation.  The  estimates, 
are  based  on  the  assumption  that  a  mason  receives  13.50  and  a 
laborer  12.00  per  day  of  8  hours, 

237.  "  <kiiarrTing.f  After  the  preliminary  expenses  of  purchas- 
ing the  site  of  a  good  quarry,  cleaning  off  the  surface  earth  and 
disintegrated  top  rock,  and  providing  the  necessary  tools,  trucks, 
cranes,  etc.,  the  total  net  expenses  tor  getting  out  the  rough  stonev 
for  masonry  ready  for  delivery  may  be  roughly  estimated  thus: 
Stones  of  such  size  as  two  men  can  readily  lift,  measured  in  piles, 
will  cost  per  cubic  yard  from  i  to  J  the  daily  wages  of  a  quarry 
laborer.  Large  stones,  ranging  from  ^  to  1  cubic  yard  each,  got  out 
by  blasting,  from  1  to  3  daily  wages  per  cubic  yard.  Larger  stones, 
ranging  from  1  to  IJ  cubic  yards  each,  in  which  most  of  the  work 
must  be  doue  by  wedges  in  order  that  the  individual  stones  shall 
come  out  in  tolerably  regular  shape  and  conform  to  stipulated  dimen- 
sions, from  2  to  4  daily  wages  per  cubic  yard.  The  lower  prices  ar& 
low  for  sandstone,  while  the  higher  ones  are  high  for  granite.  Under 
ordinary  circumstances,  about  1^  cubic  yards  of  good  sandstone  can 
be  quarried  at  the  same  cost  as  1  of  granite — or,  in  other  words, 
calling  the  cost  of  granite  1,  that  of  sandstone  will  be  i;  hence  the 
means  of  the  foregoing  limits  may  be  regarded  as  rather  full  prices 
for  sandstone,  rather  scant  for  granite,  and  about  fair  for  limestonfr  - 
or  marble. 

228.  "  Sreanng.t     ^^  t;he  first  place,  a  liberal  allowance  should 
be  made  for  waste.     Even  when  the  stone  wedges  out  handsomely 
on  all  sides  in  large  blocks  of  nearly  the  required  sfaape  sud  siz^ 
*  Publlahed  by  pennUslon. 
f  See  Note  1,  Appendix  II. 
t  Bee  Nolea  2  and  3,  Appendix  IL 


ovGoQi^lc 


164  BTONE   HABONBT.  [CHAF.  VIL 

from  ^  to  :J  of  the  rongb  block  will  generally  not  more  than  cover 
waste  of  dressing.  In  moderate-sized  blocks  (say  ayersging  aboat 
^  a  cubic  yard  each)  got  ont  by  blasting,  from  i  to  ^  will  not  be 
too  much  for  atone  of  medium  character  ae  'to  straight  splitting. 
The  last  allowance  is  about  right  for  well-ecabbled  dressing.  The 
smaller  the  stones  the  greater  must  be  the  allowance  for  waste.  In 
large  operations  it  becomes  expedient  to  have  the  Btones  dressed,  as 
far  as  possible,  at  the  qoany,  in  order  to  diminish  the  cost  of  tiana- 
portation,  which,  when  the  distance  is  great,  constitutes  an  impor- 
tant item — especially  when  hj  land  and  on  common  roads. 

289.  "  Ashlar.  Average  size  of  the  stones,  say  5  feet  long,  Z 
feet  wide,  and  1.4  feet  thick — or  two  such  stones  to  a  cubic  yard. 
Then,  supposing  the  stone  to  be  of  granite  or  gneiss,  the  cost  per 
«abic  yard  of  ashlar  facing  will  be : 

"Oetting  out  the  stone  from  Uie  quan;  by  blBstlng,  allow- 
ing i  for  WMte  In  drsMliig,  H  cubic  yards  at  $3.00 

per  yard (4  00 

Dressing  14  aq.  ft  of  face  at  86  ceals, 4  W 

Dresaliig  S2  aq.  ft.  of  beds  and  Joints  at  18  cents,    ...      fi  8S 

Net  cost  of  the  dressed  stone  at  the  quany,  .    .    .  (18  36 

'            HaullDg  (say  1  mfle),  loading,  and  unloading,    ....  1  20 

Mortar,  ssy 40 

Laying,  including  scaffold,  hoisting  machinery,  etc,      .  3  00 

Net  cost. tai  8ft 

Fn>flt  to  coDtiactor,  aay  10  per  cent 8  28 

Total  coHt  per  cubic  yard, |SS  14 

"Dreediig  will  cost  more  if  the  faces  are  to  he  rounded  or 
moulded.  If  the  stones  are  smaller  than  we  have  assumed,  there 
will  be  more  square  feet  per  cubic  yard  to  be  dressed.  If,  in  the 
foregoing  case,  the  stones  be  perfectly  well  dressed  on  all  sides,  in- 
eluding  the  back,  the  cost  per  cubic  yard  would  be  increased  about 
tlO;  and  if  some  of  the  sides  be  curved,  as  in  arch  stones,  say  112 
or  tl4;  and  if  the  blocks  be  carefully  wedged  out  to  given  dimen- 
sions, (16  or  $1S.  Under  these  conditions  the  net  cost  of  the 
dressed  atone  at  the  quarry  will  be  (36,  (31,  and  (35  per  cubic  yard, 
respectively. 

"If  the  stone  be  sandstone  with  good  natural  beds,  the  getting 
out  may  be  pat  at  (3.00  per  cubic  yard.     Face  dressing  at  36  cents 


ovGoQi^lc 


XABKBT   PBI02    OF   STONE.  155 

pot  sq,  iL,  say  t3.S4  per  cu.  yd.  Beds  and  iointa  at  13  centa  per 
sq.  fC,  say  t6.76  per  cu.  yd.  The  total  cost,  then,  is  119.55  instead 
of  t25.14  for  granite,  and  the  net  cost  117.00  instead  of  the  t21.86 
per  en.  yd.  for  granite.  The  total  coet  of  large,  well-scabbled,  ranged 
sandBtone  masonry  in  mortar  may  be  taken  at  about  tlO  per  ca.  yd. 

230.  "  Rubble.  With  stones  ayeraging  about  ^  cubic  yard  each, 
and  common  labor  at  tl  per  day.  the  coat  of  granite  rubble,  such 
as  is  generally  used  as  backing  for  the  foregoing  ashlar,  will  be  about 
as  follows : 

Oetitng  out  the  Blone  from  the  quany  by  blasting,  allow- 
ing i  for  vBst«  in  Bcsbbling,  If  cu.  yds.  ®  $8.00,      .  (8  48 

Hauling  1  mile,  loading  and  unloading 1  20 

Uortar  (2  cu.  ft,  or  1.6  struck  bushels  of  quicklime,  and 

10  cu.  ft.  or  8  atruck  buahela  of  sand  or  gravel,  and  ' 

mixing) 1  50 

Scabbliug,  laying,  scafloldlng,  hoisting  machinery,  ola.,  a  SO 

Net  coat tS  88 

Profit  to  contractor,  my  16  per  cent., 1  80 

Total  coat  per  cubic  yard t9  98 

"  Common  rubble  of  small  stones,  the  average  size  being  snch  as 
two  men  can  handle,  costs  to  get  it  out  of  the  quarry  about  80  cts, 
per  yard  of  pile,  or,  to  allow  for  waste,  say  $1.00.  Hauling  1  mile, 
^1.00.  It  can  be  roughly  scabbled  and  laid  for  tl.20  more.  Mortar, 
as  above,  tl.50.  Total  net  cost,  t4.70;  or  with  15  per  cent,  profit, 
(5.40,  at  the  above  wages  for  labor." 

231.  HUKXT  Fbicx  of  Stohs.  The  average  market  qnotationa 
to  builders  and  contractors  for  the  year  1888  were  about  as  follows, 
f.o.b.  (free  on  board)  at  the  quarry : 

Qranlte— rough (0  40  to  $0  60  per  cubic  foot. 

Limestone — common  rubble.  ...  1  00  "  1  50  percublcyard. 

"           good  lauge  rubble,    .    .  1  !»  "  3  00    "       "        " 

bridge  stone 08  "  10  per  cubic  foot 

•■            dlmennIoQ  Blone.  ...  25  '*  85    "       "         " 

copings 20  "  85    "       "        " 

Sandstone, OT  "  1  00  percublcyard. 

232.  Con  OF  HuontT.*  IT.  8.  Public  Buildings.  The  following 
table  gives  the  average  contract  price  during  the  past  few  years  for 
cutting  the  stone  for  the  United  States  government  buildings  ;t 

•  For  additional  data,  Be«  Notes  1^  Appendix  n,pBgeaBU-(6.  ' 

t  Amerloan  Anbltoot,  toL  zxit  pp.  t,  7. 


ovGoQi^lc 


BTONB  KASONBT. 


[OHAP.  TIL 


TABLE  IB. 
Stokb  for  V.  e 

.  Public  Buiu>n>as. 

KnmovBWAOE. 

Omum*. 

HID. 

Max. 

MiD. 

Mu. 

UIu. 

Hu. 

B«i»  and  Joints,  pw  aq.  R. .. . 

•«s 

•"15 

OS 
76 

et 

I  10 

•«- 

-iJ 

"ll 

-^ 

40 
50 

BO 
20 

The  following  table  shows  the  coatract  price  for  the  maBonry  (^ 
the  United  States  public  boildiogB  : 

TABLE  19. 
Cost  or  Habosbt  in  U.  S.  Public  BuiLsraw. 


Ctt.  P». 

Harriabun,  Va.... 

Cinclnoatn  0 

Denver,  Col 

Pittsburgh.  Pa.... 

168S 

to  90- 

1B84 
1888 
1880 

leSG 

70 

Columbus,  0 

•■           "        granite 

Pittsburgh.  Pa. . . . 

1H8« 

SO 

"    andeut-stonegmnfte,  BVg. 

IRftO 

1  60 

l«tt« 

a  00 

minga.  Stony  Point.  Mich.,  aandslone.  .[Fort  Wayne,  Ind.. 

18HB 

1  B» 

Rock-face  aehlar,  granite,  relainlag  wall. . . 

MempbU,  Tenn... 

1880 

1  00 

Dreaaed  coping,         "                ■•            ■■   ... 
White  s«i<rBtone.-fumlihed  only 

Dallas.  Tei 

188.1 

85 

DouDcII  Bluffs,  la. 

188.1 

1  91 

•■    "           "             ■■        «7erag8  bid. . . . 

1885 

a  19 

"    ••           "      limestone,  lowest  bid 

1H8B 

1  87 

"     "           '•             •■         average  bid 

Bock-face  asblar,  cut  and  moulded  trim- 

188S 

asfr 

1884 

a  41 

Cut  and  moulded,  Bedford  limestone 

[x)ul8vi!le.  Kv. . . . . 

188.-! 

2  0» 

IRW 

a  M 

"      "          "         limestone Hannibal,  Mo 

18SS 

1  ea 

S  27 

■*      "          "         groDite,  superstructure.. 

Pittsburgh.  Pa 

'"" 

8  0» 

jvGooi^le 


ACTUAL  COST.  1S7 

233.  Bailrosd  Huonry.  The  following  are  the  average  prices 
-actually  paid  in  the  couetraction  of  the  Cincinnati  Sonthera  Itail- 
road,  in  1873-77:* 

Elm-claas  bridge  maaonty,  per  CO.  7d. 910  88 

Beccnd-class  bridge  masonry,  Hieenwnt,  per  cu.  yd.,  .  7  40 

Second-class  bridge  masonry,  dry,  per  cu.  yd.,    ....  7  08 

FlrsUclasa  arcb  masoDiy,  per  cu.  yd 11  24 

Second-clBSs  arch  masonry,  in  eonanl,  per  cu.  yd.,  ...  8  01 

Second-class  arch  masonry,  dry,  per  cu.  yd., 7  7S 

Brick-work  in  tunnels,  per  cu.  yd., 8  SO 

Brick-work  in  buildings,  percu.  yd., 7  00 

Baz-culvert  masonry,  in  cem&nl,  per  cu.  yd., 4  89 

Box-culvert  masonry,  dry,  per  cu.  yd. 483 

Concrete,  per  cu.  yd., SS8 

Slopewalla,  percu.  yd., 4  41 

Btone  paving,  per  cu.  yd. 941 

234.  Tunnel  Hasonry.  The  following  are  the  average  priceef 
"paid  in  1883-S7  on  the  now  Croton  Aqnednct  tnnnel  which  supplies 
New  York  Oity  with  water.  The  mortar  waB  3  Band  to  1  Bosendala 
•Dement. 

1  Dimension-stone  masonry  (granite), 943  00 

Brick-work  lining,  per  cu.  yd., 10  14 

Brick-work  backing,  per  cu.  yd., 8  49 

Rubble  masonry,  lining,  per  cu.  yd. 0  OS 

Concrete  lining,  SstonetolRosendale  cement, percu.yd.,  S  67 

Concrete  lining,  6  stone  to  1  Rosendale,  per  cu.  yd.,    ,     .  S  IS 

Concrete  backing,  8  stone  to  I  Bosendale,  per  cu.  yd.,      ,,  4  78 

Concrete  backing,  6  stone  to  I  Roaendate,  per  cu.  yd.,     .  4  23 

Une- hammered  face  (3-cut)  for  cut  stone,  per  sq..  ft.,  .    .  84 

Rough-pointed  face  for  cut  atone,  per  sq.  ft,,  ...  .  50 
Additional  for  all  kinds  of  masonry  laid  In  Portland 

cement  mortar,  3  to  1,  per  cu.  yd 1  78 

Additional  for  all  kinds  of  masonry  laid  In  Rosendale 

cement  mortar,  1  to  1,  per  cu.  yd. 1  30 

336.  Bridge-pier  IDuonry.  The  following  are  the  details  of  the 
-Qost,  to  the  contractor,  of  heavy  flrat-class  limestone  masonry  for 
bridge-piers  erected  in  1887  by  a  prominent  contracting  firm  : 


ovGoQi^lc 


158  STONE  HASONBT.  [CHAP,  VII. 

Cost  of  stone  (puTCbased), (4  SO 

Sand  ukd  cemmt, S3 

FreigbC. 1  78 

Laying 140 

:             Handling  materi&k, 6S 

I^erricks,  tools,  etc 40 

Buperintendence,  oflice  expense,  eto C8 

Total  coat  per  cubic  yard $9  M 

The  followmg  data  coDcerning  the  cost  in  1887  of  graoitQ  pien 
—two  fifths  cnt-fitone  facing  and  three  fifths  rubble  backing — are 
farniehed  by  the  same  firm.    The  rock  was  rerj  hard  and  tough. 
Facing  ,'— 

Quarrying,  Including  opening  quarry, %Z  16 

Cutting  to  dimensions, 6  75 

Laying, 1  7t 

Transportation  S  mllM,  superinteadence,  and  general  ex- 
penses  20S 

Total  cost  per  cubic  yard tl4  81 

Backing:— 

Quarrying, $8  10 

I>ressiiig 8  eO 

Laying,       , 1  7S 

Bundries, 3  05 

Total  coat  per  cubic  yard, |10  50 

The  first-class  limestoae  masonry  in  the  piers  of  the  bridges 
across  the  Miseouri  at  Flattsmonth  (1879-80)  cost  the  company 
118.60  per  cubic  yard,  exclusire  of  freight,  engineering,  expenses, 
and  tools.*  The  cost  of  flret-clafls  masonry  in  smaller  piers  usually 
ranges  from  $12  to  tl4  per  cabic  yard. 

At  Chicago  in  188?  the  contract  price  for  the  masonry  in  bridge 
piers  and  abutments  was  about  as  follows :  OoDcrate,  1  Portland 
cement,  3  sand,  6  broken  stone,  19.00  per  en.  yd.;  oonorete,  1 
natural  cement,  3  sand,  5  broken  stone,  16.00  per  on.  yd.;  atone 
facing  and  coping,  $30.00  per  cu.  yd. 

236.  Aroh-cnlvert  Xasoury.  The  following  are  the  details  of 
the  cost  of  the  sandstone  arch  culvert  (613  cu.  yds.)  at  Ifichols 
Hollow,  on  the  Indianapolis,   Decatur  and  Springfield  Bailroad, 

*  Report  ot  tlie  Chief  Engineer,  Geo.  S.  UotIboil 


D.qitizeabyG00l^lc 


ACTUAL  COST. 


16t 


bnilt  in  1887.  Scale  of  wages  per  day  of  10  hours — foreman, 
♦3.50 ;  cutters,  $3.00  ;  mortar  mixer,  $1.50 ;  laborer,  $1.25  ;  water- 
boy,  50  cents ;  carpenters,  $2.50.  f 

TABLE  17. 


d® 

Oo«r. 

TowL 

cS^d. 

XatarieUi.— 

Stone— 618  CO.  yda.  of  sandstone 
Oemect— 180  bbls.  QeniiMi  Portlao 

40   •■     English      " 
80    "     Louisville  " 

$B1BS0 
88  so 

»8  17  = 
96  = 

$419  SO 
ISO  00 
iS8  78 

M 

$1.S39  25 

$1,870  48 
11  00 
SS89 
11  75 

$3  BO 

aaUTis.— 

etc. 

$1,445  62 

$2  8$ 

$884  87 
4SS  66 
121  72 
11  76 
87  60 
14  68 
7  70 

$0  OS 

$1082  08 

Prntty 

$80  00 

$0  05 

QXAMD  Total  : 

$2,507  60 
1,S2S  26 

$4,086  85 

338.  Summary  of  Cost  The  following  table,  compiled  from  a 
large  amoant  of  data,  will  be  coDvenient  for  hasty  reference.  Of 
course  any  Bach  table  must  be  used  with  caution,  since  such  items 
are  subject  to  great  Tariation. 

t  D*tB  tnrnlBlied  by  Edwin  A.  HfU,  chief 


ovGoQi^lc 


BTONB  HASOKBT. 
TABLE  18. 

BuiOtABT  OF  COBT  OF  UaBONBT. 


Arch  maaonrr,  flnt-ckas 

Arcb  masonry,  second-class  (In  cement). 

BoK-culTert  masonrv,  In  cement 

Brick  masonry  (see  g  258) 

Bridge  masonry,  flrsl-clasa 

Bridge  masonry,  aecoud-claaa  0"  cement^ 

Concrete 

Coping 

Dimenslon-BtoDe  masoniy,  granite 

Paving 

Slope- wall  masoniy 

Stjuared-atone  maaoniy 

Riprap , 

Rubble,  flrat-claaB 

Hubble,  eecond-clam  On  oerooDt) 


ovGoQi^lc 


-  / 

CHAPTEE  VIII. 
/ 

BRICK  MA80NBT. 

239.  HdSTAX.  Lime  mortar  is  generally  employed  for  brick 
tnaeonry,  porticalarly  JQ  architectural  coiiBtructioDs.  Many  of  the 
leading  railroads  lay  all  brick  masonry  in  cement  mortar,  and  the 
practice  ehoald  be  followed  more  generally.  The  weakest  part  of 
a  brick  structure  is  the  mortar.  The  primary  purpose  of  the 
mortar  is  to  form  an  adheBive  substance  between  the  bricks ;  the 
second  is  to  form  a  cushion  to  distribute  the  pressure  uniformly 
over  the  snrfoce.  If  the  mortar  is  weaker  than  the  brick,  the 
ability  of  the  masonry  to  resist  direct  compression  is  thereby  ooa- 
siderably  reduced.  For  the  reason,  see  g  13;  for  the  amoont,  see 
the  Table  19,  page  164. 

If  the  strains  upon  a  wall  were  only  those  arising  from  a  direct 
pressure,  the  strength  of  the  mortar  would  in  most  cases  be  of 
comparatively  little  importance,  for  the  crushing  strength  of  aver- 
age quality  mortar  is  far  higher  than  the  dead  load  which  under 
ordinary  circumstances  is  put  upon  a  wall ;  but,  as  a  matter  of  fact, 
in  buildings  the  load  is  rarely  that  of  a  direct  crushing  weight, 
other  and  more  important  strains  being  developed  by  the  system  of 
oonstruction.  Thus  the  roof  tends  to  throw  the  walls  out,  the  raft«ra 
being  generally  so  arranged  as  to  produce  a  couBiderable  outward 
thrust  against  the  wall.  The  action  of  the  wind  also  produces  a  side 
«train  which  is  practically  of  more  importance  than  either  of  the 
others.  In  many  eases  the  contents  of  a  building  exert  an  outward 
thrust  upon  the  walls  ;  for  example,  barrels  piled  against  the  sides 
of  a  warehouse  produce  an  outward  pressure  against  the  walls. 

In  many  brick  coostructioue  the  use  of  cement  mortar  is  abso- 
lutely necessary — as,  for  example,  in  tall  chimneys,  where  the  bear- 
ing is  BO  small  that  great  strength  of  the  cementing  material  is 
required. 

240.  The  thickness  of  the  mortar-joints  should  be  about  i  to  f 
of  an  inch.  Thicker  joints  are  very  common,  but  should  be  avoided. 
Jf  the  bricks  are  even  fairly  good,  the  mortar  is  the  weaker  part  of 


ovGoQi^lc 


16S  BRICK    UASON&T.  [CHAF.  Till. 

the  vail ;  hence  the  less  mortar  the  better.  Beeides,  a  thin  layer 
of  mortar  is  stronger  nnder  compreesion  than  a  thick  one  (see  §  16). 
The  joints  should  be  ae  thin  as  is  consistent  with  their  insuring  a  uni- 
form bearingandallowingrapidwork  in  spreading  the  mortar.  Tha 
joints  of  outside  valk  should  be  thin  in  order  to  decrease  the  dis- 
integration by  weathering.  The  joints  of  inside  walls  are  usoally 
made  from  f  to  ^  inch  thick. 

Brick  should  not  be  merely  laid,  but  every  one  should  be  rubbed 
and  pressed  down  in  such  a  manner  as  to  f orca  the  mortar  into  the 
pores  of  the  bricks  and  produce  the  maximum  adhesion  ;  with  quick- 
setting  cement  this  is  still  more  important  than  with  lime  mortar. 
For  the  beet  work  it  ia  specified  that  the  brick  shall  be  laid  with  a 
"  shove  joint ;"  that  is,  Uiat  the  brick  shall  first  be  laid  so  as  tO' 
project  over  the  one  belowj  and  be  pressed  into  the  mortar,  and 
then  be  shoved  into  its  final  position. 

Lime  mortar  is  liable  to  work  out  of  the  joints,  owing  to  the 
action  of  the  elements  and  to  changes  of  tomperatnre.  Henoe  it 
ia  customary  either  (1)  to  lay  the  face  in  mortar  containing  more 
lime  than  that  used  for  the  interior,  or  (2)  to  lay  the 
face  in  a  mortar  containing  more  or  less  cement,  or 
I  (3),  in  rare  cases,  to  point  the  joints  with  neat  cement 
''  mortar.  Whatever  thekindof  mortarneed,thefiniBh 
of  the  face  of  the  joint  is  important  The  most 
Pm  47  durable  joint  is  finished  as  shown  in  Fig.  47,  although, 
onfortnnately  for  durability,  it  is  customary  to  make  the  slope  in 
the  opposite  direction. 

841.  Since  brick  have  great  avidity  for  water.  It  is  best  to 
dampen  them  before  laying.  If  the  mortar  is  stlfi  and  the  brick 
dry,  the  latter  absorb  the  water  so  rapidly  that  the  mortar  does 
not  set  properly,  and  will  cmmble  in  the  fingers  when  dry.  Neglect 
in  this  particular  ia  the  cause  of  most  of  the  failures  of  brick-work. 
Since  an  excess  of  water  in  the  brick  can  do  no  harm,  it  is  best  te 
thoroughly  drench  them  with  water  before  laying.  lime  mortar  ia 
sometimes  made  very  thin,  so  that  the  brick  will  not  absorb  all  tho 
water.  This  process  interferes  with  the  setting  of  the  mortar,  and 
partionlarly  with  the  adhesion  of  the  mortar  to  the  brick.  Watery 
mortar  also  contracts  excessively  in  drying  (if  it  ever  does  dry), 
which  causes  undue  settlement  and,  possibly,  cracks  or  distortion. 
Wetting  the  brick  before  Uying  will  also  remove  the  duat  from  tha 
surface,  which  otherwise  would  prevent  perfect  adhesion. 


ovGoQi^lc 


BOKD.  163 

243.  Son>.  The  bricke  used  in  a  given  wall  being  of  uniform 
size  are  laid  according  to  a  uniform  syBtem,  which  ie  called  the  bond 
of  the  brick-work.  As  in  ashlar  masonry,  bo  in  brick-work,  a  header 
is  a  brick  whose  length  lies  perpendicuW  to  the  face  of  the  wall; 
and  a  atretcher  is  one  whose  length  lies  parallel  with  the  face. 
Brick  should  be  made  of  sach  a  size  that  two  headers  and  a  mortar- 
joint  will  ooonpy  the  same  length  as  a  stretcher. 

S4S.  Bnglirii  Bond.     This  consists  in  laying  entire  oonrses  of 

headers  and  stretchers,  which  some- 

;  times  alternate,  as  in  Fig.  48;  but 
■_  generally  only  one  course  of  headers 
IS  laid  for  every  two,  three,  four,  etc., 
1  courses  of  stretchers.  Id  ordiziary 
'  practice  the  custom  is  to  lay  four  to  six 
courses  of  stretchers  to  one  of  head- 
ers. The  stretchers  bind  the  walls 
together  lengthwise ;  the  headers,  crosswise.  The  proportionato 
numbers  of  the  courses  of  headers  and  stretchers  should  depend  on 
the  relative  importance  of  transverse  and  longitudinal  strength. 
The  proportion  of  one  course  of  headers  to  two  of  stretchers  is  that 
which  gives  equal  tenacity  to  the  waU  lengthwise  and  crosswise. 

In  building  brick-work  in  English  bond,  it  is  to  be  borne  in 
mind  that  there  are  twice  as  many  vertical  or  side  joints  in  a  course 
of  headers  as  there  are  in  a  course  of  stretchers ;  and  that  anless 
in  laying  the  headers  great  care  be  taken  to  make  these  Joints  very 
thin,  two  headers  will  occupy  a  little  more  space  than  one  stretcher, 
and  the  correct  breaking  of  the  joints — exactly  a  quarter  of  a  brick-^ 
will  be  lost.  This  is  often  the  case  in  carelessly  built  brick.work,  in 
which  at  intervals  vertical  joints  are  seen  nearly  or  exactly  above 
each  other  in  successive  courses. 

344.  ^smiih  Bond.     This  consists  of  a  header  and  a  stretcher 
alternately  in  each  course,  so  placed 
that  the   outer  end  of  each   header  '-   ~ 
lies  on  the  middle  of  a  stretcher  in  ' 
the    course    below    (Fig.    49).      The  : 
number    of    vertical    joints    in    each  : 
conrse  is  the  same,  eo  that  there  is  no 
risk  of  the  correct  breaking  of   the 
joints  by  a  quarter  of  a  brick  being  ^°-  "-'^'•-  »»"■ 

lost;  and  the  wall  presents  a  neater  appearance  than  one  built  in 


ovGoQi^lc 


164  BKICK  HA50NBY.  [CHAP.  TIIL 

English  bond.  The  Utter,  however,  vhen  correctly  built,  ia 
stronger  and  more  stable  than  Flemish  bond. 

24S,  Hoop-iron  Bond.  Pieces  of  hoop-iron  are  frequently  laid 
Sat  in  the  bed-joints  of  brick-vork  t«  increase  its  longitudinal 
tenacity,  abont  %  inches  of  the  ends  of  each  piece  being  bent  down 
and  inserted  into  the  vertical  joints.  Although  thin  strips  of  iron 
are  generally  employed,  it  would  be  better  to  use  thicker  pieces  ;  the 
value  of  the  iron  for  this  purpose  depends  wholly  upon  the  rigidity 
of  the  ends  which  are  turned  down,  and  this  will  vary  about  as 
the  square  of  the  thickness.  The  strip  of  iron  should  bo  nearly 
«s  thick  as  the  mortar-joint.  This  means  of  strengthening  masonry 
is  frequently  employed  over  openings  and  to  connect  interior  brick 
vails  with  stone  fronts. 

346.  C01I7BE88ITB  8TBEV0TK  (U  BEICK  KASOITBT.  Experi- 
4nents  at  Watertown,  Uass.,  with  the  United  States  testing-machine, 
upon  piers  1%  inches  square  and  from  1  ft  4  in.  to  10  ft  high,  gave 
cesalts  as  follows  :* 


TABLE  10. 
Stsenoth  or  Bbice  Mabodht  GoicrA.BED  vtith  that  c 

TBS  UORTAB. 


'  THE  BniCK  AKD 


i 

1 

r 

1 

or  TB«  8T«i(IOIH 

il 

8 

MlB, 

BUz 

HtAO. 

16 

1 

I 
1 
8 

1,908 
l.MB 

1,411 

1.972 
a.  544 

134 

18S 

103 
163 
545 
631 
8,4BS 

.06 

.18 

.10 

.11 

.00 
.13 

.17 

X 

2  mortar  (1  lime.  8  sand),  1  Rosea- 

8 

2  mortar   (1   lime,  8  saod},  1   Port- 

1  Hosendale  cement.  2  sand 

1  PorllnDd  cement,  3  sand 

fi 

.10 

.37 

4.7 

1 

3,875 

"Tests of  Uetala,  el 


"  for  the  fear  ending  Jane  SO,  1S84,  pp.  6e~tai, 


ovGoQi^lc 


COMPRESSIVE   STBEIfGTH.  165 

The  brick  had  an  average  strength  of  nearly  15,000  lbs.  per  sq. 
in.,  tested  flatwise  between  steel.  The  mortar  was  14}  months  old 
when  it  was  tested.  The  piers  were  built  by  a  common  mason,  with 
only  ordinary  care;  and  they  were  from  a  year  and  a  half  to  two 
years  old  when  tested.  Their  strength  varied  with  their  height; 
and  in  a  general  way  the  experiments  show  that  the  strength  of  a 
prism  10  ft.  high,  laid  in  either  lime  or  cement  mortar,  is  about  two 
thirds  that  of  a  1-foot  cube.  A  deduction  derived  from  so  few 
experiments  (22  in  all)  is  not,  however,  conclosive.  The  dlflerent 
lengths  of  the  piers  tested  occurred  in  about  equal  numberB.  The 
piers  began  to  show  cracks  at  one  half  to  two  thirds  of  their  ultimate 
strength. 

In  attempting  to  draw  conclnsions  from  any  experiments,  it 
must  be  borne  in  mind  continually  that  the  result  of  a  single  trial 
may  possibly  be  greatly  in  error.  In  this  case  this  pi'ecaution  is 
very  important,  since  the  difference  between  experiments  apparently 
exactly  alike  was  in  some  cases  as  much  as  50  per  cent.  A  great 
variation  in  the  results  is  charaoteristic  of  all  experiments  on  stone, 
brick,  mortar,  etc.  Except  on  the  ground  of  a  variation  in  ex- 
periments, it  is  difBcult  to  explain  why  mortar  No.  4  ia  weaker  than 
No.  2,  while  the  masonry  is  stronger  ;  or  why  the  masonry  of  No.  5 
is  stronger  than  that  of  No.  7. 

Of  course  the  apparent  efficiency  of  the  masonry,  as  given  in  th© 
table,  depends  upon  the  manner  in  which  the  strengths  of  the 
brick  and  mortar  were  determined,  as  well  as  upon  the  method  of 
testing  the  masonry.  For  example,  if  the  brick  had  been  tested  on 
end  the  apparent  efficiency  of*  the  masonry  would  have  been  con- 
siderably more  ;  or  if  the  mortar  had  been  tested  in  thin  sheets  tho 
strength  of  the  masonry  relative  to  that  of  the  mortar  would  not 
have  been  so  great.  • 

247.  Some  German  experimentsf  gave  results  as  in  the  table 
*It  Hhnuld  be  mentlotiedihat  the  mortar  with  which  these  piera  were  built  appears 
.  to  be  mncb  wealier  than  similar  monar  under  lllie  Ronditlotis.  (Compare  page  79, 
and  pages  136.  166, 188, 1B7  of  the  Keportof  Tostsof  MotaU,  etcmade  at  Watertown 
tn  1864.)  Ordinarily,  mortar  is  eight  to-  ten  times  as  strong  In  compreeslon  as  in 
tension,  whereas  the  flret  six  mortars  In  the  preceding  tabic  were  but  little  atrimger 
In  compression  Uian  snch  mortar  should  have  been  in  tension.  The  officer  in  charge 
IS  "  ucubte  to  offer  an;  eiplBoatioQ.  The  cemeut  was  bought  on  the  market ;  the 
maker's  name  is  not  known.  The  cement  was  not  tested."  However,  the  raperi- 
ments  are  consistent  with  themBclres,  and  therefore  show  relative  atretigths  correctly. 

t  Van  Nostrand'B  Engin'g  Hag.,  vol.  zzxlv.  p.  iHO,  trom  the  Abstraota  of  tba 
Inst,  of  C.  E.  (London),  vol.  79,  p,  378. 


ovGoQi^lc 


166  BEICK  KA80NBY.  [CHAP,   VIIL 

below.     It  is  not  stated  how  the  strength  of  the.  brick  or  of  the 
masonry  was  determined.*    The  term  cemeot  refers  to  Portland 
cement.    According  to  the  building  regalations  of  Berlin,  the  safe 
]oad  for  brick  masonry  is  one  tenth  of  the  results  in  the  table. 
TABLE  SO. 
RxLATiTB  Strenoth  OF  Bkick  ASS  Bbice  Habohbt. 


IAtuuoi  Cbohh- 
DT  Buck,  im  vaa. 

KmovBBioK. 

iffiS: 

TUme, 

SBwd. 

1  Cement, 
IBand. 

6,8«0 
8.6«0 
a,9S0 
3,769 
2,617 
1,190 

8.870 
1.620 
l.SSO 
1,210 
1,150 
680 

2.S0O 
1,760 
1.890 
1,820 
1,260 
570 

2.B60 
2,020 
1.610 
1,620 

1.440 
650 

8.410 

,  1.860 

1,710 

1,060 

760 

Porous  perforatod 

Table  1!)  shows  conclnsiTely  that  the  strength  of  brick  masonry 
is  mainly  dependent  upon  the  strength  of  the  mortar.  An  in- 
crease of  50  per  cent,  in  the  strength  of  the  brick  shows  no 
appreciable  effect  on  the  strength  of  the  masonry.  Notice, 
however,  that  the  masonry  in  the  fifth  line  of  Table  19  is  70  per 
cent,  stronger  than  that  in  the  first,  dne  to  the  difference  between 
a  good  Portland  cement  mortar  and  the  ordinary  lime  mortar. 
In  Table  20  notice  that  brick  laid  in  a  1  to  3  Portland  cement 
mortar  is  nearly  50  per  cent,  stronger  than  in  a  1  to  2  lime 
mortar.  Similar  experiments  f  show  that  masonry  laid  in  mortar 
composed  of  1  part  Bosendale  cement  and  2  parts  aaitd  is  56 
per  cent,  stronger  than  when  laid  in  mortar  composed  of  1  part 
lime  and  i  parts  sand.  A  member  of  the  Institute  of  CiTil  Engi- 
neers (London)  says^  that  brick-work  laid  in  lime  is  only  one  fourth 
as  strong  as  when  laid  in  clear  Portland  cement.  Probably  the  dif- 
ference in  durability  between  cement  mortar  and  lime  mortar  is 
considerably  greater  than  their  difference  in  strength. 

*  U  the  Btrength  ot  the  brick  (In  edj  line  of  ths  table)  be  repreeented  by  100,  that 
ol  lbs  tUBaoDrf  iB  44,  48,  66,  uid  63,  reapectlrelr,  which  BhowB  that  the  Talnee  In  Um 
table  were  not  derived  direOtj/  from  experiments. 

f  Report  of  BiperlTneDts  on  Building  MatedaU  for  the  Clt;  of  Philadelphia  with 
the  U.  S.  tABttng-machlue  at  Watertown.  Mbbb.,  pp.  82,  S3. 

t  Pioc  Inat.  of  C.  E.,  vol.  ztU.  p.  441. 


ovGoQi^lc 


TBAKBTEBBE  8TB&N0TH.  167 

246.  Preainie  allowed  in  Practice.  The  pressure  at  the  base  of 
a  brick  ehot-tower  in  Baltimore,  246  feet  high,  is  estimated  at  6^ 
tons  per  sq.  ft.  (abont  90  lbs.  per  sq.  in.).  The  preseure  at  the  base 
of  a  brick  chimney  at  Qlasgow,  Scotland,  468  ft.  high,  is  estimated 
at  9  tons  per  sq.  ft.  (about  125  Ibe.  per  sq.  in.);  and  in  heavy  galra 
this  is'increased  to  15  tone  per  sq.  ft.  (310  lbs.  per  sq.  in.)  on  the 
leeward  aide.  The  leading  Chicago  architects  allow  10  tons  per  sq. 
ft.  (140  lbs.  per  sq.  in.)  on  the  best  brick-work  laid  in  1  to  2  Port- 
land cement  mortar ;  8  tons  for  good  brick-work  in  1  to  2  Rosendale 
vement  mortar ;  and  5  tons  for  ordinary  brick-work  in  lime  mortar. 
Ordinary  brick  piers  have  been  known  to  bear  40  tons  per  sq.  ft 
(660  lbs.  per  sq.  in.)  for  sereral  days  without  any  sign  of  failure. 

Tables  19  and  20  appear  to  show  that  present  practice  is  very 
wanBervatiVB  with  regard  to  the  pressure  allowed  on  brick  masonry. 
According  to  Table  19  (page  164),  the  ultimate  strength  of  the  best 
fonck  laid  in  ordinary  lime  mortar  is  110  tons  per  sq.  ft. ;  if  laid 
in  1  to  3  Portland  cement  mortar,  180  tons ;  and  by  Table  30  (page 
166)  the  strength  of  ordinary  brick  in  1  to  2  lime  mortar  is  100  tons 
per  sq.  ft.,  and  in  1  to  3  Portland  cement  mortar  140  to-n?.  Prom 
the  above,  it  wonld  seem  that  reasonably  good  brick  laid  in  good 
lime  mortar  should  be  safe  under  a  preseure  of  20  tons  per  sq.  ft., 
and  that  the  best  brick  in  good  Portland  cement  mortar  should  be  safe 
under  30  tons  per  sq.  ft.  The  nominal  pressure  allowed  upon  brick 
mosoniy  depends  upon  the  kind  of  materials  employed ;  the  degree  of 
care  with  which  it  is  executed  ;  whether  it  is  for  a  temporary  or  per- 
manent, an  important  or  unimportant  structure ;  and,  it  may  be 
added,  the  care  with  which  the  nominal  maximum  load  is  estimated. 

249.  TUHSTZBai  StbevoTE  07  Bbios  KasOHKT.  Masonry  is 
seldom  employed  where  any  strain  except  direct  compression  will 
come  upon  it,  but  sometimes  it  is  subject  to  transverse  strain.  The 
transverse  strength  of  brick-work  depends  theoretically  upon  the 
tensile  strength  of  the  brick  and  upon  the  adhesion  and  cohesion 
of  the  mortar,  but  practiwilly  the  strength  of  the  mortar  deter- 
mines the  strength  of  the  masonry.  For  example,  in  the  case  of 
a  high  wall  whose  upper  portion  is  overthrown  by  a  lateral  force  or 
pressure  of  any  kind,  the  failure  is  due  either  (1)  to  the  breaking  of 
the  adhesion  in  the  bed -joints  and  of  the  cohesion  of  the  side-joints, 
or  (2)  to  the  rupture  of  the  mortar  in  the  bed-jointa  alone.  The 
latter  method  of  failare,  however,  is  improbable,  since  the  cohesion 


ovGoQi^lc 


168  BBICK    UASOKBT.  [OHAP.  TIIL 

of  cement  mortars  is  alwajs  much  greater  than  their  adbeeion  (com- 
pare §§  134  and  137);  and  hence,  in  estimating  the  resistance  of  the 
wall  to  OTertnrning,  it  becomes  necessary  to  fix  valnea  for  hotli  the 
coheaive  and  adhesive  strength  of  the  mortar  at  the  time  when  the 
stracture  is  first  esposed  to  the  action  of  the  lateral  force  or  pres- 
sare,  and  also  to  ascertain  the  relative  areas  of  beds  and  side-jointa- 
in  the  assumed  section  of  ruptore.  In  good  brick-work  the  aggro* 
gate  area  of  the  side-joints,  in  any  section  parallel  to  the  beds,  will 
amount  to  abont  one  seventh  of  the  total  area  of  such  section. 
Hence,  when  the  masonry  is  liable  to  be  subjected  to  transverse- 
strains  the  adhesive  strength  of  the  mortar  is  more  important  than 
its  cohesive  strength. 

The  adhesion  of  mortar  to  brick  or  stone  has  already  been  dis- 
cussed (§  137).  While  the  experiments  uniformly  show  a  relatively 
-  low  adhesive  power,  it  is  well  known  that  when  old  walls  are  de- 
molished the  adhesion  of  even  common  lime  mortar  is  found  to  be 
very  considerable.  Although  the  adhesive  power  of  mortu  may  be 
small  as  compared  with  its  tensile  strength,  good  brick  masonry  has. 
a  considerable  transverse  strength. 

Experiments  made  under  the  author's  direction  *  indicate  that 
bnck  beams  bonded  aa  regular  masonry  have  a  modulns  of  rapture 
equal  to  about  twice  the  tensile  strength  of  the  mortar  when  built 
with  ordinary  care,  and  about  three  times  when  built  with  great  care. 
When  the  b^ms  are  ooDstmcted  as  piers,  i.  0.,  with  no  interlocking 
action,  the  modolns  of  mptnre  is  about  equal  to  the  tensile  strength. 
of  the  mortar. 

260.  Application.  To  illustrate  the  practical  application  of  thft 
fact  that  brick-work  has  a  transverse  strength,  let  it  be  reqnired  to 
compute  the  strain  w|iich  may  come  upon  a  lintel,  or  girder  used 
to  support  a  brick  wall  over  an  opening.f 

Let  H  =  the  height,  in  feet,  of  the  wall  above  the  opening ; 
J7h  =  the  height,  in  feet,  of  the  wall  that  produces  a  maxi- 
mum strain  on  the  lintel ; 
H,  =  the  height,  in  feet,  of  the  masonry  when  it  will  just 
support  itself  over  the  opening ; 
- '  S=  the  span,  in  feet ; 

t  =  the  thickness,  in  feet,  of  the  wall ; 

*  Tek  Twcssoa&^PB,  CnlTerslt;  ot  lUlnois,  No.  T  (IBSa-eS),  pp.  3&-ST. 

f  The  principloottbe  following  compnt&tionB  Is  from  hnoHtoiiBliaJBngiaemitif 
(IiODdou),  vol.  xlT.  pp.  Uand  T2. 


ovGoQi^lc 


TRAN6TEBSE    STRENQTH.  169 

S  =  the  modulus  of  rupture,  in  pounds  per  square  inoh, 
of  the  brick-work ; 

W=  the  weight,  in  ponnds,  of  a  cubic  foot  of  the  wall. 
H'  varies  from  100  to  140  pounds,  and  for  conven- 
ience is  here  assumed  to  be  144 ;  the  error  is  always 
on  the  safe  side ; 

3f,  =  the  bending  moment  on  the  lintel,  in  pounds  per 
square  inch. 

Oonsider  the  masonry  as  a  beam  fixed  at  both  ends  and 
loaded  uniformly.  Then,  by  the  prinoiples  of  the  resistance  of 
materials,  when  the  masonry  is  just  self-supporting,  one  twelfth 
of  the  weight  of  the  wall  above  the  opening  multiplied  by  tb» 
span  is  equal  to  one  sixth  of  the  tensile  strength  multiplied  btf 
tbe  thickneBS  and  also  the  sqnare  of  the  depth  of  the  wall. 
The  weight  of  tbe  wall  above  the  opening  is  WSH.t.    Hence 


■^{WSS,t)8=\{UiR)tH:, (1) 


(3> 


Notice  that '  the  weight  of  the  wall  over  any  given  opening 
increases  as  tbe  height,  while  tbe  resistance  increases  as  the 
square  of.  the  height.  The  height  for  which  the  masonry  is 
self  supporting  is  given  by  equation  (2),  for  a  height  greater 
than  H,  the  masonry  would  be  more  than  self-supporting ;  and 
for  a  height  less  than  H,  the  masonry  would  need  extraneous 
support. 

To  find  tbe  height  of  the  wall  producing  a  maximum  stress 
in  tbe  lintel,  notice  that  the  bending  moment  on  ttie  lintel  is 
equal  to  the  moment  of  the  load  mimia  tbe  moment  of  the 
resistance  of  tbe  brick-work  over  the  opening ;  or,  in  algebruo 
language, 

Mt  =  ij(WSffl)  S  -  i{U4R)t3\ 


ovGoQi^lc 


170  BBICS  ItASONBT.  [CHAP.  TIIL 

DiflenntUtiiig  the  above  ^oatioQ,  regarding  Mi  and  H  as  the 
Tariables,  and  finding  the  raazimam  ralae  of  ^  in  the  lunal  ira;, 
veget 


The  foot  that  the  Talne  of  H^  in  equation  (3)  ia  one  half  of 
that  of  H,  in  eqnation  (3),  shows  that  the  maximam  stress  on 
the  lintel  occurs  when  the  height  of  the  wall  is  half  of  its  self- 
BUpporting  height,  at  which  time  one  half  of  the  wall  will  he 
self-snp porting  and  one  half  will  reqnirs  eztraneons  support. 
Or,  in  other  words,  the  greatest  stress  on  a  lintel  dne  to  a  wall 
of  any  height  will  not  be  greater  than  that  dne  to  a  distributed 
load  of 

iH^fi.S/  =  iir^S'(  =  nearly  18 —  pounds.    .     (4) 

SSI.  Example^.  To  apply  the  above  formula,  aesume  that  it  ia 
proposed  tc  out  a  10-foot  opening  through  an  old  brick  wall,  and 
that  it  is  desirable  to  know  whether  the  brick-work  will  be  eelf-eup- 
porting,  the  wall  rising  40  feet  above  the  top  of  the  opening.  Sub- 
stituting the  above  data  in  equation  (2)  gives 

40  =  -^-;    or    «  =  1.25  lbs.  per  eq.  In. 

Hence,  to  be  self-supporting  across  the  opening,  the  wall  must  be 
-capable  of  supporting  a  tensile  strain  of  1.25  pounds  per  sqnare 
inch.  It  would  be  poor  lime  mortar  that  would  not  bear  eight  or 
ten  times  this.  Notice  that  if  the  wall  were  only  4  feet  high  over 
the  opening,  instead  of  40  feet,  as  above,  the  strength  required 
would  be  13.5  pounds  per  square  inch. 

For  another  illustration,  assume  that  a  brick  wall  1  foot  thick 
is  to  be  built  over  a  10-foot  opening,  and  that  we  wish  to  know 
whether  a  timber  10  inchee  deep  and  12  inches  wide  will  sustain  the 
-load.  Assuming  the  beam  as  being  fixed  at  the  ends,  the  timber 
will  sustain  a  uniformly  distributed  load  of  10  tone  with  a  deflection 
of  one  twelfth  of  an  inch.  This  is  equivalent  to  the  entire  weight 
-of  the  wall  when  14  feet  high.     If  the  wall  is  to  be  carried  higher 


ovGoQi^lc 


TBANBTERSE   STBEyflTS.  171 

-th&Q  thia,  the  girder  most  be  supported  temporarily,  or  time  must 
be  givea  for  the  mortar  to  set  ' 

However,  before  the  wall  ia  14  leet  abOTe  the  openiDg,  the  brick- 
vork  at  the  bottom  will  hare  attained  some  strength,  and  therefore 
the  load  on  the  girder  will  not  be  as  great  as  above.  The  average 
strength  of  the  brick-work  will  always  be  at  least  the  average  between 
the  strength  at  the  top  and  the  bottom  ;  that  ie,  the  average  strength 
will  always  be  more  than  half  of  that  at  the  bottom.  Since  10  tone 
is  the  maximum  load  allowed  on  the  girder,  and  since  the  maximum 
load  which  comes  upon  it  is  half  of  the  entire  weight  of  the  masonry 
above  the  opening,*  the  timber  will  receive  its  maximum  load  when 
the  wall  is  twice  14  feet,  or  28  feet,  above  the  opening.  The  masonry 
m^y  be  ran  up  28  feet  without  necessitating  any  extraneous  support 
for  the  lintel,  provided  time  enough  is  allowed  for  the  mortar  to 
develop  the  average  tensile  strength  found  by  substituting  in  (4) 
the  maximum  load  allowed  on  the  girder,  and  solving  for  R.  Mak- 
ing thia  Bubetitution  gives 


,  from  which  R  =  0.90  lb.  per  sq.  in. 

With  an  averse  strength  of  0.90  lb.  per  eq.  id.,  the  wall  will 
'become  self-supporting  when  55  feet  above  the  opening. 

252.  Custom  differs  as  to  the  manner  of  estimating  the  pressure 
•on  a  girder  due  to  a  superincumbent  mass  of  masonry.  One  extreme 
consists  in  assuming  the  masonry  to  be  a  fluid,  and  taking  the  load 
on  the  lintel  as  the  weight  of  all  the  masonry  above  the  opening. 
The  opposite  extreme  consists  in  assuming  the  pressure  to  be  the 
weight  of  the  masonry  included  in  a  triangle  of  which  the  open- 
ing is  the  base  and  whose  sides  make  45°  with  this  line.  Both  of 
these  methods  diSer  materially  from  the  one  diacussed  above  ;  and 
neither  is  defensible.  As  the  wall  is  several  days  in  building,  the 
masonry  first  laid  attains  considerable  strength  before  the  wall  is 
-completed;  and  hence,  owing  to  the  cohesion  of  the  tnortar,  the  final 
weight  on  the  girder  can  not  be  equal  to  or  compared  with  any  fluid 
Tolume. 

The  principle  involved  in  the  second  method  would  be  applicable 

*  Bm  diocuHloD  o(  equation  (8),  above. 


ovGoQi^fc 


178  BRICK  MA80NET.  [OHAP.  TIIL 

to  a  wall  composed  wholly  of  perfectly  smooth  bricks.  In  a  dry 
vail,  the  angle  which  the  aide  linee  make  with  the  base  would 
depend  upon  the  bond  and  upon  the  relative  length  and  breadth  of 
the  bricks.  Assaming  the  boundary  lines  to  make  an  angle  of  45° 
2^ 
S 

which  takee  account  of  the  transverse  strength  of  the  masonry,  i.  e., 
the  frictional  and  tensile  resistance  of  the  walL  If  S  is  relatively 
large  and  S  is  email,  this  fraction  will  be  more  than  nnity,  under 
which  conditions  the  second  method  is  safe.  But  if  R  is  small  and 
ti  is  large,  then  this  fraction  is  lesa  than  one,  which  shows  that 
under  these  conditions  the  second  method  is  unsafe. 

The  method  of  §  250  is  quite  simple  and  perfectly  general.  The 
substantial  correctness  of  this  method,  illustrated  in  §  351,  is 
proven  by  the  fact  that  large  openings  are  frequently  cut  through 
walls  without  providing  any  extraneous  support;  and  also  by  the 
fact  that  walls  are  frequently  supported  over  openings  on  timbers 
entirely  inadequate  to  carry  the  load  if  the  masonry  did  not  have 
considerable  strength  as  a  beam.  The  discussion  in  §  351  also  makes 
clear  why  frequently  a  temporary  support  is  sufficient.  After  the 
masonry  has  been  laid  a  short  time,  the  strength  of  the  mortar 
causes  it  to  act  as  a  beam.  The  discussion  also  shows  the  advantage 
of  using  cement  mortar  (or  better,  quick-settiog  cement  mortar) 
when  it  is  desired  that  the  masonry  shall  early  become  self'Sup> 
porting. 

253.  Keasubekeitt  of  Bkick-wobk.  The  method  of  determin- 
ing the  quantity  of  brick  masonry  is  governed  by  voluminous  trade 
rules  or  by  local  customs,  which  are  even  more  arbitrary  than  those 
for  stone  masonry  (§  224,  which  see). 

The  quantity  is  often  computed  in  perches,  but  there  is  no  uni- 
formity of  understanding  as  to  the  contents  of  a  perch.  It  ranges 
Irom  16}  to  25  cubic  feet. 

Brick-work  is  also  often  measured  by  the  square  rod  of  exterior 
surface.  Ko  wall  is  reckoned  as  being  less  than  a  brick  and  a  half 
in  thickness  (13  or  13}  inches),  and  if  thicker  the  measurement  is 
still  expressed  in  square  rods  of  this  standard  thickness.  Unfor- 
tunately the  dimensions  adopted  for  a  square  rod  are  variable,  the 
following  values  being  more  or  less  customary  :  16}  feet  square  or 


ovGoQi^lc 


DATA  FOB  ESTIMATES.  173 

272^  square  feet,  18  feet  Bqnare  or  334  square  feet,  and  16^  square 
feet. 

The  volume  of  a  brick  is  scmetimes  used  as  a  unit  in  stating  the 
contents  of  a  wail.  The  conteata  of  the  wall  ore  found  by  multi- 
plying the  number  of  cubic  feet  in  the  wall  by  the  number  of  brick 
vhioh  it  is  assumed  make  a  cubic  foot ;  but  as  the  dimenBions  of 
brick  vary  greatly  (see  §  G2),  this  method  is  objectionable.  A  cubic 
ioot  is  often  aesnraed  to  contain  20  brick,  and  a  cubic  yard  600. 
The  last  two  quantities  are  frequently  used  interchangeably,  although 
the  assumed  volume  of  the  cubic  yard  is  thirty  times  that  of  the 
cubic  foot 

Brick-work  is  also  sometimes  measured  by  allowing  a  certain 
number  of  brick  to  each  superficial  foot,  the  number  varying  with 
ihe  thickness  of  the  wall.  A  4-inch  wall  (thickness  =  width  of  one 
brick)  is  frequently  assumed  to  contain  7  bricks  per  sq.  ft. ;  a  9-inch 
wall  (thicknesB  =  width  of  two  bricks),  14  bricks  per  aq,  ft;  a  13- 
inch  wall  (thickness  =  width  of  three  bricks),  21>  bricks  per  sq.  ft, 
etc;  the  number  of  brick  per  eqoare  foot  of  the  face  of  the  wall 
being  seven  times  the  thickness  of  the  wall  in  terms  of  the  width  of 
a  brick. 

264.  The  only  relief  from  such  arbitrary,  uncertain,  and  indefi- 
nite customs  is  to  specify  that  the  masonry  will  be  paid  for  by  the 
cubic  yard, — gross  or  net  measurement,  according  to  the  structure 
or  the  preference  of  the  engineer  or  architect 

In  engineering  the  uniform  custom  is  to  measure  the  exact  solid 
contents  of  the  wall. 

265.  Data  roB  Estduteb.  ITumber  of  Brick  Required.  Since 
the  size  of  brick  varies  greatly  (g  62),  it  is  impossible  to  state  a  rule 
which  shall  be  equally  accurate  in  all  localities.  If  the  brick  be  of 
standard  size  (8^x4x2^  inches),  and  laid  with  i-  to  |-inch  joints, 
a  cubic  yard  of  masonry  will  require  about  410  brick ;  or  a  thousand 
brick  will  lay  about  2i  cubic  yards.  It  the  joints  are  i-  to  |-inch,  a 
cubic  yard  of  masonry  will  require  about  495  brick;  or  a  thousand 
brick  will  layabout  2  cubic  yards.  With  face  brick  (8}  x  H  X  H 
inches)  and  ^-inch  joints,  a  cnbic  yard  of  masonry  will  require  about 
496  brick;  or  a  thousand  face  brick  will  lay  about  2  cubic  yards. 

In  making  estimatea  for  the  number  of  bricks  required,  an  al- 
lowance must  be  made  for  breakage,  and  for  waste  in  cutting  bnck 
to  fit  angles,  eto.    With  good  brick,  in  mataiva  work  this  allowance 


ovGoQi^lc 


174  BBIOE  HASOKST.  [OHAP.  TUt. 

need  not  exceed  lotZ  per  ceot.;  but  in  buildings  3  to  5  per  cent, 
is  uone  too  much. 

266.  Amonnt  of  Kortsr  Eeqaiz«d.  The  proportion  of  mortar 
to  brick  irill  Tsry  with  tbe  size  of  the  brick  and  with  the  thickness 
oi  the  joints.  With  the  standard  size  of  brick  (8^x4x2^  inches), 
«  cubic  yard  of  masonry,  laid  with  i-  to  J-inch  joints,  will  require 
from  0.35  to  0.40  of  a  cnbic  yard  of  mortar;  or  a  thousand  brick 
will  require  0.80  to  0.90  of  a  cubic  yard.  If  the  joints  are  ^  to  | 
inch,  a  cubic  yard  of  masonry  will  require  from  0.25  to  0,30  of  a 
cubic  yard  of  mortar;  or  a  thousand  brick  will  require  from  0.45  to 
0.55  of  a  cubic  yard.  If  the  joints  are  i  of  an  inch,  a  cubic  yard  of 
masonry  will  require  from  0.10  to  0.15  of  a  cubic  yard  of  mortar; 
or  a  thousand  brick  will  require  from  0.15  to  0.20  of  a  cubic  yard. 

With  the  above  data,  and  the  table  on  page  88,  the  amount  of 
oemmt  and  sand  required  for  a  specified  number  of  brick,  or  for  a 
given  number  of  yards  of  masonry,  can  readily  be  determined. 

257.  Labor  Bequlred.  "  A  bricklayer,  with  a  laborer  to  keep  him 
supplied  with  materials,  will  lay  on  an  average,  in  common  house> 
walls,  about  1,500  bricks  per  day  of  10  working  hours;  in  the  neater 
outer  faces  of  brick  buildings,  from  1,000  to  1,200;  in  good  ordinary 
street  fronts,  from  800  to  1,000 ;  and  in  the  very  finest  lower-stoiy 
&ces  used  in  street  fronts,  from  160  to  300  according  to  the  number 
of  angles,  etc.  In  phiin  massive  engineering  work,  he  should  aver- 
age about  2,000  bricks  per  day,  or  4  cu.  yds.  of  masonry ;  and  in 
large  arches,  about  1,500,  or  3  cu.  yds."  • 

In  the  United  States  Government  buildings  the  labor  per  thou- 
sand, inclading  took,  etc,  is  estimated  at  seven  eighths  of  the  wages 
for  ten  hours  of  mason  and  helper. 

Table  21,  opposite,  f  gives  the  actual  labor,  per  cubio  yard,  re- 
quired on  some  large  and  important  jobs. 

268,  Cmt.  In  the  conatfnction of  the  Cincinnati  Southern  R  B., 
during  1873-77,  the  brick  lining  of  tunnels  oost  tS.  50  per  co.  yd. ; 
brick-work  in  buildings,  t7.00.t  The  average  price  paid  for  the 
brick-work  in  the  new  Croton  Aqueduct  tunnel,  which  supplies  New 
York  Oity  with  water,  was,  including  everything,  (10.14  per  cu.  yd. 


*Tnntwlne'B  Englneer'a  Pooket-Book,  p.  DTI. 

t  Trans.  Am.  8oc.  ot  C.  £. 

tBeportof  tbe  CbleC  Engineer,  Dec.  1,  I3TT,  Exhibit  & 


ovGoQi^lc 


BPEC1PICATI0N8. 

TABLE  31. 
liAxat  BBQCntzD  voR  Brick  MABonrt 


LouTKur  AKo  DMcnumoH  o*  nm  HMomr. 

DA-nm^me  tiM 

Hlgfa  Bridge  Bulargemeat,  N.  T.  City— 

lining  wall  and  flat  arches  laid  with  Teiy  cIom  Jirinta. 

Wadilngton  (D.  C.)  Aqueduct— 

Cti^lar  coDdnit.  S  feet  In  diameter  with  walU  IS 

0.714 

8t.  LouI«  Water  Worka— 

New  York  Oty  Storage  Reservoir- 
Lining  of  gate-house  walls  and  archee— rough  work. . 

0.8M 

for  Hninic,  woA  |8.4d  for  baoking.    TI10  mortar  th  oompoeed  at 
1  part  BoModalo  utaral  cement  and  S  parts  of  Band.* 

In  Ghic^o  in  1887,  the  price  of  brick  laid  in  lime  in  interior 
■walls  was  about  til  per  tbonsand,  equivalent  to  about  $7  per  en.  yd. 
The  vages  of  masons  were  from  45  to  60  cent?  per  hoar,  and  of 
common  labor  from  20  to  9.5  cents  per  hoar. 

268.  Spioifioatiohb  toe  Brick  HAamnT.  For  BoildingL 
There  is  not  even  a  remote  approach  to  nniformity  in  the  specifica- 
tions for  the  brick -work  of  buildings.  Ordinarily  the  specifications 
for  the  brick  masonry  are  very  brief  and  incomplete.  The  following 
conform  closely  to  ordinary  conetraction.  Of  course,  a  higher  grade, 
of  workmanship  can  be  obtained  by  more  stringent  specificationaf 

The  brick  in  the  exterior  walls  most  be  of  good  qualitj',  hard-burned;  fine, 
compact,  and  uniform  In  texture ;  regular  In  shape,  and  uniform  In  size.}: 
One  fourth  of  the  brick  In  the  Interior  walU  may  be  what  ts  known  m  soft 
or  Mlmon  hrick  (see  3,  g  (MQ.  The  brick  must  be  thoroughly  wet  before 
being  laid.  Tlie  Joints  of  the  exterior  walls  shall  be  from  ^  to  |  Inch  tldck.g 
The  Joints  of  Interior  divl^on-walls  may  be  from  {  to  1  Inch  tldck.  The 
mortar  shall  be  composed  of  I  part  of  freah,  well-slaked  lime  and  3}  to  8  parta 

•  Report  of  the  Aqnednct  CommlBaion,  1888-87,  Table  4. 

t  For  specifications  for  masonry  for  VEuloas  porpoMS,  see  AppokUx  L 

I8eaf  ST,  pageST. 

f  For  the  beat  work,  omit  this  Item  and  Insert  the  following  :  TJu  outMe  aolb 
•AoS  bifaad  ultA  Hit  bat  pnued  Mck  of  uniform  color,  laid  in  eolord  mortar,  vHA 
jeinU  nof  exaadbig  one  aghifi  i)f  an  inch  in  thicktutt.  Face  brick  are  made  a  llttla- 
tuger  ^  flS)  than  oidlaaiy  brtck  to  compensate  tor  tbe  thinner  Joints. 


ovGoQi^lc 


176  BRICK   MASOITBY.  [CHAP.  Till. 

of  clean,  sharp  Band.*  The  lime-paste  and  the  Band  shall  be  thoroughly 
mixed  before  being  uMd.  The  joints  shall  be  veil  filled  with  the  aboTa 
tuortar ;  no  grout  shall  be  used  in  the  vork.  The  bond  must  consiBt  of  flva 
courses  of  stretchere  to  one  of  headers,  and  shall  be  bo  arranged  aa  to  thor- 
oughly bind  the  exterior  and  Interior  portions  of  the  wall  to  each  other. 

The  contractor  must  fumlah,  set  up,  and  take  away  his  own  scaffolding ; 
he  must  build  In  such  strips,  plugs,  blocks,  scantling,  etc.,  as  are  required  for 
securing  the  wood-work ;  and  must  also  assist  in  placing  all  iron-work,  as 
beams,  stairways,  anchors,  bed-plates,  etc.,  connected  with  the  brick-work. 

280.  Por  Bewen.  The  following  are  the  qtecifications  employed, 
in  1885,  in  the  constrnctioD  of  brick  sewers  in  Washington,  D.  G.  : 

"The  brat  quality  of  whole  new  brick,  burned  tiard  entirely  through,  free 
from  injurious  cracks,  with  true  even  faces,  and  with  a  cruBhing  strength  of 
not  less  tlian  5,000  pounds  per  square  inch,  shall  be  used,  and  must  be  thor- 
oughly wet  by  immersion  Immediately  before  laying.  Every  brick  is  required 
Xa  be  laid  in  full  mortar  joints,  on  bottom,  sides,  and  ends,  which  for  each 
brick  is  to  be  performed  by  one  operation.  In  no  case  is  the  joint  to  be  made 
by  working  in  moriar  after  the  brick  has  been  laid.  Every  second  course  shall 
be  laid  with  a  line,  and  Joints  shall  not  exceed  three  eighths  of  on  Incti.  The 
brick-work  of  ttke  arches  shall  be  properly  bonded,  and  keyed  as  directed  by 
the  en^eer.  No  portion  of  the  brick-work  shall  be  laid  dry  and  afterwards 
p«uted- 

"  The  moriar  shall  be  composed  of  cement  and  dry  sand,  fn  the  proportion 
K)t  800  pounds  of  cement  and  2  barrels  of  loose  sand,  thoroughly  mixed  dry, 
and  asufflcient  quantity  of  water  afterwards  added  to  form  a  rather  stiff  paste 
It  shall  be  used  within  an  hour  after  mixing,  and  not  at  all  if  once  set. 

"  The  cement  shall  be  of  the  best  quality,  freshly  burned,  and  equal  in 
«Tery  respect  lo  the  Round  Top  or  Shepardslown  cement,  manufactured  upon 
the  formula  of  the  engineer-commissioner  of  the  District  of  Columbia,  capable 
of  being  worked  for  twenty  minutes  In  mortar  without  toss  of  strength,  and 
shall  be  tested  in  such  maimer  as  the  engineer  may  direct.  After  being  mixed 
with  water,  allowed  to  set  In  air  for  twenty-four  hours,  and  then  immersed  in 
vater  for  rix  days,  the  tensile  strength  must  be  as  follows : 

Neat  cement 95  lbs.  per  sq.  in. 

One  part  cement  and  one  part  sand SS  "     "    "    " 

"      "        "        "    twoparts  "  as '    " 

"      "         "         "    three"      "  12 

"The  sand  used  shall  be  clean,  sharp,  free  from  loam,  vegetable  matter, Or 
Mher  dirt,  and  capable  of  giving  the  above  results  with  the  cement, 

'■  Hie  water  shall  be  fresh  and  clean,  free  from  earth,  dirt,  or  sewenge. 

*  For  masoar;  that  Is  to  be  snbjected  to  a  heavy  pnesnre,  omit  this  Item  and 
Insert  the  following  -.  Ttn  moriar  mtut  be  mntpoitd  qf  1  part  UiwfiiuCa,  1  part  etnwit, 
and  2  parU^dmn,  iharp  tand.  Or,  If  a  heavier  prssgnre  is  to  be  resisted,  spedly 
Uwt  some  parttonlar  grade  of  oement  mortar  Is  to  he  osed.    iSea  liii  MS  and  XtA 


ovGoQi^lc 


8PB0IPICATION8.  177 

"  Tigbt  mortar-boxes  shall  be  provided  by  the  contractor,  and  no  tnoriar 
■hall  be  made  except  Id  such  boxes. 

"  1'he  proportions  given  are  intended  to  form  a  mortar  In  which  every 
putlcle  of  sand  shall  be  enveloped  by  the  cement ;  and  this  result  must  be 
attained  to  the  satisfaction  of  the  engineer  aud  under  his  direction.  The 
thorough  mixing  and  Incorporation  of  all  materials  (preferably  by  mscbiue 
labor)  will  be  Insisted  upon.  If  by  hand  labor,  tiie  dry  cement  and  sand  shall 
be  turned  over  with  sliovels  by  skilled  workmen  not  less  than  six  times  befora 
the  water  is  added.  Afler  adding  the  waier.  the  paste  shall  again  be  turned 
over  and  mixed  with  shovels  by  billed  workmen  not  leas  than  three  limes  be- 
fore it  is  used." 

S61.  for  Archet.  The  spccificatioDs  for  the  brick  arch  masoDry 
on  the  AtohiBOD,  Topeka  and  Santa  Fi  Bailroad  are  as  follows : 

"Tbe  bricks  must  be  of  the  best  quality  of  smooth,  hard-burut,  paving 
bricks,  well  tempered  and  moulded,  of  the  usual  size,  compact,  well  Bbaped, 
free  from  lime,  cracks,  and  olher  imperfect  ions,  and  must  stand  a  pressure 
of  4,000  pounds  per  square  inch  without  crusbing.  No  tats  will  be  allowed 
In  the  work  except  for  making  necessary  closures.  All  bricks  will  be  culled 
on  the  ground  after  delivery,  and  selected  in  ftrlct  accordance  with  these 
•peclflcatlons. 

"The  mortar  must  be  made  of  1  measure  of  good  natural  hydraulic  cement 
and  3  measures  of  clean,  sharp  sand — or  such  other  proportion  as  may  be 
prescribed  by  the  engineer — well  mixed  together  with  clean  water,  In  cle«n 
mortar-beds  constructed  of  boards,  and  must  be  used  immediately  after  befng 
mixed. 

'-  The  brick  must  be  laid  flush  in  cement  mortar,  and  must  be  Iboroughly 
wet  when  laid.  AH  Joints  and  beds  must  be  thoroughly  tilled  with  mortar  so 
as  to  leave  DO  empty  spaces  whatever  In  tbe  masonry  of  the  walls  and  arches, 
which  must  be  solid  throughout.  The  thickness  of  mortar- joints  must  be  as 
follows  1  Id  the  walls  and  In  Ibe  arch  between  biicks  of  tbe  same  ring,  not  lew 
than  three  eighths  of  an  Incb  (|")  nor  more  than  one  half  Inch  (}").  lu  tbe  arch 
between  rings,  not  less  than  one  half  inch  (}")  nor  more  than  five  eij^bths  of 
an  inch  ((").  Each  brick  Is  to  be  driven  into  place  by  blows  of  a  mallet.  Tbe 
bricks  must  be  laid  in  tbe  walls  with  the  ordinary  English  bond,  five  stretcher 
courses  to  one  header  course.  They  must  be  laid  In  the  arch  In  concentric 
rings,  each  lon^tudlnal  line  of  bricks  breaking  joints  with  the  adjoining 
linea  in  tbe  same  ring  and  In  the  ring  under  it.  No  headers  to  be  used  In 
the  arch." 

262.  Bbioe  n.  flitnn  XavOIUT.  Brick  masonry  la  not  mnch 
Dsed,  except  in  the  walla  of  buildings,  in  lining  tnnncU,  and  in  con- 
atrncting  severs,  the  general  opinion  being  that  brick-work  is  in 
every  way  inferior  to  stone  masonry.  This  belief  may  have  been 
veil  fonnded  when  brick  was  made  wholly  by  hand,  by  inexpert 
operatiTe^  and  imperfectly  bnmed  in  the  old-time  kilns,  the  prod- 


ovGoQi^lc 


178  BSICK  HASONBT.  [CHAP.  VIIL 

act  being  then  generally  poor ;  bnt  thinga  have  changed,  and  sinoe 
the  manafactnre  of  brick  haa  become  a  bnBineaa  condccted  on  a 
large  ecale  by  enterprimng  men,  with  the  aid  of  a  variety  of  tnachmee 
and  improved  kilns,  the  product  is  more  r^ular  in  size  and  qoality 
and  stronger  than  formerly.  Brick  is  rapidly  displacing  stone  for 
the  largest  and  best  bnildings  in  the  cities,  particnlarly  in  Chicago 
and  St.  Peterabnig,  where  the  vicissitndes  of  the  climate  try  maaonij 
very  aeverely.  There  are  many  engineering  stmoturee  in  which 
brick  oonld  be  profitably  employed  instead  of  atone ;  as,  for  example, 
the  walla  of  boz-cnlTerte,  cattle-goards,  etc.,  wad  the  less  important 
bridge  piers  and  abntments,  particnlarly  of  highway  bridges. 

Brick-work  is  superior  to  stone  masonry  in  several  respects,  aa 
follows :  1.  In  many  localities  brick  is  cheaper  than  stone,  since 
the  former  can  be  made  near  by  while  the  latter  most  be  shipped. 
2.  As  brick  can  he  laid  by  less  skillfnl  masona  than  stone,  it  costs 
less  to  lay  it.  3.  Brick  is  more  easily  handled  than  stone,  and  can 
be  laid  vrithoat  any  hoisting  apparatas.  4.  Brick  requires  less  fit- 
ting at  corners  and  openings.  S.  Brick  masonry  is  less  liable  to 
great  weakness  throogh  inaccnrate  dressing  or  bedding.  6.  Brick- 
work resists  fire  better  than  limestone,  granite,  or  marble,  sand- 
stone being  the  only  variety  of  stone  that  can  compare  with  brick 
in  this  respect.  7.  Good  brick  stands  the  effect  of  weathering  and 
of  the  acids  in  the  atmosphere  better  than  sandstones,  and  in  dura- 
bility even  approaches  some  of  the  harder  stones  (see  §§  31-33). 
8.  All  masonry  tails  when  the  mortar  in  its  joints  disintegrates  or 
becomes  dislodged;  therefore  brick  masonry  will  endnre  the  vicisei- 
tndes  of  the  weather  as  well  as  stone  masonry,  or  even  better,  since 
the  former  nsuaUy  haa  thinner  joints. 

Brick-work  is  not  as  strong  as  ashlar  masonry,  but  costs  less ; 
while  it  is  stronger  and  costs  more  than  ordinary  rnbble. 

863.  BeiOX  XAHmT  IxrasTloira  to  WatBB.  It  sometimes  be- 
comes necessary  to  prevent  the  percolation  of  water  through  brick 
walls.  A  cheap  and  effective  process  has  not  yet  been  discovered, 
and  many  expensive  trials  have  proved  failures.  The  following 
account*  givee  the  details  of  two  experiments  that  were  entirely  snc- 
cessfnl. 

"  The  face  walls  of  the  back  bays  of  the  gate-houses  of  the  new 

•  Atattaet  of  A  pi^er  by  Wn.  L.  DMibom,  in  Tnu.  Am.  Soo.  of  C.  E.,  Ttd.  I 
IV.MS-8- 


ovGoQi^lc 


lUSONBT  IHPBE7IO08  TO  VA.TBB.  179 

Croton  reaerroir,  located  north  of  Eighty-sixth  Street,  in  Gentnl 
Park,  New  York  City,  were  bnilt  of  the  best  qnality  of  hard-hnmt 
brick,  laid  in  mortar  compoeed  of  hydranlio  cement  of  New  York. 
[Ulster  Co.  Bosendt^e]  and  sand  mixed  in  the  proportion  of  on» 
measnre'  of  cement  to  two  of  sand.  The  space  between  the  walls  was. 
4  feet,  and  was  filled  with  concrete.  The  face  walls  were  laid  np' 
with  great  care,  and  every  precsation  was  taken  to  hare  the  joints- 
well  filled  and  to  insure  gooid  work.  The  walls  are  12  inches  thick, 
and  40  feet  high;  and  the  bays,  when  full,  generally  have  36  feet  of 
water  in  them. 

"When  the  reserroir  was  first  filled  and  the  water  let  into  the 
gate-honses,  it  was  foand  to  filter  throngh  these  walls  to  a  consider- 
able amount  As  soon  as  this  was  discoTered  the  water  was  drawn 
ont  of  the  bays,  with  the  intention  of  attempting  to  remedy  or  pre- 
Tent  this  infiltration.  After  carefully  consideriug  several  modes  ol 
accomplishing  the  object  desired,  I  [Dearborn]  came  to  the  conclu- 
sion to  try  '  Sylvestei^s  Process  for  Repelling  Moisture  from  Exter 
nal  Walls.' 

"  The  process  consists  in  using  two  washes  or  solations  for  cor- 
ering  the  surface  of  the  walls — one  composed  of  Castile  soap  ani^' 
water,  and  one  of  alnm  and  water.  The  proportions  are  thre&. 
quarters  of  a  ponnd  of  soap  to  one  gallon  of  water,  and  iialf  a  pound 
of  alnm  to  four  gallons  of  water,  both  substances  to  be  perfectly 
dissolved  in  water  before  being  used.  The  walls  should  be  perfectly 
clean  and  dry,  and  the  temperature  of  the  air  not  below  50°  Fahr. 
when  the  compositions  are  applied. 

"The  first,  or  soap-wash,  should  be  laid  on,  when  boiling  hot, 
with  a  flat  brush,  taking  care  not  to  form  a  froth  on  the  brick-work. 
This  wash  should  remain  24  ^ours,  so  as  to  become  dry  and  hard 
before  the  second,  or  slum,  wash  is  applied,  which  should  be  dona 
in  the  same  manner  as  the  first.  The  temperature  of  this  wash,, 
when  applied,  maybe  60°  or  70°  Fahr.;  and  this  also  shonld  remaini 
24  hours  before  a  second  coat  of  the  soap-wash  is  pnt  on.- 
These  coats  are  to  be  applied  alternately  until  the  walls  are  made- 
imperrions  to  water.  The  alum  and  soap  thus  combined  form  an: 
insoluble  compound,  filling  the  pores  of  the  masonry  and  entirely 
preventing  the  water  from  entering  the  walls. 

"Before  applying  these  compositions  to  the  walls  of  the  bays 
tome  experiments  were  made  to  test  the  absorption  of  water  by. 


ovGoQi^lc 


180  BEICK  MABONBT.  [OHAP.  Tilt 

bricks  nnder  pressure  after  being  covered  vitii  these  washes,  in 
order  to  determine  boT  many  coats  the  walls  would  require  to  render 
them  imperrions  to  water.  To  do  this,  a  strong  wooden  box  large 
enough  to  bold  two  bricks  was  made,  pat  together  with  screws,  and 
in  the  top  was  inserted  a  1-inch  pipe  40  feet  long.  In  this  box 
wore  placed  two  bricks,  after  being  made  perfectly  dry,  which  were 
then  covered  with  a  coat  of  each  of  the  waaheB,  as  before  directed, 
and  weighed.  Tbey  were  then  subjected  to  a  column  of  water  40 
feet  high ;  and  after  remaining  a  sufflctent  length  of  time  they  were 
taken  ont  and  weighed  again,  to  ascertain  the  amount  of  water  they 
had  absorbed.  The  bricks  were  then  dried,  and  again  coated  with 
the  washes  and  weighed,  and  subjected  to  pressure  as  before,  this 
operation  being  repeated  nntil  the  bricks  were  found  not  to  absorb 
any  water.  Four  coatings  rendered  the  bricks  impenetrable  under 
the  pressure  of  a  40-foot  head.  The  mean  weight  of  the  bricks  (dry) 
before  being  coated  was  3^  lbs. ;  the  mean  absorption  was  one  half- 
pound  of  water.     A  hydrometer  was  used  in  testing  the  solutions. 

"As  this  experiment  was  made  in  the  fall  and  winter  (1863), 
after  the  temporary  roofs  were  put  on  to  the  gate<house,  artificial 
heat  hod  to  be  resorted  to  to  dry  the  walls  and  keep  the  air  at  a 
proper  temperature.  The  cost  was  10  cents  per  sq.  ft.  As  soon  as 
the  last  coat  bad  become  hard,  the  water  was  let  into  the  bays,  and 
the  walls  were  found  to  be  perfectly  impervious  to  water,  and  they 
remain  so  in  1870,  after  about  6j  years. 

264.  "The  brick  arch  of  the  footway  of  High  Bridge  is  the  arc 
of  a  circle,  29^  feet  radi,ns,  and  is  13  incbee  thick;  the  width  on  top 
is  1''  feet,  and  the  length  covered  is  1,381  feet.  The  first  two 
courses  of  the  brick  of  the  arch  are  composed  of  the  best  hard-burnt 
brick,  laid  edgewise  in  mortar  composed  of  1  part,  by  measure,  of 
hydraulic  cement  of  Kew  York  [Bosendale  natural]  and  2  parts  of 
sand.  The  top  of  these  bricks,  and  the  inside  of  the  granite 
coping  against  which  the  two  top  courses  of  brick  rest,  was  covered, 
when  perfectly  dry,  with  a  coat  of  asphalt  one  half  an  inch  thick, 
laid  on  when  the  asphalt  was  heated  to  a  temperature  of  from  360° 
to  518°  Fahr.  On  top  of  this  was  laid  a  course  of  brick  fiatwise, 
dipped  in  asphalt,  and  laid  when  the  asphalt  was  hot;  and  the  joints 
were  rnn  full  of  hot  asphalt.  On  top  of  this,  a  course  of  pressed 
brick  was  laid  flatwise  in  hydianlio  cement  mortar,  forming  the 
paving  and  floor  of  the  bridge. 


ovGoQi^lc 


HKFLOBBBOBNOK.  181 

"The  area  of  the  bridge  covered  vithaephalted brick  was  23,06fl 
■q.  ft  There  wereiued94,200  Iba.  of  asphalt^  33  bsrrelsofcoaltar, 
10  CO.  yds.  of  Band,  and  93>800  bricks.  The  asphalt  was  the  Trini- 
dad rariety ;  and  was  mixed  with  10  per  cent.,  b;  measure,  of  ooal 
tar,  and  25  per  cent,  of  sand.  The  time  occupied  was  lOd  days  of 
masons,  and  148  days  of  laborers.  Two  masons  and  two  laborers 
will  melt  and  spread,  of  the  first  coat,  1,650  sq.  ft  per  day.  The 
total  cost  of  this  coat  was  5^  oents  per  sq.  ft,  ezclosiTe  of  daty  on 
asphalt 

"  There  were  three  grooves,  2  inches  wide  by  1  inohes  deep, 
made  entirely  across  the  brick  aroh  immediately  under  the  finit 
coat  of  asphalt  thtis  dividing  the  arch  into  four  equal  parts.  The 
grooves  were  filled  with  elastic  paint  cement.  This  arrangement 
was  intended  to  guard  against  the  evil  effects  of  the  contraction  of 
the  aroh  in  winter ;  for,  since  it  was  expected  to  yield  slightly  at 
these  points  and  at  no  other,  the  elastic  cement  would  prevent  any 
leakage  there.  The  entire  experiment  has  proved  a  very  successful 
one,  and  the  bridge  has  remained  perfectly  tight 

"  In  proposing  the  above  plan  for  workiog  the  asphalt  with  the 
.  brick-work,  the  object  was  to  avoid  depending  on  a  large  continuons 
snr&ce  of  asphalt  as  is  usual  in  covering  arches,  which  very  fre> 
quently  cracks  from  the  greater  contraction  of  the  asphalt  than  that 
of  the  masonry  with  which  it  is  in  contact,  the  extent  of  the  asphalt 
on  this  work  being  only  about  one  quarter  of  an  fnch  to  each  brick. 
This  is  deemed  to  be  an  essential  element  in  the  success  of  the  im- 
pervious covering." 

366.  Xriobiscxhoe.  Masonry,  particularly  in  moist  climate 
or  in  damp  phices — as  cellar  walls, — is  frequently  disfigured  by  the 
formation  of  a  white  efflorescence  on  the  surface.  This  deposit 
generally  originates  with  the  mortar,  but  frequently  spreads  over 
the  entire  face  of  the  wall.  The  water  which  is  absorbed  by  the 
mortar  dissolves  the  salts  of  soda,  potash,  magnesia,  etc.,  contained 
in  the  lime  or  cement,  and  on  evaporating  deposits  these  salts  as  a 
white  efflorescence  on  the  surface.  With  lime  mortar  the  deposit 
is  frequently  very  heavy,  particularly  on  plastering ;  and,  usually, 
it  is  heavier  with  natnral  than  with  Portland  cement.  The  efflo- 
resoenoe  sometimes  originates  in  the  brick,  particularly  if  the  brick 
wae  burned  with  Bulphnrous  coal,  or  was  made  from  clay  contain- 
ing lioa  pyritea;  aod  when  the  briok  gets  wet,  the  water  dissolvea 


ovGoQi^lc 


J8S  BBICK   VABOXRY.  [CHAP.  VtlL 

-the  snlphates  of  Umo  and  magnesia,  and  on  evaporatiDg  leaves  tbe 
oiystals  of  these  salte  on  the  sarface.  Frequently  the  effloreecenee 
<m  the  brick  is  due  to  the  absorption  by  the  brick  of  the  impreg- 
nated water  from  the  mortar. 

This  efflorescence  ia  objectionable  because  of  the  unsightly  a|H 
pearaDce  which  it  often  prodnces,  and  also  because  the  cryatalliza- 
tion  of  these  salts  within  the  pores  of  the  mortar  and  of  the  brick 
or  stone  cansee  disint^ration  which  is  iu  many  respects  like  frost 

As  a  preveDtiTe,  Gillmore  recommends*  the  addition  of  100  lbs. 
of  quicklime  and  8  to  12  lbs.  of  any  cheap  animal  fsA  to  each  barrel 
of  cement.  The  lime  is  simply  a  vehicle  for  the  fat,  which  should 
be  thoroughly  incorporated  with  the  limo  before  slaking.  The  ob- 
ject of  the  fat  is  to  saponify  the  alkaline  salts.  The  method  is  not 
entirely  satisfactory,  since  the  deposit  is  only  made  less  prominent 
and  less  effective,  and  not  entirely  remoTcd  or  prevented. 

The  efflorescence  may  be  entirely  prevented,  whatever  its  origin, 
by  applying  Sylvester's  washes  (see  g  263)  to  the  entire  external  anr- 
foces  of  the  wall ;  and,  since  asually  the  efflorescence  is  dne  to  the 
water  absorbed  by  the  mortar,  it  can  generally  be  prevented,  and 
can  always  be  much  diminished,  by  using  mortar  which  is  itself  im-  . 
pervious  to  water  (see  g  141).  The  latter  is  the  cheaper  method, 
particularly  if  the  impervious  mortar  be  used  only  for  the  face  of 
the  joints.  If  the  wall  stands  in  damp  ground,  one  or  more  of  the 
horizontal  joints  just  above  the  surface  sbonld  be  laid  in  imperrious 
mortar,  or  better,  the  brick  for  several  courses  should  be  rendered 
impervious  and  be  laid  in  impervious  mortar  to  prevent  the  wall's 
absorbing  moisture  from  below. 

*  "IlmM,  BjitMlUo  CttamSa,  and  Koitan,"  p.  9B6> 


ovGoQi^lc 


PARTm. 

FOUNDATIONS, 


CHAPTER  IX. 
INTRODHCTORT. 

268,  Dimmion.  The  term  foaDdation  is  ordinarily  nsed  in- 
differan  Jy  for  either  the  lower  contaee  of  a  strnotiire  of  maeoiuy  or 
th«  artiJcial  arrangetneot,  whatever  its  character,  on  which  these 
ooursea  rest  For  greater  cleamess,  the  term  foundation  will  here 
be  restricted  to  the  artificial  arnuigement,  whether  timber  or  mason- 
ry, which  eapporte  the  main  structure  ;  and  the  prepared  enrface 
upon  wliich  this  artificial  structure  rests  will  be  called  the  bed  of 
the  foundation.  There  are  many  cases  in  which  this  distinction 
can  not  be  adhered  to  strictly. 

267.  IMPOETASOE  OF  THE  SUBJECT.  The  foundation,  whether 
for  the  more  important  baildings  or  for  bridges  and  oalverts,  is  the 
meet  critical  part  of  a  masonry  structare.  The  failures  of  works  of 
masonry  due  to  fanlty  workmanship  or  to  an  insufficient  thickness 
of  the  walls  are  rare  in  comparison  with  those  due  to  defective 
foundations.  When  it  is  necessary,  as  so  frequently  it  is  at  the 
present  day,  to  erect  gigantic  edifices — as  high  buildings  or  long- 
span  bridges — on  weak  and  treacherous  soils,  the  highest  constrac- 
tire  skill  is  required  to  supplement  the  weakness  of  the  Datnial 
foundation  by  snch  artificial  preparations  as  will  enable  it  to  snetain 
Buoh  massive  and  costly  burdens  with  safety. 

Probably  no  branch  of  the  engineer's  art  requires  more  ability 
and  skill  than  the  conHtrnotion  of  foundations.  The  conditions 
gOTeming  safety  are  generally  capable  of  being  calculated  with 
M  much  practical  accuracy  in  this  aa  in  any  other  part  of  a  con- 


ovGoQi^lc 


184  TovsnATioss:  niTBODCoroBT.  [chap.  IX. 

Btrnction ;  bnt,  nnfortanately,  pnctice  is  freqnentl;  based  npon 
empirical  mles  rather  than  apon  a  scientific  application  of  fnnda- 
mcDtal  principles.  It  is  nnpardonable  that  any  liability  to  danger 
or  loss  should  exist  from  the  imperfect  comprehension  of  a  snbject 
of  saohrital  importance.  Abihty  is  required  in  determining  the 
conditions  of  stability ;  and  greater  skill  is  required  in  fuLfiiling 
these  conditions,  that  the  coat  of  the  foundation  may  not  be  pro- 
portionally too  great.  The  safety  of  a  stractore  may  be  imperiled, 
or  ite  cost  unduly  increased,  according  as  its  foundations  are  laid 
vith  insufficient  stability,  or  with  provision  for  security  greatly  in 
excess  of  the  requirements.  The  decision  as  to  vbat  general  method 
of  procedure  will  probably  be  best  in  any  particnlar  case  is  a  ques- 
tion that  can  be  decided  with  reasonable  certainty  only  after  long 
experience  in  this  branch  of  engineering ;  and  after  having  decided 
npon  the  general  method  to  be  followed,  there  is  room  for  the 
exercise  of  great  skill  in  the  means  employed  to  secnre  the  desired 
end.  The  experienced  engineer,  even  with  all  the  information 
which  he  can  derive  from  the  works  of  others,  finds  occasion  for  the 
use  of  all  hia  knowledge  and  best  common  sense. 

The  determination  of  the  conditions  necessary  for  stability  can 
be  reduced  to  the  application  of  a  tew  fundamental  principles  which 
may  be  studied  from  a  text-book  ;  but  the  knowledge  required  to 
determine  beforehand  the  method  of  constmction  best  suited  to  the 
case  in  hand,  together  with  its  probable  cost,  comes  only  by  personal 
experience  and  a  careful  atndy  of  the  experiences  of  others.  The 
object  of  Part  III,  is  to  classify  the  principles  employed  in  con- 
structing fonndations,  and  to  give  such  brief  accoanta  of  actual 
practice  as  will  illastrato  the  applications  of  these  principles. 

288.  Pus  OF  PboPO>ED  HVKUmaa.  In  a  general  way,  soils 
may  be  divided  into  three  classes  :  (1)  ordinary  soils,  or  those  which 
are  capable,  either  in  their  normal  condition  or  after  that  condition 
has  been  modified  by  artificial  means,  of  sustaining  the  load  that  is 
to  be  brought  upon  them  ;  (3)  compressible  soils,  or  those  that  are 
incapable  of  directly  supporting  the  given  pressure  with  any  reason- 
able area  of  foundatioa  ;  and  (3)  aemi-liquid  soils,  or  those  in  which 
the  Suidity  is  so  great  that  they  are  incapable  of  supporting  any 
considerable  load.  Each  of  the  above  classes  gives  rise  to  a  special 
method  of  coDstructing  a  foundation. 

1.  With  a  Mil  <tf  the  first  class,  the  bearing  power  may  be  in- 


ovGoQi^lc 


PLAJT   OF  FBOPOSED  DISCUSSION.  186 

creased  by  compacting  the  Btirface  or  by  drainage  ;  or  the  area  of 
the  foandfttion  may  be  Increased  by  the  uee  of  masonry  footing 
coaraee.  Inverted  masonry  arches,  or  one  or  more  layers  of  timbers, 
railroad  rails,  iron  beuns,  etc.  Some  one  of  these  methods  is  or- 
dinarily employed  in  constructing  foundations  on  land ;  as,  for 
example,  for  buildings,  bridge  abntmenta,  sewers,  etc.  Usually  all 
of  these  methods  are  inapplicable  to  bridge  piers,  i.  e.,  for  fonuda- 
tions  under  vater,  owing  to  the  scouring  actioa  of  the  current  and 
also  to  the  obstruction  of  the  channel  by  the  greatly  extended  base 
of  the  foundation. 

2.  With  compressible  soils,  the  area  of  contact  may  be  increased 
by  supporting  the  structure  upon  piles  of  wood  or  iron,  which  are 
sustained  by  the  friction  of  the  soil  on  their  sides  and  by  the  direct 
pressure  on  the  soil  beneath  their  bases.  This  method  is  frequently 
employed  for  both  bufldings  and  bridges. 

3.  A  semi-fluid  soil  must  generally  be  removed  entirely  and  the 
structure  founded  upon  s  lower  and  more  stable  stratum.  This 
method  is  specially  applicable  to  foundations  for  bridge  piers. 

There  are  many  coses  to  which  the  above  classification  is  Dot 
strictly  applicable. 

For  oonvenieace  in  study,  the  coostruction  of  foundations  will 
be  discussed,  in  the  three  sucoeediog  chapters,  under  the  heads 
Ordinary  Foundations,  Pile  FoundtUiona,  and  Foundaiions  under 
Water.  However,  the  methods  employed  in  each  class  are  not 
entirely  distinct  from  those  used  in  the  others 


ovGoQi^lc 


CHAPTBBX. 
ORDINABY  POUNDATIONS. 

269.  Is  this  chapter  will  be  diBcnsaed  the  method  of  constnict- 
ing  the  fouDdstioiiB  for  bnildiogs,  bridge  abntment«,  caWerta,  or, 
in  general,  for  any  Btrnctnre  founded  npon  dry,  or  nearly  dry, 
ground.  This  claw  of  foundations  coald  appropriately  be  called 
Fonndations  for  BaildingB,  since  these  are  the  most  nomerons  of  the 
class. 

Jhis  chapter  is  divided  into  three  articles.  The  firat  treats  of 
the  soil,  and  includes  {a)  the  methods  of  examining  the  site  to  de- 
termine the  nature  of  the  soil,  {b)  a  discnseion  of  the  bearing  power 
of  different  soiU,  and  (c)  the  methods  of  increasing  the  bearing 
power  of  the  soil.  The  second  article  treats  of  the  method  of  de- 
signing the  footing  courses,  and  inclodes  (a)  the  method  of  deter- 
mining the  load  to  be  supported,  and  {b)  the  method  of  iucreasing 
the  area  of  the  fonndation.  The  third  contains  a  few  remarks  con- 
cerning the  practical  work  of  laying  the  foundation. 

Art.  1.  The  Soil. 

270.  EXAimrATlOB  or  THI  Sir.  The  nature  of  the  soil  to  be 
built  upon  is  evidently  the  first  subject  for  consideration,  and  if  it 
has  not  already  been  revealed  to  a  considerable  depth,  by  excava- 
tions for  buiidings,  wells,  etc.,  it  vUl  be  necessary  to  make  an  ex- 
amination of  the  subsoil  preparatory  to  deciding  upon  the  details 
of  the  foundation.  It  will  usually  be  sufficient,  after  having  dug 
the  foundation  pita  or  trenches,  to  examine  the  soil  with  an  iron 
rod  or  a  post-anger  from  3  to  5  feet  further,  the  depth  depending 
upon  the  nature  of  the  soil,  and  the  weight  and  importance  of  the 
intended  structure. 

In  soft  soil,  soundings  40  or  50  feet  deep  can  be  made  by  driving 
a  small  (say  f-inch)  gas-pipe  with  a  hammer  or  maul  from  a  tem- 
porary scaffold,  the  height  of  which  will  of  course  depend  upon  the 
Imgth  of  the  eeotionB  of  the  pipe.    If  aamplea  of  the  aoil  are  desired. 


ovGoQi^lc 


AXU.  1.]  THE  SOIL.  187 

OBO  aS-inoh  pipe  open  at  the  lover  end.  If  much  of  this  kind  of 
work  is  to  be  done,  it  is  advisable  to  fit  np  a  hand  pile-driving 
machine  (see  §  S35),  natng  a  block  of  vrood  for  the  dropping  weight. 
Borings  SO  to  100  feet  deep  can  be  made  very  ezpeditionsly  in 
common  soil  or  clay  with  a  common  wood-aoger  turned  by  men, 
with  levers  2  or  3  feet  long.  The  auger  will  bring  up  samples  snf- 
ficient  to  determine  the  nature  of  the  soil,  but  not  its  compactness, 
since  it  will  probably  be  compressed  somewhat  in  being  cut  oS. 

When  the  testing  must  be  made  through  sand  or  loose  soil,  it 
may  be  necessary  to  drive  down  an  iron  tube  to  prevent  the  soil 
from  &lling  into  the  hole.  The  sand  may  be  removed  from  the 
inside  of  the  tube  with  an  auger,  or  with  the  "sand-pump"  ased  in 
digging  artesian  wells.  When  the  subsoil  is  composed  of  varions 
strata  and  the  stmcture  demands  extraordinary  precaution,  borings 
must  be  made  with  the  tools  employed  for  boring  artesian  wells.* 

271.  If  the  builder  desires  to  avoid,  on  the  one  hand,  the  unnec- 
essarily costly  foundations  which  are  frequently  constmcted,  or,  on 
the  other  hand,  those  insufficient  foundations  evidences  of  which 
are  often  seen,  it  may  be  necessary,  after  opening  the  trenches,  to 
determine  the  supporting  power  of  the  soil  by  applying  a  test  load. 

In  the  case  of  the  capitol  at  Albany,  X.  Y.,  the  soil  was  tested 
by  applying  a  measured  load  to  a  square  foot  and  also  to  a  square 
yard.  The  machine  used  was  a  mast  of  timber  12  inches  square, 
held  vertical  by  guys,  with  a  cross-frame  to  hold  the  weights.  For 
the  smaller  area,  a  hole  3  feet  deep  was  dug  in  the  bine  clay  at  the 
bottom  of  the  fonndation,  the  hole  being  IS  inches  square  at  the 
top  and  14  inches  at  the  bottom.  Small  stakes  were  driven  into 
the  ground  in  lines  radiating  from  the  center  of  the  hole,  the  tops 
being  brought  exactly  to  the  same  level ;  then  any  change  in  the 
Bur^oe  of  the  ground  adjacent  to  the  hole  could  readily  be  detected 
and  measured  by  means  of  a  straight-edge.  The  foot  of  the  mast 
was  placed  in  ^e  hole,  and  weights  applied.  No  change  in  the 
surface  of  the  adjacent  ground  was  observed  until  the  load  reaahed 
5.9  tons  per  sq.  ft.,  when  an  nplift  of  the  surrounding  earth  was 
noted  in  the  form  of  a  ring  with  an  irregularly  rounded  surface, 
the  contents  of  which,  above  the  prerious  surface,  measured  0.09 
cubic  feet     Similar  experiments  were  made  by  applying  the  load  to 

•  For  UlaatntlODa  of  tooU  tor  thU  pnrpoM,  Me  EngbwertDg  News,  voL  ftl,  p.BSL 


ovGoQi^lc 


188  OBDINA.BT   rOUNDATIOKS.  [CHAP.  X. 

a  sqoare  yard  Tith  eseentiaJly  the  same  reaulte.  The  several  loads 
were  allowed  toreniaiD  for  some  time,  and  the  settlementa  observed.* 
Similar  experimente  were  made  in  connection  with  the  cooBtrnc- 
tion  of  the  CoDgreseiooal  Libisry  Building,  Washington,  D.  C,  with 
a  fnme  which  rested  upon  4  foot-plates  each  a  foot  square.  The 
frame  could  be  moved  from  place  to  place  on  wheels,  aod  the  test 
was  applied  at  a  number  of  places. 

272.  BUBnra  FOWXB  OF  80tU.  It  is  scarcely  oecessary  to  sa; 
that  soils  vary  greatly  in  their  bearing  power,  ranging  as  they 
do  from  the  condition  of  hardest  rock,  through  all  intermediate 
Btagee,  to  a  soft  or  semi-liquid  condition,  as  mud,  silt,  or  marsh. 
The  best  method  of  determining  the  load  which  a  specific  soil  will 
bear  is  by  direct  experiment  (§  271);  hut  good  judgment  and  ex- 
perience, aided  by  a  careful  study  of  the  nature  of  the  soil — its  com- 
pactness and  the  amount  of  water  contained  in  it — will  enable  one  to 
determine,  with  reasonable  accuracy,  its  probable  supporting  power. 
The  following  data  are  given  to  assist  in  forming  au  estimate  of  the 
load  which  may  safely  be  imposed  upon  different  soils. 

273.  Book.  The  ultimate  crushing  strength  of  stone,  as  deter- 
mined by  crushing  small  cubes,  ranges  from  180  tons  per  square 
foot  for  the  softest  stone — such  as  are  easily  worn  by  running  water 
or  exposure  to  the  weather — to  1,800  tons  per  square  foot  for  the 
hardest  siones  (see  page  II),  The  crushing  strength  of  slabs,  t.  e., 
of  prisms  of  a  less  height  than  width,  increases  as  the  height  de- 
creases. A  prism  one  half  as  high  as  wide  ia  about  twice  as  strong 
as  a  cube  of  the  same  material.  If  a  slab  be  conceived  as  being  made 
up  of  a  number  of  cubes  placed  side  by  side,  it  is  easy  to  see  why 
the  slab  is  stronger  than  a  cube.  Tbe  exterior  cubes  prevent  the 
detachment  of  the  disk-like  pieces  (Fig.  1,  page  9)  from  the  sides  of 
the  interior  cubes ;  and  hence  the  latter  are  greatly  strengthened, 
which  materially  increases  the  strength  of  the  slab.  In  testing 
cubes  and  slabs  the  pressure  is  applied  uniformly  over  the  entire 
upper  surface  of  the  test  specimen  ;  and,  reasoning  from  analogy, 
it  seems  probable  that  when  the  pressure  is  applied  to  only  a  small 
part  of  the  surface,  as  in  the  case  of  foundations  on  rock,  the  strength 
will  be  much  greater  than  that  of  cubes  of  the  same  material. 

The  table  on  page  190  contains  the  results  of  experimente  made 

*  W.  J.  Voiiptsui,  the  engbMer  fn  obarge,  in  Trans.  Am.  Soe.  C.  B.,  vol.  U.  p-  9B3. 


ovGoQi^lc 


AKT.  1.]  THE  aOIL.  189 

b;  the  author,  and  shove  conclneively  that  a  unit  of  Diaterial  htu  a 
much  greater  power  of  resigtance  wjien  it  forms  a  portion  of  a  larger 
mass  than  wfaea  isolated  in  the  manner  castomary  in  making  ex- 
periments on  crnshing  strength . 

The  ordinary  "crushing  Btrength"  given  in  next  to  the  last 
column  of  Table  23  was  obtained  bj  crushing  cubes  of  the  identical 
materials  employed  in  the  other  experiments.  The  concentrated 
pressure  vas  applied  by  means  of  a  hardened  eteel  die  thirty-eight 
Bixty-fourtha  of  an  inch  in  diameter  (area  =  0.277  eq.  in.).  All  the 
teste  were  made  between  self-adjusting  parallel  plates  of  a  hydro- 
static testing-machine.  Ifo  packing  was  used  in  either  series  of 
experiments ;  that  is  to  say,  the  pressed  surfaces  were  the  same  in 
both  series.  EoweTer,  the  block  of  limestone  7  inches  thick  (Ex- 
periments Nos.  8  and  13)  is  an  exception  in  this  respect.  This 
block  had  been  sawed  out  and  was  sligljtly  hollow,  and  it  was 
tboaght  not  to  be  worth  while  to  dress  it  down  to  a  plane.  As  pre- 
dicted before  making  the  test,  the  block  split  each  time  in  the  di- 
rection of  the  hollow.  If  the  bed  had  been  flat,  the  block  would 
doubtless  have  shown  a  greater  strength.  The  concentrated  pres- 
sure was  generally  applied  near  the  corner  of  a  large  block,  and 
hence  the  distance  from  the  center  of  the  die  to  the  edge  of  the 
block  is  to  the  nearest  edge.  Frequently  the  block  had  a  ragged 
edge,  and  therefore  these  distances  are  onl;  approximate.  The 
quantity  in  the  last  column — "Batio" — Is  the  crushing  load  per 
square  inch  for  concentrated  pressures  divided  by  the  crushing  load 
per  square  inch  for  uniform  pressure. 

The  experiments  are  tabulated  in  an  order  intended  to  show  that 
the  strength  under  concentrated  pressure  varies  (1)  with  the  thick- 
ness of  the  block  and  (^)  with  the  distance  between  the  die  and 
the  edge  of  the  material  being  tested.  It  is  clear  that  the  strength 
increases  veiy  rapidly  with  both  the  thickness  and  the  distance  from 
tho  edge  to  the  point  where  the  pressure  is  applied.  Therefore  we 
conclude  that  the  corapressiTe  strength  of  cubes  of  a  stone  gives 
little  or  no  idea  of  the  ultimate  resistance  of  the  same  material  when 
in  thick  and  extensive  layers  in  its  native  bed. 

274.  The  safe  bearing  power  of  rock  is,  certainly  not  less  than 
one  tenth  of  the  ultimate  crushing  strength  of  cvbe^;  that  is  to  say, 
the  safe  bearing  power  of  solid  rock  is  not  less  than  18  tons  per  sq. 
ft.  for  the  softest  rock  and  180  for  the  strongest.    It  is  safe  to  say 


ovGoQi^lc 


OBDINjLET  FODHDATIOlrS. 


LCHi.P.  X. 


IP* 


k 

fill 


Brick 

Llme«tone. . 
SttndstoDe. . 
LlmeMooe.  ■ 


80.100 
n.HOI 
81,046 


01,800 
59,904 
75,810 

7S,8»1 
102,900 
111,188 


1.840 
10.500 
10.100 
2,  AH 
8.408 
8.696 
4,671 
8,468 

8,696 


!  = 


14.0 
1«.0 
18. S 


16.0 
23.0 
M.O 


Clay,  wbtch  for  yean  haa  Mltily  carried,  without  appreciable  settlemeni. 


that  almost  any  rock,  from  the  hardness  of  granite  to  that  of  a  soft 
crnmbling  stone  easily  worn  by  exposore  to  the  weather  or  to  run- 
ning water,  when  well  bedded  will  bear  the  heaYiest  load  that  can 
be  brought  upon  it  by  any  masoDiy  conetrnction. 

It  scarcely  ever  occurs  in  practice  that  rock  is  loaded  with  the 
full  amount  of  weight  which  it  is  capable  of  sustaining,  as  the  extent 
of  base  necessary  for  the  stability  of  the  structure  is  generally  suffi- 
cient to  prevent  any  undue  pressure  coming  on  the  rock  beneath. 

275.  Clay.  The  clay  soils  vary  from  slate  or  shale,  which  wilt 
support  any  load  that  can  come  upon  it,  to  a  soft,  damp  clay  which 
will  squeeze  out  in  every  direction  when  a  moderately  heavy  prea- 


ovGoQi^lc 


AUT,  1.]  THE   80II»  191 

Bure  ia  bronght  upon  it.  Fouadatioas  on  ol&j  slioiild  be  laid  at 
encb  depths  as  to  be  unaffected  by  the  weather ;  since  clay,  at  even 
ooneiderable  depths,  will  gain  and  lose  considerable  water  as  the 
seasons  chaDge.  The  bearing  power  of  clayey  soils  can  be  rery 
much  improred  by  drainage  (§  ^85),  or  by  preveating  the  penetra- 
tion of  water.  If  the  foundation  is  laid  upon  undrained  clay,  care 
must  be  taken  that  ezcavations  made  in  the  immediate  vicinity  do 
not  allow  the  clay  under  pressure  to  escape  by  oozing  away  from 
under  the  building.  When  the  clay  occurs  in  strata  not  horizontal, 
great  care  is  necessary  to  prevent  this  flow  of  the  soiL  When  coarse 
sand  or  gravel  is  mixed  with  the  clay,  its  supporting  power  is  greatly 
increased,  being  greater  in  proportion  as  the  quantity  of  these 
materials  is  greater.  When  they  are  present  to  such  an  extent  that 
the  clay  is  just  sufScient  to  bind  them  together,  the  combination 
will  bear  as  heavy  loads  as  the  softer  rocks. 

276.  The  following  data  on  the  bearing  power  of  clay  will  be  of 
assistance  in  deciding  upon  the  load  that  may  safely  be  imposed 
upon  any  particular  clayey  soil.  From  the  experiments  made  in 
connection  with  the  construction  of  the  capitol  at  Albany,  K.  Y., 
as  described  in  §  271,  the  conclusion  was  drawn  that  the  extreme 
supporting  power  of  that  soil  was  less  than  6  tons  per  sq.  ft,  and 
that  the  load  which  might  be  safely  imposed  upon  it  was  2  tons  per 
sq.  ft.  "  The  soil  was  blue  clay  containing  from  60  to  90  per  cent 
of  alumina,  the  remainder  being  fine  siliceous  sand.  The  soil  con- 
tuins  from  2?  to  43,  usually  about  40,  per  cent  of  water ;  and  vari- 
ous samples  of  it  weighed  from  81  to  101  lbs.  per  cu.  ft"  In  the 
case  of  the  Gongreseional  Library  (§  271),  the  ultimate  supporting 
power  of  "  yellow  clay  mixed  with  sand  "  was  13^  tons  per  sq.  ft. ; 
and  the  safe  load  was  assumed  to  be  2^  tons  per  sq.  ft  Experi- 
ments made  on  the  clay  under  the  piers  of  the  bridge  across  the 
Missouri  at  Bismarck,  with  surfaces  1^  inches  square,  gave  an  aver- 
age ultimate  bearing  power  of  15  tons  per  sq.  ft* 

The  stifler  varieties  of  what  is  ordinarily  called  clay,  when  kept 
dry,  will  safely  bear  from  4  to  6  tons  per  sq.  ft.;  bnt  the  same  clay, 
if  allowed  to  become  saturated  with  water,  can  not  be  trusted  to 
bear  more  than  2  tons  per  sq.  ft.  At  Chicago,  the  load  ordinarily 
put  on  a  thin  layer  of  clay  (bard  above  and  soft  below,  resting  on  a 

■  Beport  o(  tbe  engineer,  Qeo.  S-  Uorlcon. 


ovGoQi^lc 


193  OBDIXABT  FOUNDATIONS.  [CHAP.  Z. 

thick  Btnitiim  of  quicksand)  is  1^  to  3  tons  per  sq.  ft;  and  the  set- 
tlement,  vhich  nsnally  reaches  a  maximam  in  a  year,  is  about  1 
inch  p«r  ton  of  load.  Experience  in  centra]  Illinois  shows  that,  if 
the  foundation  is  carried  down  below  the  action  of  frost,  the  clay 
subsoil  will  bear  1^  to  3  tons  per  aq.  ft.  without  appreciable  settling. 
Itankine  gives  the  safe  load  for  compreseible  soils  aa  1^  to  1}  tons 
persq.  ft. 

277.  Sand.  The  sandy  soils  vary  from  coarse  gravel  to  fine  sand. 
The  former  when  of  sufficient  thickness  forms  one  of  the  firmest 
and  best  foundations ;  and  the  latter  when  saturated  with  water 
is  practically  a  liquid.  Sand  when  dry,  or  wet  sand  when  prevented 
from  spreading  laterally,  forms  one  of  the  best  beds  for  a  founda- 
tion. Porous,  sandy  soils  are,  as  a  rule,  unaffected  by  stagnant 
water,  but  are  easily  removed  by  running  water ;  in  the  former  case 
they  present  no  difficnlty,  but  in  the  latter  they  require  extreme 
care  at  the  bauds  of  the  constructor,  as  will  be  considered  later. 

278.  Compact  gravel  or  clean  sand,  in  beds  of  considerable 
thickness,  protected  from  being  carried  away  by  water,  may  be 
loaded  with  8  to  10  tons  per  sq.  ft.  with  safety.  In  an  experiment 
in  France,  clean  river-sand  compacted  in  a  trench  supported  100 
tons  per  sq.  ft.  Sand  well  cemented  with  clay  and  compacted,  it 
protected  from  wat«r,  will  safely  carry  4  to  6  tons  per  sq.  ft. 

The  piers  of  the  Cincinnati  Snapension  Bridge  are  founded  on  a 
bed  of  coarse  gravel  13  feet  below  low-water,  although  solid  lime- 
stone was  only  12  feet  deeper;  if  the  friction  on  the  sides  of  the 
pier*  be  disregarded,  the  maximum  pressure  on  the  gravel  is  4  tons 
pej  sq,  ft.  The  piers  of  the  Brooklyn  Suspension  Bridge  are  founded 
44  feet  below  the  bed  of  the  river,  upon  a  layer  of  sand  2  feet  thick 
resting  upon  bed-rock ;  the  maximum  pressure  is  about  5^  tons 
per  sq.  ft. 

At  Chicago  sand  and  gravel  about  15  feet  below  the  surface  tat 
Buccessfully  loaded  with  2  to  2J  tons  per  sq.  ft.  At  Berlin  the  safe 
load  for  sandysoil  is  generally  taken  at  2  to  2^  tons  per  sq.  ft  The 
Washington  Monament,  Washington,  D.  C,  rests  upon  a  bed  of 
very  fine  sand  two  feet  thick  underlying  a  bed  of  gravel  and  bowl- 
ders; the  ordinary  pressure  on  certain  parts  of  the  fonndatiou  is 
not  far  from  11  tons  per  sq.  ft.,  which  the  wind  may  increase  to 
nearly  14  tons  per  sq.  ft. 

•  For  tlw  amount  of  sacb  MoUon,  see  ij  418-t»  and  ( ISt. 


ovGoQi^lc 


A.&I.  1.]  THS   BOIL.  193 

t79.  Bami-Liqtiid  Soili.  With  a  soil  of  this  claee,  u  mod,  silt, 
or  qaickeand,  it  is  cnatomaiy  (1)  to  remove  it  entirely,  or  (2)  to 
ask  piles,  tabea,  or  caieaone  through  it  to  a  eolid  substratum,  or 
13)  to  consolidate  the  soil  by  adding  saad,  earth,  stone,  etc.  The 
method  of  performing  these  operations  will  be  described  later.  Soils 
of  a  soft  or  semi-liqnid  character  should  never  be  relied  npon  for  a 
fonndstion  vhen  anything  better  can  be  obtained ;  but  a  heavy 
Baperstructure  may  be  supported  by  the  upward  pressure  of  a  semi- 
iiqnid  soil,  in  the  same  way  that  water  bears  up  a  floating  body.. 

According  to  Bankine,*  a  building  will  be  supported  when  the 

preesare  at  its  base  is  w  k(  _  . 1  per  unit  of  area,  in  which  ex- 
pression V)  is  the  weight  of  a  unit  volume  of  the  soil,  k  is  the  depth 
of  immersion,  and  a  is  the  angle  of  repose  of  the  soil.  It  a  =  5°, 
then  according  to  the  preceding  relation  the  supporting  power  of 
the  soil  is  1.4  ro  h  per  unit  of  area ;  if  a  =  10°,  it  is  2.0  to  A;  and 
if  cf  =  16°,  it  is  2,9  w  k.  The  weight  of  soils  of  this  class,  i.  e., 
mad,  silt,  and  quicksand,  varies  from  100  to  130  lbs.  per  cu.  ft. 
Bankine  gives  this  formula  as  being  applicable  to  any  soil ;  but  since 
it  takes  no  account  of  cohesion,  for  most  soUs  it  is  only  ronghly  ap- 
proximate, and  gives  results  too  small.  The  following  experiment 
seems  to  show  that  the  error  is  considerable.  "  A  10-foot  sqnare 
base  of  concrete  resting  on  mud,  whose  angle  of  repose  vras  5  to  1 
[a  =lli°],  bore  700  lbs.  per  sq.  ft."t  This  is  ^  times  the  result 
by  the  above  formula,  using  the  maximum  value  of  «f. 

lAXg&  buildings  have  been  senurely  founded  on  quicksand  by 
making  the  base  of  the  immersed  part  as  large  and  at  the  same  time 
«s  light  as  possible.  Timber  in  successive  layers  (§  309)  or  grillage 
on  piles  (g  330}  is  generally  used  in  such  cases.  This  class  of  fonn- 
dations  is  frequently  required  in  constructing  sewers  in  water-bear- 
ing sands,  and  though  apparently  presenting  no  difficulties,  such 
foundations  often  demand  great  skill  and  ability. 

280.  It  is  difficult  to  give  results  of  the  safe  bearing  power  of 
soils  of  this  class.  A  considerable  part  of  the  supporting  power  is 
derived  from  the  friction  on  the  vertical  ddes  of  the  foundation ; 
hence  the  bearing  power  depends  in  part  upon  the  area  of  the  aide 
surface  in  contact  vrith  the  soil.     Furthermore,  it  is  difficult  to  de- 


ovGoQi^lc 


191  OBDIKABT  FOUNDAIIOHB.  [OHAP.  X. 

termine  the  exact  snpporting  power  of  a  plastic  soil,  sinca  a  coneid- 
ereble  eettlemect  is  oertain  to  take  place  with  the  laiMe  at  time. 
The  experience  at  New  Orleans  with  alluvial  soil  tetA  a.  *«»  nxnM- 
menta*  that  have  been  made  on  quickaaad  eeeia  to  indicate  tuat 
with  a  load  of  ^  to  1  ton  per  square  foot  the  settlement  wil*  not  oe 


281.  Bearing  Power:  Sommary.     Gatheringtogethertfaeresuits 
of  the  preceding  discosBion,  we  have  the  following  table  * 

TABLE  28. 
Batb  Bbabinq  Fowkb  of  Soiu. 


Bock— the  haidart— In  thfck  layers,  in  oatlTe  bed  <g  374) 

"    equal  to  b«at  ashlar  Duaonr)'  (%  i^^i 

"       "     "    "    brick         "  "    

"       "     ■'  poor    "  "  "    

Clay,  In  thick  bed*,  always  dry  (g  376) 

..     ..      ..        ..    moderately  dry  (§  376) 

■'     aoft(8  376) 

GraTel  and  coarse  Band,  well  cemented  (§378) 

8aod,  compact  and  well  cementetl,  " 

"     clean,  dry "     

Quicksand,  alluvtal  soils,  etc.  (§  380) 


282.  Condnilon.  It  is  well  to  notice  that  there  are  Bome  prac- 
tical considerations  that  modify  the  pressure  which  may  safely  be 
pat  npoD  a  eoil.  For  example,  the  pressare  on  the  fonndation  of 
a  tall  chimney  shonld  be  considerably  less  than  that  of  the  low  ma»- 
ure  foundation  of  a  fire-proof  vault.  Id  the  former  c»8e  a  slight 
meqnality  of  bearing  power,  and  consequent  nneqnal  settling,  might 
endanger  the  stability  of  the  strncture ;  while  in  the  latter  no  eeri- 
oua  harm  wonld  reenlt.  The  pressure  per  nnit  of  area  shonld  be 
leas  for  a  light  stractare  subject  to  the  passage  of  heavy  loads — as. 


ovGoQi^lc 


UtT.  L]  THB  SOIL.  I9b 

for  example,  a  nulroad  viaduct — than  for  a  heavy  atrnctuni  aahjeot 
only  to  a  qniescent  load,  since  the  shock  and  jar  of  the  moving  load 
are  &r  more  serions  than  the  heavier  quiescent  load. 

The  determination  of  the  safe  bearing  power  of  soils,  particalar- 
Ij  when  dealing  with  those  of  a  eemi-liquid  character,  is  not  the 
only  qaestion  that  mnst  receive  oaretal  attention.  In  the  founda- 
tions tor  buildings,  it  may  be  neceesary  to  provide  a  saf^^nard 
against  the  soil's  escaping  by  being  pressed  oat  laterally  into  excava- 
tions in  the  vicinity.  In  the  foaodations  for  bridge  abntments,  it 
may  be  necessary  to  consider  what  the  effect  will  be  if  the  soil  around 
the  abatment  becomes  thoroughly  satnrated  with  water,  as  it  may 
during  a  flood;  or  what  the  effect  will  be  if  the  soil  is  deprived  of 
its  lateral  support  by  the  washing  away  of  the  soil  adjacent  to  the 
abutment.  The  provision  to  prevent  the  wash  and  nndermining 
action  of  the  stream  is  often  a  very  considerable  part  of  the  cost  of 
the  structure.  The  prevention  of  either  of  these  liabilities  is  a  prob- 
lem by  itself,  to  the  solution  of  which  any  general  discussion  will 
contribute  but  little. 

283.  iKFBOViao  THi  BxABura  Fowek  of  the  Boil.  When 
the  soil  directly  under  a  proposed  structure  is  incapable,  in  its  nor 
mal  state,  of  austaining  the  load  that  will  be  brought  upon  it,  the 
bearing  power  may  be  increased  (1)  by  increasing  the  depth  of  the 
foundation,  (2)  by  draining  the  site,  (3)  by  compacting  the  soil,  or 
(4)  by  adding  a  layer  of  sand. 

281.  iDOTeatlng  the  Depth.  The  simplest  method  of  increas- 
ing the  bearing  power  is  to  dig  deeper.  Ordinary  soils  will  bear 
more  weight  the  greater  the  depth  reached,  owing  to  their  becom- 
ing more  condensed  from  the  superincumbent  weight.  Depth  is 
especially  important  with'  cUy,  since  it  is  then  less  liable  to  be  dis- 
placed laterally  owing  to  other  excavations  in  the  immediate  vicin- 
ity, and  also  because  at  greater  depths  the  amount  of  moisture  in  it 
will  not  vary  so  much. 

In  any  soil,  the  bed  of  the  foundation  should  be  below  the  reach 
of  frost.  Even  a  foundation  on  bed-rock  should  be  below  the  frost 
line,  else  irater  may  get  under  the  foundation  through  fissures,  and, 
freezing,  do  damage. 

28S.  Drainage.  Another  simple  method  of  increasing  the  bear- 
ing power  of  a  soil  is  to  drain  it.  The  water  may  find  its  way  to 
the  bed  of  the  foundation  down  the  side  of  the  wall,  or  by  percol»- 


ovGoQi^lc 


196  OEDINABY  FOUNDATIONS.  [CHAP.  X. 

Hon  through  the  soil,  or  through  a  seam  of  sand.  In  most  casea 
the  bed  can  be  safflciently  drained  by  covering  it  with  a  layer  of 
gravel — the  thicknesa  depending  apon  the  plasticity  of  the  soil, — 
and  then  surrounding  the  building  with  a  tile-draiD  laid  a  little 
below  the  foundation.  In  extreme  cases,  it  is  ucccssury  to  enclose 
the  entire  site  with  a  puddle-wall  to  cut  oft  drainage  water  from  a 
higher  area. 

286.  Spriuga.  In  laying  foundations,  springs  are  often  met 
with,  and  sometimes  prove  very  troublesome.  The  water  may  be 
excluded  from  the  foundation  pit  by  driving  sheet  piles,  or  by  plug- 
ging the  spring  with  concrete.  If  the  flow  is  so  strong  as  to  wash 
the  cement  out  before  it  has  set,  a  heavy  canvas  covered  with  pitch, 
etc.,  upon  which  the  concrete  is  deposited,  is  sometimes  used  ;  or 
the  water  may  be  carried  away  in  temporary  channels,  until  the 
concrete  in  the  artificial  bed  shall  have  set,  when  the  water-ways 
may  be  filled  with  semi-fliiid  cement  mortar.  Below  is  an  account 
of  the  method  of  stopping  a  very  troublesome  spring  encountered 
in  laying  the  foundation  of  the  dry-dock  at  the  Brooklyn  Navy 
Yard. 

"The  dock  is  a  basin  composed  of  stone  masonry  resting  on 
piles.  The  foundation  is  42  foet  below  the  surface  of  the  gronnd 
and  3?  feet  below  mean  tide.  In  digging  the  pit  for  the  founda- 
tion, springs  of  fresh  water  were  discovered  near  the  bottom,  which 
proved  to  be  very  troublesome.  The  upward  pressure  of  the  water 
was  BO  great  as  to  raise  the  foundation,  however  heavily  it  was  loaded. 
The  first  indication  of  undermining  by  these  springs  was  thescittUng 
of  the  piles  of  the  dock  near  by.  In  a  day  it  made  a  cavity  in  which 
a  pole  was  run  down  20  feet  below  the  foundation  timbers.  luto 
this  hole  were  thrown  150  cubic  feet  of  stone,  which  settled  10  feet 
during  the  night ;  and  50  cubic  feet  more,  thrown  in  the  following 
day,  drove  the  spring  to  another  place,  where  it  burst  through  a 
bed  of  concrete  2  feet  thick.  This  new  cavity  was  filled  with 
concrete,  but  the  precaution  was  taken  of  putting  in  a  tube  so  as  to 
permit  the  water  to  escape ;  stili  it  burst  through,  and  the  opera- 
tion was  repeated  several  times,  until  it  finally  broke  out  through  a 
heavy  body  of  cement  14  feet  distant.  In  this  place  it  uudermined 
the  foundation  piles.  These  were  then  driven  deeper  by  means  of 
followers ;  and  a  space  of  1,000  square  feet  around  the  spring  was 
then  planked,  forming  a  fioor  on  which  was  laid  a  layer  of  brick  in 


ovGoQi^lc 


ART.  1.]  -I'HE  SOIL.  197 

dry  cement,  and  on  that  s  layer  of  brick  set  in  mortar,  and  the 
fouDdation  vaa  completed  orer  alL  Several  vent-holes  were  left 
through  the  floor  and  the  foandatioa  for  the  escape  of  the  water. 
The  work  was  completed  in  1851,  and  has  stood  well  ever  eince."  * 

287.  Conaolidating  the  Soil.  A  soft,  clayey  boU  can  be  greatly 
improved  by  spreading  a  thin  layer  of  sand,  dry  earth,  or  broken 
stone  over  the  bed  of  the  foundation  and  pounding  it  into  the  soil. 
If  the  soil  is  very  soft,  compacting  the  surface  will  be  insufficient ; 
in  this  case  the  soil  may  be  consolidated  to  a  considerable  depth  by 
driving  short  piles  into  it.  For  this  purpose  small  piles — say  6 
feet  long  and  6  inches  in  diameter — serve  better  than  large  ones ; 
and  they  can  be  driven  with  a  band-maul  or  by  dropping  a  heavy 
block  of  wood  with  a  tackle  attached  to  any  nmple  frame,  or  by  a 
hand  pile-driver  (§  335).  They  may  be  driven  as  close  together  a» 
neceasary,  although  2  to  4  feet  in  the  clear  is  nsnally  Bufficient. 
The  latter  method  of  compacting  the  soil  is  &r  more  efficient  .than 
poanding  the  surface.  In  the  case  of  impact  upon  earth,  the  im- 
mediate layers  are  compressed  at  once,  and  by  their  inertia  and 
adhesion  to  the  surrounding  soil  they  intercept  the  effect  of  the 
blow,  and  thus  prevent  the  consolidation  of  the  lower  strata.  Even 
though  the  effect  of  a  blow  is  not  communicated  to  any  conEiderable 
depth,  the  heavy  masses  of  masonry  make  themselves  felt  at  great 
depth,  and  hence  for  heavy  buildings  it  is  necessary  to  consolidate 
the  lower  strata.  This  can  be  done  most  easily  and  most  efficiently 
by  driving  piles  (see  Art.  3). 

In  this  connection  it  is  necessary  tp  remember  that  clay  is  com- 
pressible, while  sand  is  not.  Hence  this  method  of  consolidating 
soils  is  not  applicable  to  sand,  and  is  not  very  efficient  in  soils 
largely  composed  of  it. 

288.  flaad  Files.  Experiments  show  that  in  compacting  th& 
noil  by  driving  piles,  it  is  better  to  withdraw  them  and  immediately 
fill  the  holes  with  sand,  than  to  allow  the  wooden  piles  to  remain. 
This  advantage  is  independent  of  the  question  of  the  dnrability  of 
the  wood.  When  the  wooden  pile  is  driven,  it  compresses  the  soil 
an  amount  nearly  or  quite  equal  to  the  volume  of  the  pile,  and 
when  the  latter  is  withdrawn  this  consolidation  remains,  at  least: 
temporarily.     If  the  hole  is  immediately  filled  with  sand  this  com- 

*  DelkfleM'B  Fonndatloni  In  CompreBdble  Soils,  p.  It — a  pamphlet  pnbllsbed  tij 
Uw  Englaem'B  UepaitmeBt  of  ttic  D.  8.  Annr- 


ovGoQi^lc 


198  OBDINABT  FOCNDATIOXa  [CKAP.  t 

preeeion  ib  retained  permanently,  and  the  consolidation  may  be  still 
farther  increased  by  ramming  the  sand  in  in  thin  layers,  owing  to 
the  ability  of  the  latter  to  traosmit  preaanre  laterally.  And  further, 
the  aand  pile  will  support  a  greater  load  than  the  wooden  pile;  for, 
einco  the  sand  acts  like  innumerable  small  arches  I'eacbing  from 
one  side  of  the  hole  to  the  other,  more  of  the  load  is  transmitted  to 
the  soil  on  the  sides  of  the  hole.  To  secure  the  best  resalts,  the 
sand  should  be  fine,  sharp,  clean,  and  of  uniform  size. 

889.  When  the  piles  are  driven  primarily  to  compact  the  soil, 
it  is  customary  to  load  them  and  also  the  soil  between  them,  either' 
by  cutting  the  piles  oS  near  the  surface  and  laying  a  tight  platform 
of  timber  on  top  of  them  (see  §  320),  or  by  depositing  a  bed  of  con- 
crete between  and  over  the  heads  of  the  piles  (see  g  319). 

If  the  soil  is  very  soft  or  con  |iused  largely  of  sand,  this  method 
is  ineffective;  in  which  case  long  piles  are  driven  as  close  together 
as  is  necessary,  the  supporting  power  being  derived  either  from  the 
resting  of  the  piles  upon  a  harder  substratum  or  from  the  buoyancy 
due  to  immersion  in  the  semi-liquid  soil.  This  method  of  securiug 
a  foundation  by  driving  long  piles  is  very  expensive,  and  is  seldom 
resorted  to  for  buildings,  since  it  is  generally  more  economical  to 
increase  the  area  of  the  foundation. 

290.  Lsyen  of  Sand.  If  the  soil  is  very  soft,  it  may  be  ex- 
cavated and  replaced  by  sand.  The  method  of  using  sand  for  piles 
has  been  described  in  §  388,  which  see.  The  opportunities  for  the 
use  of  sand  in  foundations  are  numerous,  and  the  employment  of 
it  would,  in  many  constructions,  promote  economy  and  stability. 
The  simplest  method  of  using  sand  for  this  purpose  is  to  excavate 
a  trench  or  pit  to  the  proper  depth,  and  fill  it  by  depositing  succes- 
sive layers  of  sand,  each  of  which  should  be  thoroughly  settled  by 
a  heavy  beetle  before  laying  the  next.  To  cause  the  sand  to  pack 
firmly,  it  should  be  slightly  moistened  before  being  placed  in  tho 
trench. 

Sand,  when  used  in  this  way,  possesses  the  valuable  property  of 
assuming  a  new  position  of  equilibrium  and  stability  should  the 
soil  on  which  it  is  laid  yield  at  any  of  its  points ;  not  only  does  this 
take  place  along  the  base  of  the  sand  bed,  but  also  along  its  edges 
or  sides.  The  bed  of  sand  must  be  thick  enough  to  distribute  the 
pressure  on  its  upper  surface  over  the  entire  base.  There  is  no  way 
of  telling  what  this  thickness  should  be,  except  by  trial. 


ovGoQi^lc 


A.BT.  3.]  DXBIOHINO  THE  FOOTIKG.  199 

291.  The  foUowicg  exsmples,  cited  by  Trantwine,*  are  interest- 
ing as  shoving  the  enrpriBiog  effect  of  even  a  thin  la;er  of  sand 
or  gravel : 

"Some  portions  of  the  circular  brick  aqaednct  for  supplying 
Boston  with  water  gave  a  gieat  deal  of  trouble  when  its  Inches 
passed  through  running  quicksaiids  and  other  treacherous  soils. 
Concrete  was  tried,  but  the  wet  quicksand  mixed  itself  with  it  and 
killed  it.  Wooden  cradles,  etc.,  also  failed ;  and  the  diflBcnlty  was 
overcome  by  aimply  depositing  in  the  trenches  about  two  feet  in 
depth  of  strong  gravel.. 

"  Smoatou  mentions  a  stone  bridge  built  upon  a  natural  bed  of 
gravel  only  about  3  feet  thick,  overlying  deep  mud  so  soft  that  an 
iron  bar  40  feet  long  sank  to  the  head  by  its  own  weight.  Althongh 
a  wretched  precedent  for  bridge  building,  this  example  illnstrates 
the  bearing  power  of  a  thick  layer  of  well-compacted  gravel." 


Art.  2,  DBSiONiifQ  the  Footinq. 

S92.  Load  to  bi  Sottoktss.  The  first  atep  ie  to  aecertain  the 
load  to  be  supported  by  the  foundation.  This  load  consists  of  three 
parts :  (1)  the  building  itself,  (2)  the  movable  loads  on  the  floors 
and  the  snow  on  the  roof,  and  (3)  the  part  of  the  load  that  may  be 
transferred  from  one  part  of  the  foondation  to  the  other  by  the 
force  of  the  wind. 

293.  The  weight  of  the  bnilding  is  easily  ascertained  by  calcu- 
lating the  cubical  contents  of  all  the  various  materials  in  the  struct- 
ure. If  the  weight  is  not  equally  distributed,  care  must  be  taken 
to  ascertain  the  proportion  to  be  carried  by  each  part  of  the  foun- 
dation. For  esample,  if  one  vertical  section  of  the  wall  is  to  con- 
tain a  number  of  large  windows  while  another  will  consist  entirely 
of  solid  masoury,  it  is  evident  that  the  pressure  on  the  foundation 
under-the  first  section  will  be  less  than  that  under  the  second. 

In  this  connection  it  must  be  borne  in  mind  that  concentrated 
pi-essu res  are  not  transmitted,  undiminished,  through  a  solid  mass 
in  the  line  of  application,  but  spread  out  in  successively  radiating 
lines ;  hence,  it  any  considerable  distance  intervenes  between  the 
foundation  and  the  point  of  application  of  this  concentrated  load, 

I  Pooket-book  (od.  1861^  p.  SS*. 


ovGoQi^lc 


200 


OEDIXA.BT  FOUNQATIONB. 


[chap.  z. 


the  preBSure  will  be  nearly  or  quite  aniformly  distribated  over  the 
entire  area  of  the  base.  The  exact  diatribntion  of  the  presBure  can 
not  be  compnted. 

The  following  data  will  be  nsefal  in  determining  the  weight  ot 
the  BtrnctDte  ■ 

TABLE  24. 
WxiGBT  or  Uabokkt. 


Brick-work,  pressed  brick,  llita  Jolnta 

"  ordloar;  quality. 

Krft  brick,  thick  Jofnta 

COQCrete,  1  cement,  Bund,  and  6  broken  statie 

Granite— 6  per  cent,  more  ihan  the  correapondlng  Umestoae. . . 

Llmeetoae,  ashlar,  largest  blocks  and  thinnest  Joints 

"      13"lo20"coursesand|-tai'inch}olnts..„ 

"  squared-stone  (see  §  M6) 

"  rubble,  best 

Hortar,  1  Rosendale  cement  and  S  sand 

"      common  lime,  dried 

Ssudstone— 14  per  cent,  less  than  the  corre^tondiog  limestone. 


Ordinary  lathing  and  plastering  weighs  abont  10  lbs.  per  sq.  ft. 
The  weight  of  floors  is  approximately  10  lbs.  per  sq.  ft  for  dwell- 
ings ;  25  lbs.  per  sq.  ft.  for  public  bnildinga ;  and  40  or  50  lbs.  per 
sq.  ft.  for  warehouses.  The  weight  of  the  roof  varies  with  the  kind 
of  covering,  the  span,  etc.  A  shingle  roof  may  be  taken  at  10  lbs. 
per  sq.  ft.,  and  a  roof  coTered  with  slate  or  corrugated  iron  at  25 
lbs.  per  sq.  ft. 

2S4.  The  movable  load  on  the  floor  depends  upon  the  nature  ot 
the  building.  For  dwellings,  it  does  not  exceed  10  lbs.  per  sq.  ft.; 
for  large  office  buildings,  it  is  usually  taken  at  30  lbs.  per  sq.  ft. ; 
for  chnrches,  theatres,  etc.,  the  maximum  load — a  crowd  of  people 
— may  reach  100  lbs.  per  sq.  ft ;  for  stores,  warehonses,  factories, 


ovGoQi^lc 


ART,  2.]  DSBIGNIXa   THE   FOOTINO.  SOI 

«tc.,  the  load  will  be  from  100  to  400  Iba.  p«r  sq.  ft.,  according  to 
the  porpoees  for  which  they  are  used. 

The  preceding  loada  are  the  ones  to  be  need  in  determining  the 
atrength  of  the  floor,  and  not  in  designing  the  footings;  for  there 
is  no  probability  that  each  and  every  square  foot  of  floor  will  hare 
its  maximnm  load  at  the  same  time.  The  amount  of  moving  load 
to  be  aesigned  in  any  particalar  case  is  a  matter  of  jndgmeat.  At 
Chicago  in  designing  tall  steel-skeleton  office  bnildings,  it  is  the 
practice  to  assume  that  nearly  all  of  the  maximnm  lire  load  reaches 
the  girders,  that  a  smaller  per  cent,  reaches  the  colnmns,  and  that 
no  live  load  reaches  the  footings.  In  many  cities  the  bnilding  law 
■peoifiee  the  live  load  to  be  assamed  as  reaching  the  footing. 

Attention  must  be  gi?en  to  the  manner  in  which  the  weight  of 
the  root  and  floors  is  traiuderred  to  the  walls.  For  example,  if  the 
floor  joists  of  a  warehoase  ran  from  back  to  front,  it  is  erident  that 
the  bock  and  front  walls  alone  will  carry  the  weight  of  the  floors 
and  of  the  goods  placed  upon  them,  and  this  will  make  the  pressnre 
npOQ  the  foundation  under  them  considerably  greater  than  under 
the  other  walls.  Again,  if  a  Btone<front  is  to  be  carried  on  an  arch 
or  on  a  girder  having  its  bearings  on  piers  at  each  side  of  the  bnild- 
ing, it  is  manifest  that  the  weight  of  the  whole  BuperiQCumbent 
structure,  instead  of  being  distributed  equally  on  the  foundation 
under  the  front,  will  be  concentrated  on  that  part  of  the  founda- 
tion immediately  under  the  piers. 

296.  The  pressure  of  the  wind  against  towers,  tall  chimneys, 
etc,  will  cause  a  concentration  of  the  weight  of  the  structure  upon 
one  side  of  the  foundation.  The  maximum  horizontal  pressure  of 
the  wind  is  usually  taken  as  50  lbs.  per  sq.  ft.  oa  a  flat  surface  per- 
pendicular to  the  wind,  and  on  a  cylinder  at  about  30  lbs.  per  sq. 
ft.  of  the  projection  of  the  surface.  The  pressure  upon  an  inclined 
Bortace,  as  a  roof,  is  about  I  lb.  per  sq.  ft.  per  degree  of  inclination 
to  the  horizontal.  For  example,  if  the  roof  has  an  inclination  of 
30°  with  the  horizontal,  the  pressure  of  the  wind  will  be  about  30 
lbs.  per  sq.  ft 

The  effect  of  the  wind  will  be  considered  in  §g  301-1. 

299.  Abx&  BwtlTIBBD.  Having  determined  the  pressure  which 
may  safely  be  brought  upon  the  soil,  and  having  ascertained  the 
weight  of  each  part  of  the  structure,  the  area  required  for  the  foun- 
dation is  easily  determined  by  dividing  the  latter  by  the  former. 


ovGoQi^lc 


303  ORDINABY   FODNDATIONa  [CHAP.  JL. 

Then,  having  found  the  area  of  fonndation,  the  base  of  the  etruct- 
nre  must  be  extended  by  footings  of  masonry,  conorete,  timber, 
etc,  BO  as  to  (1)  cover  that  srea  and  (2)  distribute  the  pressure  uni- 
formly over  it.  The  two  items  will  be  considered  in  inverse  order. 
297.  Cevteb  07  Pbebsoxb  m  Cevteb  op  Basb.  In  construct- 
ing a  foundation  the  object  is  not  so  much  to  secure  an  absolutely 
unyielding  base  as  to  secure  one  that  will  settle  as  little  as  possible, 
and  uniformly.  All  soils  will  yield  somewhat  under  the  pressure  of 
any  building,  and  even  masonry  itself  is  compressed  by  the  weight 
of  the  load  above  it.  The  pressure  per  square  foot  should,  there- 
fore, be  the  same  for  all  parts  of  the  building,  and  particularly  of 
the  foundation,  so  that  the  settlement  may  be  uniform.  This  can 
be  secured  only  when  the  axis  of  the  load  (a  vertical  line  through 
the  center  of  gravity  of  the  weight)  passes  through  the  center  of 
the  area  of  the  foundation.  If  the  axis  of  pressure  does  not  coincide 
exactly  with  the  axis  of  the  base,  the  ground  will  yield  most  on  the 
side  which  is  pressed  most ;  and  as  the  ground  yields,  the  base  as- 
sumes an  inclined  position,  and  carries  the  lower  part  of  the  struct- 
ure with  it,  thus  producing  unsightly  cracks,  if  nothing  more. 

The  coincidence  of  the  axis  of  pressure  with  the  axis  of  resist- 
ance is  of  first  importance.  This  principle  is  self-evident,  and  yet 
the  neglect  to  observe  it  is  the  most  frequent  cause  of  failure  in  the 
foupdations  of  buildings. 

Fig.  50  is  au  example  of  the  way  in  which  this  principle  is 
violated.  The  shaded  portion 
represents  a  heavily  loaded  exte- 
rior wall,  and  the  light  portion  a 
lightly  loaded  interior  wall.  The 
foundations  of  the  two  walls  are 
rigidly  connected  together  at 
their  intersection.  The  center 
of  the  load  is  under  the  shaded 
Fia.so.  section,  and  the  center  of  the 

area  is  at  some  point  farther  to  the  left ;  consequently  the  exterior 
wall  is  caused  to  incline  outward,  producing  cracks  at  or  near  the 
comers  of  the  building.  Doubtless  the  two  foundations  are  con> 
nected  in  the  belief  that  an  increase  of  the  bearing  surface  is  of  firat 
importance ;  but  the  true  principle  is  that  the  coincidence  of  the 
axis  of  pressure  vrith  the  axis  of  resiBtance  is  the  most  important. 


ovGoQi^lc 


12T.  3.]  B^smmsa  the  pootiko.  303 

Fig.  51  is  another  illostrstion  of  the  same  priociple.    The  foao- 

dation  is  continDOua    nnder    the    opeDiog, 

and  hence  the  center  of  the  fdnDdation  is  to 

the  left  of  the  center  of  preseore ;  conse- 
quently the  wall  inclines  to  the  right,  pro- 

dncing  cracks,  usually  over  the  opening.* 
298.  The  center  of  the  load  can  he  made 

to  tall  inside  of  the  center  of  foundation  by 

extending  the  footings  outwards,  or  by  c 

tailing  the  foundations  on  the  inside.     The  - 

latter  finds  exemplification  in   the  properly  Fia.m. 

constructed  foundation  of  a  wall  containing  a  number  of  openings. 

For  example,  in  Fig.  52,  if  the  foundation  is  uniform  under  the 
entire  front,  the  center  of  pressure  must  be 
outside  of  the  center  of  the  base ;  and  conse- 
quently the  two  side  walls  yill  incline  outward, 
and  show  cracks  over  the  openings.  If  the 
width  of  the  foundation  under  the  openings 
be  decreased,  or  if  this  part  of  the  foundation 
be  omitted  entirely,  the  center  of  pressure 

n.         will  fall  inside  of  the  center  of  base  and  the 
walls  will  tend  to  Incline  inwards,  and  hence 
'•-\  be  stable. 

289.  CoudniiouB.     One  conclusion  to  be 

na.Ba.  drawn  from  the  above  examples  is  ttiat  the 

foundation  of  a  wall  should  never  be  connected  with  that  of  anotlier 

wall  either  much  heavier,  or  much  lighter  than  itself.     Both  are 

equally  objectionable. 

A  second  conclusion  is  that  the  axis  of  the  load  should  strike  a 
little  inside  of  the  center  of  the  area  of  the  base,  to  make  sure  that 
it  will  not  be  outside.  Any  inward  inclination  of  the  wall  is  ren- 
dered impossible  by  the  interior  walls  of  the  building,  the  floor- 
beams,  etc. ;  while  an  outward  inclination  can  be  counteracted  only 
by  anchors  and  the  bond  of  the  masonry.  A  slight  deviation  of  the 
axis  of  the  load  outward  from  the  center  of  the  base  has  a  marked 
effect,  and  is  not  easily  counteracted  by  anchors. 

■  For  an  acconnt  showing  the  Tlolotlon  of  thla  principle  Id  the  constmctJon  ol 
the  Cooper  InatltDte  Bnfldlng,  New  York  Citjr,  and  the  method  used  to  retnedf  lt,aee 
Hmtforv  Bngtiieir,  ToL  XlL  pp.  460-68. 


ovGoQi^lc 


204 


OBDtNABT  FOUNDAnOSB. 


[OHAP.  X. 

The  above  coucIiuioiiB  may  be  Banunarized  in  the  folloiring 
principle :  All  foundations  should  be  so  constructed  as  to  compress 
the  ground  slightly  ooitcatb  upwards,  raiher  than  oomvex  up- 
wards. On  even  eligbtly  compressible  Boils,  a  Bmall  difference  in 
the  presanre  on  the  foundation  will  be  eafficient  to  cause  the  bed  to 
become  conves  upwards.  At  Chicago,  an  omission  of  1  to  2  per 
cent  of  the  weight  (by  leaving  openings)  nsoaUy  caasee  sufficient 
convexity  to  prodace  unsightly  cracks.  With  very  dight  differences 
of  pressure  on  the  foundation,  it  is  safflcient  to  tie  the  building 
together  by  careful  bonding,  by  hoop-iron  built  in  over  openings, 
and  by  heavy  bars  bnilt  in  where  one  \to1I  joins  another. 

300.  TXBStVxman  Fibbs.  The  art  of  constructing  foanda- 
tions  on  compressible  soil  has  been  brought  to  a  high  degree  of 
development  by  the  architects  of  Chicago.  The  special  feature  of 
the  practice  in  that  city  is  what  is  called  "  the  method  of  independ- 
ent piers ;"  that  is,  each  tier  of  columns,  each  pier,  each  w^l,  etc., 
has  its  own  independent  foundation,  the  area  of  which  is  propor- 
tioned to  the  load  on  that  part.*  The  interior  walls  are  fastened  to 
the  exterior  ones  by  anchors  which  slide  iu  slots.  For  a  detailed 
account  of  the  methods  employed  in  one  of  the  best  and  largest 
buildings  erected  there,  see  Sanitary  Engineer,  Dec.  10,  1885. 

301.  Sttect  or  the  Wtn.  Overturning.  The  preceding  dib- 
onssion  refers  to  the  total  weight  that  is  to  come  upon  the  foun- 
dation. The  pressure  of  the  wind  against  towers, 
tall  chimneys,  etc.,  transfers  the  pointof  applica- 
tion of  the  load  to  one  side  of  the  foundation.  The 
method  of  compnting  the  position  of  the  center 
of  the  pressure  on  the  foundation  under  the  action 
of  the  wind  is  illustrated  in  Fig.  53,  in  which 

ABED  represents  a  vertical  section  of  the 
tower; 

d  is  a  point  horizontally  opposite  the  center  of 
the  surface  exposed  to  the  pressure  of  the 
wind  and  vertically  above  the  center  of  grav- 
no.u.  ity  of  the  tower; 

*  Thia  metfaod  wh  lint  made  koown  to  the  pnblia  bf  Frederick  Bonnun,  at  Chi- 
cago, tn  a  pamphlet  entitled  "The  Method  ot  ConitnicUiig  FonndftUoDa  oolscdated 
Pfen,"  published  b;  him  In  1872.    The  above  examples  and  principles  amfrom  that 


ovGoQi^lc 


ABT.  8.]  DESiaKING  THE  FOOTINQ.  200 

C  is  the  position  of  the  center  of  pressure  Then  there  ia  no  wind ; 

jV  IS  the  center  when  the  wind  is  acting. 
For  convonieiice,  let 

P  =  the  maxim  am  preesare  on  the  fonndation,  per  unit  of  area; 

p  =  the  pressure  of  the  wind  per  unit  of  area  (see  %  295); 

H  =  the  total  preasare  of  the  wind  against  the  exposed  surface ; 

W  =  the  weight  of  that  part  of  the  stracture  above  the  sectioa 
considered, — in  this  case,  A  B ; 

3  =  the  area  of  the  horizontal  cross  section ; 

/  =  the  moment  of  inertia  of  this  section  j 
I  =  the  distance  A  B ; 

h  =  the  distance  a  C\ 

d  =  the  distance  N  C; 
if  =  the  moment  of  the  wind. 

When  there  is  no  horizontal  force  acting,  the  load  on  ^  fi  is 
uniform ;  but  when  there  is  a  horizontal  force  acting — as,  for  ex- 
ample, the  wind  blowing  from  the  right, — the  pressure  is  greatest 
near  A  and  decreases  towards  B.  To  find  the  law  of  the  variation 
of  this  pressure,  consider  the  tower  as  a  cantilever  beam.  The 
masimum  pressure  at  A  will  be  that  due  to  the  weight  of  the  tower 
plus  the  compression  due  to  flexure ;  and  the  pressure  at  B  will  be 
the  compression  due  to  the  weight  minus  the  tension  doe  to  flexnre. 

The  antform  pressure  dne  to  the  weight  is  -^.   The  strain  at  A  dns 

to  flexnre  is,  by  the  principles  of  the  resistance  of  material^  -aj. 
Then  the  mazimnm  preeenre  per  unit  of  area  at  ^  ii 
._    W     Ml 

'^-s+n- « 

aod  the  minimTini  pteenure  at  B  is 

-=^-fJ- m- 

Equations  (1)  and  (S)  are  pertectl;  general ;  tb^  are  applioabls 
to  any  cross  section,  and  also  to  any  system  of  horizontal  and  Te^ 
tical  forces.  In  succeeding  chapters  they  will  be  employed  in 
finding  the  unit  preesare  in  masonry  dams,  bridge  piers,  arohe^ 
etc 


ovGoQi^lc 


806  OBDUTABT  BOCSDi^OSB.  \CBXr.  X. 

The  valne  of  7  in  the  above  lormnlas  is  girsD  in  Fig.  54  for  the 
sections  occurring  most  frequently  in  practice,  Notice  that  /  is  the 
dimension  parallel  to  the  direction  of  the  wind,  and  b  the  dimen- 
mon  perpendicular  to  the  directioQ  of  the  wind. 


302.  If  the  ares  of  the  Bectiou  A  B,  Fig.  53,  is  a  rectangle 
B=lb,  »XiAI=-^bV.  Substituting  these  values  in  equation  (1) 
gives 

'■=n+'^ (') 

The  moment  of  the  wind,  M,  is  eqnal  to  the  product  of  its  total 
pressure,  S,  and  the  distance,  h,  of  the  center  of  pressure  above 
the  horizontal  section  considered ;  ot  M=  H.h.  H  ia  equal  to 
the  presenre  per  nnit  of  area,  p,  multiplied  by  the  area  of  the  sur- 
face exposed  to  the  pressure  of  the  wind.  Substituting  the  above 
value  of  Jfin  equation  (3)  gives 

To  still  further  simplify  the  above  formula,  notice  iiiat  Fig.  63 
gives  the  proportion 

S:  W::NCiaC, 
from  which 

E.aC^  W.NC; 
or,  ohanging  the  nomenclature, 

H\=  Wd. 
Kotioe  that  the  last  relation  can  also  be  obtained  directly  hj  the 
principle  of  moments.    Substituting  the  value  ot  H.  h,  as  sJimve,  in 
equation  (4)  gives 

wllioh  in  a  ofrnmuent  form  for  practic&l  application. 


jvGooi^le 


AXF.  S.]  DB8IGVLN0  THS  TOOTIHO.  207 

Ad  exsmiuation  of  eqnation  (6)  shows  that  when  d  =  Jf  C  =  ^t, 
the  maximiim  presanre  at  A  is  twice  the  average.  Notice  also  that 
Doder  theae  conditionB  the  pressure  at  £  is  zero.  This  is  equiva- 
lent to  what  is  knowB,  in  the  theory  of  arohes,  as  the  principle  of 
the  middle  third.  It  shows  that  ae  long  as  the  center  of  pressnre 
lies  in  the  middle  third,  the  msximnm  pressnre  is  not  more  than 
twice  the  average  pressure,  and  that  there  is  no  tension  at  B. 

The  above  discussion  of  the  distribution  of  the  pressure  on  the 
foundation  is  amply  sufQcient  for  the  case  in  hand ;  however,  the 
subject  is  discosaed  more  fully  io  the  chapter  on  Stability  of  Masonry 
Dame  (see  Chapter  XIII). 

303.  The  average  pressure  per  unit  an  A  B  has  already  been 
adjusted  to  the  safe  bearing  power  of  the  soil,  and  if  the  maximum 
pressnre  at  A  does  not  exceed  the  ultimate  bearing  power,  the  occa- 
sionat  maximnm  pressure  due  to  the  wind  will  do  no  barm ;  but  if 
this  maximnm  exceeds  or  is  dangerouBly  near  the  ultimate  strength 
of  the  soil,  the  base  must  be  widened. 

304.  Sliding,  llie  pressure  of  the  wind  is  a  force  tending  to 
elide  the  foundation  horizontally.  This  is  resisted  by  the  friction 
caneed  by  the  weight  of  the  entire  structure,  and  also  by  the  earth 
around  the  base  of  the  foundation,  and  hence  there  is  no  need,  in 
this  connection,  of  considering  this  manner  of  failure. 

306.  DznOKiae  TEZ  PoOTJve.  The  term  footing  is  nsnally  no- 
deretood  as  meaning  the  bottom  course  or  coarses  of  masonry  which 
extend  beyond  the  &ces  of  the  wall.  It  will  be  need  here  as  apply- 
ing to  the  material — whether  maeonry,  timber,  or  iron — employed 
to.increaee  the  area  of  the  base  of  the  fonndation.  Whatever  the 
character  of  the  soil,  footings  should  extend  beyond  the  face  of  the 
wall  (1)  to  add  to  the  stability  of  the  structare  and  lessen  the  dan- 
ger of  the  work's  being  thrown  out  of  plumb,  and  (3)  to  distribute 
the  weight  of  the  stmcture  over  a  larger  area  .and  thus  decrease 
the  settlement  due  to  the  compression  of  the  ground.  To  serve 
the  first  purpose,  footings  must  be  securely  bonded  to  the  body  of 
the  wall ;  and  to  produce  the  second  effect,  they  most  have  sufficient 
strength  to  resist  the  transverse  strain  to  which  they  are  exposed. 
In  ordinary  bnildings  the  distribution  of  the  weight  ie  more  impor- 
tant than  adding  to  the  resistance  to  overturning,  and  hence  only 
the  former  will  be  considered  here. 

The  area  of  the  foundation  may  be  increased  until  the  inherent 


ovGoQi^lc 


208  OBDINABT  FOUNDATIONS.  ^CUAP.  X. 

bearing  power  of  the  area  covered  is  sufficient  to  support  the  load 
(1)  by  extending  the  bottom  courses  of  niaaonry,  or  (2)  by  tlie  sae 
of  one  or  more  layere  of  timbers,  railroad  rails,  or  steel  I-beams,  or 
(3)  by  resting  the  strnctare  upon  inverted  masonry  arches. 

306.  Off'Seti  of  Moionry  Footings.  The  area  of  the  fonndstion 
having  been  determined  and  its  ceuter  having  been  located  with 
reference  to  the  axis  of  the  load  (g  297),  the  next  step  is  to  deter- 
mine how  much  narrower  each  footing  course  may  be  tlutn  the  one 
next  below  it.  The  projecting  part  of  the  footing  resists  as  a  beam 
fixed  at  one  end  and  loaded  unUormly.  The  load  is  the  pressure 
on  the  earth  or  on  the  courne  next  below.  The  oS-set  of  such  a 
couree  depends  upon  the  amount  of  the  pressure,  the  transverse 
strength  of  the  material,  and  the  thickness  of  the  course. 

To  deduce  a  formula  for  the  relation  between  theae  qnantitieB, 
let 

P  =  the  pressure,  in  tons  per  square  foot,  t^t  the  bottom  of  the 
footing  courae  under  consideration  ; 

S  =  the  modulus  of  rupture  of  the  material,  in  pounds  per 
square  inch ; 

p  =  the  greatest  possible  projection  of  the  footing  course,  in 

inchea ; 
/  =  the  thicknees  of  the  footing  course,  in  inches. 

The  part  of  the  footing  course  that  projects  beyond  the  one  above 
it,  is  a  cantilever  beam  uniformly  loaded.  From  the  principles  of 
the  resiatauce  of  materials,  we  know  that  the  upward  pressure  of  the 
earth  against  the  part  that  projects  multiplied  by  one  half  of  the 
length  of  the  projection  is  equal  to  the  continued  product  of  one 
sixth  of  the  modulus  of  rupture  of  the  material,  the  breadth  of  the 
footing  course,  and  the  square  of  the  thickness.  Expressing  this 
relation  In  the  above  nomenclature  and  reducing,  we  get  the  for- 
mula 


or,  with  Bufflcient  acouracj, 

p=ii/^ m 

Hence  the  projection  available  with  any  given  thicknesa,  or  the 
thickness  required  for  any  given  projection,  ma;  easily  be  computed 


ovGoQi^lc 


ABT.  2.] 


DESmSIKQ  THE   FO0TI2fQ. 


209 


by  equation  (7).     Notice  that  with  the  off-set  given  by  the  above 
formala  the  stone  would  be  on  the  point  of  breaking. 

SOT,  The  margin  to  be  allowed  for  safety  will  depend  npon  the 
care  used  in  computing  the  loads,  in  solocting  the  materials  for  the 
footing  courses,  and  in  bedding  and  plucing  them.  If  all  the  loads 
have  been  allowed  for  at  their  probable  maximum  value,  and  if  the 
material  is  to  be  reasonably  uniform  in  quality  and  laid  with  care, 
then  a  comparatively  small  margin  for  safety  is  sufficient ;  but  if 
all  the  loads  have  not  been  carefully  computed,  and  if  the  job  is  to 
be  done  by  an  unknown  contractor^  aud  neither  the  material  nor 
the  work  is  to  be  carefully  inspected,  then  a  large  mai^in  is  neces- 
sary. As  a  general  rnle,  it  is  better  to  assume,  for  each  particular 
case,  a  factor  of  safety  in  accordance  with  the  attendant  conditions 
of  the  problem  than  blindly  to  use  the  results  deduced  by  the 
application  of  some  arbitrarily  assumed  factor.  The  following  table 
is  given  for  the  conrenience  of  those  who  may  wish  to  use  10  as  a 
factor  of  safety. 

TABLE  25. 
Save  Off^aet  tob  Hasomrt  Foorras  Coitrsbs,  in  Tsbub  of  thz  Thick- 

MESS  OF  THE  CotlBSE,  USINO  10  AS  A  FaCTOB  OF  BAyKTT. 

For  limitations,  see  §  808. 


B1u»«toDe  flagglag  iaee  page  18). . 

Onniie(EeepBge  18) 

Linieslone  (ai-e  |uig«  IS) 

SiiDtlBtoDe  (see  piige  18) 

Slate  (He  pnge  18) 


Bent  Hard  Brick  (we  page*  40.  41) 

Huril  Brick  (see  pages  4U,  41) 

1 1  Forlland ) 

Coucrete  (see  page  llSt)  i'i  sand  )■ 
(8  pebbles  ) 
1 1  Fonltuid  > 

Concrete  (see  page  IISp)  -(B  sand        [■ 

<  5  pebbles  ) 


To  illoBtrate  the  method  of  using  the  preceding  table,  assume 
that  it  is  desired  to  determine  the  off-set  for  a  limestone  footing 
course  when  the  pressure  on  the  bed  of  the  foundation  is  1  ton  per 
square  foot,  using  10  as  a  factor  of  safety.     In  the  table,  opposite 


ovGoQi^lc 


310  OBOmABT  FOUITDATIONS.  [CHA.P.  X. 

limestone,  ia  next  to  the  lut  ccdnmn,  ve  find  ih»  qnantit;  1.9. 
This  BhowB  that,  ander  the  conditions  stated,  the  ofl-Bet  may  be  1.9 
times  the  thickneaa  of  the  conne. 

The  Talnea  in  the  table  a^ree  Tery  veil  with  the  practioe  of  th« 
principal  architects  and  engineen  for  hammer-dreeaed  stones  laid 
in  good  cement  mortar. 

If  it  ie  desired  to  use  any  other  factor  of  safety,  it  is  only  neces- 
sary to  BubstitaU  for  R,  in  the  preceding  formula,  the  desired  frac- 
tional part  of  that  quantity  as  given  in  the  second  colnnm  of  the 
above  table.  For  example,  aasnme  that  it  is  necessary  to  use  lime- 
stone in  the  foundation,  and  that  it  is  required  to  draw  in  the  foot- 
ing courses  as  rapidly  as  possible.  Assome  also  that  the  pressun, 
P,  on  the  base  of  the  foundation  is  3  tone  per  square  foot.  If  the 
limestone  is  of  the  best,  and  if  it  is  laid  with  great  care,  it  will  be 
sufficient  to  use  1  as  a  factor  of  safety.  Under  these  condition^ 
equation  (7)  as  above  gives 

That  is,  the  projection  maybe  2.3  times  the  thickness  of  the  course. 

308.  Strictly,  the  above  compntations  are  correct  only  for  the 
lower  ofF-set,  and  then  only  when  the  footing  is  composed  of  stones 
whose  thickness  is  equal  to  the  thickness  of  the  course  and  which 
project  less  than  half  their  length,  and  which  are  also  well  bedded. 
The  resistance  of  two  or  more  conrses  to  bending  varies  as  the  square 
of  their  depth,  and  the  bending  due  to  the  aniform  pressure  on  the 
base  will  also  increase  as  the  square  of  the  sum  of  the  projections, 
and  therefore  the  suocessive  ofE-sets  should  be  proportional  to  the 
thickness  of  the  course;  or,  in  other  words,  the  Talnes  as  above  are 
applicable  to  any  course,  provided  no  stone  projects  more  than  half 
ito  length  beyond  the  top  couise. 

The  preceding  results  will  be  applicable  to  built  footing  courses 
only  when  the  pressure  above  the  coarse  is  lees  than  the  safe  strength  ' 
<d  the  mortar  (see  §  133  and  g  157a).  The  proper  projection  for 
rubble  masonry  lies  somewhere  between  the  values  given  for  stone 
and  those  given  for  concrete.  If  the  rubble  consists  of  large  stones 
well  bedded  in  good  strong  mortar,  then  the  values  for  this  class  of 
masonry  will  be  but  little  less  than  those  given  in  the  table.  If  the 
rabble  oonsistB  of  amall  irregular  stones  laid  with  PortUnd  or  nat- 


ovGoQi^lc 


ART.  2.J  DESIQITINQ  THE   FOOTOra.  ZU 

nral  cement  mortar,  the  projection  should  not  much  exceed  that 
giren  for  concrete.  It  the  mbble  is  laid  in  lime  mortar,  the  pro- 
jection of  the  footing  coarse  sboold  not  be  more  than  half  that 
alloved  when  cement  mortar  is  used.' 

309.  Timber  Footing.  In  very  soft  earth  it  would  be  inexpe- 
dient to  use  masonry  footiugB,  since  the  foundation  would  be  Tury 
deep  or  occupy  the  space  usually  devoted  to  the  cellar.  One  method 
of  OTercoming  this  difficulty  consista  in  conBtrncting  a  timber  grat- 
ing, sometimes  called  a  grillage,  by  setting  a  aeries  of  heavy  timbers 
firmly  into  the  soU,  and  laying  another  series  transversely  on  top  of 
these.  The  timbers  may  be  fostened  at  their  intorsectionB  by  spikes 
or  drift-bolts  (g  381)  if  there  is  any  possibility  of  sliding,  which  is 
unlikely  in  the  class  of  foundations  here  considered.  The  earth 
should  be  packed  in  between  and  around  the  serera]  beams,  A 
flooring  of  thick  planks,  often  termed  a  platform,  is  laid  on  top  of 
the  grillage  to  receive  the  lowest  course  of  masonry.  In  extremtt 
cases,  the  timbers  in  one  or  more  of  the  courses  are  laid  close  to- 
gether. Timber  should  never  be  used  except  where  it  will  be  alvrays 
wet. 

The  amount  that  a  course  of  timber  may  project  beyond  the  one 
next  above  it  can  be  determined  by  equation  (7),  page  208.  Making 
R  in  that  equation  equal  to  1,000 — the  value  ordinarily  used, — and 
solving,  we  obtain  the  following  results  for  the  safe  projection:  If 
the  pressure  on  the  foundation  is  0.5  ton  per  square  foot,  the  safe 
projection  is  7.5  times  the  Uiickness  of  the  coarse ;  if  the  pressure 
is  1  ton  per  square  foot,  the  safe  projection  is  5.3  times  the  thick- 
ness of  the  coarse ;  and  if  the  pressure  is  2  tons  per  square  foot,  the 
safe  projection  is  3.7  times  the  thickness  of  the  course.  The  above 
values  give  a  factor  of  safety  of  about  10.  To  use  any  other  factor, 
insert  in  equation  (7),  above,  the  corresponding  fractional  part  of  the 
ultimate  transverse  strength  of  the  particular  timber  to  be  used, 
and  solve. 

The  above  method  of  computation  is  not  applicable  to  two  or 
more  conrses  of  timber,  if  one  is  transverse  to  the  other. 

310.  This  method  of  increasing  the  area  of  the  footing  is  much 
osed  at  New  Orleans.  The  Custom-house  at  that  place  is  founded 
npon  a  3-inch  plank  flooring  laid  7  feet  below  the  street  pavement, 
A  grillage,  consisting  of  timbers  13  inches  square  laid  side  by  side, 
is  laid  npon  the  floor,  over  which  similar  timbers  are  placed  tranr 
Tersely,  2  feet  apart  in  the  clear. 


ovGoQi^lc 


SIS  OBDINAKT  P0UHDATI0N8,  [CHAP.  X. 

Most  of  the  bnildinga  of  the  World's  GolninbUn  Exposition, 
Chicago,  1893,  were  tonnded  npon  timber  footings. 

311.  Steel  Footing.  Veiy  recently,  steel,  usnallj  in  the  form 
of  railrottd  rails  or  I-beams,  baa  been  need  instead  of  timber  ia 
fonndatioQB.  The  rails  or  I-boams  are  placed  side  by  side,  and 
concrete  is  rammed  in  between  them. 

Steel  '\a  superior  to  timber  for  this  pnrpoee,  in  that  the  latter 
oan  be  used  only  where  it  is  always  wet,  while  the  former  is  not 
affected  by  Tariations  of  wetness  and  dryness.  Twenty  years'  ex- 
perience in  this  nse  of  steel  at  Chicago  shows  that  after  a  short  time 
ihe  snrfane  of  the  metal  becomes  encased  in  a  coating  which  pre- 
vents further  oxidation.  The  most  important  sdvant^e,  howeTor, 
in  this  use  of  steel  is  that  the  oS7set  can  be  much  greater  with  steel 
than  with  wood  or  Btone;  and  hence  the  foandations  may  be  shal- 
low, and  still  not  occupy  the  cellar  space. 

The  proper  projectioos  for  the  steel  beams  can  be  oompnted  by 
ft  formula  somewhat  similar  to  that  of  g  306 ;  bnt  the  steel  footing 
Ib  appropriately  a  part  of  the  steel-skeleton  constmction,  and  hence 
will  not  be  considered  here.  For  a  presentation  of  the  method 
of  compntations  formerly  employed  in  Chicago,  see  Engineering 
Newt,  Tol.  xxri.  page  133;  and  for  adverse  criticisms  thereon,  see 
md.f  pages  SfSS,  312,  415,  and  toI.  xxxii.  page  387.  Concerning 
the  effect  of  the  strength  of  the  base  of  the  column,  see  Johnson's 
"Modern  Framed  Structures,"  pages  444—46.  For  a  diHcnssioti 
which  considers  the  deflection  of  Ihe  severul  beams,  see  Engineering 
Record,  Tol.  xxxix.  pages  333-34,  354^56,  383,  407-8.  The  last 
is  the  most  exact  method  of  analysis,  and  also  seonres  the  greatest 
economy  of  material. 

31S.  XuTerted  Aroh.  Inrerted  arehes  are  frequently  bnilt  nnder 
and  between  the  bases  of  piers,  as  shown  in  Fig.  55.  Employed  in 
this  way,  the  arch  simply  distributes 
the  preeenre  over  a  greater  area;  but 
it  is  not  well  adapted  to  this  use,  for 
Ut'TKaxi::'Ti^''[jvtr''-- ji'-''^^«  (^)  ''  ^^  nearly  impossible  to  prevent 
^^r-^^^^^^'^'f^^^^4^h  ^^  ^^^  piers  of  a  series  from  being 
pushed  outward  by  the  thrust  of  the 
"^"^  arch,  and  (2)  it  is  generally  impos- 

sible, with  inverted  arches,  to  make  the  areas  of  the  different  parts 
of  the  foondatioi!  proportional  to  the  load  to  be  supported  (see  g 


ovGoQi^lc 


AST.  3.]  FBBPASISS  TSB  BED,  21S 

297).     The  only  advantage  the  inverted  arch  has  over  msBonij 
footingB  is  in  the  Bhallover  foundation  obtained. 

313.  In  a  few  caeee  masonry  pierB  have  been  ennk  to  a  solid  snb- 
stratam  by  excavating  the  material  from  the  inside,  and  then  resting 
arches  on  these  piore.  This  is  an  ezpeosive  method,  and  has  essen- 
tially the  same  objectiona  as  the  inverted  arch. 

A&T.  Z.  Feepabino  the  Bed.  ' 

314.  Ok  Bock.  To  prepare  a  rock  bed  to  receive  a  foundation 
it  is  generally  only  necessary  to  cnt  away  the  loose  and  decayed  por- 
tions of  the  rock,  and  to  drees  it  to  a  plane  snr&ce  as  nearly  perpen- 
dicular to  the  direction  of  the  pressure  as  is  practicable.  If  there 
are  any  fiaaareB,  they  should  be  filled  with  concrete.  A  rock  that 
is  very  mnch  brokeo  can  be  made  amply  secnre  tor  a  foundation  b^ 
the  liberal  use  of  good  cement  concrete.  The  piers  of  the  Niagara- 
Caotilever  Bridge  are  founded  upou  the  top  of  a  bank  of  bowlders^ 
which  were  first  cemented  together  with  concrete. 

Sometimes  it  is  neQeesary  that  certain  parts  of  a  structure 
start  from  a  lower  level  than  the  others.  In  this  case  care  should 
be  taken  (1)  to  keep  the  mortar-joints  as  thin  as  possible,  (2)  to  lay 
the  lower  portions  in  cement,  and  (3)  to  proceed  slowly  with  the 
work ;  otherwise  the  greater  quantity  of  mortar  in  the  wait  on  the 
lower  portions  of  the  slope  will  canse  greater  settling  there  and  a 
consequent  breaking  of  the  joints  at  the  stepping- places.  The 
bonding  over  the  off-sets  should  receive  particular  attention. 

316.  Ok  Pixk  Eabte.  For  foundations  in  such  earths  as  hard 
clay,  clean  dry  gravel,  or  clean  sharp  sand,  it  is  only  necessary  to 
dig  a  trench  from  3  to  6  feet  deep,  so  that  the  foundation  may  be 
below  the  disintegrating  effect  of  frost.  Provision  should  also  be 
made  for  the  drainage  of  the  bed  of  the  foundation. 

With  this  class  of  foundations  it  often  happens  that  one  part  of 
the  structure  starts  from  a  lower  level  than  another.  When  this  is 
the  case  great  care  is  required.  All  the  precantions  mentioned  in 
the  second  part^raph  of  §  314  should  be  observed,  and  great  care 
should  also  be  taken  so  to  proportion  the  load  per  unit  of  area  that 
the  settlement  of  the  foundation  maybe  uniform.  This  is  difficnlt 
to  do,  since  a  variation  of  a  few  feet  in  depth  often  makes  a  great 
difference  in  the  supporting  power  of  the  soiL 


ovGoQi^lc 


'iU  OBDINABT  VOUVDATIOKB.  [CHAP.  Z. 

316.  Ik  Wn  OBono.  The  difflcalty  in  boiIb  of  tbie  class  is  in 
dispoaing  of  the  water,  or  in  prevuntiag  the  semi-liquid  soil  from 
rnnDing  into  the  excavation.  The  difficulties  are  similar  to  those 
met  with  in  couBtnicting  ronndations  under  water — see  Chapter  XIL 
Three  general  methods  of  laying  a  foundation  in  this  kind  of  soil 
will  be  hriefly  deacribed. 

317.  Coffer-Sam.  If  the  soil  is  only  moderately  wet — ^not  satu- 
rated,— it  is  sufficient  to  inclose  the  area  to  be  ezcayated  with  sheet 
pilee  (boards  driren  vertically  into  the  ground  in  contact  with  each 
other).  This  curbing  is  a  simple  form  of  a  coffer-dam  (Art.  1, 
Chap.  XII).  The  boerds  should-  be  sharpened  wholly  from  one 
aide;  this  point  being  placed  next  to  the  last  pile  driven  causes 
them  te  crowd  together  and  make  tighter  joints.  The  sheeting  may 
be  driven  by  hand,  by  a  heavy  weight  raised  by  a  tackle  and  then 
dropped,  or  by  an  ordinary  pile-driver  (§§  336-36).  Unless  the 
amount  of  water  is  quite  small,  it  will  be  necessary  to  drive  a  double 
row  of  sheeting,  breaking  joints.  It  will  not  be  possible  to  entirely 
prevent  leaking.  The  water  that  leaks  in  may  be  bailed  out,  or 
pumped — either  by  hand  or  by  steam  (see  g  395). 

To  prevent  the  sheeting  from  being  forced  inward,  it  may  be 
braced  by  shores  placed  horizontally  from  side  te  side  and  abutting 
against  walee  (horizontal  timbers  which  rest  against  the  sheet  piles). 
The  bracing  is  put  in  snccessiyely  from  the  top  aa  the  excavation 
proceeds ;  and  as  the  masonry  is  built  up,  short  braces  between  the 
sheeting  and  the  masonry  are  substituted  for  the  long  braces  which 
previously  extended  from  side  te  side.  Iron  screws,  somewhat 
similar  to  jack-screws,  are  used,  instead  of  timber  shores,  in  exca- 
vating trenches  for  the  foundations  of  buildings,  for  sewers,  ete. 

If  one  length  of  sheeting  will  not  reach  deep  enough,  an  addi- 
tional section  can  be  placed  inside  of  the  one  already  In  position, 
when  the  excavation  has  reached  a  sufficient  depth  to  require  it. 
Ordinary  planks  8  to  13  inches  wide  and  H  or  3  inches  thick  are 
used. 

For  a  more  extended  account  of  the  use  of  coffer-dams,  see 
Chapter  XII — Foundations  Under  Water,  Art.  1 — Coffer-Dams. 

316.  In  some  oases  the  soil  is  more  easily  excavated  if  it  is  first 
drained.  To  do  this,  dig  a  hole — a  sump — inte  which  the  water  will 
drain  and  from  which  it  may  be  pumped.  If  necessary,  several 
anmpa  may  be  sunk,  and  deepened  as  the  excavation  proceeds. 


ovGoQi^lc 


JlBI.  3.]  PRBPABISQ  THE  BED,  216 

Qaicksand  or  soft  alluTinm  may  aometimee  be  pamped  out  along 
with  the  water  bj  a  centrifugal  or  a  mud  pump  (g  395  and  g  448). 
Od  large  jobs,  each  material  is  sometimea  taken  out  with  a  clam- 
Bhell  or  orange-peel  dredge  (§  412). 

319.  Concrete.  Concrete  can  frequently  be  used  advantage- 
ously  in  fouudations  in  wet  soils.  If  the  water  can  be  removed,  the 
concrete  should  be  deposited  in  continuous  layers,  about  6  inches 
thick,  and  gently  rammed  until  the  water  begins  to  ooze  out  on  the 
upper  surface  (see  g  158/).  If  the  water  can  not  be  removed,  the 
concrete  may  be  deposited  under  the  water  (see  §  IMq),  although  it 
is  more  difficult  to  insure  good  results  by  this  method  than  when 
the  concrete  is  deposited  in  the  open  air.* 

380.  Orillage.  If  the  semi-liquid  soil  extends  to  a  considerable 
depth,  or  if  the  soft  soil  which  overlies  a  solid  substratum  can  not  be 
removed  readily,  it  is  customary  to  drive  piles  at  uniform  distances 
over  the  area,  and  construct  a  grilli^e  (see  §  380)  on  top  of  them. 
This  construction  is  very  common  for  bridge  abutments  (Chapter 
XV).  The  piles  should  be  sawed  off  (§  378)  below  low-water,  which 
usually  necessitates  a  coSer-dani  (g  317,  and  Art.  1  of  Chapter  XII), 
and  the  ezcavatiou  of  the  soil  a  little  below  the  low-water  line. 

For  a  more  extended  account  of  this  method  of  laying  a  founda- 
tion, see  §§  360-82. 

321.  In  excavating  shallow  pita  in  sand  conteining  a  small 
amount  of  water,  dynamite  cartridges  have  been  soccesef nlly  used  to 
drive  the  water  out  A  hole  is  bored  with  an  ordinary  auger  and 
the  cartridge  inserted  and  exploded.  The  explosion  drives  the  wator 
hack  into  the  soil  so  far  that,  by  working  rapidly,  the  hole  can  be 
excavated  and  a  layer  of  concrete  placed  before  the  water  returns. 

322.  CovcLiruoir.  It  is  hardly  worth  while  here  to  discuss  this 
subject  further.  It  is  one  on  which  general  instruction  can  not  be 
given.  Each  case  must  be  dealt  with  according  to  the  attendant 
circumstances,  and  a  knowledge  of  the  method  best  adapted  to  any 
given  conditions  comes  only  by  experience. 


ovGoQi^lc 


CHAPTER  XL 
PILE  FOUNDATIOHS. 

3S3.  DllunriOHL  File.  Although  a  pile  is  generally  tmdeh 
stood  to  be  a  roand  timber  driveD  into  the  soil  to  support  a  load, 
the  term  has  a  variety  of  applications  which  it  will  be  well  to  explain. 

Staring  Pile.  One  used  to  sustain  a  vertical  load.  This  is  the 
ordinai'y  pile,  and  usually  is  the  one  referred  to  when  the  word  pile 
is  employed  without  qualificatios. 

Sheet  Piles.  Thick  boards  or  timbers  driven  in  close  contact 
to  inclose  a  space,  to  prevent  leakage,  etc.  Generally  they  are  con- 
siderably wider  than  thick;  but  are  sometimes  square,  in  which  case 
they  are  often  called  close  piles. 

False  Pile.  A  timber  added  to  a  pile  after  driving,  to  supple- 
ment its  length. 

Foundation  Pile.  One  driven  to  increase  the  supporting  power 
of  the  soil  under  a  foundation. 

Screw  Pile.  An  iron  shaft  to  the  bottom  of  which  is  attached 
a  broad-bladed  screw  having  only  one  or  two  turns. 

Disk  Pile.  A  bearing  pile  near  the  foot  of  which  a  disk  is  keyed 
or  bolted  to  give  additional  bearing  power. 

Pneumatic  Pile.  A  metal  cylinder  which  is  sunk  by  atmoB-- 
pherio  pressure.  This  form  of  pile  will  be  discussed  in  the  next 
chapter  (see  g  431). 

Abt.  1.  DESCKiFnoNs,  AND  Ukthodb  of  Driving. 

SH.  Isov  Fueb.  Both  cast  and  wrought  iron  are  employed  for 
ordinary  bearing  piles,  sheet  piles,  and  for  cylinders.  Iron  cylin- 
ders are  generally  sunk  either  by  dredging  the  soil  from  the  inude 
(g  415),  or  by  the  pnenmstic  process  (eee  the  next  chapter,  particu- 
larly g§  431-35).  For  another  method  of  employing  iron  cylinders, 
see  gg  364r^. 


ovGoQi^lc 


iBT.  1.]      DBsoBiPnoira,  and  xsthods  ov  dbitinq.  'in 

C^t-iron  piles  are  b^nniag  to  be  nsed  as  eabstitatea  for  com- 
mon wooden  ones.  Lnge  or  flanges  are  Qsuallj  cast  on  the  udes  of 
the  piles,  to  which  bracing  may  be  attached  for  secaring  them  in 
position.  A  wood  block  is  laid  upon  the  top  of  the  pile  to  receive 
the  hammer  used  in  driving  it;  and,  after  being  driven,  a  cap  with 
a  socket  in  its  lower  side  is  placed  upon  the  pile  to  receive  the  load. 
The  supporting  power  la  sometimes  increased  by  keying  on  an  iron 
disk.  The  advantages  claimed  for  cast-iron  piles  are:  (I)  they  are 
not  subject  to  decay;  (2)  they  are  more  readily  driven  than  wooden 
ones,  especially  in  stony  ground  or  stifl  clay;  and  (3)  they  possess 
greater  cmshing  etrength,  which,  however,  is  an  advantage  only 
when  the  pile  acts  as  a  column  (see  §  355).  The  principal  disadvan- 
tage is  that  they  are  deficient  in  transverse  resistance  to  a  suddenly 
applied  force.  This  objection  applies  only  to  the  handling  of  the 
piles  before  being  driven,  and  to  such  as  are  liable,  after  being  driven, 
to  sudden  lateral  blows,  as  from  floating  ice,  logs,  etc 

Recently,  rolled  sections  of  wroaght-iron  have  been  employed  to  a 
limited  degree  for  bearing-piles,  but  present  prices  prohibit  an  ex- 
tended use  of  wrought-iron  piles.  It  is  possible  that  iron  may  take 
the  place  of  wood  for  piles  where  they  are  alternately  wet  and  dry, 
or  where  they  are  ditBcalt  to  drive;  but  where  the  piles  are  always 
wet — aa  is  usually  the  case  in  foundation  work, — wood  is  as  dnrable 
as  iron;  and  hence,  on  account  of  cheapness,  is  likely  to  have  the 
preference. 

326.  BOBEW  Puis.  Tbesearegenerally  wholly  of  iron,  although 
the  stem  is  sometimes  wood.  The  screw  pile  usually  consists  of  a 
rolled-iron  shaft,  3  to  8  inches  in  diameter,  having  at  its  foot  one  or 
two  turns  of  a  cast-iron  screw,  the  blades  of  which  may  vary  from  1^ 
to  S  feet  in  diameter.  The  piles  ordinarily  employed  for  light- 
honsea  exposed  to  moderate  seas  or  to  heavy  fields  of  ice  have  a 
shaft  3  to  5  inches  in  diameter  and  blades  3  to  4  feet  in  diameter, 
the  screw  weighing  from  600  to  700  pounds.  For  bridge  piers, 
the  shaf fas  are  from  6  to  8  inches  and  the  blades  from  4  to  6  feet  in 
diameter,  the  screw  weighing  from  1,500  to  4,000  pounds. 

Screw  piles  were  invented  by  Mitchell  of  Belfast,  and  are  largely 
need  in  Europe,  but  not  to  any  great  extent  in  this  country.  They 
have  been  nsed  in  founding  small  light-houses  on  the  sea-shore,  for 
signal  stations  in  marine  surveying,  for  aochonge  for  buoys,  and 
for  various  purposes  inland. 


ovGoQi^lc 


218  PILE  POONDATIOSB.  [CHAP.  XI. 

For  founding  beacons,  etc. ,  the  screw  pile  has  the.  Bpecial  advaQ- 
tage  of  not  being  drawn  out  by  the  upward  force  of  the  waves  against 
the  euperstructare,  Eren  when  all  cohesion  of  the  ground  is  de> 
Btroyed  in  screwing  down  a  pile,  a  conical  mass,  with  its  apex  at  the 
bottom  of  the  pile  and  its  base  at  the  surface,  wonld  have  to  be 
lifted  to  draw  the  pile  out.  The  supporting  power  also  is  consider- 
al  1 ;  owing  to  the  increased  bearing  surface  of  the  screw  blade. 
Screw  piles  have,  therefore,  an  advantage  in  soft  soil.  They  could 
also  be  used  advant^eously  in  situations  where  the  jar  of  driving 
ordinary  piles  might  disturb  the  equilibrium  of  adjacent  atructurea. 

326.  These  piles  are  usually  screwed  into  the  soil  by  men  work- 
ing with  capstan  bara  Sometimes  a  rope  is  wound  around  the 
shaft  and  the  two  ends  pulled  in  opposite  directions  by  two  capstans, 
and  sometimes  the  screw  is  turned  by  attaching  a  large  cog-wheel  to 
the  shaft  by  a  friction-clutch,  which  is  rotated  by  a  worm-screw 
operated  by  a  hand  crank.  Of  course  steam  or  horse>power  conld 
be  used  for  this  purpose. 

The  screw  will  penetrate  most  soil  .  It  will  pass  through  loose 
pebbles  and  stones  without  much  difficulty,  and  push  aside  bowlders 
of  moderate  size.  Ordinaryclay  does  not  present  much  obetmction; 
cbeein,  dry  sand  gives  the  moat  difficulty.  The  danger  of  twisting 
off  the  shaft  limita  the  depth  to  which  they  may  be  sunk.  Screw 
piles  with  blades  i  feet  in  diameter  have  been  screwed  40  feet  into 
a  mixture  of  clay  and  sand.  The  resistance  to  sinking  increases 
very  rapidly  with  the  diameter  of  the  screw;  but  under  favorable 
(drcumstances  an  ordinary  screw  pile  can  be  sunk  very  quiCkly. 
Screws  4  feet  in  diameter  have,  in  less  than  two  hoars,  been  sunk 
by  hand-labor  90  feet  in  sand  and  clay,  the  surface  of  which  was 
20  feet  below  the  water.  For  depths  of  15  to  20  feet,  an  average  of 
4  to  8  feet  per  day  is  good  work  for  wholly  hand-labor. 

For  an  illnstrated  and  detailed  account  of  the  founding  of  a  rail- 
road bridge  pier  on  screw  piles,  see  Engineering  News,  Vol.  XIIL 
pp.  310-13. 

327.  Due  Filbs.  These  differ  but  little  from  screw  piles,  a 
flat  disk,  instead  of  a  screw,  being  keyed  on  at  the  foot  of  the  iron 
stem.  Disk  piles  are  sank  by  the  water-jet  (g  343).  One  of  the  few 
cases  in  which  they  have  been  used  in  this  country  was  in  founding 
an  ocean  pier  on  Coney  Island,  near  Kew  York  City.  The  shafts 
were  wrought-iron,  lap-welded  tubes,  8f  inches  outside  diameter,  in 


ovGoQi^lc 


ABT.  1.]         DBSCBIPTIONS,   AND  UETHODS  OF  DBITIXO.  219 

sectioQB  12  to  20  feet  loag ;  the  diska  were  2  feet  Id  diameter  and 
9  inches  thick,  and  were  fastened  to  the  shaft  by  eet-screvB.  Many 
of  the  pUes  were  57  feet  long,  of  which  17  feet  was  in  the  sand.* 

328.  Sah  Pzlxs.  For  an  account  of  the  method  of  nsing  sand 
as  piles,  see  g  3S8. 

929.  Shut  Filh.  These  are  flat  piles,  which,  being  driven 
saccessively  edge  to  edge,  form  a  vertical  or  nearly  vertical  sheet 
for  the  purpose  of  preventing  the  materials  of  a  foundation  from 
spreading,  or  of  guarding  them  against  the  undermining  action  of 
water.  They  may  be  made  either  of  timber  or  iron.  Ordinarily 
sheet  piles  are  simply  thick  planks,  sharpened  and  driven  edge  to 
«dge.  Sometimes  they  have  a  tongue  on  one  edge  and  a  correspond- 
ing groove  on  the  other,  to  aid  in  guiding  them  into  place  while 
driviug.  When  heavy  timbers  are  employed  as  sheet  piling,  wooden 
blocks  or  iron  lugs  are  fastened  on  the  edges  to  assist  in  guiding 
them  into  position.  Sheet  piles  should  be  sharpened  wholly,  or  at 
least  mainly,  from  one  side,  and  the  long  edge  placed  next  to  the 
pile  already  driven.  This  causes  them  to  crowd  together  and 
make  comparatively  close  joints. 

When  a  space  is  to  be  inclosed  with  sheet  piling,  two  rows  of 
gnide  piles  are  first  driven  at  regular  intervals  of  from  6  to  10  feet, 
and  to  opposite  sides  of  these,  near  the  top,  are  notched  or  bolted  a 
pair  of  parallel  string-pieces,  or  wales,  from  6  to  10  inches  square, 
so  fastened  to  the  guide  piles  as  to  leave  a  space  between  the  wales 
equal  to  the  thickness  of  the  sheet  piles.  If  the  sheeting  is  to  stand 
more  than  8  or  10  feet  above  the  ground,  a  second  pair  of  wales  is 
required  near  the  level  of  the  ground.  The  sheet  piles  are  driven 
(§§  334-45)  between  the  wales,  working  from  both  ends  towards 
the  middle  of  the  space  between  a  pair  of  guide  piles,  so.  that  the 
last  or  central  pile  acts  as  a  wedge  to  tighten  the  whole. 

330.  WODDEV  BEAUVe  Pubb.  Spruce  and  hemlock  answer 
very  well,  in  soft  or  medium  soils,  for  foundation  piles  or  for  piles 
always  under  water ;  the  hard  pines,  elm,  and  beech,  for  firmer 
soils ;  and  the  hard  oaks,  for  still  more  compact  soils.  Where  the 
pile  is  alternately  wet  and  dry,  white,  or  post  oak  and  yellow  or 
southern  pine  are  generally  used. 

*  For  a  dotted  uid  lUostrated  deacrlptfon  of  tbia  work,  aee  an  Mtlole  hj  Cbarlet 
Maodonald,  C.E.,  In  Tnns.  An.  Soo.  of  C.  E.,  Vcd.  Vm.  pp.  837-87. 


ovGoQi^lc 


220  PILE  FOUNDATIONS.  [CHAP.  H 

Piles  shonld  never  be  less  than  8  inches  in  diameter  at  the  small 
end  and  never  more  than  18  inches  at  the  large  end.  Specifications 
nenally  require  that  these  dimeneiona  shall  not  be  less  than  10  nor 
more  than  14  inches  respectively.  Piles  should  be  straight-grained, 
should  be  trimmed  close,  and  should  have  the  bark  removed. 

331.  Specifloations  Ua  Filet.  The  ordinary  specifications  are 
abont  as  follows  :* 

Pile*,  whether  used  In  foundatloos,  tr«8tle-vork,  or  pile  bridges,  eb&ll  be 
of  good  quality,  Musd,  while  oak^or  such  other  timber  as  tbe  engineer  may 
direct,  not  less  than  i«n  inches  (10")  in  diameter  at  the  soialler  end  and 
14  inches  (14")  at  the  larger,  and  of  such  lengths  m  the  engineer  may  require. 
Tbey  must  be  stroigbt-giatned,  must  be  trimmed  close,  and  must  have  all  the 
bark  taken  oB  before  being  driven.  They  must  be  cut  oS  square  at  the  butt, 
and  be  properly  sharpened.  If  required  by  the  engineer,  the  point  shall  be 
■liod  with  iron  shoes  [tee  g  882],  and  the  bead  hooped  with  iron  bands  of  ap- 
,  proved  dze  and  form  [see  §  883],  which  will  be  p^d  for  by  tbe  pound. 

332.  Pile  Caps  and  Shoes.  To  prevent  braising  and  splitting 
in  driving,  2  or  3  inches  of  the  bead  is  usually  chamfered  oft.  As 
an  additional  means  of  preventing  splitting,  the  head  is  often 
hooped  with  &  strong  iron  band,  2  to  3  inches  wide  and  ^  to  1  inch 
thick.  The  expense  of  removing  these  bands  and  of  replacing  the 
broken  ones,  and  the  consequent  delays,  led  to  the  introduction, 
recently,  of  a  cap  for  tbe  protection  of  the  head  of  the  pile.  The 
cap  consiste  of  a  cast-iron  block  with  a  tapered  recess  above  and 
below,  the  chamfered  head  of  the  pile  fitting  into  theJower  recess 
and  a  coshion  piece  of  hard  wood,  upon  which  the  hammer  falls, 
fitting  into  the  upper  one.  The  cap  preserves  the  head  of  the  pile, 
adds  to  the  effectiveness  of  the  blows  (§  361),  and  keeps  the  pile  head 
in  place  to  receive  the  blows  of  the  hammer. 

A  further  advantage  of  the  pile  cap  is  that  it  saves  piles.  In 
hard  driving,  without  the  cap  the  head  is  crushed  or  broomed  to 
such  an  extent  that  the  pile  is  adzed  or  sawed  off  several  times 
before  tt  is  completely  driven,  and  often  after  it  is  driven  a  portion 
of  the  head  must  be  sawed  off  to  secure  sound  wood  upon  which  to 
rest  the  grilhige  or  platform  (§  380).  In  ordering  piles  for  any  ' 
special  work  where  the  driving  is  bard,  allowance  most  be  made  for 
this  loss. 

Files  are  generally  sharpened  before  being  driven,  and  some- 

■Bee  also  "Piling"  in  the  general  apeclflcations  (or  railway  masonir,  as  given  Id 
Appendix  L 


ovGoQi^lc 


AKT.  1.]         DSSCRIPnOKB,   AND  MBTH0D8  OP  DRIVING.  231 

times,  parttcnlarty  iu  etODj  ground,  the  point  is  protected  by  an 
iron  shoe.  The  shoe  may  be  only  two  V-shaped  loops  of  bar  iron 
placed  over  the  point,  in  planes  at  right  angles  to  each  other,  and 
spiked  to  the  piles ;  or  it  may  be  a  wrought  or  cast  iron  socket,  of 
which  there  are  a  nnmber  of  forms  on  the  market. 

839.  Bplioing  PUei.  It  frequently  happens,  in  driving  piles  in 
iwampy  places,  for  false-works,  etc.,  that  a  single  pile  is  not  long 
enough,  in  which  case  two  are  spUoed  together.  A  common  method 
of  doing  this  is  as  follows  :*  after  the  first  pile  is  driven  its  head  is 
cat  off  sqnare,  a  hole  2  inches  in  diameter  and  13  inches  deep  is 
bored  in  its  head,  and  an  oak  treenail,  or  dowel-pin,  33  inches 
long,  is  driven  into  the  hole  ;  another  pile,  similarly  squared  and 
bored,  is  placed  upon  the  lower  pile,  and  the  driving  continued. 
Spliced  in  this  way  the  pile  is  deficient  in  lateral  stiSnese,  and  the 
npper  section  is  liable  to  bounce  off  while  driving.  It  is  better  to  < 
reinforce  the  splice  by  flatting  the  sides  of  the  piles  and  nailing  on, 
with  say  S-inch  spikes,  four  or  more  pieces  3  or  3  inches  thick,  4  or 
b  inches  wide,  and  4  to  6  feet  long.  In  the  erection  of  the  bridge 
over  the  Hudson  at  Foughkeepsie,  H.  Y.,  two  piles  were  thus 
spliced  tc^^her  to  form  a  single  one  130  feet  long. 

Piles  may  be  made  of  i;ny  required  length  or  oross-aection  by 
bolting  and  fishing  together,  sidewise  and  lengthwise,  a  number  of 
squared  timbers.  Such  piles  are  frequently  used  as  guide  piles  in 
sinking  pneumatic  caissons  (g  436).  Hollow-built  piles,  40  inches 
in  diameter  and  SO  feet  long,  wore  used  for  this  purpose  iu  con- 
structing the  St.  liouis  Bridge  (§  457).  They  were  sunk  by  pump- 
ing the  sand  and  water  from  the  inside  of  them  with  ^  sand  pump 
(§  «8). 

384.  Pnx-DBnmrs  Haoeihes.  Pile-driving  machines  may  be 
classified  according  to  the  chamcter  of  the  driving  power,  which 
may  be  (1)  a  falling  weight,  (3)  the  force  of  an  explosive,  or  (3)  the 
erosive  action  of  a  jet  of  water.  Plies  are  sometimes  set  in  holes 
bored  with  a  well>anger,  and  the  earth  rammed  around  them.  This 
is  quite  common  in  the  construction  of  small  highway  bridges  in 
the  prairie  States,  a  10-  or  a  12-inch  auger  being  generally  used. 
The  varions  pile-driving  machines  will  now  be  briefly  described  and 
compared. 

is  tot  RaUioad  Haaamr,  aa  glvcD  In 


ovGoQi^lc 


223  PILE  FOmTDATIONS.  [CHAF.  ZI. 

336.  Srop-hiamer  File-diiTer.  The  ubusI  method  of  driving 
pilea  is  by  a  encceeaion  of  blows  given  with  s  heavy  block  of  wood 
or  iron — called  a  ram,  monkey,  or  hammer — which  is  carried  by  a 
rope  or  chain  passing  over  a  pulley  fixed  at  the  top  of  an  upright 
frame,  and  allowed  to  fall  freely  on  the  head  of  the  pile.  The 
machine  for  doing  this  is  called  a  drop-hammer  pile-driver,  or  a 
monkey  pile-driver — aenally  the  former.  The  machine  is  generally 
placed  upon  a  car  or  scow. 

The  frame  consists  of  two  uprights,  called  leaders,  from  10  to  60 
feet  long,  placed  about  2  feet  apart,,  which  guide  the  falling  weight 
in  its  descent.  The  leaders  are  either  wooden  beams  or  iron  chau- 
uel-beams,  usnally  the  former.  The  hammer  is  generally  a  mass  of 
iron  weighing  from  500  to  4,000  pounds  {usoaUy  about  2,000)  with 
grooves  in  its  sides  to  fit  the  guides  and  a  staple  in  the  top  by  which 
it  is  raised.  The  rope  employed  in  raising  the  hunmer  is  usually 
wonnd  up  by  a  steam-engine  placed  on  the  end  of  the  scow  or  car, 
opposite  the  leaders. 

A  car  pile-driver  is  made  especially  for  railroad  work,  the 
leaders  resting  upon  an  aniiliary  frame,  by  which  piles  may  bo 
driven  14  to  16  feet  in  advance  of  the  end  of  the  track ;  and  the 
frame  is  pivoted  bo  that  piles  may  be  driven  on  either  side  of  the 
track.  This  method  of  pivoting  the  frame  carrying  the  leaders  is 
also  sometimes  applied  to  a  machine  need  in  driving  pUee  for  foun- 
dationa 

In  railroad  construction,  it  ie  not  possible  to  use  the  pile-driving 
car  with  ita  steam-engine  in  advance  of  the  track  ;  hence,  in  this 
kind  of  work,  the  leaders  are  often  set  on  blocking  and  the  ham- 
mer is  raised  by  horsee  hitched  directly  te  the  end  of  the  rope. 
Portable  engines  also  are  sometimeB  used  for  this  purpose.  Occa- 
sionally the  weight  is  raised  by  men  with  a  windlass,  or  by  pulling 
directly  on  the  rope. 

A  machine  used  for  driving  sheet  piles  differs  from  that  de- 
scribed above  in  one  particular,  viz. :  it  has  but  one  leader,  in  front 
of  which  the  hammer  moves  up  and  down.  With  this  construction, 
the  machine  can  be  brought  close  up  to  the  wall  of  a  coffer-dam 
(g  317  and  §  390],  and  the  pile  already  driven  does  not  interfere 
with  the  driving  of  the  next  one, 

336.  There  are  two  methods  of  detaching  the  weight,  i.  e.,  of 
letting  the  hammer  fall :  (1)  by  a  nipper,  and  (2)  by  a  friction-clutch. 


ovGoQi^lc 


ABT.  1.]         DBBCKIFTI0K5,    AXD   UETHODS  OP  DRXTINO.  233 

1.  The  nipper  congista  of  a  block  which  slides  freely  between 
the  leaders  and  which  carries  a  pair  of  hooke,  or  tongs,  projecting 
from  ita  lower  side.  The  tongs  are  so  arranged  that  when  lowered 
on  to  the  top  of  the  hammer  they  aatomatically  catch  in  the  staple 
in  the  top  of  the  hammer,  and  hold  it  while  it  ie  being  lifted,  until 
they  are  disengaged  by  the  upper  ends  of  the  arnu  striking  a  pair  of 
inclined  surfaces  in  another  block,  the  trip,  which  may  be  placed 
between  the  leaders  at  any  elevation,  according  to  the  height  of  fall 
desired. 

With  this  form  of  machine,  the  method  of  operation  is  as  fol- 
lows :  The  pile  being  in  place,  with  the  hammer  resting  on  the  bead 
of  it  and  the  tongs  being  hooked  into  the  staple  in  the  top  of  the 
hammer,  the  rope  is  wonnd  np  until  the  upper  ends  of  the  tongs 
strike  the  trip,  which  disengages  the  tongs  and  lets  the  hammer 
fall.  As  the  hoisting  rope  is  unwound  the  nipper  block  follows  the 
hammer,  and,  on  reaching  it,  the  tongs  automatically  catch  in  the 
staple,  and  the  preceding  operations  may  be  repeated.  This  method 
is  objectionable  owitig  to  the  length  of  time  required  (o)  for  the 
nipper  to  descend  after  the  hammer  has  been  dropped,  and  (A)  to 
more  the  trip  when  the  height  of  fall  is  changed.  Some  manufac- 
turers of  pile-driving  machinery  remove  the  last  objection  by  making 
an  adjustable  trip  which  is  raised  and  lowered  by  a  light  line  pass- 
ing over  the  top  of  the  leaders.     This  is  a  valuable  improvement. 

When  the  rope  is  wound  up  by  steam,  the  maximum  speed  is 
from  6  to  14  blows  per  minute,  depending  upon  the  distance  the 
hammer  falls.  The  speed  can  not  be  increased  by  the  skill  of  the 
operator,  although  it  could  be  by  making  the  nipper  block  heavier. 

2.  The  method  bynsing  s,  frtction-clutch,  or  friction-drum,  as  it 
is  often  called,  consists  in  attaching  the  rope  permanently  to  the 
staple  in  the  top  of  the  hammer,  and  droppmg  the  hammer  by  set- 
ting free  the  winding  drum  by  the  use  of  a  friction-clutch.  The 
advantages  of  this  method  are  (a)  that  the  hammer  can  be  dropped 
from  any  height,  thns  secaring  a  light  or  heavy  blow  at  pleasure; 
and  {b)  that  no  time  is  lost  in  waiting  for  the  nipper  to  descend  and 
in  adjusting  the  trip. 

When  the  rope  is  wound  up  by  steam,  the  speed  is  from  20  to 
30  blows  per  minute,  but  is  largely  dependent  upon  the  skill  of  the 
man  who  controls  the  friction-clutch.  The  hammer  is  caught  on 
the  rebound,  is  elevated  with  the  speed  of  a  falling  body,  and  hence 


ovGoQi^lc 


284  PILE  FOUNDATIONS.  [CHAP.  II, 

the  absolute  maximum  speed  is  attained.  The  rope,  by  which  the 
hammer  is  elevated,  retards  the  falling  weight ;  and  hence,  for  an 
equal  effect,  this  form  requires  a  beafier  hammer  than  when  the 
nipper  is  used.  Although  the  frictioo-dram  pile-driver  is  much 
more  efScient,  it  is  not  as  generally  nsed  as  the  nipper  driver.  The 
former  is  a  little  more  expensiTe  in  first  cost. 

337.  Btcam-hammer  File-driveT.  As  regards  frequency  of  use, 
the  next  machine  is  probably  the  steam-hammer  pile-driver,  invented 
by  Naamyth*  in  1839.  It  consists  essentially  of  a  steam  cylinder 
(stroke  about  3  feet),  the  piston-rod  of  which  carries  n  weight  of 
about  3,500  pounds.  The  steam-cylinder  is  fastened  to  and  between 
the  tops  of  two  I-beams  about  8  to  10  feet 
long,  the  beams  being  united  at  the  bottom  by 
a  piece  of  iron  in  the  shape  of  a  frustum  of  a 
cone,  which  has  a  hole  through  it.  The  under 
side  *>{  this  connecting  piece  is  cut  out  so  as  to 
fit  the  top  of  the  pile.  The  striking  weight,  which 
works  up  and  down  between  the  two  I-beams 
as  guides,  has  a  cylindrical  projection  on  the 
bottom  which  passes  through  the  hole  in  the 
piece  connecting  the  feet  of  the  guides  and 
strikes  the  pile.  The  steam  to  operate  the  ham- 
mer is  conveyed  from  the  boiler  through  a  flex- 
ible tube.  Fig.  56  shows  the  striking  weight  of 
the  latest  form  of  steam-hammer.  It  differs 
from  that  described  above  in  having  four  rods 
for  guides,  instead  of  the  two  I-beams. 

The  whole  mechanism  can  be  raised  and 
lowered  by  a  rope  passing  over  a  pulley  in  the 
top  of  the  leaders.  After  a  pile  has  been  placed 
in  position  for  driving,  the  machine  is  lowered 
upon  the  top  of  it  and  entirely  let  go,  the  pile 
being  its  only  support.  When  steam  is  admitted 
below  the  piston,  it  rises,  carrying  the  striking 
weight  with  it,  until  it  strikes  a  trip,  which 
'^-  •*■  cuts  off  the  steam,  and  the  hammer  falls  by  its 

own  weight.    At  the  end  of  the  down  stroke  the  valves  are  again 

•  It  ia  ordinarily  called  Naamytb'R  hammer,  but  Bourdon  ahonld  at  least  ahaio 
Ifae  credit  (see  Bng^titrbig  Xem.  vol.  xlii.  pp.  59,  eO). 


ovGoQi^lc 


AST.  1.]        DBBCEIPTIOHS,   AND  METHODS  OP  DEIVIHO.  386 

aatom&tically  reversed,  aod  the  stroke  repeated.  Sy  altering  the 
adjustment  of  tUa  trip-piece,  the  length  of  stroke  (and  thus  the 
force  of  the  blows)  can  be  increased  or  diminiBhed.  The  admiBsion 
and  escape  of  steam  to  and  from  the  cylinder  can  also  be  controlled 
directly  by  the  attendant,  and  the  nnmber  of  blowa  per  minute 
is  increased  or  diminished  by  regulating  the  supply  of  steam.  The 
machine  can  give  60  to  80  blows  per  minato. 

3S8.  Drop-hammer  ti.  Steam-hammer,  The  drop-hammer  is 
capable  of  driving  the  pile  against  the  greater  resistance.  The 
maximum  fall  of  the  drop-hammer  is  40  or  50  feet,  while  that  of 
the  steam-hammer  is  about  3  feet.  The  drop-hammer  ordinarily 
weighs  about  1  ton,  while  the  striking  weight  of  the  Bteam-hammer 
usually  weighs  about  H  tons.  The  energy  of  the  maximum  blow 
of  the  drop-hammer  is  45  foot-tons  (=  45  ft.  X  1  ton),  and  the 
energy  of  the  maximum  blow  of  the  steam-hammer  is  4.5  foot-tons 
(=  3  ft.  X  1}  tons).  The  energy  of  the  maximum  blow  of  the 
drop-hammer  is,  therefore,  about  10   times  that  of  tho  steam- 


However,  the  eflectiveness  of  a  blow  does  not  depend  alone  upon 
its  energy.  A  considerable  part  of  the  enei^  is  invariably  lost  by 
the  compression  of  the  materials  of  the  striking  surfaces,  and  the 
greater  the  velocity  the  greater  this  loss.  An  extreme  illustratioD 
of  this  would  be  trying  to  drive  piles  by  shooting  rifle-bullets  at 
them.  A  1-toa  hammer  falling  45  ft.  has  10  times  the  energy  of  a 
l|-ton  hammer  falling  3  ft.,  but  in  striking,  a  far  larger  part  of  th« 
former  than  of  the  latter  is  lost  by  the  compression  of  the  pile  head. 
In  constracttDg  the  foundation  of  the  Brooklyn  dry  dock,  it  wac 
practically  demonstrated  that  "there  was  little,  if  any,  gain  in 
having  the  fall  more  than  45  feet."  The  loss  due  to  tbe  comprea- 
sioD  depends  upon  the  material  of  the  pile,  and  whether  the  head  of 
it  is  bruised  or  not.  The  drop-ltammer,  using  the  pile-cap  and  the 
frictioD-dmm,  can  drive  a  pile  against  a  considerably  harder  reslaU 
ance  than  the  steam-hammer. 

It  is  frequently  claimed  that  the  steam-hammer  can  drive  a  pile 
i^^inst  a  greater  resistance  than  the  drop-hammer.  As  compared 
with  the  old  style  drop-hammer,  t.  «.,  without  the  friotion-drum 
and  the  pile^Mp,  this  is  probably  true.  Tbe  striking  of  tbe  weight 
upon  the  head  of  the  pile  splits  and  brooms  it  Tory  much,  which 
materially  diminishes  tbe  eflectiTenees  of  the  blow.    In  hard  driving 


ovGoQi^lc 


21S6  PILE  TOVTSDATIOSB.  [CHAP.  ZI, 

with  the  drop-hammer,  without  the  pile-cap,  the  heads  of  the  piles, 
even  when  hooped,  will  crush,  bulge  ont,  and  freqneatly  split  for 
many  feet  below  the  hoop.  For  this  reason,  it  is  sometimes  speci- 
fied that  piles  shall  not  be  driven  with  a  drop-hammer. 

The  rapidity  of  the  blows  is  an  important  it«m  as  affecting  the 
efficieaoy  of  a  pilenlriver.  If  the  blows  are  delivered  rapidly, 
the  soil  does  not  have  sufficient  time  to  recompact  itself  about 
the  pile.  AVith  the  steam-driver  the  blows  are  delivered  in  such 
quick  snocession  that  it  is  probable  that  a  second  blow  is  de- 
livered before  the  pile  has  recovered  from  the  distortion  produced 
by  the  first,  which  materially  increases  the  efleottTeness  of  the 
second  blow.  In  this  respect  the  steam-hammer  is  superior  to  the 
drop-hammer,  and  the  friction-clntch  driver  is  snperior  to  the 
nipper  driver. 

Id  soft  soils,  the  steam-hammer  drives  piles  faster  than  either 
form  of  the  drop-hammer,  since  after  being  placed  in  position  on 
the  head  of  the  pile  it  pounds  away  without  the  loss  of  any  time. 

9S9.  In  a  rough  way  the  first  cost  of  the  two  drivers — excluEdve 
of  scow  or  car,  hoisting  engine,  and  boiler,  which  are  the  same  in 
each — is  about  tSO  for  the  drop-hammer  driver,  and  about  tSOO  for 
the  steam-driver.  Of  course  these  prices  will  vary  greatly.  The  per 
cent,  for  wear  and  tear  is  greater  for  the  drop-hammer  than  for  the 
steam-hammer.  For  work  at  a  distance  from  a  machine-shop  the 
steam-driver  is  more  liable  to  cause  delays,  owing  to  breakage  of 
some  part  which  can  not  be  readily  repaired. 

3M..  Onnpowder  Pile-driver.  This  machine  was  invented  by 
Shaw,  of  Philadelphia,  in  1870.  The  expansive  force  of  gunpowder 
is  utilized  both  in  driving  the  pile  and  ia  raising  the  ram.  The 
essential  parts  of  the  machine  are  the  ram  and  gtin.  The  former 
consists  of  a  mass  of  iron  weighing  generally  about  1,500  pounds, 
which  terminates  below  in  a  sort  of  piston  ;  this  piston  fits  tightly 
into  a  chamber  in  another  mass  of  iron,  the  gun.  The  ram  travels 
between  vertical  guides  much  as  ia  the  other  machines ;  and  the 
gun  and  ram  are  hoisted  as  is  the  steam-hammer.  The  ram  having 
been  raised  to  the  top  of  the  guides,  and  the  gun  placed  upon  the 
top  of  the  pile,  a  cartridge  of  from  1  to  3  ounces  of  gunpowder 
is  placed  in  the  cylinder,  or  gun,  and  the  ram  is  allowed  to  descend. 
The  piston  enters  the  cylinder,  compresses  the  air,  and  generates 
heat  enough  to  ignite  the  cartridge,  when  the  ezpansive  force  of 


ovGoQi^lc 


XBT.  1.]        DESCBIPTIONB,   AKD  KBTBODS  OF  DBIYIKO.  3S7 

the  powder  forces  the  pile  down  and  the  ram  up.  A  cartridge  is 
thrown  into  the  gon  each  time  as  the  nun  ascends.  The  rapidi^ 
of  the  blows  is  limited  h;  the  akill  of  the  operator  sod  by  the  heat- 
ing of  the  gon.  Thirty  to  forty  blows,  of  from  S  to  10  feet  each, 
can  be  made  per  minute. 

341.  The  only  adTantage  of  this  machine  is  that  the  hammer 
does  not  come  in  contact  with  the  head  of  the  pile,  and  hence  does 
not  injure  it  The  disadvantages  are  (1)  that  it  is  of  no  assistaiice 
in  handling  the  pile ;  (2)  that  it  is  not  economical ;  (3)  that  the 
gases  soon  destroy  the  gnn  ;  (i)  that  a  leakage  of  gas  occnrg  aa  the 
gan  gets  hot,  which  renders  it  less  efficient  as  the  rapidity  of  firing 
is  increased ;  and  (5)  that  the  gnn  gets  so  hot  as  to  explode  the 
cartridge  before  the  descent  of  the  ram,  which,  of  coarse,  is  an 
entire  loss  of  the  explosive.  Its  first  cost  is  great.  It  is  not  now 
nsed. 

342.  Driving  PilM  with  Dynamite.  It  has  been  proposed  to 
drive  piles  by  exploding  dynamite  placed  directly  npon  the  top  of 
the  pile.  It  is  not  known  that  this  method  has  been  need  except 
in  a  few  instances.  It  would  be  a  slow  method,  but  might  prove 
valuable  where  only  a  few  piles  were  to  be  driven  by  saving  the 
transportation  of  a  machine ;  or  it  might  be  employed  in  locations 
where  a  machine  could  not  be  operated,  llie  higher  grades  of 
dynamite  are  most  suitable  for  this  purpose.* 

343.  Driving  Files  with  Water  Jet  Although  the  water  jet 
is  not  strictly  a  pile-driving  machine,  the  method  of  sinking  piles 
by  its  use  deserves  careful  attention,  because  it  is  often  the  cheapest 
and  sometimes  the  only  means  by  which  piles  can  be  sunk  in  mud, 
silt,  or  Band. 

The  .method  is  very  simple.  A  jet  of  water  is  forced  into  the 
soil  just  below  the  point  of  the  pile,  thus  loosening  the  soil  and 
allowing  the  pile  to  sink,  either  by  its  own  weight  or  with  very  light 
blows.  The  water  may  be  conveyed  to  the  point  of  the  pile  through 
a  flexible  hose  held  in  place  by  staples  driven  into  the  pile ;  and 
after  the  pile  is  sunk,  the  hose  may  be  withdrawn  for  use  again. 
An  iron  pipe  may  be  substituted  for  the  hose.  It  seems  to  make 
very  little  difference,  either  in  the  rapidity  of  the  sinking  or  in  the 
accuracy  with  which  the  pile  preserves  its  position,  whether  the 
nozzle  is  exactly  nnder  the  middle  of  the  pile  or  not 

"  F<x  s  brief  dcMclpticm  of  exploalTM,  Me  pp.  U9-M. 


ovGoQi^lc 


tSS  nut  rorsDATiovs.  [chap,  xl 

The  mter  jet  aeenu  to  hare  beep  first  naed  in  aigmeering  in 
1852,  at  the  taggeation  of  Genenl  Geo.  R  McCkUui.  It  hw  been 
extennTely  employed  on  the  nndy  shores  of  the  Golf  and  Sooth 
Atfauitic  States,  where  the  compactnesa  of  the  nnd  makes  it  diiE' 
cult  to  obtain  suitable  foundations  for  ligbt-bonaes,  wbarres,  etc 
Another  reason  for  its  use  in  that  section  is  that  the  palmetto  piles 
— the  onlj  ones  that  will  reaist  the  isTSgea  of  the  teredo— are  too 
soft  to  withstand  the  blows  of  the  drop-hammer  pile-driTer.  Bj 
emplojiDg  the  water  jet  the  neceaaitj  for  the  nse  of  the  pile-haminer 
is  remored,  and  conaeqaentlj  palmetto  pilea  become  aTailabl& 
The  jet  has  also  been  employed  in  a  great  rarie^  of  ways  to  &cili> 
tate  the  passage  of  common  piles,  screw  and  disk  pfles,  cylinders, 
caissons,  etc.,  etc,  through  earthy  materiaL' 

844.  The  efficiency  of  the  jet  depends  upon  the  increased  fluidity 
given  to  the  material  into  which  the  piles  are  snnk,  the  actnal  dis- 
placement of  material  being  small.  Hence  the  efficiency  of  the  jet  is 
greatest  in  clear  sand,  rand,  or  soft  clay ;  in  gravel,  or  in  saud  con- 
taining ft  large  percentage  of  giarel,  or  in  hard  clay,  the  jet  is  almost 
useless.  For  these  reasons  the  engine,  pamp,  hose,  and  nozzle 
should  be  arranged  to  delirer  large  quantities  of  water  with  a  mod- 
erate force,  rather  than  smaller  quantities  with  high  initial  Telocity. 
In  graTel,  or  in  sand  containing  considerable  gravel,  some  benefit 
might  result  trora  a  velocity  sufficient  to  displace  the  pebbles  and 
drive  them  from  the  vicinity  of  the  pile ;  but  it  is  evident  that 
any  practicable  velocity  wonid  be  powerless  in  gravel,  except  for  a 
very  limited  depth,  or  where  circumstances  favored  the  prompt 
removal  of  the  pebbles. 

The  error  most  frequently  made  in  the  application  of  the  water 
jet  is  in  using  pumps  with  insufficient  capacity.  Both  direct-acting 
and  centrifngal  pumps  are  frequently  employed.  The  former 
afkrds  the  greater  power ;  but  the  latter  has  the  advantage  of  a  less 
first  cost,  and  of  not  being  damaged  aa  greatly  by  sand  in  the  water 
used. 

The  pumping  plant  used  in  sinking  the  diak^pilee  for  the  Coney 
Island  pier  (see  g  327),  "  consisted  of  a  WorthiDgton  pump  with  a 
13-inch  steam  cylinder,  Sj-inch  stroke,  and  a  water  cylinder  7^ 
inches  in  diameter.     The  suction  hose  was  4  inches  in  diameter, 

*  B«e  »  pampbkl— "  TIm  WbWt  Jet  ma  mi  Aid  to  Englneeriiig  Coiwtnictlitt"— 
pnUtalwd  (UBl)  bj  the  Engtaieer  DepwUneot  wt  the  U.  S.  Arm;. 


ovGoQi^lc 


AKT.  1,]       DEBCEIPTI0ir8,   AND  METHODS  OF  DEITING.  22> 

and  the  diechsrge  hose,  which  was  of  fonr-plj  gum,  waa  3  inches. 
The  boiler  was  upright,  iZ  inches  in  dinmeter,  8  feet  high,  and 
contained  63  tubes  2  inches  in  diameter.  An  abundtince  of  eteam 
was  supplied  by  the  boiler,  after  the  exhaust  had  been  turned  into 
the  smoke-stack  and  soft  coal  used  as  fuel.  An  average  of  about 
160  pounds  of  coal  was  consumed  in  sinking  each  pile.  With  the 
power  above  described,  it  was  found  that  piles  could  be  driven  in 
clear  sand  at  the  rate  of  3  feet  per  minute  to  a  depth  of  I'Z  feet ; 
after  which  the  rate  of  prt^ese  gradually  diminished,  until  at  18 
feet  a  limit  waa  reached  beyond  which  it  waa  not  practicable  to 
go  without  considerable  loss  of  time.  It  frequently  happened  that 
the  pile  would  '  bring  up '  on  some  tenacious  material  which  waa 
assumed  to  be  clay,  and  through  which  the  water  jet,  unaided, 
could  not  be  made  to  force  a  passage.  In  such  cases  it  was  found 
that  by  raising  the  pile  about  6  inches  and  allowing  it  to  drop  sud- 
denly, with  the  jet  still  in  operation,  and  repeating  as  rapidly  as 
pOBsiblc,  the  obstruction  was  finally  overcome ;  although  in  some  in- 
stances five  or  six  hours  were  consumed  in  sinking  as  many  feet."  * 

In  the  shore-protection  work  on  the  Great  I^kes,  under  the 
direction  of  the  United  States  Army  engineers,  the  pumping  plant 
"consisted  of  a  vertical  tubular  boiler,  with  an  attached  engine 
having  an  8  K  12-inch  cylinder,  and  giving  about  130  revolutions  per 
minute  to  a  43-inch  driving-wheel.  A  No.  4  Holly  rotary  pump, 
with  18-inch  pulley,  was  attached  by  a  belt  to  the  driving-wheel  of 
the  engine,  giving  about  300  revolutions  per  minute  to  the  pump. 
The  pump  was  supplied  with  a  4-inch  suction  pipe,  and  discharged 
through  a  3-inch  hose  about  50  feet  in  length.  The  hose  waa  pro- 
vided with  a  nozzle  3  feet  in  length  and  2  inches  in  diameter.  The 
boiler,  engine,  pump,  and  pUe-driver  were  mounted  on  a  platform 
12  feet  iu  width  and  24  feet  in  length,"  f 

345.  Jtt  VI.  Hammer.  It  is  hardly  possible  to  make  a  compari- 
son between  a  water- jet  and  a  hammer  pile-driver,  as  the  conditions 
most  favorable  for  each  are  directly  opposite.  For  example,  sand 
yields  easily  to  the  jet,  but  o£Fers  great  resistance  to  driving  with 
tile  hammer ;  on  the  other  hand,  in  stiff  day  the  hammer  is  much 

*Chw.  McDonald,  in  Tniu.  Am.  Soc  otC.  E.,toI.  vlll.  pp.  227-87. 
t "  The  Wst<a^«t  u  ui  Aid  to  En^neeriDg  Congtmction,"  p.  II ;— •  pampblM 
pabllihed  (1B81)  by  the  BngiiMei  Department  ol  the  U.  8.  Annr. 


ovGoQi^lc 


tSO  FILE   TOUHDATIOHS.  [CHAP.  XL 

more  ezpeditioiu.  For  inland  work  the  hunmer  is  better,  owing  to 
the  difficnttf  of  obtaining  the  large  qnantitiea  of  water  required  for 
ihe  jet ;  bnt  for  river  and  harbor  work  the  jet  is  the  most  adran- 
tageouB,  Under  eqnall;  favorable  conditions  there  is  little  or  no 
difference  In  cost  or  speed  of  the  two  methods.* 

The  jet  and  the  hammer  are  often  adTantageonaly  need  together, 
especially  in  stiff  els;.  The  efficiency  of  the  water-jet  can  be  greatly 
increased  by  bringing  the  weight  of  the  pontoon  npon  which  the 
machinery  is  placed,  to  bear  npon  the  pile  by  means  of  a  block  and 
tackle. 

346.  Con  or  Pnxa.  At  Chicago  and  at  points  on  the  Missis- 
sippi above  SL  Xjoais,  piiiepiU-  cost  from  10  to  15  cents  per  lineal 
foot,  according  to  length  and  location.  Soft-wood  piles,  including 
rock  elm,  can  be  had  in  almost  any  locality  for  8  to  10  cents  per 
foot.  Oak  pile*  20  to  30  feet  long  cost  from  10  to  1'^  cents  per 
foot ;  30  to  40  feet  long,  from  13  to  14  cents  per  foot ;  40  to  60 
feet  long,  from  30  to  30  cents  per  foot. 

347.  Cor  or  Fni  Sstma.  There  are  many  items  that  affect 
the  cost  of  work,  which  can  not  be  inclnded  in  a  brief  sommaty,  bat 
which  mnst  not  be  forgotten  in  using  such  data  in  making  *i*™'^faia. 
Below  are  the  det^ls  for  the  seven^  classes  of  work.  < 

848.  Eallroad  Conitoiietion.  The  following  table  is  a  snnunaiy 
of  the  cost,  to  the  contractor,  of  labor  in  driving  piles  (ezclnsiTe  of 
hauling)  in  the  construction  of  the  Chicago  branch  of  the  Atchiaon, 
Topeka  and  Santa  F^  R.  R.  The  piles  were  driven,  ahead  of  the 
track,  with  a  horse-power  drop-hammer  weighing  2,200  pounds. 
The  average  depth  driven  was  13  feet.  The  table  includes  the 
cost  of  driving  piles  for  abutments  for  Howe  trass  bridges  and 
for  the  false  work  for  the  erection  of  the  same.  These  two  items 
add  considerably  to  the  average  cost.  The  contractor  received 
the  same  price  for  all  classes  of  work.  The  work  was  as  varied  as 
such  jobs  usually  are,  piles  being  driven  in  all  kinds  of  soil.  Owing 
to  the  large  amount  of  railroad  work  in  progress  in  1887,  the  cost 
of  material  and  labor  was  about  10  per  cent,  higher  than  the  aver- 
age of  the  year  before  and  after.  Cost  of  labor  on  pile-driver :  1 
foreman  at  $4  per  day,  6  laborers  at  %%,  2  teams  at  13.50;  total  cost 
of  labor  =  ^3  per  day. 

•  Beport  of  Chlet  of  Bngliwen  U.  8.  A.,  ISSS,  i^  ia64-» 


ovGoQi^lc 


ABl.  I.]       DXSOBIPnONS,   AND  1IRTH0D8  OF  DBITUro. 


231 


Covr  OF  PiiiB  Ditimifl  in  Railkoad  CoimntnmoiT. 

Number  of  pllci  included  In  UiU  report 4,409 

"  Uueal  feet  lucluctnt  In  thU  report 109,S68 

ATersffe  lenph  of  tbe  piles,  in  feet.... 24.8 

Number  of  da^  emptoyed  iu  driviDg 494 

"  lineal  feet  driven  per  day 881.8 

Cost  of  driving,  per  pile 93. 68 

• '    foot 10.4   cent*. 

349.  Bailroad  Kspain.  The  following  are  the  data  of  pile 
driving  for  repatra  to  bridges  on  the  ludianapolis,  Decatar  and 
Springfield  R.  R.  The  work  was  done  from  December  21, 1885,  to 
oannary  5,  1886.  The  piles  varied  from  12  to  32  feet  in  length, 
the  aTerage  being  a  little  oTer  21  feet.  The  average  distance  driveo 
waa  about  10  feet.  The  hammer  weighed  1,650  pounds ;  the  last 
&11  was  37  feet,  and  the  corresponding  penetration  did  not  exceed 
2  inches.  The  hammer  was  laised  by  a  rope  attached  to  the  draw- 
bar of  a  locomotire — comparatiTely  a  very  expensiTe  way. 
TABLE  a». 
Cost  or  Pusa  wok  Bkiime  Rxpaibb.  ' 


iTun  or  Exrnn*. 

Total. 

PaaPiu. 

PUFOM. 

'^■■K"5;.t^"rt'5:5!"ii^'".'^..v.v::,:;::: 

Z^„.^™w.  .™o.p^t«^  ^  .H^.  «  dap. 

**^'"-f^teSJ^^ipi.ii.:::::::::::.:;;::::;:::: 

TI.U 

so.oe 

iw.w 

$1.™ 

•SM.M 

On  the  same  road,  9  piles,  each  20  feet  long,  were  driven  9  feet, 
for  bnmping-poata,  with  a  1,650-ponnd  hammer  dropping  17  feet. 
The  hammer  waa  raised  with  an  ordinary  crab-winch  and  single 
line,  with  double  crank  worked  by  four  men.  The  cost  for  labor  waa 
8.3  cents  per  foot  of  pile,  and  the  total  expense  was  31.6  sen  is  per  foot. 

350.  Bridge  Constmotion.  The  following  table  gives  the  cost 
of  labor  in  driving  the  piles  for  the  Northern  Pacific  R.  R.  bridge 
Over  the  Bed  River,  at  Grand  Forks,  Dakota,  constructed  in  1887. 
The  soil  was  sand  and  clay.  The  penetration  nnder  a  3,350>poimd 
hammer  falling  30  feet  was  from  2  to  4  inches.  The  foreman  r»> 
eeired  $5  per  d»y,  the  stationary  engineer  t3.50,  and  laborerB  t2. 


ovGoQi^lc 


FILB  rocaDATiovs. 


[chap.  zi. 


TABLE  ST. 
Govt  at  Labob  oi  DBmMS  Pilbb  di  Bmdcb  CoHnBOcnoB. 


r  1 1 


i»«>l  lajH 


IB      I    W 


■.ScM.  IMMH 


«  Id  i»dK  to  get  M  llM  Mwlns. 

861.  Fonadation  Tilet.  The  contract  price  for  the  fonndatioii 
p0ee — ^white  oak — for  the  railroad  bridge  over  the  Mimoiui  BiTer,  at 
Sibley,  Ho.,  waa  22  cente  per  foot  for  the  piles  and  28  cents  per  foot 
for  driring  and  sawing  oS  below  water.  They  were  50  feet  Ic  j& 
and  were  driven  in  aand  and  grsrel,  in  a  coffer-dam  16  feet  deep, 
by  a  drop-hammer  weighing  3, 303  ponnds,  blling  36  feet.  The  b&m' 
mer  was  raised  by  steam  power. 

3S2.  In  the  coustrnction  of  a  railroad  in  southern  Wisconsin 
daring  1886-87,  the  contract  price — the  lowest  competitiTe  bid — ^for 
the  piles,  in  place,  under  the  piers  of  several  large  bridges  averaged 
as  in  the  following  table.  The  piles  were  driven  in  a  strong  current 
and  sawed  off  under  water,  hence  the  comparatively  great  ezpenae, 
TABLE  28. 
OoKTUCT  Pbicb  at  FocHDAnoir  Pnxs. 


HinauLorPn* 

KnmorDatnM. 

Comucr  FHoa  rck  Lmu,  Foot. 

PorPll>HMdi8Mn>d 

Oak 
Oak 

OrdlnsiT 
Bird 

40cenu 
40    " 
48    " 
00    " 

IScenU 
M    " 
3S     ■■ 
80    " 

jvGooi^le 


AXt.  3.]  BXARUrO  POWEB  OF  FILES.  83S 

353.  In  1887  the  contract  price  for  piles  in  the  foaDdations  ol 
bridge  piers  in  the  river  at  Chicago  vas  36  cents  per  foot  of  pile 
left  in  the  foundation.  This  pricn  covered  cost  of  timber  (10  to  15 
cents),  driving,  and  cutting  off  IS  to  14  feet  below  the  surface  of 
the  water, — about  17  feet  being  left  in  the  foondatioQ. 

The  cost  of  driving  and  sawing  off  may  be  estimated  about 
OS  follows  :  (17  + 13)  feet  of  pile  at  13  cents  per  foot  =  13.90  ;  17 
feet  of  pile,  left  in  the  structure,  at  35  cents  per  foot  =  (5.95. 
t6.95  —  93.90  =  92.05  =  the  cost  per  pile  of  driving  and  sawing  oil, 
which  is  equivalent  to  near);  7  cents  per  foot  of  total  length  of  pile. 
In  this  case  the  waste  or  lose  in  the  pile  heads  cut  off  adds  consider- 
ably  to  the  cost  of  the  piles  remaining  in  the  structore.  In  mak- 
ing estimatfis  this  allowance  should  never  be  overlooked. 

361.  Harbor  and  &inr  Work.  In  the  shore-protection  work  at 
Chicago,  done  in  1883  by  the  Illinois  Central  R  B.,  a  crew  of  9 
men,  at  a  daily  expense,  for  labor,  of  (17.35,  averaged  65  piles  per  10 
hoars  in  water  7  feet  deep,  the  piles  being  31  feet  long  and  being 
driven  14  feet  into  the  sand.  The  cost  for  labor  of  handling,  sharp- 
ening, and  driving,  was  a  little  over  36  cents  per  pile,  or  1.9  cents 
per  foot  of  distance  driven,  or  1.1  cents  per  foot  of  pile.*  Both 
steam-hammere  and  water-jets  were  used,  but  not  together.  Notice 
that  this  is  very  cheap,  owing  (1)  to  the  use  of  the  jet,  (3)  to  little 
loss  of  time  in  moving  the  driver  and  getting  the  pDe  exactly  in  the 
predetermined  place,  (3)  to  the  piles  not  being  sawed  off,  and  (4) 
to  the  skill  gained  by  the  workmen  in  a  long  job. 

On  the  Mississippi  River,  under  the  direction  of  the  U.  8. 
Army  engineers,  the  cost  in  1883  for  labor  for  handling,  sharpen- 
ing, and  driving,  was  13.11  per  pile,  or  30  cents  per  foot  driven 
The  piles  were  35  feet  long,  the  depth  of  water  15.5  feet,  and  the 
depth  driven  13,6  feet.  The  water-jet  and  drop-hammer  were  used 
together.  The  large  cost  was  due,  in  part  at  least,  to  the  current* 
which  was  from  3  to  6  miles  per  hour,  f 

Aet.  3.  Bearisg  Poweb  of  Piles. 
36S.  Two  cases  must  be  distinguished  ;  that  of  columnar  piles  or 
those  whose  lower  end  rests  upon  a  hard  stratum,  and  that  of  ordi- 
nary bearing  piles  or  those  whose  supporting  power  is  due  to  the 


ovGoQi^lc 


284  PILE  FOCNDATIONa  [CHAP.  XL 

triction  of  the  earth  on  the  sides  of  the  pile.  In  the  first  cose,  the 
hearing  power  is  limited  by  the  strength  of  the  pile  considered  ae  a 
column  ;  and,  since  the  earth  prevents  lateral  deflection,  at  least  to 
a  conaidenible  degree,  the  strength  of  anch  a  pile  will  approximate 
closely  to  the  crushing  strength  of  the  material.  This  class  of  piles 
needs  no  further  consideration  here. 

3fie.  Xetkoim  of  DBTiBMoraia  Svpfobtdtq  Fovxb.  There 
are  two  general  methods  of  determining  the  supporting  power  of 
ordinary  bearing  piles:  first,  by  considering  the  relation  between  the 
supporting  power  and  the  length  and  size  of  the  pile,  the  weight  of 
the  hammer,  height  of  tall,  and  the  distance  the  pile  was  moved  by 
the  last  blow ;  or,  second,  by  applying  a  load  or  direct  pressure  to 
each  of  a  number  of  piles,  observing  the  amount  each  will  support, 
and  expressing  the  result  in  terms  of  the  depth  driven,  size  of  pile, 
and  kind  of  soil.  The  first  method  ia  applicable  only  to  piles  driven 
by  the  impact  of  a  hammer ;  the  second  is  applicable  to  any  pile, 
no  matter  how  driven. 

1.  If  the  relation  between  the  supporting  power  and  the  length 
and  size  of  pile,  the  weight  of  the  hammer,  the  height  of  fall, 
and  the  distance  the  pile  was  moved  by  the  last  blow  can  be  stated 
in  a  formula,  the  supporting  power  of  a  pile  can  be  found  by  insert- 
ing these  quantities  in  the  formula  and  solving  it.  The  relation 
between  these  quantities  must  be  determined  from  a  consideration 
of  the  theoretical  conditions  involved,  and  hence  such  a  formula  is 
a  rational  formnh. 

3.  By  applying  the  second  method  to  piles  under  all  the  con- 
ditions likely  to  occur  in  practice,  and  noting  the  load  supported, 
the  kind  of  soil^  amount  of  surface  of  pile  in  contact  with  the  soil, 
etc.,  etc.,  data  could  be  collected  by  which  to  determine  the  sup- 
porting power  of  any  pile.  A  formula  ezpresaing  the  supporting 
power  in  terms  of  these  quantities  is  an  empiricat formula. 

357.  KATroiTAL  TOEMITLAB.  The  deduction  of  a  rational  for- 
mula  for  the  supporting  power  of  a  pile  is  not,  strictly,  an  appro- 
priate subject  for  mathematical  investigation,  as  the  conditions  can 
not  be  expressed  with  mathematical  precision.  However,  ae  there 
is  already  a  great  diversity  of  formulas  in  common  use,  which  give 
widely  divergent  results,  a  careful  investigation  of  the  subject  is 


The  present  practice  in  determining  the  bearing  power  of  piles  is 


ovGoQi^lc 


ABT.  2.]  BBi.BINQ  POWEB  OF  PILES.  235 

neither  scientific  nor  creditable.  Many  engineers,  instead  of  Jn- 
quiring  into  the  relative  meritfl  of  the  different  formnlaB,  take  an 
average  of  all  the  formnlaa  they  can  find,  and  feel  that  they  have  a 
result  based  on  the  combined  wisdom  of  the  profession.  This  prac- 
tice is  exactly  like  that  of  the  ship's  surgeon  who  ponred  all  his 
medicines  into  a  black  jag,  and  whenever  a  sailor  was  ailing  gave 
him  a  spooufnl  of  the  mixture.  Other  engineers,  knowing  the  great 
diversity  and  general  unreliability  of  the  formulas,  reject  them 
all  and  trust  to  their  own  experience  and  judgment.  The  self- 
reliant  engineer  UBually  chooees  the  latter  course,  while  the  timid 
one  trusts  to  the  former. 

To  correctly  discriminate  between  the  several  formulas,  it  ia 
necessary  to  have  a  clear  anderstanding  of  all  the  conditions  in- 
volved. The  object  of  the  following  discussion  is  to  discover  the 
general  principles  which  govern  the  problem. 

~  -  358.  When  the  ram  strikes  the  bead  of  the  pile,  the  first  effect 
^  IS  to  compress  both  the  head  of  the  pile  and  the  ram.  The  more 
the  ram  and  pile  are  compressed  the  greater  the  force  required,  until 
finally  the  force  of  compression  ia  sufficient  to  drive  the  pile  through 
the  soil.  The  amount  of  the  pressure  on  the  head  of  the  pile  when 
it  begins  to  move,  ia  what  we  wish  to  determine. 

To  produce  a  formula  for  the  pressure  exerted  upon  the  pile  by 
the  impact  of  a  descending  weight,  let 
^'  =  the  weight  of  the  ram,  in  tone ; 
w  =   "        "         "      pile     " 
S  =  the  aectiou  of  the  ram,  in  sq.  ft; 
8  =    "        "        "      pile     "    " 
L  =  the  length  of  the  ram,  in  feet ; 
1=    "        "         "      pile     " 

E_=  the  co-efficient  of  elasticity  of  the  ram,  in  tona  per  sq.  ft ; 
e=   "      "  "        "  "      pile      "      "    "    '* 

i  =  the  height  of  fall,  in  feet ; 

d  =  the  penetration  of  the  pile,  t.  e.,  the  distance  the  pile  is 
moved  by  the  last  blow,  in  feet.  The  distance  d  ia  the 
amount  the  pile  as  a  whole  moves,  and  not  the  amount 
the  top  of  the  head  moves.  This  can  be  fonnd  accu- 
rately enough  by  measuring  the  movement  of  a  point, 
say,  2  or  3  feet  below  the  head. 
P  =1  the  pressure,  in  tone,  which  will  juat  move  the  pile  theivery 


ovGoQi^lc 


SS6  PILB  TODHDATIONB.  [CHAP.  XL 

Btnall  distance  d, — ^that  is  to  eay,  the  pressara  prodnoed 
bj  the  last  blow;  or,  briefly,  P  maj  be  called  the  snp 
porting  pover. 
Then  Wh  is  the  accnmnlated  energy  of  the  ram  at  the  instant  it 
Btrikea  the  head  of  the  pile.    This  energy  is  spent  (1)  in  compresB- 
ing  the  ram,  (2)  in  compressing  the  head  of  the  pile,  (3)  in  moving 
the  pile  as  a  whole  against  the  resistance  of  the  soil,  (4)  in  overcom- 
ing the  inertia  of  the  pile,  (5)  in  overcoming  the  inertia  of  the  soil 
at  the  lower  end  of  the  pile,  and  (6)  by  the  friction  of  the  ram 
against  guides  and  air.     These  will  be  considered  in  order. 

1.  The  energy  consumed  in  compressing  the  hammer  is  repre- 
eented  by  the  product  of  the  mean  preaanre  and  the  compreBsion,  or 
shortening,  of  the  ram.  The  pressure  at  any  point  in  a  striking 
weight  varies  as  the  amount  of  material  above  that  point ;  that  is  to 
say,  the  pressure  at  any  point  of  the  hammer  varies  inversely  as  its 
distance  from  the  lower  anr&ce.  The  pressure  at  the  lower  surface 
is  P,  and  that  at  the  upper  one  is  zero ;  hence  the  mean  pressure 
is  i  i*.  From  the  principles  of  the  resistance  of  materials,  the  com- 
pression, or  the  shortening,  is  ^^t  in  which  p  is  the  uniform  pres- 
sure. From  the  above,  p  =  ^  P.  Consequently  the  shortening  is 
I  PL 

If  the  fibers  of  the  face  of  the  ram  are  not  seriously  crushed,  the 
mean  pressure  will  be  one  half  of  the  maximum  pressure  due  to  im- 
pact ;  or  the  mean  pressure  during  the  time  the  ram  and  pile  are 

being  compressed  is  ^P.     Then  the  euergy  consumed  \s-j~^y,. 

The  yielding  of  the  material  of  the  ram  is  probably  small,  and  might 
be  omitted,  but  as  it  adds  no  complication,  as  will  presently  appear, 
it  is  included. 

2.  The  mean  pressure  on  the  head  of  the  pile  is  ^  P,  as  abovei 
For  simplicity  assume  that  the  pile  is  of  uniform  section  through- 
ouL  To  determine  the  shortening,  notice  that  for  the  part  of  the 
pile  above  the  ground  the  maximum  pressure  is  uniform  through- 
out, but  that  for  the  part  under  the  surface  the  maximum  pressure 
varies  as  some  function  of  the  length.  If  the  soil  were  homogeneous, 
the  pressure  would  vary  about  as  the  length  in  the  ground ;  and 


ovGoQi^lc 


AXr.  3.]  BEABIITQ  FOWEB  Of  FILES.  S3? 

1  PI 
hence  the  shorteniiig  wonld  be  -^  — .     Bnt,  remembering  that  the 

resistance  ia  gBnerally  greater  at  the  lower  end  than  at  the  upper, 

and  that  any  swaying  or  Tibration  of  the  upper  end  will  atill  further 

diminish  the  resistance  near  the  top,  it  is  probable  tbat  the  mean 

pressure  is  below  the  center.    It  will  here  be  assumed  that  the  mean 

pressure  on  the  fibers  of  the  pile  is  two  thirds  of  that  on  the  liead, 

2  PI 
which  is  equivalent  to  assuming  that  the  shortening  is  —  — ,  when 

the  pile  is  wholly  immersed.     If  only  a  part  of  the  pile  is  in  contact 

PI'       ^  PI       P  /         &\ 

with  the  soil,  the  shortening  will  be [-  -  — *  =  — [l'  -f  -  /  ), 

86  i  86  86\  o      J 

in  which  I'  is  the  exposed  portion  and  /,  the  part  Immersed.     For 
simplicity  in  the  following  discussion  the   shortening  of  the  pile 


the  top  projects  above  the  ground,  it  will  only  bo  necessary  to  sub* 

stitute  (I'  -f  i'l)  fot*  I  ii>  equations  (1)  and  (3)  below. 

1P*1 
Then  the  energy  lost  in  the  compression  of  the  pile  is  -  — . 

3.  The  energy  represented  by  the  penetration  of  the  pile  is  Pd. 

4.  In  the  early  stage  of  the  contact  between  the  ram  and  the 
pile,  part  of  the  energy  of  the  ram  is  being  used  up  in  oyercoming  the 
inertia  of  the  pile ;  but  in  the  last  stage  of  the  compression,  this 
energy  is  given  out  by  the  stoppage  of  the  pile.  At  most,  the  effect 
of  the  inertia  of  the  pile  is  small ;  and  hence  it  will  be  neglected. 

5.  The  energy  lost  in  overcoming  the  inertia  of  the  soil  at  the 
lower  end  of  the  pile  will  vary  with  the  stiffness  of  the  soil  and  with 
the  velocity  of  penetration.  It  is  impossible  to  determine  the  amount 
of  this  resistance,  and  hence  it  can  not  be  included  in  a  formula. 
Omitting  this  element  causes  the  formula  to  give  too  great  a  support- 
ing power.  The  error  involved  can  not  be  very  great,  and  is  to  be 
covered  by  the  factor  of  safety  adopted. 

6.  The  friction  of  the  ram  against  the  guides  and  against  the  air 
diminishes  the  effect  of  the  blow,  but  the  amount  of  this  can  not  be 
computed.  Omitting  this  element  will  cause  the  formula  for  the 
supporting  power  to  give  too  great  a  result.  The  friction  against 
the  air  increases  very  rapidly  with  the  height  of  fall,  and  hence  the 


ovGoQi^lc 


S88  riLH  P0DNDATI0N8.  [CHAP.  XL, 

OQAller  the  fall  the  more  Dear!;  will  the  formula  give  the  true  sap- 
porting  power. 

8S9.  Eqoating  the  energy  of  the  falling  weight  with  that  con* 
mmed  in  compreaeing  the  pile  and  tarn,  and  in  the  penetiatioQ  of 
tlw  pile,  aa  discnwed  in  paiagrsphs  1,  3,  and  3  above,  we  have 


Joiving  equation  (1)  gives 


36  d"  5"  £'«•«• 


iLs9  +  iiS£^{ZL»«-\-ilSBy 

3Lf6  +  4lSS' 


V) 


(2) 


An  examination  of  eqnation  (3)  shows  that  the  prassnre  upon  the 
pile  ■rnnvB  with  the  height  of  fall,  the  weight,  aection,  length,  and 
coefficient  of  elaaticitj  of  both  ram  and  pile,  and  with  the  penetra- 
tion. It  is  easy  to  see  that  the  weight  of  the  ram  and  the  height 
of  the  fall  sbonld  be  included.  The  penetration  is  the  only  element 
which  varies  with  the  nature  of  the  soil,  and  bo  of  conrse  it  also 
should  be  included.  It  is  not  so  easy  to  see  that  the  length,  section, 
and  co-efficient  of  elasticity  of  the  material  of  the  pile  and  ram 
should  be  included.  If  any  one  will  try  to  drive  a  large  nail  into 
hard  wood  with  a  piece  of  leather  or  rubber  intervening  between 
the  hammer  and  the  head  of  the  nail,  he  will  be  impressed  with  the 
fact  that  the  yielding  of  the  leather  or  rubber  appreciably  diminishes 
the  effectiveness  of  the  blow.  Esseutially  the  same  thing  occnrs  in 
trying  to  drive  a  large  nail  with  a  small  hammer,  except  that  in  this 
case  it  is  the  yielding  of  the  material  of  the  hammer  which  dimin- 
ishes the  effect  of  the  blow.  In  driving  piles,  the  materials  of  the 
pile  and  ram  act  as  the  rubber  in  the  first  illustration;  and,  reason- 
ing by  analogy,  those  elements  which  determine  the  yielding  of  the 
materials  of  the  pile  and  ram  should  be  included  in  the  formula. 
Obvionsly,  then,  the  pressure  due  to  impact  will  be  greater  the 
harder  the  material  of  the  pile.  Notice  also  that  if  the  head  of  the 
pile  is  bruised,  or  "broomed,"  the  yielding  will  be  increased;  and, 
conseqnently,  the  pressure  due  to  the  blow  will  be  decreased. 


ovGoQi^lc 


ISC.  3.]  BXASUTQ  FOWEB   OF  FILES.  ^39 

860.  Tbfl  Anthor'i  FonniilA  for  Pnotloe.  To  simpli^  eqwttin 
(2),  pat 

e  3S»« 

and  tlieii  equation  (2)  beoomes 

P  =  V2q  Wh  +  q'd'-qi.      ....     (3) 

Equation  (3)  can  be  Bimplified  still  further  by  compatiiig  q  tot 
tbe  conditions  as  the;  ordinarily  occur  in  practica  Of  conrse,  in 
this  case  it  will  only  be  possible  to  aasnuie  some  arerage  ralne  for 
the  various  quantities.  Aesnme  tbe  section  of  the  pile  to  be  0.6  sq. 
ft;  tbe  section  of  the  ram,  3  sq.  ft.;  the  length  of  the  ram,  3.5  ft; 
the  length  of  the  pile,*  25  ft. ;  the  co-efiBcient  of  elasticity  of  the 
ram,  1,080,000  tons  per  sq.  ft;  and  tbe  co-efficient  of  elasticity  of 
the  pile,  108,000  tons  per  sq.  ft  (an  average  valne  for  oak,  elm, 
pine,  etc,  but  not  for  palmetto  and  other  soft  woods).  Oompnting 
tbe  corresponding  value  of  q,  we  find  it  to  be  5,160;  but  to  secure 
round  numbers,  we  may  take  it  at  5,000,  which  also  gives  a  little 
additional  security. 

Equation  (3)  then  becomes 

P  =  10O{VWh+{5Ody-50d),      ...    (4) 

which  ia  the  form  to  be  tised  in  practice. 

Equation  (4)  is  approximate  because  of  the  assumptions  made  in 
deducing  equation  (1),  and  also  because  of  the  averse  valne  taken 
for  q;  bnt  probably  the  error  oooaeioned  by  these  approximations  ia 
not  material. 

361.  Notice  that,  since  the  co-efficient  of  elasticity  of  sound 
material  was  used  in  deducing  the  value  of  q,  equation  (4)  is  to  be 
applied  only  on  condition  that  the  last  blow  is  Btrnck  upon  sound 
wood;  and  therefore  the  head  of  the  test  pile  should  besawed  off  so 
as  to  present  a  solid  surface  for  the  last,  or  test,  blow  of  the  hammer. 
{This  limilaiion  is  exceedingly  important.)  Since  the  penetration 
per  blow  can  be  obtained  more  accurately  by  taking  tbe  mean  dis- 
tance for  two  or  three  blows  than  by  measuring  the  distance  for  a 
single  one,  it  is  permissible  to  take  the  mean  penetration  of  two  or 


ovGoQi^lc 


240  FILE   FOL'NDATIOXS.  [CHAP.  XI. 

three  blows;  but  their  number  and  force  should  be  such  as  not  to 
crnsh  the  bead  of  the  pile. 

In  this  oonnectioD  the  foUoiring  table,  giren  b;  Don.  J.  Vhitte- 
more,  in  the  Transactions  of  the  American  Society  of  Civil  Engi- 
neers, Tol.  xiL  p.  4i'i,  to  show  the  gain  in  efficiency  of  the  driving 
power  by  cutting  off  the  brniaed  or  broomed  head  of  the  pile,  is  very 
instmctivB.  The  pile  vraa  of  green  Norway  pine;  the  ram  was  of 
the  Naamyth  type,  and  weighed  2,800  ponnds. 

Qaih  IK  EmctKHCT  aw  thh  Dsiyine  Powkr  bi 
Cdttdiu  oft  tbb  Broomed  Head  or  tex  Fu^. 

....        S  blows. 


Sd  ft.  of  penetraliou  required 


Olh 


10th 

llth    "            "               "           109 

12th    "             '•               "           168 

18th    "             "               "           237 

14th    ■'            "               "            «M 

Head  of  ilie  pile  adzed  off. 

ISth  ft.  of  penetration  required 37S 

16th    ■'             "               ■•           6J3 

ITth    ■'             "               "            882 


Total  number  of  blows 6,238 

TTotice  that  the  average  penetration  per  blow  was  8  J  times  greater 
during  the  15th  foot  than  during  the  14th;  and  nearly  i  times 
greater  in  the  19th  than  in  the  18th.  It  does  not  seem  unreason- 
able to  believe  that  the  first  blovrs  after  adzing  the  head  off  were 
correspond  ill  gly  more  effective  than  the  later  ones;  consequently, 
it  is  probable  that  the  first  blows  for  the  15th  foot  of  penetratioa 
were  more  than  &  times  as  efficient  as  the  last  ones  for  the  14th  foot, 
and  also  that  the  first  blows  for  the  19th  foot  were  8  or  10  times 
more  efficient  than  the  last  ones  for  the  18th  foot.  Notice  also  that 
aince  the  head  was  only  "adzed  off,"  it  is  highly  probable  that  the 
spongy  wood  was  not  entirely  removed. 


ovGoQi^lc 


ilXI,  2.]  BEAfilNO    POWER  OF   PILES.  S41 

II  the  penetration  for  the  last  blow  before  the  head  was  adzed  ofF 
■were  used  in  the  formula,  the  apparent  supporting  power  would  be 
Tery  much  greater  than  if  the  penetration  for  the  first  blow  after 
adzing  off  is  employed.  This  Bhows  how  anscientific  it  is  to  pre- 
«cribe  a  limit  for  the  penetration  without  specifying  the  accompany- 
ing condition  of  the  head  of  the  pile,  as  is  ordinarily  done. 

362,  Weiabaoh'a  Formnla,    Equation  (2),  page  238,  ip  essentially 
equivalent  to  Weisbach's  formula  for  the  supporting  power  of  a  pile. 
Weisbach  assumes  that  the  pressure  is  uniform  throughout,  and 
■obtains  the  formula* 
ffff. 


P=(^^)(/^^^7^r^_4  .  („ 


, .  ,    „      SE        ,  _       se 
m  which  H  =  —^,  and  R^  =  -y. 

363.  Bankine's  Formula.  Equation  (2),  page  238,  is  also  essen- 
tially eqnivalent  to  Rankiue's  formula ;  and  differs  from  it,  only 
because  he  assumes  the  pressure  to  Tary  directly  as  the  length  of 
the  pile,  and  neglects  the  compression  of  the  ram.  Bankine'g 
f ormnls  is  \  

p  =  /t£^+i^-^f-',    ...     ,6) 

EqaatioD  (2)  differs  from  WeiBbach's  and  Bankine's  on  the  safe 
«ide. 

364,  Ekpisical  Fosmtua.  General  Prinoiples.  (1)  An  empiri- 
•cal  formula  should  be  of  correct  formj  (2)  the  constants  in  it  should 
be  correctly  deduced ;  and  (3)  the  limits  within  which  it  ia  applica- 
ble should  be  stated. 

For  example,  suppose  that  it  were  desired  to  determine  the 
equation  of  the  straight  line  A  B,  Fig.  57. 
Since  the  given  line  is  straight,  wc  will  as- 
sume that  the  empirical  formuiii  is  of  the 
form  y  =  m  X.    Wo  might  find  wi  by  m 
ing  the  ordinates  1,  2,  3,  and  place  n 
to  th^ir  mean.     If  1,  2,  3,  be  the  numerical 
ralues  of  the  respective  ordinates,  the  for- 
mula becomes  y  =  %x,  which  gives  the  line  "1^ 
0  C.    The  mean  ordinate  to  0  C  is  equal  to  r^-  "■ 

-the  mean  ordinate  ia  A  B,  but  the  two  are  not  by  any  means  tha 
's  TniMlKloi))!  p.  701' 


ovGoQi^lc 


i4&  PILE   P0CNDATI0S8.  [CHAP.  XI. 

aame  line.  It  is  evident  that  this  empirical  formula  is  of  the  ^rrong: 
form. 

For  another  illnstration,  assume  that  some  law  is  correctly  repre- 
sented by  the  curve  A  B,  Fig.  58.  The  form 
of  the  empirical  formula  may  be  such  as  to 
give  the  curve  CD.     These  curves  coincide 

a        J  exactly  at  two  points,  and  the  mean  ordinate 

\^^       "~^>/    to   the    two  is  the   same.      To   use  a  com- 
S  \  mon  eipreseion,  we  may  say  that,   "on  the 

average,  the  empirical  formula  agrees  exactly 

Fio.  u.  with  the  facts ;"  but  it  is,  nevertheless,  not. 

even  approximately  true.  The  constants  were  not  correctly  de- 
duced. 

Even  if  of  the  correct  form  and  correctly  deduced,  an  empirical 
formula  can  be  safely  applied  only  within  the 
limits  of  those  values  from  which  it  was  deter-  , 
mined.     For  esample,  a  law  may  be  repre- 
eent«d  by  the  curve  A  B,  Fig.    59.       From  Tf|- 
obaervatious  made  in  the  region  C  E,  the  em-  Fio.  lo. 

pirical  formula  lias  been  determined,  which  gives  the  curve  C  E  D^ 
which  between  the  limits  C  and  E  is  all  that  can  be  desired,  but 
which  is  grossly  in  error  between  the  limits  fand  D.  To  use  an 
empirical  formula  intelligently,  it  is  absolutely  necessary  that  the 
limits  within  which  it  is  applicable  should  be  knowu. 

Of  course,  the  observations  from  which  the  empirical  formula 
was  deduced  can  not  be  used  to  test  the  correctness  of  the  formula; 
such  a  procedure  can  check  only  the  mathematical  work  of  deriving^ 
the  constants. 

Elementary  as  the  preceding  principles  are,  many  empirical 
formulas  are  worthless  owing  to  a  disregard  of  these  conditions  in 
deducing  them. 

365.  Comparison  of  Empirical  Tormolas.  We  will  now  briefly 
consider  the  empirical  formulas  that  are  most  frequently  employed 
to  determine  the  supporting  power  of  piles.* 

HamcrlVs  formula  for  the  dynamic  effect  of  a  falling  body  is  f 
■  P  =  4.426  W  V,  "as  deduced  from  experiments." 

The  experiments  consisted  in  letting  a  weight  of  a  few  onnces 


ovGoQi^lc 


ART.  2.]  BEAKtNa  POWBE  OF  PILES.  243 

&U  a  few  inches  npon  a  coiled  spring ;  and  henoe  the  formula  is 
entirely  inapplicable  to  pile  driving. 

Beavfoy's  fommla  is  P  =  0.5003  ff"  F",  "as  determined  by 
experiment."  This  fonnala  was  deduced  under  the  same  conditions 
as  Hasweli's,  and  hence  is  useless  for  pile  driving.  The  difference 
between  the  formulas  is  due  to  the  fact  that  Hoswell  used  only  on© 
weight  and  one  spring,  and  varied  the  height  of  the  fall,  while  Beau- 
foy  employed  one  weight  and  Bprings  of  such  relative  etifiness  as 
would  etop  the  weight  in  nearly  the  eame  distance  for  different 
heights  of  fall.*  Notice  that  Haswell'e,  and  also  Beanfoy's  formula, 
would  give  the  same  bearing  power  for  all  soils,  other  things  being 
the  same. 

Nystrom'8form'ula\\sP  =  -7-^^-Y — ttj-    In  a  later  book,J  Nys- 

trom gives  the  formala  P  =  j  ~j~>  assuming  that  "about  25  per 

cent,  of  the  energy  of  the  ram  is  lost  by  the  crushing  of  the  head  of 
the  pile."  Both  of  these  formulas  are  roughly  approximate,  theo- 
retical formulas,  although  frequently  cited  tis  "  practical  formulas." 

Mason's  formula  %  ie  P  =  j^^=-~ — r-v     As'   in   the    precedinff 

cases,  this  is  frequently  referred  to  as  a  "  practical  formula ;"  but  an. 
examination  of  the  original  memoir  shows  that  it  is  wholly  a  theo- 
retical formula  with  no  pretensions  of  being  anything  else.  It  is 
also  sometimes  referred  to  as  having  been  "  tested  by  a  series  of 
experiments ;"  but  apparently  the  only  basis  for  this  is  that  th© 
piles  upon  which  Fort  Mon^omery  (Rouse's  Point,  N-  Y.)  stood 
from  1846  to  1850  without  any  sign  of  failure,  when  tested  by  this 
formula,  showed  a  co-efiBcient  of  safety  of  3^^-  '^^'^  evidence  is  not 
conclusive:  (1)  the  factor  is  large  enough  to  cover  a  considerable 
error  in  the  formula;  (2)  since  the  foi-mula  assumes  that  all  of  the 
energy  in  the  descending  ram  is  expended  in  overcoming  the  resist- 
ance to  penetration,  the  compnted  bearing  power  is  too  small,  and 
consequently  the  co-efficient  of  safety  is  oven  greater  than  aa  stated; 

•  Van  Nostrancl's  Bngln'g  Mag.,  vol  xvil.  p.  836. 
t  NjMroni's  Pooket-Book,  p.  158. 
t  New  HecbsniCi,  p.  184. 

j  Reflistauce  at  Piles,  J.  L.  Mason,  p.  8;  Ho.  5  of  Papers  on  FrsotlOttl  BnglneeTtng, 
published  by  tbe  KngiiieeriDg  Deportinent  of  the  U.  B.  Armf. 


ovGoQi^lc 


244  PILE   FOUNDATIONS.  [CHAP.  XI. 

and  (3)  it  is  probably  safe  to  say  that  after  a  pile  has  stood  a  short 
time  its  bearing  pover  is  greater  than  at  the  moment  the  drivlDg 
ceased,  owing  to  the  settlement  of  the  earth  about  it. 

Sander's  formula*  is  P'  =  -o~r'  *°  'l^ich  P'  is  the  safe  bear- 
ing power.  This  formula  was  deduced  on  the  assumptions  that  the 
energy  of  the  falling  weight  was  wholly  employed  in  forcing  the 
pile  into  the  ground, — i.  e.,  on  the  aeeumptiou  that  Pd=  Wb,  or 

P  =  —J-, — and  that  the  safe  load  waa  one  eighth  of  the  ultimate 

supporting  power.  It  is  therefore  a  roughly  approximate,  theoreti- 
cal formula. 

Notice  that,  since  some  of  the  enei^y  is  always  lost,  Pd,  the 
«nergy  represented  by  the  movement  of  the  pile,  must  always  be 
less  than  Wh,  the  energy  of  the  hammer;  hence,  P  is  always  lees 

than— T-;  or,  in  mathematical  language,  P<—t~-  This  relation  is 
very  useful  for  determining  the  greatest  possible  value  of  the  sup- 
porting power.     P  will  always  be  considerably  leas  than-T— ;  and 

this  difference  is  greater  the  lighter  the  weight,  the  greater  the 
foil,  the  softer  the  material  of  the  pile,  or  the  more  the  head  is 
bruised.  When  d  is  very  small,  say  i  inch  or  less,  the  difference  is 
so  great  as  to  make  this  relation  useless. 

Trautwine's  formula,^  in  the  nomenclature  of  page   235,  is 

P=  ■     It  was  deduced  from   the  observed  supporting 

power  of  piles  driven  in  soft  soil.  Strictly  speaking,  it  is  applicable 
only  under  conditions  similar  to  those  from  which  it  was  deduced ; 
and  hence  it  is  inapplicable  for  hard  driving  and  to  piles  whose 
heads  are  not  bruised  about  the  same  amount  as  were  the  experi- 
mental ones.  No  formula  can  be  accnrate  which  does  not,  in  some 
way,  take  cognizance  of  the  condition  of  the  liead  of  the  pile.  For 
example,  experiments  Nos.  3  and  4  of  the  table  ou  page  346  are 
the  same  except  in  the  condition  of  the  heads  of  the  piles,  and  yet 


ovGoQi^lc 


ART.   2.1  BEAHINQ   POWEft  OF   PILES.  HiS 

the  load  supported  by  the  former  was  3|  times  that  sapported  by  the 

latter.     This  formula  ia  not  applicable  to  piles  drireii  with  a  eteam 

hammer,  since  according  to  it  the  energy  represented  by  the  sinking 

of  the  pile  is  greater  than  the  total  energy  in  the  deecendinf^  weight. 

For  example,  if  W  =  IJ  tons,  A  =  2  feet,  and  d=l  inch  =  ^^  of  a 

Wit 
foot,  the  formnia  P  <  —r-  becomes  P  <  36   tons.     Trautwine'a 
a 

formula  gives  /*  =  49  tons;  that  is  to  say,  Trantwine's  formala 

makes  the  sapporting  power  one  third  more  than  it  would  be  if  >(9 

energy  were  lost. 

Engineering  News  formula,*  the  most  recent  and  the  most 

popular,  is  f"  =   .,        ,  in  which  P '  is  the  safe  load  in  tons;  aud 

d'  is  the  penetration,  iu  inchta,  under  tbe  last  blow,  which  is 
assumed  to  be  appreciable  and  at  an  approximately  naiform  rate. 

366.  Tlie  Author's  Empirical  Formula.  Certain  aaBamptJons 
and  approximations  were  maije  in  deducing  equation  (3),  page  339. 
If  it  is  thought  not  desirable  to  trust  entirely  to  theory,  thea  the 
formnia 


P=V%qWh-^q*d'-qd     .     .     .    .        (7) 

may  be  considered  as  giving  only  the  form  which  the  empJiica) 
formula  should  have.  Under  this  condition  q  becomes  a  numerical 
co-efficient  to  be  determined  by  experiment,  which  must  be  mad» 
by  driving  a  pile  and  measuring  d,  after  which  the  BUBtaining  power 
must  be  determined  by  applying  a  direct  pressure.  The  last,  or 
test,  blow  should  be  struck  on  sound  wood. 

367.  Table  29  gives  all  the  experiments  ou  the  supporting 
power  of  piles  for  which  the  record  is  complete.  Unfortunately 
these  experiments  do  not  fulfill  the  conditions  necessary  for  a  propel 
determination  of  q  in  equation  (T).  It  is  known  that  in  some  of  th« 
cases  the  head  of  the  pile  was  contiderably  broomed,  and  there  is 
internal  evideuce  that  this  was  so  in  the  others. 

The  data  of  the  following  table  substituted  in  equation  (7)  give 
values  of  q  from  1.5  to  337,  with  an  average  of  130.  The  range  of 
these  results  ghows  the  inconsistency  of  the  experiments,  and  the 
Bmallneea  of  the  average  shows  that  the  last  blow  was  not  Btrncl*  in 
sound  wood.     This  value  of  q  is  of  no  practical  use 

•  Enginrrring  Xnrt.  vol.  xx.  pp.  511.  B12  (Doe.  M,  1888,. 


ovGoQi^lc 


KLB  FOCKDATIOira. 
TABLE  39. 

OK  TBK  SuPFOBTQIa 


[chap.  XI. 


PowKB  OF  PhiH, 


s^ 


CircnUr  of  the  Office  o(  Chief  of  Eaglneen 

U.  8.  A..  Nov.  13,  ■81,  pp.  2,  8. 
Trautwiue'ft  Po(Aet-Book,  H.  188S,  p.  64& 
Jour.  Frank.  Inst.,  vol.  SS,  p.  101. 
DelafleM's  "Foiuukiioiu  In  Campreadble  Sotli,' 


pp.  1 
ginee 


leen'  bepaitmeiit  o: 
TniitwlDS  In  Baiiivad  Oattlt.  July  8, 1887,  p. 


368.  Aa  confirming  the  reliability  of  the /orm  of  eqnatioDB  (3), 
^4),  and  (7),  it  is  intereeting  to  not)be  that  A.  C.  Hertiz*  fonnd, 
from  the  records  of  the  driving  and  afterwards  pulling  np  of  nearly 
■400  piles,  the  following  relation : 


d- 


Wh 


P_ 
500' 


-which  may  be  pnt  in  the  form 

P=  4/500  Wh  +  {250  rf)'  -  250  d.   . 


(8) 


Equation  {8)  has  exactly  the  form  of  equation  (3),  page  239, 
although  deduced  in  an  entirely  different  way.  The  value  (250)  of 
the  constant  q  in  equation  (8)  is  lees  than  that  in  equation  (4), 
page  239,  which  shows  that  the  heads  of  the  piles  were  broomed. 
The  value  of  q  in  equation  (8)  ia  greater  than  that  deduced  from  tho 
data  of  Table  29,  which  shows  that  the  piles  from  which  equation 
(8)  was  determined  were  not  bruised  as  much  a&  those  in  the  above 
table. 

369.  SuFPOBime  Fowbe  DETEBinirED  bt  BXFERUixirT.  It  is 
not  certain  that  the  bearing  power  of  a  pile  when  loaded  with  a  con- 
tinued quiescent  load  will  be  the  same  as  that  during  the  very  short 


ovGoQi^lc 


^BT.  2.]  BEABINO    POWER   OF   FILES.  M7 

period  of  the  blow.  The  friction  on  the  sides  of  the  pile  will  have 
a  greater  effect  in  the  former  case,  nhile  the  reaiBtance  to  penetra- 
tion of  the  point  will  be  greater  in  the  latter.  This,  and  the  fact 
that  the  supporting  power  of  piles  sank  by  the  water-jet  can  be 
determined  in  do  other  way,  shows  the  necessity  of  ezperimentB  to 
determine  the  bearing  power  under  a  steady  load. 

Unfortunately  no  extended  experiments  have  been  made  in  this 
'direction.  We  can  give  only  a  collection  of  as  many  details  as  pos- 
.sible  concerning  the  piles  under  actual  structures  and  the  loads 
which  they  sustain.  In  this  way,  we  may  derive  some  idea  of  the 
sustaining  power  of  piles  under  various  conditions  of  actual  practice. 

370.  intimate  Load.  In  constructing  a  light-house  at  Proctors- 
Tille,  La.,  in  1856-57,  a  test  pile,  12  inches  square,  driven  29.5  feet, 
bore  29.9  tons  without  settlement,  but  with  31.2  tons  it  "settled 
slowly."  The  soil,  as  determined  by  borings,  had  the  following 
character :  "  For  a  depth  of  9  feet  there  was  mud  mixed  with 
sand  ;  then  followed  a  layer  of  sand  abont  5  feet  thick,  next  a  layer 
of  sand  mixed  with  clay  from  4  to  C  feet  thick,  and  then  followed 
^e  clay.  By  draining  the  site  the  surface  was  lowered  about  6 
inches.  The  pile,  by  its  own  weight,  sank  5  feet  4  inches."  The 
above  Ibad  is  equivatent  to  a  frictional  resistance  of  600  lbs.  per 
sq.  ft.  of  surface  of  pile  in  contact  with  the  soil.  This  pile  is  No. 
1  of  the  table  on  p^e  246. 

At  Philadelphia  in  1873,  a  pile  was  driven  15  ft.  into  "soft  river 
mud,  and  5  hours  after  7.3  tons  caused  a  sinking  of  a  very  small 
fraction  of  an  inch ;  under  9  tons  it  sank  i  of  an  inch,  and  under 
15  tons  it  sank  5  ft."  The  above  load  is  equivalent  to  320  lbs. 
per  sq.  ft.  of  surface  of  contact.  This  pile  is  No.  2  of  the  table  on 
page  246. 

In  the  construction  of  the  dock  at  the  Pensacola  navr  yard,  a  pile 
.driven  16  feet  into  clean  white  sand  austained  a  direoBvpnll  of  43 
tons  without  movement,  while  45  tons  cHused  it  to  rise  slowly;  and 
-46  tons  were  required  to  draw  the  pile.  This  is  equivalent  to  a  fric- 
tional resistance  of  1,900  lbs.  per  sq.  ft.  This  pile  is  No.  4  of  the 
table  on  p.  246. 

"  In  the  construction  of  a  foundation  for  an  elevator  at  Buffalo, 
N.  Y.,  a  pile  15  inches  in  diameter  at  the  large  end,  driven  18  ft., 
bore  25  tons  for  27  hours  without  any  ascertainable  effect.  The 
■weight  was  then  gradually  increased  until  the  total  load  on  the 


ovGoQi^lc 


248  PILE  FOUNDATIONS.  [OHAP.  XI- 

pile  WM  37i  tons.  Up  to  thb  weight  there  had  been  no  depreesioa 
of  the  pile,  bat  vith  37^  tone  there  was  a  gradual  depreaaioQ  which 
aggregated  ^  of  an  inch,  bejond  which  there  waa  no  depression 
until  the  weight  was  increased  to  50  tons.  With  50  tons  there  wa^ 
a  further  depression  of  |  of  an  inch,  making  the  total  depression 
1}  inches.  Then  the  load  was  increased  to  75  tons,  under  which 
the  total  depression  reached  3^  inches.  The  experiment  was  not 
carried  beyond  this  point.  The  soil,  in  order  from  the  top,  was- 
as  follows  :  3  ft  of  blue  clay,  3  ft  of  grarel,  5  ft  of  stiff  red  clay, 
2  ft  of  quicksand,  3  ft  of  red  clay,  2  ft  of  gravel  and  sand,  and 
8  ft  of  very  stiff  bine  clay.  All  the  time  during  this  experiment 
there  were  three  pile-drivers  at  work  on  the  foundation,  thus  keep- 
ing up  a  tremor  in  the  ground.  The  water  from  Lakfe  Erie  had 
free  access  to  the  pile  through  the  gravel."*  This  is  equivalent 
to  a  frictional  resistance  of  1,850  lbs.  per  sq.  ft  This  is  pile  No.  &■ 
of  the  table  on  page  246. 

S71.  In  m^ng  some  repairs  at  the  Hull  docks,  England,, 
several  hundred  sheet-piles  were  drawn  out  They  were  Vi  X  10 
inches,  driven  an  average  depth  of  18  feet  in  stiff  blue  clay,  and 
the  average  force  required  to  pull  them  was  not  less  than  35.  S 
tons  each.  The  frictional  resistance  was  at  least  1,875  lbs.  per  sq. 
ft  of  surface  in  contact  with  the  soil,  f 

372,  Safe  Load.  The  piles  under  the  bridge  over  the  Missouri 
at  Bismarck,  Dakota,  were  driven  33  ft.  into  the  sand,  and  suataia 
20  tons  each— equivalent  to  a  frictional  resistance  of  600  lbs.  per  sq. 
ft.  The  piles  at  the  Flattsmouth  bridge,  driven  28  ft  into  the 
sand,  sustain  less  than  13}  tons,  of  which  about  one  fifth  is  live- 
load, — equivalent  to  a  frictional  resistance  of  300  lbs.  per  sq.  ft 

At  the  Hull  docks,  England,  piles  driven  16  ft  into  "  alluvial 
mud  "  sustain  at  least  30  tons,  and  according  to  some  25  tons ;  for 
the  former,  the  friction  is  about  800  lbs.  per  sq.  ft  The  piles 
under  the  Koyal  Border  bridge  "  were  driven  30  to  40  ft  into  sand 
and  gravel,  and  sustain  70  tons  each," — the  friction  being  about 
,  1,400  lbs.  per  sq.  ft 

373.  "The  South  Street  bridge  approach,  Philadelphia,  fell  by 
the  sinking  of  the  foundation  piles  under  a  load  of  24  tons  each. 

•  By  coarttsr  of  John  C.  Tr»atwliie,  Jc,  tzom  prlnte  correspondsnce  of  John  &. 
Payne  and  W.  A.  Haven,  «DglD«ere  Id  charge, 
t  Proa.  Iiut  of  C.  £.,  vol.  Ixlv.  pp.  311-19. 


ovGoQi^lc 


Art.  3.]  bkabing  powbb  op  piles.  24» 

They  were  drivea  to  an  abiolate  stoppage  by  a  l-ton  hammer  fall- 
ing 33  feet.  Their  length  was  from  24  to  4L  feet.  The  piles  vere 
driTSQ  through  mud,  then  tough  olay,  and  into  hard  gravel."* 
According  to  Trantwine's  formula  their  ultimate  supporting  power 
was  164  tona,  and  according  to  the  Engineering  News  formula  th« 
safe  load  was  64  tona.  It  is  probable  that  the  last  blow  was  strnck 
on  a  broomed  head,  which  wonld  greatly  reduce  the  penetration, 
and  that  consequently  their  enpporting  power  was  greatly  over- 
estimated.  If  the  penetration  when  the  last  blow  was  struck  on 
eound  wood  were  2  inches,  then  according  to  Trantwine's  formula 
Uie  ultimate  supporting  power  was  64.7  tona,  and  according  to  the 
Engineering  Newt  formula  the  safe  load  was  31.3  tone. 

374.  SUTPOBTDtO  FOTEB  07  SOBZW  LSli  DiBE  FiLBS.  The  sup- 
porting power  depends  upon  the  nature  of  the  soil  and  the  depth  to 
which  the  pile  is  sunk.  A  screw  pile  "  in  soft  mud  aboYe  clay  and 
«and "  supported  1.8  tons  per  sq.  ft  of  blade.t  A  disk  pile  in 
"  quicksand  "  stood  5  tons  per  sq.  ft.  under  vibrations.  X  Charles 
McDonald,  in  constructing  the  iron  ocean-pier  at  Coney  Island,  as- 
sumed that  the  safe  load  upon  the  flanges  of  the  iron  disks  sunk  into 
the  sand,  was  5  tons  per  sq.  ft. ;  but  "  many  of  them  really  snpport 
as  much  as  6.3  tons  per  sq.  ft.  continually  and  are  subject  to  occa- 
sional loads  of  8  tons  per  sq.  ft.,  without  causing  any  settlement 
that  can  be  detected  by  the  eye."§ 

376.  Faoiob  or  Satitt.  On  account  of  the  many  uncertainties 
in  connection  with  piles,  a  wide  margin  of  safety  is  recommended  by 
all  authorities.  The  factor  of  safety  i-anges  from  2  to  12  according' 
to  the  importance  of  the  structure  and  according  to  the  faith  in  the 
formula  employed  or  the  experiment  taken  as  a  guide.  At  best, 
the  formulas  can  give  only  the  supporting  power  at  the  time  when 
the  driving  ceases.  If  the  resistance  is  derived  mainly  from  fric- 
tion, it  is  probable  that  the  supporting  power  increftses  for  a  time 
after  the  driving  ceases,  since  the  co-efficient  of  friction  is  usually 
greater  after  a  period  of  rest  If  the  supporting  power  is  derived 
mainly  from  the  resistance  to  penetration  of  a  stifl  substratum,  the 
bearing  power  for  a  steady  load  will  probably  be  smaller  than  the 

•  TraoB.  Am.  Soc.  of  C.  E.,  voL  vIL  p.  aM. 
t  Proc.  InBt  of  C.  E„  vol  xvll.  p.  «L 

X  Ibid.,  p.  443.        ' 

ITrans.  Am.  Soo.  C.  E.,  vol.  Till.  p.  236. 


ovGoQi^lc 


350  PILE   FOCNDATIONS.  [CHAP.  XI. 

force  reqaired  to  drive  it,  as  most  materials  require  a  less  force  to 
change  their  form  slowly  than  rapidly.  K  the  soil  adjoining  the 
piles  becomes  wet,  the  supporting  power  will  be  decreased;  and 
vibrations  of  the  Btrncture  will  have  a  like  effect. 

The  formnlas  in  use  for  determining  the  supporting  power  of 
piles  are  so  unreliable,  that  it  is  quite  impOBaible  to  determine  the 
factor  of  safety  for  any  existing  structure  with  anything  like  accu- 
racy. 

The  factor  to  be  employed  should  vary  with  the  nature  of  the 
fltmcture.  For  example,  the  abutments  of  a  etone  arch  should  be 
fioustrncted  eo  that  they  will  not  settle  at  all ;  but  if  a  railroad  pile 
trestle  settles  no  serious  damage  is  done,  since  the  track  can  be 
flhimmed  up  occasionally.  In  a  few  cases,  a  small  settlement  has 
taken  place  in  a  railroad  trestle  when  the  factor  of  safety  was  3  or 
4,  as  computed  by  equation  (4),  page  239. 

Art.  3.  Arbanqeueitt  of  the  Foundation. 

376.  SiBPOSITIOR  OF  THE  PiLEB.  The  length  of  the  piles  to  be 
used  is  determined  by  the  nature  of  the  soil,  or  the  conveniencea 
for  driving,  or  the  lengths  most  easily  obtained.  The  safe  bearing 
power  maybe  determined  from  the  data  presented  in  §g  370-73,  or, 
better,  by  driving  a  teat  pile  and  applying  equation  (4),  page  239. 
Then,  knowing  the  weight  to  be  supported,  and  having  decided 
upon  the  length  of  piles  to  be  used,  and  having  ascertained  their 
safe  bearing  power,  it  isan  easy  matter  to  determine  how  many  piles 
are  required.  Of  course,  the  number  of  piles  under  the  different 
parts  of  a  structure  should  be  proportional  to  the  weights  of  those 
parts. 

If  the  attempt  is  made  to  drive  piles  too  close  together,  they  are 
liable  to  force  each  other  up.  To  avoid  this,  the  centers  of  the 
piles  should  be,  at  least,  SJ  or  3  feet  apart.  Of  course,  they  may 
be  farther  apart,  if  a  less  number  will  give  sufficient  supporting 
power,  or  if  a  greater  area  of  foundation  is  necessary  to  prevent 
overturning. 

When  a  grillage  (§  380)  is  to  be  placed  on  the  head  of  the  piles, 
great  care  must  be  taken  to  get  the  latter  in  line  so  that  the  lowest 
course  of  grillage  timber,  in  this  case  called  capping,  may  rest 
squarely  upon  all  the  piles  of  a  row.     In  driving. under  water,  a 


ovGoQi^lc 


ART.  3.]  ABRANOEHEXT   OF  THE   FOUNDATION.  S51 

convenieDt  waj  of  markiug  the  poaitiooB  of  the  piles  is  to  conBtmct 
a  light  frame  of  narrow  boards,  called  a  spider,  in  which  the  posi- 
tion  of  the  pilog  is  indicated  hy  a  small  square  opening.  This  frame 
may  be  held  in  place  by  fastening  it  to  the  sides  of  the  coffer-dam, 
or  to  the  piles  already  driven,  or  to  temporary  supporte.  Under 
ordinary  circnmstances,  it  is  reasonably  good  work  if  the  center 
of  the  pile  is  under  the  cap.  Files  frequently  get  considerably  out 
of  place  in  driving,  in  which  case  they  may  sometimes  be  forced 
back  with  a  block  aud  tackle  or  a  jack-screw.  When  the  heads  of 
the  piles  are  to  be  covered  with  concrete,  the  exact  position  of  the 
piles  is  comparatively  an  unimportant  matter. 

In  close  driving,  it  is  necessary  to  commence  at  the  center 
of  the  area  and  work  towards  the  sides ;  for  if  the  central  ones  are 
left  antil  the  last,  the  soil  may  become  so  consolidated  that  they 
can  scarcely  be  driven  at  all. 

377.  Butt  TB,  Top  Down.  According  to  Kankine*  all  piles 
should  be  driven  large  end  down,  having  first  been  sharpened  to  a 
point  1^  to  3  times  as  long  as  the  diameter  of  the  pile.  This  is  at 
least  of  doubtful  utility.  If  the  pile  is  supported  wholly  by  fric- 
tion, then  the  supporting  power  will  be  greater  when  the  small  end 
is  down.  If  the  soil  Is  semi-liquid,  the  buoyancy  would  be  slightly 
greater  when  the  large  end  is  down  ;  but  the  buoyancy  constitutes 
but  a  very  small  part  of  the  supporting  power,  and  the  difference 
in  buoyancy  between  top  and  bottom  down  is  still  less.  If  the  pile 
derives  its  support  mainly  from  a  solid  substratum,  then  its  bearing 
power  would  be  greater  with  the  large  end  down  ;  but,  in  this  case, 
it  should  not  be  sharpened.  For  close  driving,  it  is  frequently 
recommended  that,  to  prevent  the  piles  from  forcing  each  other  up, 
they  should  be  driven  butt  end  down.  K"otice,  however,  that  if 
the  soil  is  non-compressible,  as  pure  sand,  or  if  the  piles  are  driven 
80  close  as  to  compress  the  soil  considerably,  it  will  rise  acd  carry 
the  piles  with  it,  whether  they  were  driven  with  the  big  or  the  little 
end  down.  Piles  are  generally  driven  small  end  down,  but  never- 
theless practical  experience  shows  that  there  are  conditions  in  which 
it  is  apparently  impossible  to  drive  them  in  this  way,  even  in 
comparatively  isolated  positions.  These  conditions  appear  to  occur 
most  frequently  in  swamps,  and  in  connection  with  quicksand. 

•  "  civil  Englnearing, "  p.  603. 


ovGoQi^lc 


S62  PILE  FOUNDAnONS.  [CHAP.  SI. 

378.  SATraa-OFT  THX  Files.  When  piles  are  driven,  it  ia. 
geoerall;  necessary  to  e&w  tbem  off  either  to  bring  them  to  tbe^ 
eame  height,  or  to  get  the  tops  tower  than  they  can  be  driyen,  or  tO' 
Becnre  Bound  wood  upon  which  to  rest  the  timber  platform  that 
carricB  the  masonry.  When  above  water,  pilee  are  nenally  sawed  off 
by  hand ;  and  when  below,  by  machinery — usually  a  circular  saw  on 
a  vertical  shaft  held  between  the  leaders  of  the  pile  driver  or  mounted 
upon  a  special  frame,  and  driven  by  the  engine  used  in  driving  the 
piles.  The  saw-Bhaft  ia  eometimea  attached  to  a  vertical  shaft  held 
between  the  leaders  by  parallel  bars,  by  which  arrangement  the  saw 
can  be  swung  in  the  arc  of  a  circle  and  several  piles  be  cut  off  with- 
out moving  the  machine.  The  piles  are  sometimes  sawed  off  with 
what  is  called  ft  pendulum  saw,  i.e.,  a  saw-blade  fastened  between  ' 
two  arms  of  a  rigid  frame  which  extends  into  the  water  and  is  free- 
to  swing  about  an  axis  above.  The  saw  is  swung  by  men  pushing- 
on  the  frame.  The  first  method  is  the  better,  particularly  when 
the  piles  are  to  be  sawed  off  under  mud  or  silt. 

Considerable  care  is  reqnired  to  get  the  tops  cnt  off  in  a  hori- 
zontal plane.  It  is  not  necessary  that  this  shall  be  done  with  mathe-^ 
matical  accuraoy,  since  if  one  pile  does  stand  up  too  t&r  the  excess- 
load  upon  it  will  either  force  it  down  or  crush  the  cap  until  the 
other  piles  take  part  of  the  weight.  Under  ordinary  conditions,  It 
ia  a  reasonably  good  job  if  piles  on  land  are  sawed  within  half  an 
inch  of  the  same  height ;  and  under  water,  within  one  inch-  When 
a  machine  is  used  on  land,  it  is  usually  mounted  upon  a  track  ^nd 
drawn  along  from  pile  to  pile,  by  which  device,  after  having  leveled 
up  the  track,  a  whole  row  can  be  sawed  off  with  no  farther  atten- 
tion. When  sawing  under  water,  the  depth  below  the  surface  is. 
indicated  by  a  mark  on  the  saw-shaft,  or  a  tai^t  on  the  saw- 
shaft  is  observed  npon  with  a  leveling  instrument,  or  a  leveling  rod 
ia  read  upon  some  part  of  the  saw-frame,  etc.  In  sawing  piles  off 
under  water,  from  a  boat,  a  great  deal  of  time  ia  consumed  (par- 
ticularly if  there  is  a  current)  in  getting  the  boat  into  position, 
ready  to  begin  work. 

Piles  are  frequently  sawed  off  under  10  to  15  feet  of  water,  and 
occasionally  under  20  to  25  feet. 

379.  FnniHIHO  THB  FoinniATIOir.  There  are  two  cases:  (1> 
when. the  heads  of  the  piles  are  not  under  water ;  and  (2)  when  they 
are  under  wat«r. 


ovGoQi^lc 


ABT.  3.]  AERANGEMEinr  OF  THE  FOUNDATION.  263 

1.  When  the  piles  are  not  under  water  there  are  t^in  two  cases : 
i(fl)  when  a  timber  grillage  is  used  ;  and  (i)  when  coitcreit  alone  u 
mBed. 

2.  When  the  piles  are  eawed  ott  under  water,  the  timber  Htmct* 
ure  (in  this  case  called  a  crib)  which  intervenes  between  the  piles 
and  the  masonry  ia  put  together  first,  and  then  sunk  into  place.  The 
construction  is  esBentially  the  same  as  when  tbe  piles  are  not  under 
water,  but  differs  from  that  case  in  the  manner  of  getting  the  tim- 
ber into  its  final  resting  place.  The  methods  of  constructing  foun- 
dations under  water,  including  that  by  the  use  of  timber  cribs,  will 
be  discussed  in  Art.  2  of  the  next  chapter. 

380.  Pilei  and  Grillage.  This  ia  a  stout  frame  of  one  or  more 
courses  of  timber  drift-bolted  or  pinned  to  the  tops  of  the  piles 
and  to  each  other,  upon  which  a  floor  of  thick  boards  is  placed  to 
receive  the  bottom  courses  of  masonry.  For  illustrated  examples, 
see  Fig.  84,  page  3C3,  Fig.  86,  page  380,  and  Fig.  90,  page  386. 

The  timbers  which  rest  upon  the  beads  of  the  piles,  called  caps, 
are  usually  about  I  foot  square,  and  are  fastened  by  boring  a  hole 
through  each  and  into  the  head  of  the  pile  and  driving  into  the 
hole  a  plain  rod  or  bar  of  iron  having  a  slightly  larger  cross-section 
"than  the  hole. 

381.  These  rods  are  called  drifi-hoUt,  and  are  usually  either 
-ttrod  1  inch  in  diameter  (driven  into  a  j-inch  anger  hole) ,  or  a 
hax  1  inch  square  (driven  into  a  l-inch  hole).  Formerly  jag-bolts, 
■or  rag-bolts,  i.  e.,  bolts  whose  sides  were  jagged,  or  barbed,  were 
used  for  this  and  similar  purposes ;  but  universal  experience  shows 
that  smooth  roda  hold  much  tbe  better.  In  some  oxperimenta 
made  at  tbe  Poughkeepsie  bridge  (g  414),  it  whs  found  that  a  I-inch 
rod  driven  into  a  ^|-inch  hole  in  hemlock  required  on  the  average 
s  force  of  3(  tons  per  linear  foot  of  rod  to  withdraw  it;  and  a  1-inch 
rod  driven  into  aj-inch  hole  in  white  or  Norway  pine  required 
5  tons  per  linear  foot  of  rod  to  withdraw  it.*  The  old-style  j^- 
bolt  was  square  becanse  it  was  more  easily  barbed ;  and  probably 
this  is  the  reason  why  square  drift-bolts  are  now  more  common. 
Another  advantage  of  the  round  drift-bolt,  over  the  square  one,  is 
that  the  former  does  not  cut  or  tear  the  wood  as  much  as  the  latter. 
The  ends  of  the  rods  should  be  slightly  rounded  with  a  hammer. 

Transverse  timbers  are  put  on  top  of  the  caps  and  drift-bolted 
lo  them.     Old  bridge-timbers,  timbers  from  false  works,  etc.,  are 
■  ForMdltlonal  data,  see  Note  8,  page  HT. 


ovGoQi^lc 


254  PILE  FOrNDATIOJfS.  [CHAP.  XI. 

frequently  used,  and  are  ordinarily  as  good  for  this  purpose aa  new. 
As  many  courses  may  be  added  as  is  necessary,  each  perpendicular 
to  the  one  beVow  it.  The  timbers  of  the  top  course  si-e  laid  close 
together,  or,  as  before  stated,  a  floor  of  thick  boards  is  added  on  top 
to  receive  the  masonry. 

This  form  of  construction  is  very  common  in  the  fonndAtions  ot 
bridge  abutments.  Of  course  no  timber  should  be  used  in  a  foun- 
dation, except  where  it  will  always  be  wet 

382.  FiLEB  AND  CoVCRETE.  A  thick  layer  of  concrete,  resting; 
partly  on  the  heads  of  the  piles  and  partly  on  the  soil  between 
them,  is  frequently  employed  instead  of  the  timber  grillage  aa  above. 
Objection  is  sometimes  made  to  the  platform  (§  380)  as  a  bed  for  a 
foundation  that,  owing  to  the  want  of  adhesion  between  wood  and 
mortar,  the  masoury  might  slide  off  from  the  platform  if  any  un- 
equal settling  should  take  place.  To  obviate  this,  the  concrete  is 
frequently  substituted  for  the  grillage  and  platform. 

However,  there  is  but  alight  probability  that  a  foundation  will 
ever  fail  on  account  of  the  masonry's  sliding  on  timber,  since,  ordi- 
narily, this  could  take  place  only  when  the  horizontal  force  is 
nearly  half  of  the  downward  pressure.*  This  could  occur  only 
with  dams,  retaining  walls,  or  bridge  abutments,  and  rarely,  if 
ever,  with  these.  One  of  the  fundamental  principles  of  all  masonry 
construction  is  to  build  the  courses  perpendicular  to  the  line  of 
pressure,  which  condition  alone  would  prevent  slipping.  Any  pos* 
sibility  of  slipping  can  be  prevented  also  by  omitting  one  or  mora 
of  the  timbers  in  the  top  course — the  omitted  timbers  being  per- 
pendicular to  the  direction  of  the  forces  tending  to  produce  sliding; 
— or  by  building  the  top  of  the  griilage  in  the  form  of  steps,  or  by 
driving  drift-bolts  into  the  platform  and  leaving  their  upper  ends 
projecting. 

Although  the  use  of  concrete,  as  above,  may  not  be  neoeesary  to 
prevent  sliding,  it  adds  materially  to  the  supporting  power  of  th« 
foundation;  it  utilizes  the  bearing  power  of  the  soil  between  the 
piles  as  well  aa  the  supporting  power  of 'the  piles  themselves, 
which  is  a  very  important  consideration  in  soft  soils.  Another  ad- 
vantage of  this  form  of  construction  is  that  the  concrete  can  be  lai(i 
without  exhausting-  the  water  or  sawing  off  the  piles.     Frequentli 

•See  labia 86,  page 819. 


ovGoQi^lc 


ABT.  3.]  ABBAKGEUEITC  OF  THS  F0UNDA.T10N.  3S& 

concrete  can  also  be  need  advaatageonsly  in  conoection  with  timber 
grillage  to  paclc  in  aroand  the  timbers. 

383.  LATEXAI.  TnLDDtO.  Notico  that,  although  the  masonry 
maj  not  elide  off  from  the  timber  platform  (g  38:^),  the  foundation 
may  yield  laterally  by  the  piles  themselves  being  pushed  over.  If 
the  piles  reach  a  firm  subsoil,  it  will  help  matters  a  little  to  remoTO 
the  upper  and  more  yielding  soil  from  aroand  the  tops  of  the  piles 
and  fill  in  with  broken  stone ;  or  a  wall  of  piles  may  be  driven 
around  the  fonndation — at  some  distance  from  it, — and  timber 
braces  be  placed  between  the  wall  of  piles  and  the  foundation. 
When  the  foundation  can  not  be  buttressed  in  front,  the  structure 
may  be  prevented  from  moving  forward  by  rods  which  bear  on  the 
face  of  the  wall  and  are  connected  with  plates  of  iron  or  blocks  of 
stone  imbedded  in  the  earth  at  a  distance  behind  the  wall  (se^ 
§  551),  or  the  thrust  of  the  earth  against  the  back  of  the  wall  may 
be  decreased  by  supporting  the  earth  immediately  behind  the 
foundation  proper  upon  a  grillage  and  platform  resting  on  piles,  or 
the  same  result  may  be  attained  by  constructing  relieving  arches 
against  the  back  of  the  wall  (see  g  55^). 

384.  CDSHDro'B  File  Foohbatios.  The  desire  to  -utilize  the 
cheapness  aud  efficiency  of  ordinary  piles  as  a  foundation  for  bridge 
piers  and  at  the  same  time  secure  greater  durability  than  is  pos- 
sible with  piles  alone,  led  to  the  introduction  of  what  is  known  aa 
Goshing's  pile  foundation,  first  used  in  1868,  at  India  Point,  Hhode 
Island.  It  consists  of  square  timber  piles  in  intimate  contact  with 
each  other,  forming  a  solid  mass  of  bearing  timber.  Surrounding 
the  pile  claster  is  an  envelope  of  cast  or  wrought  iron,  sunk  in  the 
mud  or  silt  only  enough  to  protect  the  piles,  all  voids  between  piles 
and  cylinders  being  filled  with  hydraulic  concrete. 

Several  such  foundations  have  been  used,  and  have  proved 
satisfactory  in  every  respect.  The  only  objection  that  has  ever 
been  urged  against  them  is  that  the  piles  may  rot  above  the  water 
line.  If  they  do  rot  at  all,  it  will  be  very  slowly ;  and  time  alone 
can  tell  whether  this  is  an  important  objection. 

In  making  a  foundation  according  to  the  Gushing  system,  the 
piles  may  be  driven  first  and  the  cylinder  sunk  over  them,  or  the 
piles  can  be  driven  inside  the  cylinder  after  a  few  sections  are 
in  place.  In  the  latter  case,  however,  the  cylinders  may  be  sub- 
jected to  undue  strains  and  to  subse<}uent  damage  from  shock  and 


ovGoQi^lc 


•256  PILE  rODNDATlOKS.  [CHAP.  XI. 

vibration;  and  besides,  the  sawiug  off  of  the  piles  would  be  very 
-difficult  and  inconveuient,  and  they  wonld  have  to  be  left  at  irreg- 
ular heights  and  with  battered  tops.  On  the  other  hand,  if  the 
piles  are  driven  first,  there  is  danger  of  their  spreading  and  there* 
by  interfering  with  the  sinking  of  the  cylinder. 

The  special  advanti^es  of  the  Cnshing  piers  are :  (I)  cheapness, 
(2)  ability  to  resist  scour,  (3)  small  coDtiHction  of  the  water  way, 
and  (4)  rapidity  of  construction. 

369.  Example.  The  railroad  bridge  over  the  Tenas  River,  near 
Mobile,  rests  on  Gushing  piers.  There  are  thirteen,  one  being  a 
pivot  pier.  Each,  excepting  the  pivot  pier,  is  made  of  two  cast- 
iron  cylinders,  6  feet  in  exterior  diameter,  located  16  feet  between 
centers.  The  cylinders  were  cast  in  sections  10  feet  long,  of  metal 
1^  inches  thick,  and  united  by  interior  flanges  3  inches  thick  and 
-3  inches  wide.  The  sections  are  held  together  by  40  bolts,  each 
1^  inches  in  diameter.  The  lower  section  in  each  pier  was  pro- 
vided with  a  cutting-edge,  and  the  top  section  was  cast  of  a  length 
sufficient  to  bring  the  pier  to  its  proper  elevation. 

The  pivot  pier  is  composed  of  one  central  cylinder  6  feet  in 
-diameter,  and  six  cylinders  4  feet  in  diameter  arranged  bexagonally. 
The  radios  of  the  pivot  circle,  measuring  from  the  centers  of  cylin- 
ders, is  l'Z\  feet.  Jilach  cylinder  is  capped  with  a  cast-iron  plate 
8J  inches  thick,  secured  to  the  cylinder  with  twenty  1-inch  bolts. 

The  piles  are  sawed  pine,  not  less  than  10  inches  square  at  the 
-small  end.  They  were  driven  first,  and  the  cylinder  sunk  over 
them.  In  each  of  the  large  cylinders,  13  piles,  and  in  each  of  the 
.smaller  cylinders,  5  piles,  were  driven  to  a  depth  not  less  than  30 
feet  below  the  bed  of  the  river.  The  piles  had  to  be  in  almost  per- 
fect contact  for  their  whole  length,  which  was  secured  by  driving 
their  points  in  contact  as  near  as  possible,  and  then  pulling  their 
tops  together  and  holding  them  by  8  bolts  1^  inches  in  diameter. 
In  this  particular  bridge  the  iron  cylinders  were  sunk  to  a  depth 
not  less  than  10-feet  below  the  river  bed  ;  but  usually  they  are  not 
sunk  more  than  3  to  7  feet.  The  piles  were  cnt  off  at  low  water, 
the  water  pumped  out  of  the  cylinder,  and  the  latter  then  filled  to 
the  top  with  concrete. 


ovGoQi^lc 


CHAPTER  XIL 
FOUOTJATIONS  UMDER  WATER. 

386.  The  clasa  of  fotrndationB  to  be  diBcusBed  in  this  chapter 
iiould  appropriatol;  be  called  Foundations  for  Bridge  Piers,  since 
the  latter  are  aboiit  the  only  ones  that  are  laid  under  water.  In  this 
class  of  work  the  chief  difficulty  is  in  excluding  the  water  prelim- 
inary to  the  preparation  of  the  bed  of  the  foundation  and  the  con- 
«truction  of  the  artificial  structure.  This  nsnally  requires  great 
resources  and  care  on  the  part  of  the  engineer.  Sometimes  the 
preservation  of  the  foundation  from  the  scouring  action  of  the  cur- 
rent is  an  important  matter. 

PreTenting  the  undermining  of  the  foundation  is  generally  not  a 
matter  of  much  difficulty.  In  quiet  water  or  in  a  sluggish  stream 
bat  little  protection  is  required ;  in  which  case  it  is  sufficient  to  de- 
posit a  mass  of  loose  stone,  or  riprap,  aronnJthe  base  of  the  pier, 
if  there  is  danger  of  the  riprap's  being  undermined,  the  layer  must 
be  extended  farther  from  the  base,  or  be  made  so  thick  that,  if 
undermined,  the  stone  will  fall  into  the  cavity  and  prevent  further 
damf^e.  A  willow  mattress  sank  by  placing  stones  upon  it  is  an 
economical  and  efficient  means  of  protecting  a  structure  against 
ecour.  A  pier  may  be  protected  also  by  inclosing  it  with  a  row  of 
piles  and  depositing  loose  rock  between  the  pier  and  the  piles.  In 
minor  structures  the  foundation  may  be  protected  by  driving  sheet 
piles  around  it. 

If  a  bage  qnanti^  of  stone  be  deposited  around  the  base  of  the 
pier,  the  velocity  of  the  current,  and  consequently  its  scouring 
action,  will  be  increased.  Such  a  deposit  is  also  an  obstruction  to 
navigation,  and  therefore  is  seldom  permitted.  In  many  cases  the 
•only  absolute  security  is  in  sinking  the  foundation  below  the  scour- 
ing action  of  the  water.  The  depth  necessary  to  secure  this  adds  to 
the  difficulty  of  preparing  the  bed  of  the  foundation. 

387.  The  principal  difficulty  in  laying  a  foundation  under  water 
consists  in  excluding  the  water.  If  necessary,  masonry  can  be  laid 
under  water  by  divers ;  but  this  ia  very  expensive  and  is  rarely  re- 
ported to. 


ovGoQi^lc 


S68  FOUNDATIONS   CHDEB  WATBB.  [CHAF.  XH. 

There  are  five  methoda  in  nae  for  laying  foundatioDB  under  water: 
(1)  the  method  of  excluding  the  water  from  the  bed  of  the  founda- 
tion by  the  uee  of  a  coffer-dam;  (3)  the  method  of  founding  the 
'  pier,  without  excluding  the  water,  by  means  of  a  timber  crib  but- 
mounted  by  a  water-tight  box  in  which  the  masonry  ia  laid;  (3)  the 
method  of  sinking  iron  tubes  or  masonry  wells  to  a  solid  substratnm 
by  excavating  inside  of  them;  (4)  the  method  in  which  the  water  ia. 
excluded  bythe  presence  of  atmospheric  air;  and  (5)  the  method  of 
freezing  a  wall  of  earth  around  the  site,  inside  of  which  the  excava- 
tion can  be  made  and  the  masonry  laid.  These  several  methods  will 
be  discussed  separately  in  the  order  named. 


Abt.  1.  The  Goffeb-Dau  Pbocebb. 

388.  A  coffer-dam  is  an  inclosure  from  which  the  initer  is  pumped 
and  in  which  the  masonry  is  laid  in  the  open  air.  This  method  con- 
eists  in  constructing  a  coSer-dam  around  the  site  of  the  proposed 
foundation,  pumping  out  the  water,  preparing  the  bed  of  the  fonn-- 
datioQ  by  driving  piles  or  otherwise,  and  laying  the  masonry  on  the- 
inside  of  the  coffer-dam.  After  the  masonry  is  above  the  water  the- 
coffer-dam  can  be  removed. 

389.  ConTBUCnm  of  ths  Sak.*  The  construction  of  coffer- 
dams varies  greatly.  In  still,  shallow  water,  a  well-built  bank  of* 
clay  and  gravel  is  sufficient.  If  there  is  a  slow  current,  a  wall  of 
bags  partly  filled  with  clay  and  gravel  does  fairly  well;  a  row  of 
cement  barrels  filled  with  gravel  and  banked  up  on  the  outside  haa- 
also  been  used.  If  the  water  is  too  deep  for  any  of  the  above- 
methods,  a  single  or  double  row  of  sheet  piles  may  be  driven  and 
banked  np  on  the  outside  with  a  deposit  of  impervious  soil  sufBcient. 
to  prevent  leaking.  If  there  ia  much  of  a  current,  the  puddle  on 
the  outside  will  be  washed  away;  or,  if  the  water  ia  deep,  a  large- 
quantity  of  material  will  be  required  to  form  the  puddle-waM;  and 
hence  the  preceding  methods  are  of  limited  application. 

390.  The  ordinary  method  of  conatructing  a  coffer-dam  in  deep- 
water  or  in  a  strong  current  is  shown  in  Fig.  60,  The  area  to  bo 
inclosed  ia  first  aurrounded  by  two  rows  of  ordinary  piles,  m,  m.  On 
the  outside  of  the  main  piles,  a  little  below  the  top,  are  bolted  two- 

«  See  also  I  SIT,  page  214. 


ovGoQi^lc 


ABT.  I.]  THE  COFFEB-DAU   PBO0E8S.  Z59 

loDgitadinal  pieces,  w,  w,  called  walea;  and  on  the  inside  are  fastened 
two  similar  pieces,  g,  g,  which  serve  as  guides  for  the  sheet  piles,  s,  x, 
while  being  driven.  A  rod,  r,  connects  the  top  of  the  opposite 
maia  piles  to  prevent  spreading  when  the  puddle  is  put  in.  The 
timber,  /,  is  pat  on  primnrily  to  carry  the  footway,/,  and  is  some- 
times notched  over,  or  otherwise  fastened  16,  the  pieces  w,  w  to  pre- 
vent the  puddle  space  from  spreading,  b  and  b  are  braces  extend- 
ing from  one  side  of  the  coffer-dam  to  the  other.  These  braces  are 
put  in  position  Buccessively  from  the  top  as  the  water  is  pumped 


ont;  and  as  the  masonry  is  built  up,  they  are  removed  and  the  sides 
of  the  dam  braced  by  short  struts  rcBting  against  the  pier. 

The  resistance  to  overturning  is  derived  principally  from  the 
main  piles,  m,  m.  The  distance  apart  and  also  the  depth  to  which 
they  should  be  driven  depends  upon  the  kind  of  bottom,  the  depth 
of  water,  and  the  danger  from  floating  ice,  \q^,  etc.  Roles  and 
formulas  are  here  of  but  tittle  use,  judgment  and  experience  being 
the  only  guides.  The  distance  between  the  piles  in  a  row  is  usually 
from  4  to  6  feet. 

The  dimensions  of  the  sheet  piles  (§  329)  employed  will  depend 
npon  the  depth  and  the  number  of  longitudinal  waling  pieces  used. 
Two  thicknesses  of  ordinary  2-inch  plank  are  generally  employed. 
Sometimes  for  the  deeper  dame,  the  sheet  pilesare  timbers  lO  or  1:^ 
inches  square. 

The  thickness  of  the  dam  will  depend  upon  (1)  the  width  of  gang^ 
iray  required  for  the  workmen  and  machinery,  (2)  the  thickness  re- 


ovGoQi^lc 


360  ftJCNDATlONS   CSDEE  WATER.  [CHAP.  XII. 

quired  to  prevent  OTtfrturnitig,  and  (3)  th<i  tliickaess  of  puddle 
DecessBrj  to  prevent  leakage  through  the  wall.  The  thickness  of 
shallow  dams  will  UBually  \>b  determined  by  the  first  consideration  ; 
but  for  deep  dams  the  thickness  will  be  governed  by  the  second  or 
third  requirement.  If  tht<  braces,  b,  b,  are  omitted,  aa  is  sometimes 
done  for  greater  Gonvenience  in  working  in  the  coffer-dam,  then  the 
main  piles,  m,  m,  must  \m  stronger  and  the  dam  wider  in  order  to 
resist  the  lateral  pressure  of  the  water.  A  rule  of  tiiumb  frequently 
used  for  this  case  is:  "For  depths  of  less  than  10  feet  make  the 
width  10  feet,  and  for  depths  over  10  feet  give  an  additional  thick- 
ness of  1  foot  for  each  additional  3  feet  of  wall."  Trautwine's  rule 
is  to  make  the  thickness  of  the  puddle-wall  three  fourths  of  its 
height;  but  in  no  case  is  the  wall  to  be  less  than  4  feet  thick.  If 
the  coffer-dam  is  well  braced  across  the  inclosed  area,  the  puddle- 
wall  may  vary  from  3  feet  for  shallow  depths  to  10  feet  for  great 
depths;  the  former  width  has  been  successfully  employed  for  depths 
of  18  to  30  feet,  although  it  is  considerably  less  than  is  customary. 

The  puddle-wall  should  be  constructed  of  impervious  soil,  of 
which  gravelly  clay  is  best.  It  is  a  common  idea  that  clay  alone,  or 
«lay  and  fine  sand,  is  best.  With  pure  clay,  if  a  thread  of  water  ever 
ao  small  finds  a  passage  under  or  through  the  puddle,  it  will  steadily 
wear  a  larger  opening.  On  the  other  hand,  with  gravelly  clay,  if 
the  water  should  wash  out  the  clay  or  fine  sand,  the  larger  particles 
will  fall  into  the  space  and  intercept  fii'st  the  coarser  sand,  and 
next  the  particles  of  loam  which  are  drifting  in  the  current  of  water; 
and  thus  the  whole  mass  puddles  itself  better  than  the  engineer 
could  do  it  with  his  own  hands.  An  embankment  of  gravel  is  com- 
paratively safe,  and  becomes  tighter  every  day.  While  a  clay  em- 
bankment may  be  tighter  at  first  than  a  gravelly  one,  it  is  always 
liable  to  breakage.  Before  putting  in  the  puddling,  all  soft  mud 
and  loose  soil  should  be  removed  from  between  the  rows  of  sheet 
piles.  The  puddling  should  be  deposited  in  layers,  and  compacted 
as  much  as  is  possible  without  causing  the  sheet  piles  to  bulge  so 
much  as  to  open  the  joints. 

391.  Coffer-dams  are  sometimes  constructed  by  building  a  strong 
crib,  and  sinking  it  The  crib  may  be  composed  either  of  uprights 
framed  into  caps  and  sills  and  covered  on  the  outside  with  tongued 
and  grooved  planks,  or  of  squared  timbers  laid  one  on  top  of  the 
-other,  Ic^-house  fashion,  and  well  calked.     The  outer  uprights  are 


ovGoQi^lc 


ART,  l.J  THE   COFPER-])A»    PBOCEBS.  ii6\ 

braced  against  the  meide  uprighte  and  sills  to  prevent  cmshing 
inwards.  This  crib  may  be  bnilt  on  land,  launched,  towed  to  itB 
final  place,  and  snnk  by  piling  stones  on  top  or  by  throwing  tbem 
into  cella  of  the  crib-work  which  are  boarded  up  for  that  pnrpoBe. 
The  bottom  of  the  stream  may  be  leveled  off  to  receive  the  crib  by 
dredging,  or  the  dam  may  be  made  tight  at  the  bottom  by  driving 
sheet  piles  around  it.  The  crib  must  be  securely  bolted  together 
(see  §  381)  vertically,  or  the  buoyancy  of  the  water  will  lift  off  the 
upper  courses. 

A  movable  coffer-dam  is  sometimes  constructed  in  the  same 
general  way,  except  that  it  is  made  in  halves  to  allow  of  removal 
from  around  the  finished  pier.  The  two  halves  are  joined  together 
by  fitting  timbers  between  the  projecting  eourses  of  the  crib,  and 
then  passing  long  bolts  vertically  through  the  several  courses.  Some 
of  the  compartments  are  made  water-tight  to  facilitate  the  move- 
ment of  the  crib  from  place  to  place." 

Coffer-dams  are  also  built  by  sinking  an  open  crib,  similar  to  the 
above,  and  then  sheeting  it  on  the  outside  by  driving  piles  around 
it  after  it  is  sunk.    For  shallow  depths,  this  method  is  very  efficient. 

392.  Sometimes  two  coffer-dams  are  employed,  one  inside  of  the 
other,  the  outer  one  being  used  to  keep  out  the  water,  and  the  inner 
one  to  keep  the  soft  material  from  flowing  into  the  excavation.  The 
outer  one  may  be  constructed  in  any  of  the  ways  described  above. 
The  inner  one  is  usually  a  frame-work  sheeted  with  boards,  or  a  crib 
of  squared  timbers  built  Ic^-house  fashion  with  tight  joints.  The 
inner  crib  is  sunk  (by  weighting  it  with  stone)  as  the  excavation 
proceeds.  The  advantages  of  the  use  of  the  inner  crib  are  (1)  that 
the  coffer-dam  is  smaller  than  if  the  saturated  soil  wore  allowed  to 
take  its  natural  slope  from  the  inside  of  the  dam  to  the  bottom  of 
the  excavation  ;  (3)  the  space  between  the  crib  .and  the  dam  can  be 
kept  full  of  impervious  material  in  case  of  any  trouble  with  the  out- 
side dam  ;  (3)  the  feet  of  the  sheet  piling  are  always  covered,  which 
lessens  the  danger  of  undermining  or  of  an  inflow  of  water  and  mud 
under  the  dam  ;  and  (4)  it  also  reduces  to  a  minimum  the  material 
to  be  excavated. 

393.  Iron  has  been  used  in  a  tew  instances  as  a  sheeting  for  cof- 
fer-dams.   Plates  are  riveted  together  to  form  the  walls,  and  stayed 

*  For  ftn  Ulnetnted  eismple,  gee  Froc  Engineer's  Club  of  Phlladelpbla,  vol.  tv- 


ovGoQi^lc 


363  FOUNDATIONS   UNDER  WATEE.  [CHAP.  XH. 

oD  the  inside  by  horizontal  rings  made  of  angle  iron.     Wood  is 
cheaper  and  more  easily  wrought,  and  therefore  generally  preferred. 

394.  Leaka&E.  a  serious  objection  to  the  use  of  cofFer-dams  is 
the  difficulty  of  preventing  leakage  under  the  dam.  One  of  the 
simplest  devices  to  prevent  this  is  to  deposit  a  bank  of  gravel  around 
the  outside  of  the  dam ;  then  if  a  vein  of  water  escapes  below  the 
aheet  piling,  the  weight  of  the  gravel  will  crush  down  and  fill  the 
hole  before  it  can  enlarge  itself  enough  to  do  serious  damage.  If  the 
coffer-dam  is  made  of  crib-work,  short  sheet  piles  may  be  driven 
around  the  bottom  of  it ;  or  hay,  willows,  etc.,  may  be  laid  around 
the  bottom  edge,  upon  which  puddle  and  stones  are  deposited  ;  or 
a  broad  flap  of  tarpaulin  may  be  nailed  to  the  lower  edge  of  the 
crib  and  spread  out  loosely  on  the  bottom,  upon  which  stones  and 
puddle  are  placed.  A  tarpaulin  is  frequently  used  when  the  ^ 
bottom  is  very  irregular, — in  which  ease  it  would  cost  too  much  to 
level  oft  the  site  of  the  dam  ;  and  it  is  particularly  useful  where  the 
ttottom  is  rocky  and  the  sheet  piles  cau  not  be  driven. 

When  the  bed  of  the  river  is  rock,  or  rock  covered  with  but  a 
few  feet  of  mud  or  loose  soil,  a  coffer-dam  only  sufficiently  tight  to 
keep  out  the  mud  is  constructed.  The  mud  at  the  bottom  of  the 
inclosed  area  is  then  dredged  out,  and  a  bed  of  concrete  deposited 
under  the  water  (§  154).  Before  the  concrete  hae  set,  another  coffer- 
dam is  constructed,  inside  of  the  first  one,  the  latter  being  made  water- 
tight at  the  bottom  by  settling  it  into  the  concrete  or  by  driving 
sheet  piles  into  it.  However,  the  better  and  moi-e  usual  method  is 
to  sink  the  masonry  upon  the  bed  of  concrete  by  the  method  de- 
scribed in  Art  2  (pages  266-71). 

It  is  nearly  impossible  to  prevent  considerable  leakage,  unless  the 
"bottom  of  the  crib  rests  upon  an  impervious  stratum  or  the  sheet 
piles  are  driven  into  it.  AVater  will  find  its  way  through  nearly  any 
^iepth  or  distance  of  gravelly  or  sandy  bottom.  Trying  to  pump  a 
river  dry  through  the  sand  at  the  bottom  of  a  coffer-dam  is  expen- 
sive. However,  the  object  is  not  to  prevent  all  infiltration,  but  only 
to  so  reduce  it  that  a  moderate  amount  of  bailing  or  pumping  will 
keep  the  water  out  of  the  way.  Probably  a  coffer-dam  was  never 
built  that  did  not  require  considerable  pumping;  and  not  infre- 
quently the  amount  is  very  great, — so  great,  in  fact,  as  to  make  it 
clear  that  some  other  method  of  constructing  the  foundation  should 
Jiave  been  chosen. 


ovGoQi^lc 


ABI.  I.]  THE  COFFEB-DAH   PBOCESS.  £63 

Seams  of  aand  are  veij  troublesome.  Logs  or  stones  under  the 
edge  of  the  dftm  are  also  a  cause  of  considerable  annoyance.  It  is 
fiometimes  beat  to  dredge  away  the  mud  and  loose  soil  from  the  site 
of  the  proposed  coffer-dam ;  but,  when  this  is  necessary,  it  is  usu- 
ually  better  to  construct  the  foundation  without  the  use  of  a  coffer* 
dam, — see  Art.  2  of  this  chapter  (page  366).  Coffer^ma  should 
be  used  only  in  very  shallow  water,  or  when  the  bottom  is  clay  or  . 
some  material  impervious  to  water. 

395.  Pofflpi.  Incontrtructingfoundations,  it  iefrequentlynecee- 
ssry  to  do  considerable  bailing  or  pumping.  The  method  to  be  em- 
ployed  in  any  particular  case  will  vary  greatly  with  the  amount  of 
water  present,  the  depth  of  the  excavation,  the  appliances  at  hand, 
etc.  The  pumps  generally  used  for  this  kind  of  work  are  (1)  the  ordi- 
nary wooden  haud-pump,  (3)  the  steam  siphon,  (3)  the  pulsometer, 
and  (4)  the  centrifugal  pump.  Rotary  and  direct-acting  steam 
pumps  are  not  suitable  for  use  iu  foundation  work,  owing  to  the 
deleterious  effect  of  sand,  etc.,  in  the  water  to  be  pumped. 

1.  Hand  Power.  When  the  lift  is  small,  water  can  be  bailed 
out  faster  than  it  can  be  pumped  by  hand ;  but  the  labor  is  propor- 
tionally more  fatiguing.  The  ordinary  hand  found ation-pnmp  con- 
sists  of  a  straight  tube  at  the  bottom  of  which  is  fixed  a  common 
flap  valve,  and  in  which  works  a  piston  carrying  another  valve.  The 
tube  is  either  a  square  wooden  box  or  a  sheet-iron  cylinder, — usually 
the  latter,  since  it  is  lighter  and  more  durable.  The  pump  is  oper- 
ated by  applying  the  power  directly  to  the  upper  end  of  the  piston- 
rod,  the  pnmp  being  held  ii  position  by  stays  or  ropes.  There  are 
more  elaborate  foundation-pumps  on  the  market, 

2.  The  gleam  siphnn  la  the  simplest  of  all  pumps,  since  it  has 
DO  movable  parts  whatever.  It  coiisista  essentially  of  a  discbarge 
pipe — open  at  both  ends— through  the  side  of  which  enters  a  smaller 
pipe  having  its  end  bent  up.  The  lower  end  of  the  discharge  pipe 
dips  into  the  water  ;  and  the  small  pipe  connects  with  a  steam  boiler. 
The  steam,  in  rnshing  out  of  the  small  pipe,  carries  with  it  the  air 
in  the  upper  end  of  the  discharge  pipe,  thus  tending  to  form  a 
vacuum  in  the  lower  end  of  that  pipi.> ;  the  water  then  rises  in  the 
discbarge  pipe  and  is  carried  out  with  the  steam.  Although  it  is 
possible  by  the  use  of  large  quantities  of  steam  to  raise  small  quan- 
tities of  water  to  a  great  height,  the  steam  siphon  is  limited  prac- 
tically to  lifting  water  only  a  few  feet.    Its  cheapnese  and  simplicity 


ovGoQi^lc 


364  POUXDATIOXS  USDEB  WATBR.  [CHAP.  XIE 

are  recommendations  in  its  &Tor,  and  itB  efficiency  is  oot  much  less 
than  that  of  other  forms  of  pumps.  A  common  form  of  the  steam 
siphon  resembtes,  in  external  appearance,  the  Eada  sand-pnmp 
represented  in  Fig.  66  (page  293). 

3.  The  pulso?neler  is  an  improved  form  of  the  steam  siphon.  It 
may  properly  be  called  a  steam  pump  which  dispenses  with  all  mov- 
able parts  except  the  valves.  The  height  to  which  it  may  lift  water 
is  practically  unlimited. 

4.  The  centrifugal  pump*  consists  of  a  set  of  blades  revolving  in 
a  short  cylindrical  case  which  connects  at  its  center  with  a  saction 
(or  inlet)  pipe,  and  at  its  circumference  with  a  dischai^  pipe.  The- 
blades  being  made  to  revolve  rapidly,  the  air  in  the  case  is  carried 
outward  by  the  centrifugal  force,  tending  to  produce  &  vacuum  in 
the  suction  pipe ;  the  water  then  enters  the  case  and  is  discharged 
likewise.  The  distance  from  the  water  to  the  pump  is  limited  by 
the  height  to  which  the  ordinary  pressure  of  the  air  will  raise  the 
water ;  I  but  the  height  to  which  a  centrifagsl  pomp  can  lift  the 
water  is  limited  only  by  the  velocity  of  the  outer  ends  of  the  revolv- 
ing blades.  "When  a  quick  application  with  a  discharge  of  lai^ 
quantities  of  water  is  the  most  important  consideration,  the  cen- 
trifugal pump  is  of  great  value.  Since  there  arc  no  valves  in  action 
while  the  pump  is  at  work,  the  centrifugal  pump  will  allow  sand 
and  large  gravel — in  fact  almost  anything  that  can  enter  between 
the  arma — to  pass.  Pumps  having  a  6-inch  to  10-inch  discharge 
pipe  are  the  sizes  most  frequently  used  in  foundation  work. 

396.  Phepabisb  the  Fouhdatios.  After  the  water  is  pumped 
out,  the  bed  of  the  foundation  may  be  prepared  to  receive  the 
masonry  by  any  of  the  processes  described  in  §§  2^3-91,  which  see. 
Ordinarily  the  only  preparation  is  to  throw  out,  nsually  with  hand 
shovels,  the  soft  material.  The  masonry  may  be  started  directly 
upoa  the  hard  substratum,  or  upon  a  timber  grillage  resting  on 
the  soil  (§§  309-10)  or  on  piles  (§  380). 

397.  Cost.  It  is  universally  admitted  that  estimates  for  th& 
cost  of  foundations  under  water  are  very  unreliable,  and  none  are 
more  so  than  those  contemplating  the  use  of  a  coffer-dam.  The 
estimates  of  the  most  experienced  engineers  frequently  differ  greatly 


ovGoQi^lc 


AET.  1.]  THE  COPPEB-BAM   PROCESS.  266 

from  the  actual  cost.     The  difQculties  of  the  case  have  already  bees 
discuased  (§  394). 

For  the  cost  of  piles  and  driving,  see  §§  346-5i.  .The  timber 
will  cost,  according  to  locality,  anywhere  from  $15  to  $25  per 
thoneand  feet,  board  measure.  The  coat  of  labor  in  placing  the 
timber  can  not  be  giTen,  since  it  varies  greatly  with  the  design,  size, 
depth,  etc.  The  iron  in  drift-bolts,  screw-bolts,  and  spikes,  is 
usually  estimated  at  3^  to  5  cents  per  pound  in  place.  Excavation  ' 
in  coffer-dams  frequently  costs  as  high  as  tl  to  91.50. per  cubic 
yard,  including  the  neceaeary  pumping. 

398.  Example.  The  following  example  is  interesting  as  show- 
ing the  cost  under  the  most  favorable  conditions.  The  data  are  for 
a  railroad  bridge  across  the  Ohio  River  at  Point  Pleasant,  W.  Va.* 
There  were  three  250-foot  spans,  one  400-foot,  and  one  200-foot. 
There  were  two  piers  on  land  and  four  in  the  water ;  and  all  ex- 
tended about  90  feet  above  low  water.  The  shore  piers  were 
founded  on  piles — driven  in  the  bottom  of  a  pit — and  a  grillage,  con- 
crete being  rammed  in  around  the  timber.  The  foundations  under 
water  were  laid  by  the  use  of  a  double  coffer-dam  (§  Z92).  The 
water  was  10  feet  deep  ;  and  the  soil  was  3  to  6  feet  of  sand  and 
gravel  resting  on  dry,  compact  clay.  The  foundations  consisted  of 
a  layer  of  concrete  1  foot  thick  on  the  clay,  and  two  courses  of 
timbers.  The  quantities  of  materials  in  the  siz  foundations,  and 
the  total  cost,  are  as  follows  : 

PlDettmberin  cribs  insldeof  coffer-dams,  and  in  fotiDdMione,  378,310  ft.  B.U. 

Oak  timber  in  cofler  dams,  mAia  and  gheet  piliog 344,412  ■■     " 

Poplar  timber  in  cofferdams , 8.587  "     " 

Rouod  piles  in  fouaJutlon  and  coffer-dams I8,S71  Hd.  ft. 

ExcBvation  In  foundaliona 4,843  cu.  yds. 

Concrete       "  "  649"      " 

Riprap 687   "      " 

The  total  cost  of  fouodalions,  including  labor  of  all  kinds,  derricks,  barges, 
engines,  pumps,  iron,  tools,  ropes,  and  everyttiiDg  necessaiy  for  tbe  rapid  com- 
pletion of  tbe  work,  was  f<M,e53.63. 

In  the  construction  of  the  bridge  over  the  Miasonri  River,  near 
Plattamouth,  Neb.,  a  concrete  foundation  49  feet  long,  21  feet 
wide,  and  32  feet  deep,  laid  on  shore,  the  excavation  being  through 
clay,  bowlders,  ahale,  and  soapstone,  to  bed-rock  (33  feet  below 

•  Sngbuering  Mat,  vol.  xitL  p.  388. 


ovGoQi^lc 


'266  FODNDATIONS  CNDEB  WATER.  [CHAP,  311. 

Enrface  of  the  water),  coat  139,607.23,  or  (43.81  per  yard  for  the 
■concrete  laid,* 

399.  For  the  relative  coat  of  foundations,  see  Art.  6,  page  309. 

400.  CoHCllFBiOH.  Uncertainty  as  to  what  trouble  and  expeose  a 
coffer-dam  will  develop  usually  causes  engineers  to  choose  some  other 
method  of  laying  the  foundations  for  bridge  piers.  Cofler-dams 
are  applicable  in  shallow  depths  only ;  hence  one  objection  to  found- 
ing bridge  piers  by  this  process,  particularly  in  rivers  subject  to 
scour  or  liable  to  ice  gorges,  is  the  danger  of  their  being  either  un- 
dermined or  pushed  off  the  foundation.  When  founded  in  mud  or 
sand,  the  first  mode  of  failure  is  most  to  be  feared.     This  danger  is 

■diminished  by  the  use  of  piles  or  large  quantities  of  riprap;  but 

■such  a  foundation  needs  constant  attention.  When  founded  on 
rock,  there  is  a  ^wssibility  of  the  piers  being  pushed  off  the  founda- 

'  tion ;  for,  since  it  ia  not  probable  that  the  coffer-dam  can  be  pumped 
perfectly  dry  and  the  bottom  cleaned  before  laying  the  masonry  or 
depositing  the  concrete,  there  is  no  certainty  that  there  is  good 
anion  between  the  base  of  the  pier  and  the  bed-rock. 

Coffer-dams  are  frequently  and  advantageously  employed  in 
laying  foundations  in  soft  soils  not  under  water,  as  described  in 

.§§316-21  (pages  214-15). 

AaT.  2.  The  Geib  and  Open-Caisson  Procbss. 

401.  ])EranTI05fl.  Unfortunately  there  is  an  ambiguity  in  the 
nse  of  the  word  caisson.  Formerly  it  always  meant  a  strong,  water- 
tight box  having  vertical  sides  and  a  bottom  of  heavy  timbers,  in 
which  the  pier  is  built  and  which  sinks,  as  the  masonry  is  added, 
until  its  bottom  rests  upon  the  bed  prepared  for  it.  With  the  in- 
troduction ot  the  compressed-air  process,  the  term  caisson  was  ap- 
plied to  a  strong,  water-tight  box — open  at  the  bottom  and  closed 
at  the  top — upon  which  tlie  pier  is  built,  and  which  sinks  to  the 
bottom  as  the  masonry  is  added.  At  present,  the  word  oaiBson  gen- 
erally has  the  latter  meaning.  In  the  pneumatic  process,  a  water- 
tight box — open  at  the  top — is  usually  constructed  on  the  roof  of 
the  working  chamber  {"  pneumatic  chamber"),  inside  of  which  the 
masonry  is  built ;  this  box  also  is  called  a  caisson.     The  caisson 


o.GoQi^lc 


AST.  it-l  THE   CfilB   AND  OPEN-CAISSON    PROCESS.  267 

open  at  the  bottom  is  liometimeB  called  an  inverted  caisBOD,  and  the 
■one  open  at  the  top  an  erecl  caisson.  The  latter  when  built  over 
■an  inverted,  or  pnenm&tic,  caisson,  is  somctimeB  called  a  coSer-dam. 
For  greater  cleameBS  the  term  caisson  will  bo  used  for  the  inverted, 
or  pneumatic,  caisson  ;  and  the  erect  caisson,  which  is  built  over  a 
pneumatic  caisson,  will  be  called  a  coffer-dam.  A  caisson  employed 
in  other  than  pneumatic  work  will  be  called  an  open  caisson. 

402.  Feikciple.  This  metliod  of  constructing  the  foundation 
consists  in  building  the  pier  in  the  interior  of  an  open  caisson, 
which  sinks  as  the  masonry  is  added  and  finally  rests  upon  the  bed 
prepared  for  it.  The  masonry  usually  extends  only  a  foot  or  two 
below  extreme  low  water,  the  lower  part  of  the  structure  being  com- 
posed of  timber  crib-work,  called  simply  a  crib.  The  open  caisson  is 
built  on  the  top  of  the  crib,  which  is  practically  only  a  thick  bottom 
for  the  box.  The  timber  is  employed  because  of  the  greater  facil- 
ity with  which  it  may  be  put  into  place,  as  wilt  appear  presently. 
Timber,  when  always  wet,  is  as  dorabte  as  masonry  ;  and  ordinarily 
there  is  not  much  difference  in  cost  between  timber  and  stone. 

If  the  soil  at  the  bottom  is  sott  and  unreliable,  or  if  there  is 
-danger  of  scour  in  case  the  crib  were  to  rest  directly  npon  the  bot- 
tom, the  bed  is  prepared  by  dredging  away  the  mud  (§  407)  to  a 
«ufficient  depth  or  by  driving  piles  which  are  afterwards  sawed  off 
{§  3T8)  to  a  horizontal  plane. 

403.  COMBTBircTlOH  07  THE  CAIB80E.  The  constructioD  of  the 
caisson  differs  materially  with  its  deptli.  The  simplest  form  is 
made  by  erecting  studding  by  toenailing  or  tenoning  them  mto 
the  top  course  of  the  crib  and  spiking  planks  on  the  outside.  For 
a  caisson  6  or  8  feet  deep,  which  is  about  as  deep  as  it  is  wise  to 
try  with  this  simple  construction,  it  is  sufRcient  to  use  studding  6 
inches  wide,  3  inches  thick,  and  6  to  8  feet  long,  spaced  3  feet  apart, 
mortised  and  tenoned  into  the  deck  course  of  the  crib.  The  sides 
and  floor  (the  upper  course  of  the  crib)  should  be  thoroughly  calked 
with  oakum.  The  sides  may  be  braced  from  the  masonry  as  the 
sinking  proceeds.  When  the  crib  is  grounded  and  the  masonry  is 
above  the  water,  the  sides  of  the  box  or  caisson  are  knocked  off. 

When  the  depth  of  water  is  more  than  8  to  10  feet,  the  caisson 
is  constructed  somewhat  after  the  general  method  shown  in  Fig.  61. 
The  sides  are  formed  of  timbers  framed  together  and  a  covering  of 
thick  planks  on  the  outside.     The  joints  are  carefully  calked  to 


ovGoQi^lc 


S68  F0CSDATI0N8  CNDER  WATEB.  [CHAP.  Xn. 

make  the  caissoQ  water-tight.  In  deep  caissoOB,  the  ddes  can  he 
bailt  up  as  the  masoary  progresBeB,  and  thna  not  be  in  the  waj  ol 
the  masons.  The  sides  and  bottom  are  held  together  onl;  bj  thd 
heavy  vertical  rods  ;  and  after  the  caisson  has  come  to  a  bearing 
Qpon  the  soil  and  after  the  masonry  is  above  the  water,  the  rods  are 
detached  and  the  sides  removed,  the  bottom  onJy  remaining  aa  a 
part  of  the  permanent  structnre. 

For  an  illustration  of  the  form  of  caisson  employed  in  sinking  a 
fonndatioD  by  the  compressed-air  process,  see  Plate  I. 

404.  The  caisson   shonld    be    so    contrived    that    it   cao   be 


groanded,  and  afterwards  raised  in  case  the  bed  is  fonnd  not  to 

be  accurately  leveled.  To  effect  this,  a  small  sliding  gate  is  some* 
times  placed  in  the  side  of  the  caisson  for  the  parpose  of  filling  it 
with  water  at  pleasure.  By  means  of  this  gate,  the  caisson  can  be 
filled  and  grounded;  and  by  closing  the  gate  and  pumping  out  the 
vrater,  it  can  be  set  afloat.  The  same  resnlt  can  be  accomplished  by 
putting  on  and  taking  ofE  stone. 

Since  the  caisson  is  a  heavy,  unwieldy  mass,  it  is  not  possible  to 
control  the  exact  poeition  In  which  it  is  sunk  ;  and  hence  it  should 
be  larger  than  the  base  of  the  proposed  pier,  to  allow  for  a  little  ad- 
justment to  bring  the  pier  to  the  desired  location.    The  margin  to 


ovGoQi^lc 


6.BT.  2.]  THB  CBIB  AND  OPEN-CAISSON  PEOCBSS.  268 

be  allowed  will  depend  upon  the  depth  of  water,  size  of  cuBson^ 
iacilitioB,  etc  A  foot  all  round  Ib  probably  none  too  much  under . 
favorable  conditions,  and  generally  a  greater  margin  should  b6 
allowed. 

406.  COMSTKUCnoir  or  THS  Csib.  The  crib  is  a  timber  struct- 
ore  below  the  caissoQ,  which  tranBmite  the  pressure  to  the  bed  of 
the  foundation.  A  crib  is  esaentially  a  grillage  (see  g  309  and  §  380) 
which,  instead  of  being  built  in  place,  ia  first  constructed  and  then 
sunk  to  its  final  resting  place  in  a  single  mass.  A  crib  is  usually 
thicker,  i,  e.,  deeper,  than  the  grillage.  If  the  pressure  ia  great,  the 
-crib  is  built  of  successive  courses  of  squared  timbers  in  contact;  but 
if  the  pressure  ia  small,  it  is  built  more  or  less  open.  In  either 
case,  if  the  crib  is  to  rest  upon  a  soft  bottom,  a  few  of  the  lower 
courses  are  built  open  so  that  the  higher  portions  of  the  bed  may 
be  squeezed  into  these  cells,  and  thus  allow  the  crib  to  come  to  an 
«ven  bearing.  If  the  crib  ia  to  rest  upon  an  uneven  rock  bottom, 
the  site  is  first  leveled  up  by  throwing  in  broken  stone.  If  the  bot- 
tom is  rough  or  sloping,  the  lower  courses  of  the  crib  are  sometimes 
made  to  conform  to  the  bottom  as  nearly  as  pbssible,  as  determined 
from  soundings.  This  method  requires  care  and  judgment  to  pre- 
vent the  crib  from  sliding  off  from  the  inclined  bed,  and  should  be 
used  with  gi'oat  caution,  if  at  aU. 

The  crib  is  usually  built  afloat.  Owing  to  the  buoyancy  of  the 
water,  about  one  third  of  a  crib  made  wholly  of  timber  would  pro- 
ject above  the  water,  and  would  require  an  inconveniently  lai^ 
weight  to  sink  it ;  therefore,  it  is  best  to  incorporate  considerable 
stone  in  the  crib-work.  If  the  crib  ia  more  or  less  open,  this  Ib 
-done  by  putting  a  floor  into  some  of  the  open  spaces  or  pockets, 
which  are  then  filled  with  stone.  If  the  crib  is  to  be  solid,  about 
every  third  timber  is  omitted  and  the  space  filled  with  broken  stone. 

The  timbers  of  each  course  should  be  securely  drift-bolted  (§  381) 
to  those  of  the  course  below  to  prevent  the  buoyancy  of  the  upper 
portion  from  palling 'the  crib  apart,  and  also  to  prevent  anj  possi- 
tiility  of  the  upper  part's  sliding  on  the  lower. 

406.  Tdoeb  IK  FomrsATloiiB.  The  free  use  of  timber  in' 
foundations  is  the  chief  difference  between  American  and  European 
nuthods  of  founding  masonry  in  deep  water.  The  consideration 
that  led  to  its  introduction  in  foundations  was  its  cheapness.  Many 
of  the  more  important  bridges  built  some  years  ago  rest  upon  cril>- 


ovGoQi^lc 


S70  FOUNDATIONS   UNDER   WATEB,  [CHAP.  XTU 

work  of  Toniid  logs  notched  at  their  intersection  and  secured  by- 
drift-boltB.  At  preeeni,  cribs  are  always  built  of  squared  timber. 
As  a  rnle,  there  is  now  but  very  little  difference  between  the  cost 
of  timber  and  masonry  in  foundations.  The  principal  advantage- 
in  the  use  of  the  timber  in  fonndations  under  water  is  the  facility- 
witli  which  it  is  put  into  position.  Soft  wood  or  timber  which 
in  the  air  has  comparatively  little  durability,  is  equally  as  good 
for  this  purpose  as  the  hard  woods.  It  has  been  oonclnsiyely  proved 
that  any  kiud  of  timber  will  last  practically  forever,  if  completely 
immersed  in  water. 

407.  EXCATATDTQ  THS  BITB.  When  a  pier  is  to  be  founded  in 
a  sluggish  stream,  it  is  only  neceeeary  to  excavate  a  hole  m  the^ 
bed  of  the  stream,  in  which  the  crib  {or  the  bottom  of  the  caisson)' 
may  rest.  The  excavation  is  usually  made  with  a  dredge,  any  form 
of  which  can  be  employed.  The  dipper -dredge  is  the  best,  bnt  thfr 
clam-shell  or  the  endless  chain  and  bucket  dredge  are  sometimes 
used.  If  the  bottom  is  sand,  mud,  or  silt,  the  soil  maybe  removed 
(1)  by  pumping  it  with  the  water  through  an  ordinary  centrifugal 
pump  (§  395), — the  aiiction  hoae  of  which  Js  kept  in  contact  with, 
or  even  a  little  below,  the  bottom, — or  (2)  by  the  Eads  sand-pnmp' 
(§  448).  With  either  of  these  methods  of  excavating,  asimple  frama 
or  light  coffer-dam  may  be  sunk  to  keep  part  of  the  loose  soU  fronk 
running  into  the  excavation. 

408.  If  the  stream  is  shallow,  the  current  swift,  and  the  bottom 
soft,  the  site  may  be  excavated  or  scoured  out  by  the  river  itself. 
To  make  the  current  scour,  construct  two  temporary  wing-dams, 
which  diverge  up  stream  from  the  site  of  the  proposed  pier.  The- 
wings  can  be  made  by  driving  stout  stakes  or  small  piles  into  tho 
bed  of  the  stream,  and  placing  solid  panels—made  by  nailing  ordi- 
nary boardsto  light  uprights — against  the  piles  with  theirloweredgs 
on  the  bottom.  The  wings  concentrate  the  current  at  the  location 
01  the  pier,  increase  its  velocity,  and  cause  it  to  scour  out  the  bed  of 
the  stream.  This  process  requires  a  little  time,  usually  one  to  three 
days,  but  the  coat  of  construction  and  operation  is  comparatively 
slight. 

When  the  water  is  too  deep  for  the  last  method,  it  is  sometimes 
possible  to  suspend  the  caisson  a  little  above  the  bed  of  the  stream, 
in  which  case  the  current  will  remove  the  sand  and  silt  from  under 
it.     At  the  bridge  over  the  Mississippi  at  Quincy,  111.,  a  hole  ID  feet 


ovGoQi^lc 


SKI.  3.]  DEBDQING  THBOCQH  WBLLfl.  371 

deep  was  thus  sconred  out.  If  the  water  is  already  heavily  charged 
with  sedimeDt,  it  may  drop  the  aedimeat  od  striking  the  crib  and 
thus  fill  up  instead  of  scour  out.  Notwithstanding  the  hole  ia 
liable  to  be  filled  up  by  the  gradoal  action  of  the  current  or  by  a 
sudden  flood,  before  the  crib  has  been  placed  in  its  final  position, 
this  method  ia  frequently  more  expeditious  and  less  expensive  than 
using  a  coffer- dam. 

409.  It  the  crib  should  not  rest  squarely  upon  the  bottom,  it. 
can  BOmetimee  be  brought  down  with  a  water-jet  (§  34j)  in  the. 
hands  of  a  diver.  However,  the  engineer  should  not  employ  a 
diver  unless  absolutely  necessary,  aa  it  is  very  expensive. 

410.  If  the  soft  soil  extends  to  a  considerable  depth*,  or  if  the 
necessary  spread  of  foundation  can  not  be  obtained  without  an  un- 
desirable obstruction  of  the  channel,  or  if  the  bottom  ia  liable  to- 
scour,  then  piles  may  be  driven,  upon  which  the  crib  or  caisson  maj 
finally  rest.  Before  the  introduction  of  the  compreaeed-air  process, 
this  was  a  very  common  method  of  founding  bridge  piers  in  onr- 
westem  rivers ;  and  it  is  still  frequently  employed  for  small  piers. 
The  method  of  driving  and  sawing  oft  the  piles  has  already  been 
described — see  Chapter  XI. 

The  mud  over  and  around  the  heads  of  the  pilea  may  be  sucked 
off  with  a  pump,  or  it  may  be  scoured  out  by  the  current  (g  408). 
The  attempt  ia  sometimes  made  to  increase  the  bearing  power  of  the- 
foundation  by  filling  in  between  the  heads  of  the  piles  with  broken 
stone  or  concrete ;  but  this  is  not  good  practice,  as  the  stone  does, 
but  little  good,  is  difficult  to  place,  and  ia  liable  to  get  on  top  of  the- 
piles  and  prevent  the  crib  from  coining  to  a  proper  bearing. 

Abt.  3.  Dredoinq  Throuqh  Wells. 

411.  A  timber  crib  is  frequently  sunk  by  excavating  the  material 
through  apartments  left  for  that  purpose,  thn^  undermining  the 
crib  and  causing  it  to  sink.  Hollow  iron  cylinders,  or  wells  of 
masonry  with  a  strong  curb,  or  ring,  of  timber  or  iron  beneath  them^ 
are  sunk  in  the  same  way. 

This  method  is  applicable  to  foundations  both  on  dry  land  and 
under  water.  It  is  also  sometimes  employed  in  sinking  shafts  ia 
tunneling  and  mining. 

41S.  XXCATATOSB.     The  soil  is  removed  from  under  the  crib. 


ovGoQi^lc 


27S  FOtniDATIOlIS   UXDEB  WATER.  [CHAP.  XII. 

vith  a  clom-ahell  dredge,  or  with  ao  endless  chain  and  bncket 
dredge,  or  with  the  Eads  sand-pump,  or,  for  small  jobs,  with  the 
sand-pump  employed  in  driving  artesian  wells. 

The  clam-shell  dredge  coasists  of  the  two  halves  of  a  hemi- 
spherical shell,  which  rotate  about  a  horizontal  diameter ;  the  edges 
of  the  shell  are  forced  into  the  soil  by  the  weight  of  the  machine 
itself,  and  the  pull  upon  the  chain  to  raise  the  excavator  draws  the 
two  halves  together,  thus  forming  a  hemispherical  bucket  which  ^ 
incloses  the  material  to  be  excavated.  The  Morris  and  Gumming 
dredge  consists  of  two  quadrants  of  a  short  cylinder,  hinged  and 
operated  similarly  to  the  above.  The  orange-peel  dredge  (shown  atf 
A  in  Fig.  63,  page  374)  appears  to  have  the  preference  for  this  kind 
of  work.  It  consists  of  a  frame  from  which  are  suspended  a  num- 
ber of  spherical  triangular  spades  which  are  forced  vertically  into 
the  ground  by  their  own  weight;  the  pull  upon  the  excavator  to 
lift  it  out  of  the  mud  draws  these  triangles  leather  and  encloses 
the  earth  to  be  excavated.  There  are  several  forms  of  dredges 
similar  to  the  above,  bat  differing  from  tbem  in  details. 

For  a  description  of  the  Eads  sand-pump,  see  §-448. 

413.  In  one  case  in  France,  the  soil  was  excavated  by  the  aid  of 
iwmpressed  air.  An  8-)nch  iron  tube  rested  on  the  bottom,  with  its 
top  projecting  horizontally  above  the  water ;  and  compressed  air  was 
discharged  through  a  small  pipe  into  the  lower  end  of  the  g-inch 
tube.  The  weight  of  the  air  and  water  in  the  tube  was  less  than 
an  equal  height  of  the  water  outside  ;  and  hence  the  water  in  the 
tube  was  projected  from  the  top,  and  carried  with  it  a  portion  of  the 
mud,  sand,  etc.  Pebbles  and  stones  of  considerable  size  were  thus 
thrown  out.     See  §  447. 

414.  Voted  Exaicplebl— Pooghkeepiie  Bridge.  The  Pongh- 
keepsie  bridge,  which  crosses  the  Hudson  at  a  point  about  75  miles 
above  New  York  City,  is  founded  upon  cribs,  and  is  the  boldest  ex- 
ample of  timber  foundation  on  record.  It  is  remarkable  both  for 
the  size  of  the  cribs  and  for  the  depth  of  the  foundation. 

There  are  four  river  piers.  The  crib  tor  the  largest  is  100  feet 
long,  60  feet  wide  at  the  bottom  and  40  feet  at  the  top,  and  104 
feet  high.  It  is  divided,  by  one  longitudinal  and  six  transverse 
walls,  into  fourteen  compartments  through  which  the  dredge  worked. 
The  side  and  division  walls  terminate  at  the  bottom  with  a  12"  X 
I'Z"  oak  stick,  which  served  as  a  cutting  edge.     The  exterior  walls 


ovGoQi^lc 


ABT.  3.]  DBBDGINO  THROUGH  WELLS,  273 

and  the  loDgitndinal  diTisiou  vail  were  built  solid,  o!  triaugnlar 
cross  section,  for  ^0  feet  above  the  cutting  edge,  and  above  that 
they  were  hollow.  The  gravel  used  to  sink  the  crib  weis  deposited 
in  these  hollow  walls.  The  longitudinal  walls  were  securely  tied  to 
each  other  by  the  end  and  cross  division  walla,  and  each  course  of 
timber  was  fastened  to  the  one  below  by  450  1-inch  drift-bolts  30 
inches  long.  The  timber  was  liemlock,  I'i  inches  square.  The 
fourteen  compartments  in  which  the  clam-sbell  dredges  worked 
wei-e  10  X  12  feet  in  tlie  clear.  The  cribs  were  kept  level  while 
sinking  by  excavating:  from  fii'st  one  and  then  the  other  of  the  com- 
partments. Gnwel  was  added  to  the  pockets  as  the  crib  sunk, 
When  hard  bottom  was  reached,  the  dredging  pockets  were  filled 
with  concrete  deposited  under  water  from  boxes  holding  one  cubic 
yard  each  and  opened  at  the  bottom  by  a  latch  and  trip-line. 

After  the  crib  was  in  position,  the  masonry  was  started  in  a 
floating  caisson  which  finally  rested  upon  the  top  of  the  crib. 
Sinking  the  crib  and  caisson  separately  is  a  departure  from  the 
ordinary  method.  Insteadof  usinga  floating  caisson,  it  isgenei-ally 
considered  better  to  construct  a  coffer-dam  on  top  of  the  crib,  in 
which  to  start  the  masonry.  If  the  crib  is  sunk  first,  the  stones 
which  are  thrown  into  the  pockets  to  sink  it  are  liable  to  be  loft  ' 
projecting  above  the  top  of  the  crib  and  thus  prevent  the  caisson 
from  coming  to  a  full  and  fair  bearing. 

The  largest  crib  was  snnk  through  about  53  feet  of  water,  20 
feet  of  mud,  45  feet  of  clay  and  sand,  and  17  feet  of  sand  and 
gravel.  It  rests,  at  1:I4  feet  below  liigh  water,  upon  a  bed  of  gravel 
16  feet  thick  overlying  bed-rock.  The  timber  work  is  110  feet  high, 
including  the  floor  of  the  caisson,  and  extends  to  14  feet  below  high 
water  (7  feet  below  low  water),  at  which  point  the  masonry  com- 
mences and  rises  39  feet.  On  top  of  the  masonry  a  eteel  tower  100 
feet  high  is  erected.  The  masonry  in  pUn  is  25  x  87feet.  and  has 
nearly  vertical  faces.  The  lower  chord  of  the  channel  span  is  130 
feet  and  the  rail  is  212  feet  above  high  water. 

The  other  piers  are  nearly  as  large  as  the  one  here  described. 
The  cribs  each  contain  an  average  of  2,500,000  feet,  board  meusur*?, 
of  timber  and  350  tons  of  wronght  iron. 

415.  Atoha&laya  Bridge.  This  bridge  is  over  the  Atcbafaluya 
bayou  or  river,  at  Morgan  City,  La.,  about  80  miles  west  of  New 
Orleans.     The  soil  is  alluvial  to  an  unknown  depth,  and  is  subject 


ovGoQi^lc 


£74  TOOITDATIOKS  UKDER  WATER.  [OHAP.  Zn. 

to  rapid  and  extensive  scour ;  and  no  stone  suitable  for  piers  could 
be  found  within  reasonable  distance.  Hence  iron  cylinders  were 
adopted.  They  are  fonndation  and  pier  combined.  The  cylinders 
were  snnk  120  feet  below  high  water — from  70  to  115  feet  below  the 
mud  line — by  dredging  the  material  from  the  inside  with  an  orange- 
peel  ezcavator.  Fig.  63  shows  the  excavator  and  the  appliances 
for  handling  the  cjUndera. 


Fid.  (B.— Bixccd  Iboh  Piut  bt  Dbidqimi. 

The  cylinders  are  8  feet  in  ontside  diameter.  Below  the  lerel 
of  the  river  bed,  they  are  made  of  cast  iron  1^  inchee  thick,  in 
lengths  of  lOJ  feet ;  the  sections  were  bolted  together  throngh  in- 
side flanges  with  1-inch  bolts  spaced  5  inches  apart.  Above  the 
river  bottom,  the  cylinders  are  made  of  wronght-iron  plates  ^  inches 
thick,  riveted  together  to  form  short  cylindrical  sectidne  with  angle 
iron  flanges.  The  bolts  and  spacing  to  unite  the  sections  are  the 
same  as  in  the  cast-iron  portions. 

The  cylinders  were  fflled  with  concrete  and  capped  with  a  heavy 


ovGoQi^lc 


AET.  3.]  DBEDOINO  THBOnOH  WELLS.  27S 

caet-iron  plate.     Two  each  cylinderB,  braced  together,  form  the  pier 
between  two  250-feet  apaiis  of  a  railroad  bridge. 

The  only  objection  to  Buch  piers  relates  to  their  Btabilitj.  These 
have  Btood  satisfactorily  since  lttti3, 

416.  Eavkeibnry  Bridge.  The  bridge  over  the  Hawkesbury 
River  in  Bouth-eaatern  Australia  is  remarkable  for  the  depth  of  the 
foundation.  It  ia  founded  upon  elliptical  iron  caissons  48  x  30  feet 
at  th6  cutting  edge,  which  rest  upon  a  bed  of  hard  gravel  126  feet 
below  the  river  bed,  185  feet  below  high  water,  aii.\  i^'J  feet  below 
the  tirack  on  the  bridge.  The  soil  penetrated  was  mud  and  sand. 
The  caisBonB  were  sunk  by  dredging  through  three  tubes,  8  feet  in 
diameter,  terminating  in  bell-monthed  eztenaiouB,  which  met  the 
catting  edge.  The  spaces  between  the  dredging  tabes  and  the 
onter  shell  were  filled  with  gravel  as  the  sinking  progressed.  The 
caissons  were  filled  to  low  water  with  concrete,  and  above,  with  cut- 
stone  masonry. 

417.  Brick  Cyliadera.  In  Germany  a  brick  cylinder  was  sunk 
SSG  feet  for  a  coal  shaft.  A  cylinder  35}  foet  in  diameter  was  snnk 
76  feet  through  sand  and  graTel,  when  the  frictional  reBistance 
became  so  great  that  it  could  be  sunk  no  further.  An  interior 
cylinder,  15  feet  in  diameter,  was  then  started  in  the  bottom  of  the 
larger  one,  and  Bunk  180  feet  further  through  running  quicksand. 
The  soil  was  removed  without  exhansting  the  wator. 

A  brick  cylinder — outer  diameter  46  feet,  thickness  of  wait  3 
feet — was  sunk  40  feet  in  dry  sand  and  gravel  without  any  difficulty. 
It  was  built  IS  feet  high  (on  a  wooden  curb  31  inches  thick),  and 
weighed  300  tons  before  the  sinking  was  begun.  The  interior  earth 
was  excavated  slowly,  bo  that  the  sinking  was  about  1  foot  per  day, 
— the  walls  being  built  up  as  it  sank. 

In  Europe  and  India  masoury  bridge  piers  are  sometimes  sunk 
by  this  procesa,  a  sufficient  number  of  vertical  openings  being  left 
through  which  the  material  is  brought  up.  It  is  generally  a  tedioua 
and  slow  operation.  To  lessen  the  friction  a  ring  of  masonry  is  some- 
times built  inBide  of  a  thin  iron  shell.  The  last  was  the  method  em- 
ployed in  putting  down  the  foundations  for  the  new  Tay  bridge, " 

418.  I^CTIOVAL  Bebutasoe.  The  friction  between  cylinders 
Knd  the  soil  depends  upon  the  nature  of  the  soil,  the  depth  sunk, 
and  the  method  osed  in  sinking.     If  the  cylinder  ia  aunk  by  either 

*  For  in  QlitatnUd  Mooont,  aee  SKgingiring  Acu*,  voL  xlT.  pp.  66-68. 


ovGoQi^lc 


876 


FODNDATIONS  UNDEB  WATBE. 


[chap.  in. 


of  the  pnenmatic  procesaea  (§§  425  and  4S6),  the  flow  of  the  water 
or  the  air  along  the  sidea  of  the  tabe  greatly  dimtDiehee  the  fric- 
tion.    It  ie  impoBBible  to  give  any  very  defiaite  data.  ' 

The  following  table  *  gives  the  Talues  of  the  co-efBcient  of  fric- 
tion f  for  materials  and  surfaces  which  occur  in  sinking  foundations 
■  for  bridge  piers.  Each  result  is  the  average  of  at  least  ten  experi- 
mente.  "All  materials  were  rounded  off  at  their  face  to  sledge 
shape  and  drawn  lengthwise  and  horizontally  over  the  gravel  or 
sand,  the  latter  being  leveled  and  bedded  as  solid  as  it  is  likely 
to  be  in  its  natural  position.  The  riveted  sheet  iron  contained 
twenty-five  rivets  on  a  surface  of  2.53  x  1-67  =  4.23  square  feet; 
the  rivet-heads  were  half-round  and  \^  inch  in  diameter."  Notice 
that  for  dry  materials  and  also  for  wet  gravel  and  sand,  the  frictional 
resistance  at  starting  is  smaller  than  during  motion,  which  is  con- 
trary to  the  ordinary  statement  of  tlie  laws  of  friction. 
TABLE  80. 

Co-KFTICIKNT  OF  FfilCTlOS  OF  MATERIALS  AITD  SOBFACEfl  trSBD  IH  FOOK- 
SATIONB, 


ElSD  ov  IUtsbmu. 


m 


si 


Pioe  (BBwed)  on  gravel  acd  Mod. . 
Sbect  iroD  'without  rivets  on  s&nd. . . 
"    with  "      "      "    ... 

Cast  iron  ( un planed)  on  s&nd 

Qraolte  (roughly  worked)  on  sand. . 
Pine  (Bswed)  on  sand 


419.  Valuei  from  Actual  Praotloe.  Cast  Iron.  During  the 
construction  of  the  bridge  over  the  Seine  at  Orival,  a  caetriron 

'  *  Bf  A.  SchmoU  In  "  Zeltschrltt  des  Verelnea  DentBCher  iDgenlenre,"  aa  repnb- 
Habed  In  Selected  Abstiacte  of  loBt.  ot  C.  E.,  vol.  111.  pp.  298-303, 

t  The  co-efflotent  ot  friction  Is  equal  to  the  total  trictlon  divided  bj/  the  touu 
Dornul  presBore;  that  ia  to  ear,  It  la  the  friction  per  unit  ot  praaanie  perpendlcnlnr 
lo  the  soilMea  In  contact. 


ovGoQi^lc 


AKT.  S.]  DBEDOINQ  THBODOH  WELLS.  377 

cylinder,  BtaDding  in  an  extenBive  and  rather  uniform  bed  of  graToI, 
and  having  ceased  to  move  for  thirty-two  honrs,  gave  a  frictional  re- 
BiBtaDce  of  nearly  200  lbs.  per  aq.  ft.*  At  a  bridge  over  the  Dannbe 
near  Stadlau,  a  cylinder  Bunk  18.75  feet  into  the  soil  (the  lower  3.75 
feet  being  "solid  clay")  gave  a  frictional  resistance  of  100  lbs.  per 
sq.  ft.*  According  to  some  Enropean  experiments,  the  friction  of 
cast-iron  cylinders  in  sand  and  river  mnd  was  from  400  to  600  lbs. 
per  sq.  ft  for  small  depths,  and  800  to  1,000  for  depths  from  20  to 
30  feet.t  At  the  first  Harlem  River  bridge,  New  York  City,  the 
frictional  resistance  of  a  cast-iron  pile,  while  the  soil  around  it  was 
still  loose,  was  5S8  lbs.  per.  sq.  ft.  of  surface ;  and  later  716  lbs.  per  sq. 
ft.  did  not  move  it.  From  these  two  experiments,  McAlpine,  the  en- 
gineer in  charge,  concluded  that  "  1,000  lbs.  per  sq.  ft.  is  a  safe  value 
for  moderately  fine  material."  J  At  the  Omaha  bridge,  a  cast-iron 
pile  sunk  87  feet  in  sand,  with  15  feet  of  sand  on  the  inside,  could  not 
be  withdrawn  with  a  pressare  equivalent  to  254  lbs.  per  sq.  ft.  of 
surface  in  contact  with  the  soil  ;  and  after  removal  of  the  sand  from 
the  inside,  it  moved  with  SOO  lbs.  per  sq.  ft.§ 

WrougM  Iron.  A  wrought-iron  pile,  penetrating  19  feet  into 
coarse  sand  at  the  bottom  of  a  river,  gave  280  lbs.  per  sq.  ft;  an- 
other, in  gravel,  gave  300  to  335  lbs.  per  sq.  ft.| 

Matonry.  In  the  silt  on  the  Clyde,  the  friction  on  brick  and 
concrete  cylinders  was  about  3j  tons  per  sq.  ft.^  The  friction  on 
the  brick  piers  of  the  Duflerin  (India)  Bridge,  through  clay,  was 
WW  lbs.  per  sq.  ft** 

Fneumalic  Caissons.  For  data  on  the  frictional  resistance  of 
pneumatic  caissons,  see  §  455. 

Piles.  For  data  on  the  frictional  resistance  of  ordinaiy  piles, 
see  g§  370-71. 

420.  Con.  It  is  difficult  to  obtain  data  under  this  head, 
since  but  comparatively  few  foundations  have  been  put  down 
by  this  process.    Furthermore,  since  the  cost  varies  so  much  with 

*  Tu  Noatraod's  Engln'g  Hag.,  toL  xx.  pp.  121-22. 
t  Proc.  Insl,  of  C.  E.,  vol.  L  p.  131. 

t  McAlploe  In  Jour.  Fraak.  InsL,  voL  Iv.  p.  106 ;  alao  Proc  Init.  of  C.  S.,  nL 
XXVU.  p.  286. 

f  y*a  Nostrand'B  Engfn'g  Hog.,  vol.  vllL  p.  47L 
I  Proc  Inst,  of  C.  E.,  vol.  iv.  p.  200. 
T  Ibid.,  vol.  iiziT.  p.  HG. 
**  Snffinetrinff  JVmi,  voL  zti.  p.  IBO. 


jvGooi^le 


278  FOUKDATIOITS  UNDER  WATBK.  [CHAP.  XIL 

the  depth  of  water,  stren^h  of  cnrreiit,  kind  of  bottom,  danger  of 
floods,  requirementa  of  DavigatioQ,  etc,  etc.,  no  such  data  are  valu- 
able onlees  accompanied  by  endless  details, 

Crlbi.  The  materials  in  the  cribs  will  cost,  in  place,  aboat  as 
follows :  timber  from  $30  to  140  per  thousand  feet,  board  measure ; 
drift  and  screw  bolts  from  3(  to  5  cents  per  pound ;  concrete  from 
$4  to  (6  per  cnbic  yard.  Under  ordinarily  favorable  conditions,  the 
sinking  by  dredging  will  cost  about  (1  per  cubic  yard. 

Iron  Tabei.  Wrought-irou  plate  work  will  cost,  exclusive  of 
freight,  from  3  to  4^  cents  per  pound ;  cast-iron  tubes,  exclusive  of 
freight,  1^  to  2  cents  per  pound. 

4S1.  For  the  relative  cost  of  different  methods,  see  Art.  6 
of  this  chapter. 

422.  CovcLunoH.  A  serious  objection  to  this  method  of  sink- 
ing foundations  is  the  possibility  of  meeting  wrecks,  logs,  or  other 
obstructions,  in  the  underlying  materials ;  but  unlesa  the  freezing 
process  (see  Art.  5  of  this  chapter)  shall  prove  all  that  is  claimed 
for  it,  the  method  by  dredging  through  tubes  or  wells  is  the  only 
one  that  can  be  applied  to  depths  which  much  exceed  100  feet— the 
limit  of  the  pneumatic  process. 

Abt.  4.     Pnkumatio  PaOOHSB.     ■ 

424.  The  principle  involved  is  the  utilization  of  the  difference 
between  the  pressure  of  the  air  inside  and  outside  of  an  air-tight 
chamber.  The  air-tight  chamber  may  be  either  an  Iron  cylinder, 
which  becomes  at  once  foundation  and  pier,  or  a  box— open  below 
and  a:i' -tight  eisewhere — upon  the  top  of  which  the  masonry  pier 
rests.  The  former  is  called  a  pneumatic  pile;  the  latter  a  pneu- 
matic caisson.  The  pneumatic  pile  is  seldom  used  now.  There 
are  two  processes  of  utilizing  this  difference  of  pressure, — the 
vacuum  and  thspUnum. 

426.  VAOmnc  Pbockh.  The  vacuum  process  consists  in  ex- 
hausting the  air  from  a  cylinder,  and  using  the  pressure  of  the  at- 
mosphere upon  the  top  of  the  cylinder  to  force  it  down.  Exhausting 
the  air  allows  the  water  to  flow  past  the  lower  od^  into  the  air- 
chamber,  thus  loosening  the  soil  and  causing  the  cylinder  to  sink. 
By  letting  the  air  in,  the  water  subsides,  after  which  the  exhaustion 
may  be  repeated  and  the  pile  sunk  still  farther.     The  vacuum 


D.qitizeabyG00l^lc 


AWr.  4.]  PNBtTMATIC  PR0CK8S.  279 

slioald  be  obtained  Buddenly,  so  thnt  the  pressare  of  the  atmosphere 
shall  have  the  effect  of  a  blow ;  hence,  the  pile  is  connected  by  a 
large  flexible  tube  with  a  large  air-chamber — naually  monnted  upon 
a  boat, — from  which  the  air  ia  exhausted.  When  communication  is 
opened  between  the  pile  and  the  receiver,  the  air  rushes  from  the 
former  into  the  latter  to  establish  equilibrium,  and  the  external 
pressure  causes  the  pile  to  sink. 

To  increase  the  rapidity  of  sinking,  tbe  cylinders  may  be  forced 
down  by  a  lever  or  by  an  extra  load  applied  for  that  purpose.  In 
case  the  resistance  to  sinking  is  very  great,  the  material  may  be  re- 
moved from  the  inside  by  a  aand-pniap  (g  448),  or  an  orange-peel 
or  clam-shell  dredge  (g  413) ;  bat  ordinarily  no  earth  is  removed 
from  tbe  inside.  Cylinders  have  been  sunk  by  this  method  5  or  6 
feet  by  &  single  exhaustion,  and  84  feet  in  6  hours. 

The  vacuum  proeeBs  has  been  superseded  by  the  plenum  process. 

426.  Flbhux,  ok  Coxtbebhes-ais,  Pbocsbb.  The  plenum,  or 
compressed-air,  process  consists  in  pumping  air  into  the  air-chamber, 
eo  ae  to  exclude  the  water,  and  forcing  tbe  pile  or  caisson  down  by 
a  load  placed  upon  it.  An  air-lock  (§  431)  is  so  arranged  that  the 
workmen  can  pass  into  the  caisson  to  remove  the  soil,  logs,  and 
bowlders,  and  to  watch  the  progress  of  the  sinking,  withont  re- 
leasing the  pressure.  The  vacuum  process  is  applicable  only  in  mud 
or  sand;  but  the  compressed-air  process  can  be  applied  in  all  kinds 
of  soil. 

427.  HiSTOBT  07  TezuMATIC  FBOCEMEa.  It  is  said  that  Papin, 
the  eminent  physicist — bom  at  Blois  in  1647, — conceived  the  idea 
of  employing  a  continued  supply  of  compressed  air  to  enable  work- 
men to  build  under  a  large  diving-bell.  In  1779,  Coulomb  pre- 
sented to  the  Paris  Academy  of  Science  a  paper  detailings  a  plan  for 
executing  all  sorts  of  operations  under  water  by  the  use  of  com- 
pressed air.  His  proposed  apparatus  was  somewhat  like  that  now 
in  general  use. 

In  England  in  1831,  Earl  Dnndonald,  then  Lord  Cochrane,  took 
out  a  patent  for  a  device  for  sinking  tubular  shafts  through  earth 
and  water,  by  means  of  compressed  air.  His  air-lock  was  much  like 
modern  ones,  and  was  to  be  placed  at  the  top  of  the  main  shaft. 
Hie  invention  was  made  with  a  view  to  its  use  in  tunneling  under 
the  Thames,  and  in  similar  enterprises.  In  1841,  Bush  also  took 
out  a  patent  in  England  for  a  plan  of  sinking  foundations  by  the 


ovGoQi^lc 


260  FOUNDATIOKS  CHDBB  VATBB  [CHAP.  XH. 

aid  of  compressed  air.  A  German,  by  name  Q.  Pfaon  Mailer,  made 
a  somewhat  similar  design  for  a  bridge  at  Majence,  in  1850 ;  but  as 
hia  plan  was  not  executed,  it  was,  like  the  patents  of  Cochrane  and 
Bush,  little  known  till  legal  controrersiee  in  regard  to  patent-rights 
dragged  them  from  obscurity. 

42B.  The  first  practical  application  of  the  plenum  process  waA 
made  in  France  in  1841  by  M.  Triger.  In  order  to  reach  a  vein  of 
coal  on  a  sandy  island  in  the  Loire,  opposite  to  Chalons,  he  sunk 
an  iron  tube  about  40  inches  in  diameter,  some  60  feet,  by  the 
blows  of  heavy  weights.  The  fine  sand  was  removed  from  the  in- 
terior by  means  of  a  scoop  bucket.  On  reaching  a  layer  of  coarse 
gravel,  he  could  not  force  the  tube  through.  He  therefore  capped 
his  tube  with  an  air-lock,  and  by  compressed  air  forced  out  the 
water  which  bad  all  the  while  filled  the  tube,  and  sent  workmen  to 
the  bottom.  The  pressure  he  used  was  never  greater  than  two  at- 
mospheres. The  water  was  discharged  through  a  small  tube,  into 
which,  several  feet  from  the  bottom,  a  jet  of  air  was  allowed  to 
enter,  thus  diminishing  the  specific  gravity  of  the  column  till  it 
was  rapidly  blown  out.  In  1845,  Triger  read  a  paper  on  the  sinking 
of  a  tube  about  6  feet  in  diameter  to  a  depth  of  82  feet  by  the  same 
method,  and  suggested  the  use  of  it  for  the  conetmction  of  deep 
foundations  for  bridges. 

Dr.  Potts,  of  England,  generally  has  the  credit  of  inventing  the 
vacuum  process,  for  which  he  took  out  a  patent  in  1848.  Many 
times  in  sinking  foundations  by  the  vacuum  process,  the  com- 
pressed-air process  was  resorted  to  so  that  men  could  enter  the  pile 
to  remove  obetractions ;  and  finally  the  many  advantages  of  the 
compressed-air  process  caused  it  to  entirely  supersede  the  vacuum 
process.  At  present  the  term  "pneumatic  process"  is  practically 
BynoDymone  with  compressed-air  process. 

429.  The  first  foundations  sunk  entirely  by  the  compressed-ur 
process  were  the  pneumatic  piles  for  the  bridge  at  Bochester,  Eng- 
land, put  down  in  1851.    The  depth  reached  was  61  feet. 

The  first  pneumatic  caisson  was  employed  at  Kehl,  on  the  east- 
ern border  of  France,  for  the  foundations  of  a  r^boad  bridge  across 
the  Rhine. 

480.  The  first  three  pneumatic  pile  foundations  in  America 
were  constructed  in  South  Carolina  between  1856  and  1860.  Im- 
mediately aftor  the  civil  war,  a  number  of  pneumatic  piles  were 


ovGoQi^lc 


&BT.  4.]  PKEnUATIO  FKOCBSS.  381 

ronk  in  vestem  rivera  for  bridge  piers.  Tbe  first  pneumatic  cais- 
sons in  America  were  those  for  the  St.  Louis  bridge  (g  457),  put 
down  in  1870.  At  that  time  th^se  were  the  largest  caissons  ever 
constructed,  and  the  depth  reached — 109  feet  6^  inches — ^has  not 
yet  been  exceeded. 

Of  late  years,  the  pnenmatio  caisson  has  almost  entirel;  saper- 
seded  the  pneumatic  pile ;  in  fact  the  plenom-pnenmatic  caisson 
has  almost  entirely  saperseded,  except  in  very  shallow  water  or  in 
water  over  about  80  cr  100  ft.  deep,  ill  other  methods  of  founding 
bridge  piers. 

431.  'PhzOIUTIO  PII2B.  Although  pneumatic  cylinders  are  now 
rarely  employed,  they  will  be  briefly  described  because  of  their 
historic  interest. 

The  cylinders  are  made  of  either  wrought  or  cast  iron.  The 
wrought-iroQ  cylinders  are  composed  of  plates,  about  half  an  inch 
thick,  riveted  together  and  strengthened  by  angle  irons  on  the  in- 
side,  and  reinforced  at  the  cuttting  edge  by  plates  on  the  outside 
both  to  increase  the  stiffness  and  to  make  the  hole  a  little  larger  so 
as  to  diminish  friction.  The  cast-iron  cylinders  are  composed  of 
sections,  from  6  to  10  feet  long  and  2  to  8  fe^t  in  diameter,  bolted 
together  by  inside  flanges,  the  lower  section  being  cast  with  a  sharp 
edge  to  facilitate  penetration.  Two  of  these  tubes,  braced  together, 
are  employed  for  ordinary  bridge  piers  ;  and  sis  small  ones  around 
a  large  one  for  a  pivot  pier.  They  are  filled  with  concrete,  with  a 
few  courses  of  masonry  or  a  heavy  iron  cap  at  the  top. 

Fig.  63  shows  the  arrangement  of  the  essential  parts  of  a  pneu- 
matic pile.  The  apparatus  as  shown  is  arranged  for  sinking  by  the 
plenum  process ;  for  the  vacuum  process  the  arrangement  differs 
only  in  a  few  obvious  particnlars.  The  upper  section  constitutes 
the  aif'lock.  The  doors  a  and  h  both  open  downwards.  To  enter 
the  cylinder,  the  workmen  pass  into  the  air-lock,  and  close  the 
door  a.  Opening  the  cock  d  allows  the  compressed  air  to  entor  tbe 
lock ;  and  when  the  pressure  is  equal  on  both  sides,  the  door  b  is 
opened  and  the  workmen  pass  down  the  cylinder  by  means  of  a  ladder. 
To  save  loss  of  air,  the  air-lock  should  be  opened  veiy  seldom,  or 
made  very  small  if  required  to  be  opened  often. 

The  air-supply  pipe  connects  with  a  reservoir  of  compressed  air 
on  a  barge.  If  the  air  were  pumped  directly  into  the  pile  without 
(he  intervention  of  a  storage  reservoir,  as  was  done  in  tiie  early  ap* 


ovGoQi^lc 


S62  vomsmxTiose  usdeb  wamb.  [ckap.  m. 

plications  of  the  plenam  process,  even  a  momentaiy  stoppage  of  tiie 
imgine  Tonld  endanger  the  lives  of  the  workmen. 

432,  The  soil  may  be  excavated  by  ordinary  hand  tools,  elevated 
to  the  air-lock  by  a  windlass  and  bucket,  and  passed  out  through 
the  main  air-lock.  Sometimes  a  double  air-lock  with  one  large  and 
sne  small  compartment  ia  nsed,  the  former  being  opened  only  to  let 
gangs  of  workmen  pass  and  the  latter  to  allow  the  passage  of  the 


-k^'i 


Fm.  et.— FmnuTic  Piu. 

skip,  or  bucket,  containing  the  excavated  materiaL  Sometimes  an 
auxiliary  lock,  gf,  is  employed.  The  doors  /  and  g  are  so  con- 
nected by  parallel  bars  (not  shown)  that  only  one  can  be  opened  at 
I  time.  The  excavated  material  is  thrown  into  the  chute,  the 
door/  is  closed,  which  opens  g,  and  the  material  discharges  itself 
on  the  outside. 

Mud  and  sand  are  blown  out  with  the  sand-lift  (g  447}  or  sand- 
pump  (§  448)  without  the  use  of  any  air-lock. 

433.  The  cylinders  are  guided  in  their  descent  by  a  frame-work 
resting  upon  piles  or  upon  two  barges.  One  of  the  chief  difficoltiee  in 


D.qitizeabyG00l^lc 


ART.  4.]  PNEUKATIC  PKOCBSS.  2S3 

sinking  pneumatic  piles  is  to  keep  them  vertioal.  If  the  cylinder 
becomes  inclined,  it  can  generally  be  righted  (1)  b;  plaoiog  wooden 
wedges  ander  the  lower  side  of  the  cutting  edge,  or  .f3)  by  excavat- 
ing under  the  upper  side  bo  that  the  air  may  escape  and  loosen  the 
material  on  that  side,  or  (3)  by  drilling^ holes  through  the  upper- 
most side  of  the  cylinder  through  which  air  may  escape  and  loosen 
the  soil,  or  (4)  by  straining  the  top  over  with  props  or  tackle.  If 
several  pneumatic  piles  are  to  form  a  pier,  they  should  be  sunk  one 
at  a  time,  for  when  sunk  at  the  same  time  they  are  liable  to  mn 
together. 

434.  Bearing  Power.  The  frictional  resistance  of  iron  cylinders 
has  been  discussed  In  §§  418-19,  page  375-77,  which  see. 

McAlpine,  in  sinking  the  piers  of  the  Harlem  bridge.  New  York 
City,  devised  a  very  valuable  but  simple 
and  cheap  method  of  increasing  the  bear- 
ing power  of  a  pneumatic  cylinder  (see 
fig.  64).     He  attached  to  the  lower  end  ; 
of  the  cylindrical  colnmn  a  hollow  conical  ■ 
iron  section,  the  large  end  of  which  is  , 
much  larger  than    the  main  cylinder.  V 
The  base  of  the  pier  was  still  further  in- 
creased   by    driving    short    sheet    piles  '; 
obliquely  under  the  lower  edge  of  the 
conical  base  and  removing  the  soil  from  Pio.  M. 

under  them,  after  which  the  whole  WEB  filled  in  with  concrete.* 

Id  cold  climates  the  contraction  of  the  iron  cylinder  upon  the 
masonry  filling  might  rupture  the  former;  hence,  it  is  sometimes 
recommended  to  fill  the  pile  below  the  frost  line  with  asphaltic  con- 
crete. It  has  also  been  proposed  to  line  the  cylinders  with  thick, 
soft  wood  staves,  which  will  compress  under  the  contraction  of  the 
Iron  cylinder.  However,  the  danger  from  this  cause  is  not  very 
serious;  for,  after  the  concrete  has  set,  it  is  strong  enough  to 
support  the  load  if  the  iron  case  were  removed. 

43fi.  After  the  cylinder  has  reached  the  required  depth,  concrete 
enough  to  seal  it  is  laid  in  compressed  air;  and  when  this  has 
set,  the  remainder  can  be  laid  in  the  open  air.  A  short  distance 
at  the  top  is  usually  filled  with  good  masonry,  and  a  heavy  iron  cap 
put  over  all. 

*  Jour.  Frank.  lost.,  vol.  Iv.  pp.  06  uid  1T7. 


ovGoQi^lc 


284  FOUKDATIONB  USDBB  WATER.  [CHAP.  XIL 


436.  PxinuTlo  Caubobi.  A  pDenmatic  caiseoD  is  an  ii 
box — opea  below,  bnt  air-tight  and  watet^ tight  elsewhere, — upon  the 
top  of  which  the  masonry  pier  is  built.  The  eseeiitial  difference 
hetweea  the  pneniDatic  pile  and  the  pneumatic  caisson  is  one  of  de- 
grce  rather  than  one  of  quality.  Sometimes  the  caisson  envelope 
the  entire  masonry  of  the  pier ;  bnt  in  the  usual  form  t!ie  masonry 
eoTelops  the  iron  cylinder  and  rests  upon  an  enlargement  of  the 
lower  end  of  it  The  pneamatic  pile  is  sunk  to  the  final  depth  be- 
fore fbeing  filled  with  concrete  or  masonry;  but  with  the  caisson 
the  masonry  is  built  upward  while  the  whole  pitir  is  being  sunk 
downward,  the  masonry  thus  forming  the  load  which  forces  the 
caisson  into  the  soiL  A  pneumatic  caisson  is,  practically,  a  gigantic 
diving  bell  upon  the  top  of  which  the  masonry  of  the  pier  rests. 

Fig.  65  IB  a  section  of  a  pier  of  the  bridge  across  the  Missouri 
Birer  near  Blair,  Neb.,*  and  shows  the  general  arrangement  of  the 
pier  and  pneumatic  caisson.  The  tube  extending  through  the  mid- 
dle of  the  caisson  and  pier,  known  as  the  air-ahaft,  is  for  the  ascent 
and  descent  of  the  men.  The  air-lock — situated  at  the  junction  of 
the  two  cylinders  which  form  tho  air-ehaft — consists  of  a  short  sec- 
tion of  a  lai^e  cylinder  which  envelops  the  ends  of  the  two  sections 
of  the  air-shaft,  both  of  which  communicate  with  the  air-lock  by 
doors  as  shown  in  Fig.  65.  The  apartment  in  which  the  men  are 
at  work  is  known  as  the  working  chamber  or  air-chamber.  The 
small  cylinders  shown  on  each  side  of  the  air-shaft  are  employed  in 
supplying  concrete  for  filling  the  working  chamber  when  the  sinking 
is  completed.  The  pipes  seen  in  the  air-chamber  and  projecting 
above  the  masonry  are  employed  in  discharging  the  mud  and  sand, 
as  will  he  described  presently.  The  timbers  which  appear  in  the 
lower  central  portion  of  the  working  chamber  are  parte  of  the  trusses 
which  support  the  central  portions  of  the  roof  of  the  caisson. 

The  masonry  is  usually  begun  about  2  feet  below  low  water,  the 
space  intermediate  between  the  masonry  and  the  roof  of  the  working 
chamber  being  occupied  by  timber  crib-work,  either  built  solid  or 
filled  with  concrete.  In  Fig.  65  the  masonry  rests  directly  upon 
the  roof  of  the  air-chamber,  which  construction  was  adopted  for  the 
channel  piers  of  this  bridge  to  reduce  to  a  minimum  the  obstrnctioa 
to  the  flow  of  the  water. 

Frequently  a  coffer-dam  is  built  upon  the  top  of  the  crib  (see 
*  ITrom  the  report  of  Oeo.  8.  Morlson,  chief  engliieer  of  the  bridge. 


jvGooi^le 


AKT.  4.]  PNECMATIC   PROCESS.  285 

Plate  I);  but  in  this  particular  cage  the  maeopry  was  kept  aboTe  the 
enrface  of  the  water,  hence  no  coffer-dam  was  emplojed.     When 


Pio.  W.— PmnMiTic  Ciii 


the  coffer-dam  ia  not  used,  it  is  necessary  to  regulate  the  rate  of 
sinking  by  the  speed  with  which  the  masonry  can  be  built,  which  is 
liable  to  cause  inconvenience  and  delay.     When  the  coffer-dam  is 


ovGoQi^lc 


S86  FOUNDATIONS  UNDBB  WATBB.  [CHAP.  ZU. 

dispensed  with,  it  is  Qecessary  to  go  on  with  the  construction  of  the 
masonry  whether  or  not  the  additional  weight  is  needed  in  sinking 
tne  caisson. 

437.  The  details  of  the  conatmction  of  pnenmatic  caisBons  can 
be  explained  beat  by  the  description  of  a  puiicnlar  case. 

438.  tovtntknm  o?  the  Eatbi  db  Okacx  Bbidgi.  Foldine 
Plate  I  *  shows  the  details  of  the  conBtrnction  of  the  caisson,  crib, 
and  coffer-dam  employed  in  1884  in  sinking  pier  No.  8  of  the 
Baltimore  and  Ohio  R.  R.  bridge  across  the  Susquehanna  Rirer  at 
flavre  de  Grace,  Ud.  The  timber  work  of  Fig.  66  (page  293)  also 
shows  some  of  the  detuls  of  the  constmction  of  the  walls  of  the 
working  chamber. 

439.  The  CaiMon.  The  details  of  the  construction  of  the  caisson 
areas  follows:  Six  courses  of  timber,  12  X  12  inch,  one  lying  on  top 
of  tbe  other,  formed  the  skeleton  of  the  walls  of  the  working  cham- 
ber. These  timbers  were  first  put  up  witb  a  batter  of  $  of  an  inch 
horizontal  to  1  foot  vertical;  they  were  not  halved  at  the  corners, 
but  every  alternate  piece  was  carried  through  with  a  full  section, 
"log-house"  feshion.  These  timbers  were  fastened  at  the  comers, 
intersections,  and  several  intermediate  points,  with  drift-botts  (g  381) 
1  inch  square  and  S2  inches  long.  Inside  of  this  timber  shell,  three 
courses  of  3-inch  plank,  placed  diagonally,  were  spiked  to  the  hori- 
zontal timbers  and  to  each  other  by  6-inch  and  7-inch  boat-spikes. 
Inside  of  the  diagonal  planking  was  another  conree  of  3-inch  plank 
placed  vertically  and  well  spiked,  the  head  of  each  spike  being 
wrapped  with  oakum  to  prevent  leakage.  The  vertical  seams  were 
thoroughly  calked. 

A  strong  and  thoroughly  braced  trues  (see  also  Fig.  66,  page  393) 
was  next  erected  longitudinally  through  the  center  of  the  working 
chamber.  The  first  course  in  the  deck  of  the  working  chamber  was 
then  placed  in  position  on  the  central  truss  and  side  watts.  The  work- 
ing chamber  was  9  feet  3  inches  high  from  bottom  of  shoe  to  the 
underside  of  deck,  which  was  higher  than  required  for  working,  bnt 
was  adopted  so  as  to  permit  greater  depth  of  the  central  truss.  Out^ 
side  of  the  horizontal  timbers,  after  tbey  had  been  adzed  to  a  true 
surface,  were  then  placed  the  12-  by  14-incli  sticks  (shown  at  the  ct- 

*  Compiled  from  the  oii^aa]  working  dfawlDga.  The  accompuiriDg  deecrlpUon 
It  Irom  personal  Inspection  sided  bj  an  article  In  Si^n»ering  Seat  by  CoL  Wm.  V 
PauoD,  engineer  in  charge. 


ovGoQi^lc 


ABT.  4.J  PNErMATIC  PROCESa  281 

treme  left  of  Fig.  66)  15  feet  long,  exteDdiDg  2  feet  below  the  bottom 
horizoatal  timber  and  having  their  lower  ends  beveled  as  shown. 
These  timbers  extended  6  feet  above  the  horizontal  members, 
and  were  shouldered  at  the  upper  end  so  that  three  of  the  deck  - 
courses  rested  upon  them.  Four  screw-bolts  were  passed  through 
each  outside  post  and  through  the  entire  wall;  and,  in  addition  to 
these,  two  drift-bolts,  1  inch  square  and  30  inches  long,  in  each  ver- 
tical served  to  more  thoroughly  bind  the  wall  t<^tber.  This  com- 
.  pound  of  timber  and  planking  formed  the  walls  of  the  working 
chamber.  After  the  first  deck  coarse  was  in  place,  a  few  pieces  of 
the  second  course  were  laid  diagonallj  to  give  it  stiffness;  the  under- 
side of  this  deck  or  roof  was  then  lined  with  planks  and  thoronghlj 
calked,  and  a  false  bottom  put  into  the  working  chamber  prepara- 
tory to  launching  it. 

After  the  caisson  was  launched  the  deck  courses,  eight  in  all, 
were  pat  on.  The  fiivt  course  was  made  of  single-length  timbers, 
reaching  from  inside  to  inside  of  the  vertical  wall  poets,  and  resting 
on  top  of  the  horizontal  timbers  aad  Inside  plauking  and  also  on  the 
top  chord  of  the  central  truss,  and  being  fastened  to  these  members 
by  22-inch  drift-bolts.  The  second  course  was  laid  diagonally  and 
was  made  of  varying  lengths  of  timbers.  The  third  course  was  laid 
from  side  to  side  across  the  caisson,  and  the  fourth  course  lon^- 
tadinally  and  resting  on  the  shoulders  of  the  13  X  14  inch  verticals. 
The  fifth  course  was  laid  across,  the  siith  diagonally — croBBing  the 
second  course, — and  the  seventh  and  eighth  conraes  extended  to  the 
extreme  outside  limits  of  the  caisson  and  rested  on  the  heads  of  the 
vertical  posts.  This  general  arrangement  of  the  top  courses,  resting 
as  they  did  on  the  heads  and  shoulders  of  the  outside  verticals,  gave 
ft  direct  bearing  on  the  poets  and  relieved  the  wall  bolts  of  the  great 
shearing  strain  to  which  they  would  otherwise  have  been  subjected. 

The  outside  poets  were  bolted  to  the  deck  conraes  by  one  3-foot 
screw-bolt  and  two  30-inch  drift-bolta,  fastening  them  to  the  longi- 
tudinal and  diagonal  courses  respectively.  The  several  deck  courses 
were  bolted  to  each  other  by  22-inch  drift-bolts  (not  shown  in  the 
illustrations),  spaced  5  feet  apart  along  each  stick.  All  the  timbers 
in  the  deck  were  bedded  in  cement  mortar  and  the  vertical  joints 
were  grouted,  so  as  to  give  a  full  and  uniform  bearing  for  aach  stick 
and  also  decrease  the  leakage  and  danger  from  fire. 

The  center  truss  (see  also  Fig.  66)  was  constructed  to  bear  s  unt 


D.qitizeabyG00l^ic  — 


88d  FOUNDATIONS   UNDER  WATER.  [CHAP.  XIL 

formly  (tistributed  load,  or  to  act  aa  a  cantileTer.  It  was  composed 
of  a  t<o^  and  bottom  chord,  each  made  of  two  12  x  12  inch  eticks, 
with  posts  and  diagonals  of  wood,  and  Terticat  and  dit^na]  tie-roda 
IJ  inchiD  diametec;  the  iron  vertical  rods  extended  tbroagh  the 
tint  deck  courses,  and  the  top  chord  was  also  bolted  to  the  deck 
with  drift-boltB.  The  object  of  this  was  to  unable  the  truss  to  act 
as  a  stiffening  rib  to  the  deck,  independently  of  its  action  ae  a 
girder.  The  bottom  chord  was  also  extended  to  the  ends,  and  by 
means  of  straps  and  bolts  acted  both  as  a  strut  and  tie>brace  for  the 
ends  of  the  caisson,  and  constituted  the  only  end  bracing. 

The  sides  of  the  caissons  were  braced  against  outside  prcssnres  by 
16  X 16  inch  timbers  abutting  against  the  walls  and  bottom  chord  of 
the  center  truss,  and  against  preesnre  from  the  inside  by  S-inch  iron 
tie-rods  extending  from  out  to  out  of  the  caisson,  none  of  which  are 
shown.  All  the  timber  used,  except  the  planking  and  outside  pot^ts 
and  the  bracing  in  the  working  chamber,  was  12x12  inch.  Iron 
straps,  ext«ndiDg  6  feet  on  tliu  sides  and  ends,  were  placed  at  the 
comers  and  bolted  to  the  caisson  timbers.  These  straps  were  made 
of  bar-iron  3x1  inch  and  prevented  spreading  of  the  walls  of  the 
caisson  under  excessive  pressure  within.  Planks  were  spiked  to  the 
lower  part  of  the  posts ;  and  also  a  narrow  plank,  called  a  shoe,  was 
spiked  under  the  bottom  of  the  posts  (see  Fig.  66). 

440.  "  The  construction  was  simple  and  strong  ;  in  no  case  vms 
there  any  bending  or  springing  of  the  walls.  The  arrangement  of 
the  cutting  edge  with  square  shoulders  was  a  departure  from  the 
ordinary  V-ahape  (compare  Figs.  65  and  66,  pages  286  and  293), 
and  was  found  to  possess  many  advantages.  It  enabled  the  men  to 
better  regulate  the  sinking  of  the  caisson  by  giving  an  increased  bear- 
ing surface.  With  this  support,  the  material  could  be  cleaned  out 
from  under  one  side  or  end  ;  the  caisson  could  be  leveled ;  and,  if 
the  material  was  softer  in  one  spot  than  another,  the  caisson  could 
be  prevented  from  tipping.  It  further  afforded  a  good  surface  for 
blocking  np  when  it  vras  found  desirable  to  support  the  caisson 
during  the  removal  of  the  material ;  and  it  gave  also  greater  security 
in  case  of  a  'blow-out'  hr  the  failure  of  air-pressure,"* 

When  it  is  anticipated  that  gravel  or  bowlders  will  be  met  with 
in  sinking,  the  cutting  edee  is  usually  shod  with  iron.  The  iron 
cutting  edge  was  omitted  in  all  the  caissons  for  this  bridge,  and  it  is 
*  Col.  Wta.  H.  Patlon,  engUieer  Id  cbarge  tor  tbe  nllroad  companr. 


ovGoQi^lc 


ART.  4.]  FKEUKATTC    FBOCEBS.  389 

claimed  that  the  experience  here  shows  that  "  in  no  case  is  an  iron 
shoe  either  adrantageouB  or  necessary." 

441.  The  Crib.  The  construction  of  the  crib  ia  shown  very  fully 
in  Plate  I.  The  timbers  were  all  12  X  IS  inches  square,  bolted  to 
each  other  by  33-inch  drift-bolta — spaced  5  or  6  feet  apart, — and 
were  dovetailed  at  the  corners  and  connections.  The  parts  of  all 
the  walla  of  the  crib  were  firmly  bolted  to  the  deck  of  the  caiason. 

Ordinarily  the  division  walls  of  the  crib  are  bailt  vertically  from 
top  to  bottom ;  but  in  this  case,  they  were  off-set,  as  shown,  to 
secure  a  better  bond  in  the  mass  of  concrete.  If  the  walls  are  built 
solid  from  top  to  bottom,  the  concrete  filling  ia  thereby  divided  into 
a  number  of  separate  monolithic  columns ;  bat  in  the  construction 
as  above,  the  concrete  forma  practically  a  single  solid  mass.  The 
walls  are  built  solid,  owing  to  the  difficulty  of  getting  the  concrete 
thoroughly  packed  in  around  so  many  timbers.  Large  stones,  such 
as  could  be  handled  by  one  man,  were  bedded  in  mortar  as  the  sno- 
cesstve  layers  of  concrete  were  formed,  and  over  and  around  these 
another  layer  of  concrete  was  rammed.  In  most  localities  there  is 
but  little  difference  in  cost  between  a  solid  timber  crib  and  one  with 
timber  pockets  filled  with  concrete. 

442.  The  Coffer-dam.  Uprights  were  first  placed  at  intervals  of 
about  5^  feet,  and  connected  by  mortise  and  tenon  to  caps  and 
silla.  This  frame-work  was  held  down  to  the  crib  by  rods  3  inches 
in  diameter,  having  hooks  at  the  lower  end  which  passed  into  eye- 
bolts  in  the  sides  of  the  crib.  On  the  sides  of  the  dam,  the  upper 
end  of  these  rods  passed  through  13  X  13  inch  timbers  resting  on 
the  sides  of  the  dam  and  projecting  about  3  feet  outside ;  and  at  the 
ends  of  the  dam,  they  passed  thruugh  short  pieces  bolted  to  one  of 
the  cross  timbers  and  projecting  beyond  the  end  of  the  dam. 

Owing  to  the  great  depth  required,  the  coffer-dam  waa  built  in 
sections,  the  connecting  rods  being  made  in  sections  with  swivel 
connections.  The  second  section  was  not  added  until  the  depth 
sunk  required  it.  When  the  top  section  of  the  dam  was  put  on, 
the  projecting  ends  of  the  timbers  through  which  the  connecting 
rods  passed  were  sawed  off.  The  bottom  section  was  sheeted  with 
thre?  courses  of  3-inch  plank,  and  the  top  section  with  two  thick- 
neeseg.  The  joint  between  the  coffer-dam  and  the  crib,  and  also 
'he  sheeting,  were  well  calked. 

The  sides  of  the  coffer-dam  were  braced  against  the  pressure  of 


ovGoQi^lc 


S90  FOimDATIONB  CNDSB  WATBK,  [CHAP.  XII. 

the  water,  by  13  X  12  inch  timbers  restiog  on  the  top  of  e&ch  seo- 
tioQ,  and  by  a  syBtem  of  bracing  in  the  middle  of  each  eection. 
When  the  maaonry  woa  completed,  the  coSer-dam  was  remored  by 
disconnecting  the  vertical  rods. 

443.  Maehi&ery  Bai^ e.  The  machinery  barge  was  an  ordinary 
flat-boat  fitted  ap  for  the  purpose.  At  one  end  of  the  barge  there 
were  three  boilers  each  of  fifty  horse-power.  In  the  middle  were 
two  large  air-compressom,  designed  by  the  contracting  engineer. 
Gen.  Wm.  Sooy  Smith.  One  furnished  all  the  compressed  air  re- 
quired, the  other  being  ready  for  nse  in  case  of  any  accident  or 
break-down.  At  the  other  end  of  the  boat  were  two  Worth  ingtou 
steam  pumps  to  furnish  water  for  the  excavating  plant  naed  in  the 
caiBSOtt.  There  were  also  a  small  engine  and  a  dynamo  which  fnr- 
nisbed  the  current  for  the  electric  lamps  used  in  the  caisson  and,  at 
night,  on  the  outside. 

444.  Katerial  Keqnired.  Table  31  gives  the  dimeneionB  and 
quantities  of  materials  in  the  pneumatic  foundations  of  this  bridge, 
and  Table  32  (page  ZOi)  gives  the  cost 

TABLE  81, 

DniBKBioKS  Am*  QuANTiTiEB  OF  Matrrialb  ih  Fouhdatiohb  or 

Havre  de  Grace  Bridoe.* 


DncuFTUur. 

Hdhub  or  TO»  Pira, 

n. 

IIL 

IV. 

vm. 

IX 

M.3 
tS.B 

;!| 

♦0.0 

K03,47S 

in,sss 

SIOSB 
1.84B 

iS 

tn.» 

EB.S 

«:o 

'bt'oT 
jijn? 

1,SW 
111.BI 

siBn 

TOO 
S,fiM 

n.4 
u.s 

IT.S 

IIB.WB 
10M18 

J 

a.aa 

JD.fl 

a£.8 

•li 

si! 

Tin 

'■mut    '■       "     ■  "    ■■ 

tt.B 

Tlmbar  In  Uie  c«<M>n,   Imt,  board  meuun. 
"  crib.  ■hufUi.  etc.,           •■       -    ... 

*  Tba  data  br  oootUa;  of  SonjsmlUi  A  Co.,  omlrmclorm  for  the  pneumatic  (oundatloni. 

445.  Fonriiur  07  thi  Aix-logk.     Before  the  construction  of 
the  St.  Louis  bridge  the  air-look  had  always  been  placed  at  the  tap 


ovGoQi^lc 


ART.  4.]  FNSUICATIO   PB00BB8.  291 

of  the  air-Bh&ft,  and  was  of  ench  conBtrnotion  th&t  to  leog^lieD  the 
shaft,  as  the  caisson  sunk,  it  was  necessary  to  detac'j  the  lock^  add 
a  seotion  to  the  shaft,  and  then  replace  the  lock  on  top.  This  vas 
not  only  inconyenient  and  an  interrnptioii  to  the  other  work,  bnt 
reqoired  the  men  to  climb  the  entire  distanoe  under  compressed 
air,  Thich  is  exceedingly  fotigaing  {see  g  460).  To  overcome  theee 
objections,  Eads  placed  the  air-lock  at  the  bottom  of  the  shaft. 
This  position  is  objectionable,  since  in  case  of  a  "  blov-ont,"  i'.  e., 
a  rapid  leakage  of  air, — not  an  nnfretjnent  occurrence, — the  men 
may  not  be  able  to  get  into  the  lock  in  time  to  escape  drowning.  If 
the  lock  is  at  the  top,  they  can  get  ont  of  the  way  of  the  water  by 
climbing  up  in  the  shaft. 

At  the  Havre  de  Grace  bridget  the  air-shaft  was  constructed  of 
wrought  iron,  in  sections  15  feet  long.  The  air-lock  was  made  hj 
placing  diaphragms  on  the  inside  flanges  of  the  opposite  ends  of  the 
top  section.  A  new  section  and  a  third  diaphragm  could  be  added 
without  disturbing  the  air-lock ;  and  when  the  third  diaphragm 
was  in  place,  the  lower  one  was  removed  preparatory  to  using  it 
again.  Some  engineers  compromise  between  these  two  positions, 
and  leave  the  air-lock  permanently  at  some  intermediate  point  in 
the  pier  (see  Fig.-  65,  page  285). 

446.  EXCATATOBS.  In  the  early  application  of  the  pnenmatio 
method,  the  material  was  excavated  with  shovel  and  pick,  elevated 
in  buckets  or  bags  by  a  windlass,  and  stored  in  the  air-lock.  When 
the  fur-Iock  was  full,  the  lower  door  was  dosed,  and  the  air  in  the 
lock  was  allowed  to  escape  until  the  npper  door  could  be  opened, 
and  then  the  material  was  thrown  ont.  This  method  was  expensive 
and  slow. 

In  the  first  application  of  the  pneumatic  procees  in  America 
(g  430),  Qen.  Wm.  Sooy  Smith  invented  the  auxiliary  air-lock,  jr/. 
Fig.  63  (page  283),  through  which  to  let  out  the  excavated  mate- 
rial. The  doors,  /  and  g,  are  ho  connected  together  that  only  one 
of  them  can  be  opened  at  a  time.  The  excavated  material  being 
thrown  into  the  chute,  the  closing  of  the  door  /  opens  g,  and  the 
material  slides  out.  This  simple  device  is  said  to  have  increased 
threefold  the  amount  of  work  that  could  be  done. 

447.  Band-lift.  This  is  a  device,  first  nsed  byCten.  Wm.  Sooy 
Smith,  for  forcing  the  sand  and  mud  out  of  the  caisson  by  means 
of  the  pressore  in  the  working  chamber.    It  oonsiHts  of  a  pipe. 


ovGoQi^lc 


292  FOUNDATIONS    UNDER   WATEK.  [CHAP.  XII. 

rescblDg  from  the  working  chamber  to  the  Barface  (see  Fig.  63  aod 
Plate  I),  controlled  by  a  valve  in  the  working  chamber.  The  sand 
is  heaped  np  aroand  the  lower  end  of  the  pipe,  the  valve  opened, 
and  the  pressure  foroes  a  continnons  stream  of  air,  sand,  and  water 
ap  and  ont.     For  another  application  of  this  principle,  see  g  413. 

In  sand,  this  method  of  excavating  is  very  efficient,  being  eight 
to  ten  times  as  expeditions  ae  the  aaxiliary  air-look.  Of  course, 
the  efficiency  varies  with  the  depth,  i.  e.,  with  the  pressure.  When 
the  8oil  18  so  impervioas  that  the  water  in  the  working  chamber  can 
not  be  forced  out  under  the  edge  of  the  caisson,  it  is  made  to  pass 
through  the  sand-lift  pipe. 

The  "goose-neck,"  or  elbow  at  the  top  of  the  discharge  pipe,  is 
worn  away  very  rapidly  by  the  impact  of  the  ascending  sand  and 
pebbles.  At  the  Havre  de  Grace  bridge,  it  was  of  chilled  iron  4 
inches  thick  on  the  convex  side  of  the  curve,  and  even  then  lasted 
only  two  days.  At  the  Brooklyn  bridge,  the  discharge  pipe  ter- 
minated with  a  straight  top,  and  the  sand  was  discharged  against  a 
block  of  granite  placed  in  an  inchned  position  over  the  upper  end. 

Although  the  sand-lift  is  efficient,  there  are  some  objections  to 
it :  (1)  forcing  the  sand  ont  by  the  pressure  in  the  cylinder  de- 
creases the  pressure,  which  causes,  particularly  in  pnenmatic  piles  or 
small  caissons,  the  formation  of  vapors  so  thick  as  to  prevent  the 
workmen  from  seeing;  (2)  the  diminished  pressure  allows  the 
water  to  flow  in  under  the  catting  edge  ;  and  (3)  if  there  is  much 
leakage,  the  air-compressors  are  unable  to  supply  the  air  fast 
enough. 

448.  Xnd-pomp.  During  the  construction  of  the  St.  Louis 
bridge,  Gapt.  Eads  invented  a  mud-pump,  which  is  free  from  the 
above  objections  to  the  sand-lift,  and  which  in  mud  or  silt  is  more 
efficient  than  it.  This  device  is  generally  called  a  sand-pump,  but 
is  more  properly  a  mnd-pump. 

The  principle  involved  in  the  Eads  pump  is  the  same  as  that 
employed  in  the  atomizer,  the  inspirator,  and  the  injector;  riz.,  the 
principle  of  the  indnced  current.  This  principle  ia  utilized  by  dis- 
charging a  stream  of  water  with  a  high  velocity  on  the  outside  of  a 
small  pipe,  which  prodnces  a  partial  vacuum  in  the  latter ;  when 
the  pressure  of  the  air  on  the  outside  forces  the  mud  through  the 
small  pipe  and  into  the  current  of  water  by  which  the  mud  is 
Ukrried  away.    The  current  of  water  is  the  motive  power. 


ovGoQi^lc 


PNEUUATIC   PROCESS. 


Fig.  66  ie  an  interior  view  of  the  caieaon  of  the  Baltimore  and 
Ohio  R.  R.  bridge  at  Havre  de  Grace,  Md.,  and  shows  the  general 
arrangement  of  the  pipee  and  mud-pnmp.    The  pnmp  itself  is  a 


ovGoQi^lc 


394  FODNDATIOSS  UlTDEB  WATEB.  [cHAP.  XIL 

hollow  pesr-shaped  casting,  about  15  inches  in  diameter  and  15 
inches  long,  a  section  of  which  is  shown  in  the  comer  of  Fig.  66. 
The  water  is  forced  into  the  pump  at  a,  impingee  against  the  coni- 
cal casing,  d,  flows  around  this  lining  and  escapes  upwards  through 
a  narrow  anonlar  space,  /.  The  interior  casing  gives  the  water  an 
even  distribution  around  the  end  of  the  suction  pipe.  The  flow  of 
the  water  through  the  pump  can  be  regulated  by  screwing  the  suc- 
tion pipe  in  or  out,  thus  closing  or  opening  the  annular  space,  y^ 
To  prevent  the  too  rapid  feeding  or  the  entrance  of  lumps,  which 
might  choke  the  pipe,  a  strainer — simply  a  short  piece  of  pipe, 
plugged  at  the  end,  having  a  series  of  ^-inch  to  J-inch  holes  bored 
in  il — was  put  on  the  bottom  of  the  suction  pipe.  The  discharge 
pipe  of  the  mud-pump  terminates  in  a  "goose-neck"  through 
which  the  material  is  discharged  horizontally. 

The  darkly  shaded  portions  of  the  section  of  the  pump  wear 
away  rapidly  ;  and  hence  they  are  made  of  the  hardest  steel  and 
conatructed  ao  aa  to  be  readily  remored.  Different  engineers  bare 
different  methods  of  providing  for  the  renewal  of  theae  parts,  the 
outline  form  of  the  pump  varying  with  the  method  employed.  The 
pump  used  at  the  St.  Louis  bridge  was  cylindrical  in  outline,  but 
otherwise  essentially  the  same  as  the  above. 

449.  In  order  to  use  the  mud-pump,  the  material  to  be  exca- 
vated is  first  mixed  into  a  thin  paste  by  playing  upon  it  with  a  jet 
of  water.  This  pump  is  used  only  for  removing  mud,  silt,  and  soil 
containing  small  quantities  of  sand  ;  pure  sand  or  soil  containing 
large  quantities  of  sand  ia  "  blown  out  "  with  the  sand-lift. 

The  water  is  delivered  to  the  mud-pump  under  a  pressure,  ordi- 
narily, of  SO  or  90  pounds  to  the  square  inch.  At  the  St.  Louis 
bridge,  it  was  found  that  a  mud-pump  cf  3J-incb  bore  waa  capable 
of  raising  20  cubic  yards  of  material  120  feet  per  hour,  the  water 
pressure  being  150  pounds  per  square  inch.* 

450.  Hirater-colnmiL  A  combination  of  the  pneumatic  process 
and  that  of  dredging  in  the  open  air  through  tubes  has  been  em- 
ployed extensively  in  Europe.  It  seems  to  have  been  used  first  at 
the  bridge  ocrosa  the  Rhine  at  Kehl.  The  same  method  woa  uaed 
at  the  Brooklyn  bridge.      The  principle  is  rudely  illustrated  in 

*  HlBtorf  of  th«  St.  LonU  Bridge,  p.  Sia 


ovGoQi^lc 


J<> 

Jtr 

^ 

^~ 

/~H^r*i4 

& 

CAjimitr'   \ 

N 

B 

W^ 

ABT.  4.]  PSSVUXJIO  PR00K88.  29S 

Fig.  67.  The  central  shaft,  which  is  open  top  and  bottom,  project! 
a  little  below  the  cutting  edge, 
and  is  kept  fnli  of  water,  the 
greater  height  of  water  in  the 
coIantQ  balanciDg  the  pressure 
of  the  air  in  the  chamber.  The 
workmen  simply  push  the  mate- 
rial under  the  edge  of  a  water- 
shaft,  from  whence  it  ia  exca- 
vated by  a  dredge  (§  412). 

461.  Blasting.  Bowlders  or 
points  of  rock  may  be  blasted  in 
compressed  air  without  auy  ap- 
preciable danger  of  a  "Wow- 
out"  or  of  injuring  the  ear- 
drums of  the  workmen.  This  '^  "'■ 
point  was  settled  in  sinking  the  foundations  of  the  Brooklyn  bridge ; 
and  since  then  blasting  has  been  resorted  to  in  many  cases.  Bowl- 
ders are  sometimes  "  carried  down,"  i,  e.,  allowed  to  remain  on  the 
surface  of  the  soil  in  the  working  chamber  as  the  excavation  pro- 
ceeds,  and  subsequently  imbedded  in  the  concrete  with  which  the 
air-chamber  is  filled. 

4fi2.  Kate  OV  Smcnra.  The  work  in  the  oaisBon  usually  con- 
tinues day  and  night,  winter  and  summer.  The  rate  of  progress 
varies,  of  course,  with  the  kind  of  soil,  and  particularly  with  the 
number  of  bowlders  encountered.  At  the  Havre  de  Grace  bridge, 
the  average  rate  of  progress  was  1.37  ft.  per  day ;  at  Plattsmouth, 
3.22  ft.  ;  and  at  Blair,  1.75  ft.  per  day. 

453.  OuiDnie  THE  Cajbbos.  Formerly  it  was  the  custom  to 
control  the  descent  of  the  caisson  by  suspension  screws  connected 
with  a  frame-work  resting  upon  piles  or  pontoons.  In  a  strong 
current  or  io  deep  water,  it  may  be  necessary  to  support  the  caisson 
partially  in  order  to  govern  its  descent ;  but  ordinarily,  the  suspension 
is  needed  only  until  the  caisson  is  well  imbedded  in  the  soil.  The 
caisson  may  be  protected  from  the  current  by  constructing  a  break- 
water above  and  producing  dead  water  at  the  pier  site. 

After  the  soil  has  been  reached,  the  caisson  can  be  kept  in  its 
course  by  removing  the  soil  from  the  cutting  edge  on  one  side  or 
the  other  of  the  caisson.     In  case  the  cuseon  does  not  settle  dovm 


D.qitizeabyG00l^lc 


296  POCNDAHOKS  DNDEE  WATBE.  [CHAP.  XII. 

after  the  soil  has  been  remoyed  from  under  the  cutting  edge,  a  re- 
duction of  a  few  pounds  in  the  air  pressure  in  the  working  chamber 
is  usually  sufficient  to  produce  the  desired  reenlt.  At  the  Havre  de 
Grace  bridge,  it  was  found  that  by  allowing  the  discharged  mate- 
rial to  pile  np  against  the  outside  of  the  caisson,  the  latter  could 
bemored  laterally  almost  at  will  The  top  of  the  caisson  was  made 
3  feet  larger,  all  round,  than  the  lower  course  of  masonry,  to  allow 
for  deriatioD  in  sinking.  The  deviation  of  the  caisson,  which  was 
founded  90  feet  below  the  water,  was  less  than  18  inches,  even 
though  neither  suspension  screws  nor  guide  piles  were  employed. 

In  sinking  the  foundations  for  the  bridge  over  the  Missouri 
Biver  near  Sibley,  Ho.,  it  was  necessary  to  move  the  caisson  con- 
siderably horizontally  without  sinking  it  much  farther.  This  was 
accomplished  by  placing  a  number  of  posts — 13  inches  square — 
in  an  inclined  position  between  the  roof  of  the  working  chamber 
and  a  temporary  timber  platform  resting  on  the  ground  below. 
When  these  posts  bad  been  wedged  np  to  a  firm  bearing,  the 
air  pressure  was  released.  The  water  flowing  into  the  oaisson 
loosened  the  soil  on  the  outside,  and  the  weight  of  the  caisson  com- 
ing on  the  inclined  posts  caused  them  to  rotate  about  their  lower~ 
ends,  which  forced  the  caisson  in  the  desired  direction.  In  this 
way,  a  lateral  movement  of  3  or  4  feet  was  secured  while  sinking 
about  the  same  distance. 

A  caisson  is  also  sometimes  moved  laterally,  while  sinking, 
by  attaching  a  cable  which  is  anchored  off  to  one  side  and  kept 
taut. 

4M.  A  new  method  of  controlling  the  descent  of  the  caisson  has 
been  recently  introduced,  which  is  specially  valuable  in  swift  cur- 
r«nta  or  in  rivers  subject  to  sudden  riEcs.  It  was  used  first  in  the 
construction  of  the  piers  for  a  bridge  across  the  Yazoo  Kiver  near 
Ticksbui^  Miaa.  A  group  of  73  piles,  each  40  feet  long,  was  driven 
into  the  river  bed,  and  sawed  off  under  the  vrater  ;  the  caisson  was 
then  floated  into  place,  and  lowered  until  the  heads  of  the  piles 
rested  against  the  roof  of  the  working  chamber.  As  the  work 
proceeded,  the  piles  were  sawed  off  to  allow  the  caisson  to  sink. 
One  of  the  reasons  for  employing  piles  in  this  case,  was  that,  if  the 
caisson  did  not  finally  rest  upon  bed-rock,  they  would  assist  in  sup- 
porting the  pier. 

That  such  ponderous  masses  can  be  so  certainly  guided  in  their 


ovGoQi^lc 


AKT.  4.]  PNEUMATIC  PROOB88.  297 

descent  to  bed-rock,  is  not  the  least  valtiable  nor  least  ioterestiiig 
&Gt  connected  with  this  method  of  sinking  fonndatione. 

456.  TSICTIOVAI.  BziUTAiros,  At  the  Havre  de  Qrace  bridge, 
the  normal  friotional  reeistanee  on  the  timber  sides  of  the  pneamatic 
caisson  vas  280  to  350  lbs.  per  sq.  ft.  for  depths  of  40  to  80  feet, 
the  soil  being  silt,  sand,  and  mud ;  when  bowlders  were  encoun- 
tered, the  resistance  was  greater,  and  when  the  air  escaped  in  large 
qnantities  the  resistance  was  less.  At  the  bridge  over  the  Missouri 
Kiver  near  Blair,  Xeb.,  the  frictional  resistance  usually  ranged  be- 
tween 350  and  450  Iba.  per  sq.  ft.,  the  soil  being  mostly  fine  sand 
with  some  coarse  sand  and  gravel  and  a  little  clay.  At  the  Brook- 
lyn bridge  the  frictional  resistance  at  times  was  600  lbs.  per  eq.  ft. 
At  Cairo,  in  sand  and  gravel,  the  normal  friction  wiui  about  600  lbs. 
per  sq.  ft. 

For  data  on  the  friction  of  iron  cylinders  and  masonry  shaftA, 
see  |g  418-19,  pages  2V5-77;  and  for  data  on  the  friction  of  ordi- 
nary piles,  see  §§  370-73,  pages  347-48. 

166.  FlLUFe  THE  Ais-OHAHBEK.  When  the  caisson  has 
reached  the  required  depth,  the  bottom  ts  leveled  off — by  blasting, 
if  necessary, — and  the  working  chamber  and  shafts  are  filled  with 
concrete.  Sometimes  only  enough  concrete  is  placed  in  the  bottom 
to  seal  the  chamber  water-tight,  and  the  remaining  space  is  filled 
with  sand.  This  was  done  at  the  east  abutment  of  the  St  Louis 
bridge,  the  sand  being  pamped  ia  from  the  river  with  the  sand- 
pump  previously  used  for  excavating  the  material  from  under  the 
caisson. 

467.  Voted  Exahfibl  The  St.  Louis  Bridge.  The  founda- 
tions of  the  steel-arch  bridge  over  the  Mississippi  at  St.  Louis  are 
the  deepest  ever  sunk  by  the  pneumatic  process,  and  at  the  time  of 
construction  {1870)  they  were  also  very  much  tbe  largest.  The 
caisson  of  the  east  abutment  was  an  irregular  hexagon  in  plan, 
83  X  70  feet  at  the  base,  and  64  x  48  feet  at  the  top — 14  feet  above 
the  catting  edge.  The  working  chamber  was  9  feet  high.  The 
cutting  edge  finally  rested  on  the  solid  rock  94  feet  below  low 
water.  .  The  maximum  emersion  was  109  feet  8^  inches,  the  greatest 
depth  at  which  pneumatic  work  has  yet  been  done.  The  othui' 
caissons  were  almost  as  large  as  the  one  mentioned  above,  but  were 
not  sunk  as  deep. 

The  caissons  were  constructed  mainly  of  wood ;  but  the  sido 


ovGoQi^lc 


S9S  FOITHDATIONa   DNDEB  WATEB.  [CHAF.  XII. 

wsIIh  and  the  root  were  covered  with  plate  iron  to  prevent  leakage, 
and  strengthened  by  iron  girders  on  the  insida  -  T%iB  was  the  first 
jmemnatic  caisson  coiiBtracted  in  America ;  and  the  ase  of  large 
qnsntitiea  of  timber  was  an  important  innovation,  and  has  become 
one  of  the  distinguishing  characteristics  of  American  practice.  In 
all  subsequent  experience  in  this  country  (except  as  mentioned  in 
§  458),  the  iron  lining  for  the  working  chamber  has  been  dispensed 
with.  The  masonry  rested  directly  upon  the  roof  of  the  caisson, 
i.  e.,  QO  crib-work  was  employed.  In  sinking  the  first  pneumatic 
foundation  an  iron  coffer-dam  was  built  upon  the  top  of  the  caisson ; 
but  the  last — the  largest  and  deepest — was  sunk  without  a  coffer- 
dam,— a  departure  from  ordinary  European  practice,  which  is  occa- 
sionally followed  in  this  country  (see  §  436). 

468.  The  Brooklrii  Bridge.  The  foundations  of  the  towers  of 
the  suspension  bridge  over  the  East  Eiver,  between  New  York  City 
and  Brooklyn,  are  the  largest  ever  sunk  by  the  pneumatic  process. 
The  foundation  of  the  New  York  tower,  which  was  a  little  larger 
and  deeper  than  the  other,  was  rectangular,  173  X  102  feet  at  the 
bottom  of  the  foundation,- and  157  x  77  feet  at  the  bottom  of  the 
masonry.  The  caisson  proper  was  31J  feet  high,  the  roof  being  a 
solid  mass  of  timber  22  feet  thick.  The  working  chamber  was  9^ 
feet  high.  The  bottom  of  the  foundation  is  78  feet  below  mean 
high  tide,  and  the  bottom  of  the  masonry  is  46^  feet  below  the 
same.  From  the  bottom  of  the  foundation  to  the  top  of  the 
balustrade  oit  the  tower  is  354  feet,  the  top  of  the  tower  being  376 
feet  above  mean  high  tide. 

To  make  the  working  chamber  ui^-tight,  the  timbers  were  laid 
in  pitch  and  all  seams  calked  ;  and  in  addition,  the  sides  and  the 
roof  were  covered  with  plate  iron.  As  a  still  further  precaution, 
the  inside  of  the  air-chamber  was  coated  with  varnish  made  of  rosin, 
menhaden  oil,  and  Spanish  brown. 

For  additional  details  see  the  several  annual  reports  of  the  en- 
gineers in  charge,  and  also  numerous  articles  in  the  engineering 
newspapers  and  magazines  from  18C9  to  1873. 

469.  Forth  Bridge.  For  an  illnBtrated  account  of  the  pueumatu 
foundation  work  of  the  bridge  across  the  Frith  of  Forth,  Eng- 
land, see  Engineeriitfi  Newf,  vol.  xiii.  pages  242-43.  The  caissons 
employed  there  differed  from  those  described  above  (1)  in  being 
made  almost  wholly  of  iron,  (3)  in  an  elaborate  system  of  cages  for 


ovGoQi^lc 


ABT.  4.]  FKEUHATIC   PB0CES3.  209 

hoisting  the  material  from  the  ineide,  and  (3)  in  the  use  of  inter- 
locked hydraulic  apparatns  to  open  and  close  the  air-locks.  Each 
of  the  two  deep-water  piers  consists  of  four  cylindrical  caissons 
?0  feet  in  diameter  the  de^>eBt  of  which  rests  96  feet  below  high 
tide. 

460.  Phtkolobioal  XvnoT  W  COXPBMBED  AlK.  In  the  ap- 
plication of  the  compressed-air  process,  the  qaestion  of  the  ability 
of  the  hnman  system  to  bear  the  increased  pressure  of  the  air  be- 
comes very  important. 

After  entering  the  air-lock,  ae  the  pressure  increases,  the  first 
sensation  experienced  is  one  of  great  heat.  As  the  pressure  is  still 
further  increased  a  pain  is  felt  in  the  ear,  arisiog  from  the  abnormal 
pressure  upon  the  ear-drum.  The  tubes  extending  from  the  back 
of  the  month  to  the  bony  cavities  Over  wbich  this  membrane  is 
stretched,  are  so  very  minute  that  compressed  air  can  not  pass 
through  them  with  a  rapidity  sufficient  to  keep  up  the  equilibrium 
of  pressure  on  both  sides  of  the  drum  (for  which  purpose  the  tubes 
were  designed  by  nature),  and  the  excess  of  pressure  on  the  ontaide 
causes  the  pain.  These  tubes  can  be  distended,  thus  relieving  the 
pain,  by  the  act  of  swallowing,  or  by  closing  the  nostrils  with  the 
thiimb  and  finger,  shutting  the  lips  tightly,  and  intlatiag  the 
cheeks.  Either  action  facilitates  the  passage  of  the  air  through 
these  tubes,  and  establishes  the  eqailibrinm  desired.  The  relief  is 
only  momentary,  and  the  act  must  be  repeated  from  time  to  time, 
as  the  pressure  in  the  air-lock  increases.  This  pain  is  felt  only 
while  the  air  in  the  lock  is  beiug  "equalized,"  i.  e.,  while  the  air  is 
being  admitted,  and  is  most  severe  the  first  time  compressed  air  is 
encountered,  a  little  experience  geuerully  removing  all  unnleaaant 
sensations.  The  passage  through  the  lock,  both  going  in  and  com- 
ing out,  should  be  slow  ;  that  is  to  say,  the  compressed  air  should 
be  let  in  and  out  gradually,  to  give  the  pressure  time  to  equalize 
itself  throughout  the  various  ports  of  the  body. 

When  the  lungs  and  whole  system  are  filled  thoroughly  with 
the  denser  air,  the  general  effect  is  rather  bracing  and  exhilarating. 
The  increased  nmonnt  of  oxygen  breathed  in  compressed  air  very 
much  accelerates  the  organic  functions  of  the  body,  and  hence  labor 
in  the  caisson  is  more  exhaustire  than  in  the  open  air :  and  on  get- 
ting outside  again,  a  reaction  with  a  general  f  aeling  of  prostration 
sets  in.    At  moderate  depths,  however,  the  laborers  in  the  caisson. 


ovGoQi^lc 


300  FOUNDATIOITS  UNDEB  WATBK.  [OBAP.  XII. 

after  a  little  experience,  feel  no  bad  effects  from  the  compressed  air, 
either  while  at  work  or  afterwards. 

Bemainlng  too  long  in  the  working  chamber  cansee  a  form  of 
paralysis,  recently  named  caisson  disease,  which  is  sometimes  fatal 
The  injarions  effect  of  compressed  air  is  much  gr«iter  on  men  ad- 
dicted to  the  nse  of  intoxicating  liquors  than  on  others.  Only 
sound,  able-l^ied  men  should  be  permitted  to  work  in  the  cusson. 

In  passing  throngh  the  air-lock  on  leaving  the  air-chamber,  the 
workman  experiences  a  great  lose  of  heat  owing  (1)  to  the  expan- 
sion of  the  atmosphere  in  the  lock,  (2)  to  the  expansion  of  the  free 
gases  in  the  cavitiea  of  the  body,  and  (3)  to  the  liberation  of  the 
gases  held  in  solution  by  the  liquids  of  the  body.  Hence,  on  com- 
ing out  the  men  should  be  protected  from  currents  of  air,  sbonld 
drink  a  cup  of  strong  hot  coffee,  dress  warmly,  and  lie  down  for  a 
short  time. 

461.  No  physiolo^cal  difficulty  is  encountered  at  small  depths ; 
bat  this  method  is  limited  to  depths  not  mnch  exceeding  100  feet, 
owing  to  the  deleterious  effect  of  the  compressed  air  upon  the  work- 
men. At  the  east  abutment  of  the  St.  Louis  bridge  (§  457),  the 
caisson  was  sunk  110  feet  below  the  surface  of  the  water.  Except 
in  this  instance,  the  compressed-air  process  has  never  been  applied 
at  a  greater  depth  than  about  90  feet.  Theoretically,  the  depth,  in 
feet,  of  the  lower  edge  of  the  caisson  below  the  surface  divided  by 
33  is  equal  to  the  number  of  atmospheres  of  pressure.  The  press- 
ure is  never  more  than  this,  and  sometimes,  owing  to  the  fric- 
'  tional  resistance  to  the  flow  of  the  water  through  the  soil,  it  is  a 
little  less.  Therefore  the  depth  does  not  exactly  indicate  the 
preaanre  ;  but  the  rule  is  sufQciently  exact  for  this  purpose.  At  St. 
Louis,  at  a  depth  of  110  feet,  the  men  were  able  to  work  in  the 
compressed  air  only  four  hours  per  day  in  shifts  of  two  hours  each, 
and  even  then  worked  only  part  of  the  time  they  were  in  the  air- 
chamber. 

With  reasonable  care,  the  pneumatic  process  can  be  applied  at 
depths  less  than  80  or  dO  feet  without  serious  consequences.  At 
great  depths  the  danger  can  be  greatly  decreased  by  observing  the 
following  precautions,  in  addition  to  those  referred  to  above :  (1)  In 
hot  weather  cool  the  air  before  it  enters  the  caisson  ;  *  {'i)  in  cold 


ovGoQi^lc 


ART.  4.]  PHEUICATIC  PH0CES8.  301 

weather  warm  the  air  Id  the  lock  vben  the  men  come  out ;  and 
(3)  raiee  and  lower  them  b;  machinery. 

For  as  exhaustive  acconnt  of  theTarione  aspects  of  this  sabject, 
see  Dr.  Smith's  article  on  the  "  Phydological  Effect  of  Comprened 
Air,"  in  the  Report  of  the  Engineer  of  the  Brooklyn  Bridge.* 

462.  Cost.  The  contract  for  pneumatic  foundation  is  usually 
let  at  specified  prices  per  nnit  for  the  materish  left  permanently  in 
the  structure  and  for  the  materia)  excavated,  inclnding  the  neces- 
sary labor  and  tools.  The  prices  for  material  in  place  are  about  as 
follows  :  Timber  in  caisson  proper,  from  (40  to  150  per  thousand 
feet,  board  measure,  according  to  the  locality  in  which  the  work  is 
done ;  and  the  timber  in  the  crib-work  and  coffer-dam  about  (5  to 
t7  per  thousand  less.  The  concrete,  which'is  usually  composed  of 
broken  stone  and  sufficient  I  to  2  or  1  to  3  Portland  cement  mortar 
to  completely  fill  the  voids,  costs,  exclusive  of  the  cement,  from  (5  to 
t?  per  cubic  yard  for  that  in  the  crib,  and  about  twice  this  sum  for 
that  in  the  air-chamber  and  under  the  cutting  edge,  The  wrought- 
iron  spikes,  drift-bolts,  screw-bolts,  and  cast-iron  washers  cost  from 
3|  to  6  cents  per  pound.f  The  caisson  and  filling  costs  from  (14  to 
(30  per  cubic  yard  ;  and  the  crib  and  filling  from  (8  to  (10. 

The  price  for  sinking,  incladtng  labor,  tools,  machinery,  etc., 
ranges,  according  to  the  kind  of  soil,  from  18  to  40,  or  even  60, 
cents  per  cubic  foot  of  the  volume  found  by  multiplying  the  area 
of  the  caisson  at  the  cutting  edge  by  the  final  depth  of  the  latter 
below  low  water.  In  sand  or  silt  the  cost  is  18  to  20  cents,  and  in 
stiff  clay  and  bowlders  40  to  50  cents. 

463.  Examples.  The  table  on  page  302  gives  the  details  of  the 
coat  of  the  pneumatic  foundation  of  the  Havre  de  Grace  bridge,  as 
fally  described  in  gg  438-44. 

The  t»ble  on  page  303  gives  the  details  of  the  cost  of  the  pnen- 
matic  caissons  of  the  bridge  across  the  Missouri  River  near  Blair, 
Neb.  Thecaieeons  (Fig.  65,  page  285)  were54feetlong,  24  feet  wide, 
and  17  feet  high.  In  the  two  shore  piers,  Nos.  I  and  IV  of  the 
table,  the  caissons  were  surmounted  by  cribs  20  feet  high  ;  but  in 
the  channel  piers,  the  masonry  rested  directly  upon  the  roof  of  the 

■  PrlM  EsM7  of  tlie  Alnmnl  Anodstloii  of  the  College  of  Pbrsiclaiu  and  anc- 
BMDS  ot  New  Totk  atf,  1S7S. 

t  There  Me  nanallr  from  140  to  ISO  ponnda  of  Iron  per  thonund  feet  (board  iimm- 
nie)  of  timber. 


ovGoQi^lc 


FODNDAnONS  UNDEB 


[cHAF.  xn. 


TABLETS. 
Con,  to  THS  B.  B.  Co.,  or  Foukdattoiis  or  Hatsb  db  Gk&cb  Budsk." 


Kmon  or  Tn  Pio. 

tL 

UL 

rv. 

vm. 

IX. 

Diptt^fll  outUiic  «!«•  Mow  knr  wu<r. 

U.S 

•»,««■« 

n,8a 

MS1.14 
I.B)1.H 

1tOJS.M 

ro.T 

B«.T 

idbIsos 

110.088.44 

1.M7.15 

r.oiT.so 

IB8T 
S.tU.19 
1,4MS6 

■11 
S;SS 

S0.> 

n.s 

„..,- 

•ffiS 
■iSS:S 

in.sn 

IIS.ir8.0T 
!.»».40 

"S 

1.T4S.H 
S1,M1.III> 

Depth  of  eutUuc  sdee  below  mod  lliM. 
(oUl  COM,  pw  DM  on.  yd 

3&8 

m.ssi 

10T.8B8 
ttl.TeT.86 

gj:a^lJi.^,i«oiyd:: 

•^•s-fs 

C«(  a(  ^<ikl^?'^Ml^pErc!!!  ft  .rf 
OooonM  below  cnulng  vils*,  a  »li.»  -  - 

sg».tt 

io,au,Qa 

es,oig.4T 
isn 

T1.MS,1S 

ti.isa 

wjM.aB 

10»,848.« 

tow  muuirr,  iDoludtng  coSor^tuni. 

M.M 

ATsnge  loMJ  com  of  tbe  loundaUoo,  to  R.  K.  Co.,  par  d«  cubic  yard ma. 

caisson.     The' work  waa  done,  in  J883-83,  by  the  bridge  companj^s 
men  under  the  direction  of  the  engineer. 

464.  Id  1869-72,  thirteen  cylinders  were  sunk  by  the  plennm- 
pnenmatic  process  for  the  piers  of  a  bridge  orer  the  Schuylkill 
Eiyer  at  South  Street,  Philadelphia.  There  were  three  piers,  one 
of  which  waa  a  piTot  pier.  There  were  two  cylindere,  8  feet  ia 
diameter  and  83  feet  long,  sunk  through  32  feet  of  water  and  30 
feet  of  "  sand  and  tough  compact  mud  intermingled  with  bowlders;" 
two  cylinders,  8  feet  in  diameter  and  57  feet  long,  sunk  through  22 
feet  of  water  and  5  feet  of  soil  as  above ;  one  cylinder,  6  feet  in 
diameter  and  64  feet  long,  sunk  through  'JS  feet  of  water  and  18 
feet  of  soil  as  above  ;  and  8  columns,  4  feet  in  diameter  and  aggre- 
gating 507  feet,  sunk  through  22  feet  of  water  and  18  feet  of  soil 
OS  above.  A  10-foot  section  of  tbe  8-foot  cylinder  weighed  14,600 
pounds,  of  the  6<foot,  10,800  pounds,  and  of  the  4-foot,  6,800 
ponnds.  The  cylinders  rested  upon  bed-rock,  and  were  bolted  to 
*  Data  bf  emuteey  ot  So^amlUt  A  Co.,  coDtractdDK  engineers  tor  the  pnenmmtio 


ovGoQi^lc 


PHBUMATIO  PEOCESa. 


303 


AKT.  4.] 

It.    The  actual  cost  to  the  contractor,  exclneJTe  of  tools  and  ma- 
chineiy,  was  as  in  Table  34  (page  304). 
TABLB  88. 
Con  or  Phbdhatio  Fduhtoltiohb  aw  Blaix  Bbidob,* 


tt  oktaMin  vu  hnrerad  afWr  oomple- 
ib  it  coMdk  «dsa  bekiir  nirface  of 


Crib  and  mllnc. 

Air-lock,  ibftfu, 

SIdUdk  oainoo.  ooal  o(,  tnalivUns  anicllon  aiid  re- 

■aofkl  ol  macblaenr 

SlaUnc  caUaod,  coat  of,  par  eqbia  foot  of  dlapUce- 

ment  below  position  of  cuUin(  edite  wbeo 

oalMonwHOompistal 

Stalling  calnon,  coac  of.  per  cobio  foot  o(  diaplaoe- 

menC  below  aiufacB  of  water 

._. . of.peroublo  toot  at  < 


$II.T58. 
7.MS.IB 
I, (81 .10 


"1 


l.UdBO 
0.888.18 


Arerass  ooet  t  of  tha  foundaUona,  per  CQbto  j-ard tVl.TO. 

465.  "ExcaTatlon  in  the  Brooklyn  caiesou  J  cost  for  labor 
only,  including  the  men  on  top,  about  (5.25  per  cubic  yard 
[19  cents  per  cubic  foot].  Runoiog  the  six  air-compressora 
.  added  to  this  $3.60  per  hour,  or  about  47  cents  per  yard ;  lights 
added  tO.56  more;  and  these  with  other  contingencies  nearly 
equaled  the  cost  of  labor.  The  great  cost  was  due  to  the  ezceBsiTe 
hardness  of  the  material  over  much  of  the  surface,  the  caisson  finally 
resting,  for  nearly  its  whole  extent,  on  a  mass  of  bowlders  or  bard- 
pan^     The  concrete  in  the  caisson  cost,  for  every  expense,  about 

*  Complied  from  the  report  of  Geo.  S.  Horlaon,  oUef  eugtneer  of  tbe  biidgg. 

t  Rxclnslve  ot  engineering  eipenaea  and  coat  ot  tools,  macUuery,  and  bnlldlngs. 
In  a  note  to  the  anthor,  Hr.  Horison,  tbe  engineer  of  the  bridge  aafa :  "  It  la  Impoe- 
■Ible  to  divide  tbe  bnlldlnga,  tool*,  and  engineering  Bipenam  betveen  the  Bubetmct- 
nre  and  other  portions  of  the  work.  The  balk  of  Uie  items  ot  tools  and  machlcerr 
[(lS,a(N.S8},  however,  relates  to  tbe  foondatlonB."  The  engineering  ezpenaea  and 
bnlldlnga  were  nearly  3  per  cenL  of  the  total  cost  of  the  entire  bridge.  The  ooet  ot 
tools  and  machinery  was  equal  to  a  little  over  IS  per  oent.  of  tbe  ooat  ot  tbe  tonnda- 
tiona  as  above.  Inclnding  these  Items  would  add  neariy  one  lizUt  t( 
the  laat  thne  11dm. 

1  For  a  brief  deacriptlon,  see  f  456. 


ovGoQi^lc 


FOUNDATIONS  UNDEB  WATEE. 


[chap.  XIL 


TABLE  U. 
Cost  or  Precxatio  Piles  at  Phtladslphu  nr  1889-73.* 


Com  oCcul  Iron,  a  tfiO-Wper  ton 

"     "  bolu.  &IH  oonW  per  lb 

"     "  grouied  rubble  maaonry  (ezdiulTe  of  labor^,  i^  $tl.M 

"     "  (InlclnK.andlByiDg  nuBOurr 

ToM  oonof  (be  eyllodert  in  ptaos 

Com  of  iron  per  line*l  root  or  orlldder  

**    "  mMeri«)i  tor  Diaaop.T  per  lineal  tooC  arcrlioder.  .. 
"     "  ■InklntcaadlajIngmuoDrrperllneBirootoIayliiidei 

Total  oo«t,t  per  lineal  foot,  of  crllnder  Id  place  . . 


4m.84 


li(.ivrr,«o 
s:o.i» 

S.77B.KT 


tl5.50  per  cabic  yard.  The  caisson  aod  filling  together  aggregated 
16,898  cnbic  yards ;  and  the  approximate  cost  per  yard  for  every 
expense  was  $20.71."  (  The  foundation  therefore  cost  about  t30 
per  cnbio  yard. 

The  pneumatic  fonndations  for  the  channel  piers  of  the  bridge 
over  the  Missouri  at  Plattsmouth,  Neb.,  cost  as  follows:  One 
foundation,  consisting  of  a  caisson  50  ft.  long,  20  ft.  wide,  and  15.5 
ft.  high,  surmonnted  by  a  crib  14.15  ft.  high,  snnk  through  13  ft. 
of  water  and  20  ft.  of  soil,  cost-H9.29  per  cubic  yard  of  net  volume. 
Another,  consisting  of  a  caisson  50  ft.  long,  20  ft.  wide,  and  15.5 
ft.  high,  surmounted  by  a  crib  36.25  ft.  high,  snnk  through  10 
ft.  of  water  and  44  ft.  of  soil,  cost  914.45  per  cnbic  yard  of  net 
volume,  g 

468.  European  Examples.  The  following^  is  interesting  as 
showing  the  cost  of  pneumatic  work  in  Europe : 

"At  Moolins,  cast-iron  cylinders,  8  feet  2^  inches  in  diameter, 
with  a  filling  of  concrete  and  sunk  33  feet  below  water  into  marl, 
cost  $62.94  per  lineal  foot,  or  (29.71  for  the  iron  work,  and  933.23 


*  Compiled  from  an  article  bf  D.  HoN.  Stanfler,  engtneer  Id  abwge.  In  Tmiu.  Am. 
800.  o(  C.  E.,  ¥ol.  yll.  pp.  3S7-S09. 

t  Ezcltulve  of  tools  and  machinery. 

I F.  CoUlngwood,  aaalBtaDt  en^oeer  Brooklni  bridge,  In  Tntns.  Am.  Boc.  of  C.  S. 

(  Complied  from  the  report  of  Geo.  B.  Morl«ni,  chief  engliieer  of  the  bridge. 

T  Bjr  Jnlea  OaDdard,  as  tmnslnted  from  the  French  by  L.  F.  VemoD-Haroonrt  for 
the  Proceedings  of  the  Iiutituce  of  Civil  Eagtneers  (London). 


ovGoQi^lc 


ABT.  4.]  PITBUIIATIO  PROCESS.  309 

for  sinking  and  concrete.  At  Argenteail,  with  cylindere  11  feet  10 
inches  in  diameter,  the  sinking  atone  cost  (42.13  per  lineal  foot 
[nearly  (10  per  cubic  yard],  where  a  cylinder  was  sunk  53}  feet  in 
three  hundred  and  ninety  hours.  [The  total  cost  of  this  founda- 
tion was  (34.09  per  cubic  yard,  see  table  on  page  310.]  At  Orival, 
where  a  cylinder  was  suuk  49  feet  in  twenty  days,  the  coat  of  sinking 
was  (36.83  per  lineal  foot.  At  Bordeiiux,  with  the  same-sized 
cylinders,  a  gang  of  eight  men  conducted  the  sinking  of  one  cylin- 
der, and  UBually  34  cubic  yards  wei-e  excavated  every  twenty-four 
hours.  The  greatest  depth  readied  was  55|  feet  below  the  ground, 
and  71  feet  below  high  water.  In  tJie  regular  course  of  working,  a 
cylinder  was  sunk  in  from  nine  to  fifteen  days,  and  the  whole  opera- 
tion, including  preparations  and  filling  with  concrete,  occupied  on 
the  average  35  days.  One  cylinder,  or  e  half  pier,  cost  on  the  aver- 
age (11,S98.40,  of  which  (1,461  was  for  sinking.  M.  Morandi^re 
estimates  the  total  cost  of  a  cylinder  sunk  like  those  at  Argenteuil, 
to  a  depth  of  50  feet,  at  (7,012.80. 

467.  "Considering  next  the  cost  of  piersof  masonry  on  wrought- 
iron  caissons  of  excavation,  the  foundations  of  the  Lorient  viaduct 
over  the  Scorff  cost  the  large  sum  of  (24. 11  per  cubic  yard,  owing  to 
difficulties  caused  by  the  tides,  the  labor  of  removing  the  bowlders 
from  nnderaeath  the  caisson,  and  the  lai^  coet  of  plant  for  only 
two  piers.  The  foundation  of  the  Kehl  bridge  cost  stiil  more,  about 
(38.23  *  per  cubic  yard  ;  but  this  can  net  be  regarded  as  a  fair  iu- 
Btance,  being  the  first  attempt  [see  g  429]  of  the  kind. 

"The  foundations  of  the  Nantes  bridges,  sunk  56  feet  below 
low-water  level,  cost  about  (14.84  per  cubic  yard.  The  average 
coet  per  pier  was  as  follows  : 

CalsMD  (41  fe«t  4  fochea  by  14  feet  S  inches),  50  loiu  of  wrougbl 

iron®(n6.88 (5.844 

CoSer-dBm,  8  toos  of  wrought  iron  ®  (58.44 175 

Excavation.  916  cubic  fards  @  (4.47 4.0nt 

Concrete 4,188 

Haacmry,  plant,  etc 1.8T0 

Average  coat  per  pier (16,166 

"One  pier  of  the  bridge  over  the  Mouse  at  Rotterdam,  with  a 

■  Notice  the  iltghl  inoonslirteiiof  between  tbia  qnuitltr  and  tbe  one  Id  tba  thlid 
line  from  the  laat  of  tbe  table  on  page  810,  both  being  from  tbe  same  anfcle. 


ovGoQi^lc 


306  FOUNDATIONS  UNDSS  WATER.  [CQAP.  XII. 

caisBon  of  222  tons  and  a  cofler-dam  casing  of  94  tons,  and  sank  75 
feet  below  high  water,  cost  $70,858,  or  $13.97  per  cabic  yard. 

"  The  Yiohy  bridge  has  five  piers  bailt  on  caissons  34  feet  by  13 
feet,  and  two  abutments  on  caissons  26  feet  by  34  feet.  The  foun- 
dations were  sunk  23  feet  in  the  gronnd,  the  upper  portion  con- 
Biating  of  ahingle  and  conglomerated  gravel,  and  the  laet  10  feet  of 
marl.     The  cost  of  the  bridge  was  aa  followa : 

lolerest  far  eight  moDOw,  and  depredation  of  plant  worth  (19,480. .  t8,8W 

Coat  of  prepsratioDB,  approach  bridge,  and  atagiog 4,IKH 

OOMona  (tereD),  150}  lou  ®  IU&.B8 17,106 

BinkiDg 9,8i8 

Concrete  and  maaonry B,80S 

Contrartor'a  bonus  and  genenl  ezpenaeB 6,107 

Total  coat  of  five  foundattona 947,141 

The  cost  per  cubic  yard  of  the  foundation  below  low  water  was 
tl6.69,  of  which  the  sinking  alone  cost  $3.50  in  gravel,  and  $4.37 
in  marl 

"At  St.  Maurice,  the  cost  per  cubic  yard  of  foundation  was 
$15.94,  exclusive  of  staging." 

468.  CORCLnnoH.  Except  in  very  shallow  or  very  deep  water, 
the  compressed-air  process  has  almost  entirely  snperseded  all  others. 
The  following  are  some  of  the  adrantages  of  this  method.  1.  It  is 
reliable,  since  there  is  no  danger  of  the  caisson's  being  stopped, 
before  reaching  the  desired  depth,  by  sunken  logs,  bowlders,  etc., 
or  by  excessive  friction,  as  in  dredging  through  tubes  or  shafts  in 
cribs.  2.  It  can  be  used  regardless  of  the  kind  of  soil  overlying  the 
rock  or  ultimate  foundation.  3.  It  is  comparatively  rapid,  since 
the  sinking  of  the  caisson  and  the  building  up  of  the  pier  go  on  at 
the  same  time.  4.  It  is  comparatively  economical,  since  the  weight 
added  in  sinking  is  a  part  of  the  foundation  and  is  permanent,  and 
the  removal  of  the  material  by  blowing  out  or  by  pumping  is  aa 
uniform  and  rapid  at  one  depth  as  at  another, — the  cost  only  being 
increased  somewhat  by  the  greater  depth.  5.  This  method  allovrs 
ample  opportunity  to  examine  the  ultimate  foundation,  to  level  the 
bottom,  and  to  remove  any  disintegrated  rock.  6.  Since  the  rock 
can  be  hiid  bare  and  be  thoroughly  washed,  the  concrete  can  be  com- 
menced upon  a  perfectly  clean  surface ;  and  hence  there  need  be  no 
qaestioD  as  to  the  stability  of  the  foundation. 


ovGoQi^lc 


AST.  6.]  THE  FEEEZING  PBOCESS. 


Aet.  5.  The  Fbebzinq  Proobsb. 

469.  TanoiPIX  The  presence  of  water  has  alirays  1)6611  the 
great  obat&cle  in  foundation  work  and  in  shaft  sinking,  and  it 
is  only  very  recently  that  any  one  thought  of  transforming  the 
liquid  soil  into  a  solid  wall  of  ice  aboat  the  space  to  be  excavated. 
The  method  of  doing  this  consists  in  inclosing  the  site  to  be  ex- 
caTated,  by  driving  into  the  ground  a  number  of  tubes  through 
which  a  freezing  mixture  ie  made  to  circulate,  Thrae  consist  of  a 
large  tube,  closed  at  the  lower  end,  inclosing  a  smaller  one,  open  at 
the  lover  end.  The  freezing  mixture  is  forced  down  tho  inner 
tube,  and  rises  through  the  outer  one.  At  the  top,  these  tubes 
connect  with  a  reserroir,  a  refrigerating  machine,  and  a  pump. 
The  freezing  liquid  is  cooled  by  an  ice-making  machine,  and  theo. 
forced  through  the  tubes  ontil  a  wall  of  earth  is  frozen  around: 
them  of  sufficient  thickness  to  stand  the  external  pressure,  when 
the  excaTation  can  proceed  as  in  dry  ground. 

470.  HiSTOBT.  This  method  was  iavented  by  F.  K.  Poetscb, 
i/l.D,,  of  Aschersleben,  Prussia,  in  1883.  It  has  been  applied  in. 
but  three  cases.  The  first  was  at  the  Archibald  colliery,  near 
Sohweidlingen,  Prussia,  where  a  Toia  of  quicksand,  20  feet  thick,  waff 
encountered  at  a  depth  of  about  150  feet  below  the  surface.  Her& 
twenty-three  pipes  were  used,  and  3fi  days  consumed  in  the  freezing 
process,  under  local  difficulties.  The  second  was  at  the  Centrum 
mine,  near  Berlin,  where  about  107  feet  of  quicksand,  etc.,  was 
penetrated.  Engineers  had  been  baffled  for  years  in  their  attempts, 
to  sink  a  shaft  here  ;  bat  in  33  days  Mr.  Poetsch  had,  with  only  16 
freezingtubes,  secured  a  6-foot  wall  of  ice  uround  the  shaft  area,  and 
the  shi^t  was  excavated  and  curbed  without  difficulty.  The  third 
piece  of  work  was  at  the  Eimilia  mine,  Fensterwalde,  Austria,  in. 
1885,  where  an  Sj-foot  shaft  was  sunk  through  115  feet  of  quick- 
sand.* 

471.  DSTAILB  07  TEE  Pbocksb.  In  the  last  case  mentioned 
above,  "  12  circulatory  tubes  were  used,  sunk  in  a  circle  about  14. 
feet  in  diameter,  from  13  to  15  days  being  required  to  sink  them  t^ 
depth  of  about  100  feet.    The  outside  tubes  were  8^  inches  in 

*  As  this  TolnmB  IB  going  throDf^  the  pre«8,  this  msthod  ii  belog  applied  In  two 
plaoes  la  tlila  ooiuaT^IicD  Uonntaln,  Hlch.,  and  Wyoming,  Penit.— In  »tniHng 


ovGoQi^lc 


808  FODNDiiTIONB  UKDEB  WA.TEB.  [CHA.F.  XIL 

diameter,  and  made  of  plate  iron  0.15  inch  thick.  The  tabes  were 
sunk  by  aid  of  the  water-jet.  They  were  giveo  a  very  slight  incli- 
nation outward  at  the  bottom  to  avoid  any  deviation  in  Binking 
that  might  interfere  with  the  line  of  the  shaft.  The  freezing 
liquid  employed  was  a  solution  of  chloride  of  calcium,  which  cun- 
gc»lB  at  a  temperature  of  —85"  0.  (  —31°  F.).  The  circulation  of 
the  liquid  through  the  tubes  was  secured  by  a  -small  pump  with 
a  pistoa  6  inches  in  diameter  and  a  12-inch  stroke.  At  the  begin- 
ning of  the  operation,  this  pump  made  30  double  strokes  per  min- 
ute, which  was  equivalent  to  the  passage  of  0.6  gallon  of  the  liquid 
through  each  tube  per  minute ;  at  the  end  of  the  operation,  when 
it  was  only  aeceBsary  to  maintain  the  low  temperature,  the  pump 
strokes  were  reduced  to  15  per  minute.  The  refrigerating  machiue 
employed  was  one  of  a  model  guaranteed  by  the  maker  to  produce 
1,100  pounds  of  ice  per  hour.  The  motive-power  was  supplied  by 
a  small  engine  of  about  5  horse-power.  The  ammoniac  pump  had 
a  piston  2.8  inches  in  diameter  and  a  d.3-inch  stroke,  and  made  30 
strokes  per  minute.  The  pressure  maintained  was  about  10  atmos- 
pheres. The  quantity  of  ammoniacal  liquid  necessary  to  charge 
the  apparatus  was  381  gallons ;  and  under  normal  conditions  the 
daily  consumption  of  this  liquid  was  0.78  gallon. 

'*  The  actual  shaft  excavation  was  commenced  53  days  after  the 
freezing  apparatus  had  been  set  in  motion.  The  freezing  machine 
was  in  operation  340  days.  The  work  was  done  without  difficulty, 
and  a  progress  of  1.64  feet  per  day  was  made.  The  timbering  was 
v^ry  light,  but  no  internal  pressure  of  any  kind  was  observed.  The 
brick  masonry  used  for  finally  lining  the  shaft  was  about  11  inches 
thick.  When  the  shaft  was  finished,  the  tubes  were  withdrawn 
without  diflScnIty,  by  circulating  through  them  a  hot,  instead  of  a 
cold,  solution  of  the  chloride  of  calcium,  thus  thawing  them  loose 
from  the  surrounding  ice.  The  tubes  were  entirely  uninjured,  and 
could  be  used  (^^in  in  another  similar  operation. 

472.  "The  material  in  the  above  plant  is  estimated  to  have  cost 
tl5,000,  and  94,800  more  for  mounting  and  installation.  The  daily 
expense  of  conducting  the  freezing  process  is  estimated  at  (11,  llie 
total  expense  for  putting  down  the  shaft  is  estimated  at  9138.66  per 
linear  foot."*  The  last  is  equivalent  to  about  92.25  per  cubic  foot. 
).  at,  2S,  tnuulatod  from  Li  Binlt  Viva  nt  Juw  U, 


ovGoQi^lc 


ABT.  ti.J  GOHFARIBON  07  HETHODS.  309 

473.  Kodlfloation  for  Foundationi  under  Tater.  For  sinking 
foondationB  under  water,  two  methods  of  applying  this  process  hare 
been  proposed.  One  of  these  consists  in  combining  the  pnenmatio 
and  freezing  processes.  A  pneumatic  caisson  is  to  be  snnk  a  short 
distance  into  the  river-bed,  and  then  the  congealing  tnbee  are 
applied,  and  the  entire  mass  between  the  caisson  and  the  rock  is 
frozen  solid.  When  the  freezing  is  completed,  the  caisson  will  be 
practically  sealed  against  the  entrance  of  water,  and  the  air-lock  can 
be  removed  and  the  masonry  built  up  as  in  the  open  air. 

The  other  method  consiBtB  in  sinking  an  open  caisson  to  the 
river-bed,  and  putting  the  freezing  tubes  down  through  the  water. 
When  the  congelation  is  completed,  the  water  can  be  pumped  out 
and  the  work  conducted  in  the  open  air. 

471.  AsvAKTAaBB  Clahced.  It  is  claimed  for  this  process  that 
it  is  expeditious  and  economical,  and  also  that  it  is  particularly 
valuable  in  that  it  makes  possible  an  accurate  estimate  of  the  total 
cost  before  the  work  is  commenced, — a  condition  of  affairs  unat- 
tainable by  any  other  known  method  in  equally  difficult  ground.  It 
has  an  advantage  over  the  pneumatic  process  in  that  it  is  not  limited 
by  depth.  It  can^  applied  horizontally  as  vifell  as  vertically,  and 
hence  is  specially  nseful  in  sub-aqueous  tunneling,  particularly  in 
soils  which,  with  compressed  air,  are  treacherous. 

475.  SIFFICULTIEB  AITTICIFATED.  So  far  it  has  been  used  only 
in  sinking  shafts  for  mines.  Two  difficulties  are  anticipated  in  ap- 
plying  it  to  sink  foundations  for  bridge  piers  in  river  beds  ;  viz., 
(1)  the  difficulty  in  sinking  the  pipes,  owing  to  striking  sunken  logs, 
bowlders,  etc.;  and  (3)  the  possibility  of  encountering  running 
water,  which  will  thaw  the  ice-wall.  These  difficulties  are  not  in- 
snrmonntable,  but  experience  only  can  demonstrate  how  serious 
they  are. 

476.  Cost.     See  g  473,  and  compare  with  table  on  page  310l 

Art.  6.    GouPARiaoN  of  Methods 

477.  The  fallowing  comparison  of  the  different  methods  is  from 
an  article  by  Jules  Qaudard  on  Foundations,  as  translated  by  L.  F. 
Vernon- Harcourt  for  the  proceedings  of  the  Institute  of  Civil  En- 
gineers (London).  Except  as  showing  approximate  relative  costs,  in 
Europe,  it  is  not  of  much  value,  owing  to  improvement  made  since 
the  article  was  written,  to  the  differences  between  European  and 


ovGoQi^lc 


310 


TOUVDATIOSS  UKDKB 


[chap.  xn. 


AmericBn  practice,  *Bd  to  differences  in  cort  of  nwteittk  in  the  two 

«onntrie& 

478.  "  1L  Cntizette  Desnoycn  has  framed  a  cbMification  of  the 
metkods  of  foondationa  most  soitable  for  different  depths,  and  also 
an  estimate  of  the  cost  of  each.  Theae  estiioBtes,  howerer,  most  be 
considered  merely  approximate,  as  nnforeseen  circumstances  pro- 
dace  conndeisble  Tariations  in  works  of  this  nature. 


"When  the  fonndations  consist  of  disconnected  pillars  or  piles, 
the  above  prices  most  be  applied  to  the  whole  cubic  content,  includ- 
ing the  interrals  between  the  parts ;  but  of  course  at  an  eqoal  cost 
■olid  piers  are  tbe  best. 

479.  "  For  pile-work  foundations  the  square  yard  of  base  is  prob- 
ably a  better  unit  than  the  cubic  yard.  Thus  the  foundationa  of 
the  Vernon  bridge,  with  piles  from  24  to  31  feet  long,  and  with 
cross-timbering,  concrete,  and  caisson,  cost  t70  per  square  yard  of 
base.  According  to  estimates  made  by  HIL  Picquenot,  if  the  fonn- 
dations had  been  pnt  in  by  means  of  oompreseed  sir,  the  cost  would 
have  been  (159.64  ;  with  a  caisson,  not  water-tight,  sunk  down, 
(66.37  ;  with  concrete  ponied  into  a  space  inclosed  with  sheeting, 
(62,33 ;  and  by  pnmping,  (83.56  per  square  yard  of  baae." 


ovGoQi^lc 


PART  IV, 

MASONRY  STRTJCTUREa 


CHAPTEB  Xia 

HASONRT   DAU8. 

480.  It  is  not  the  intention  here  to  disctisH  erery  featare  of 
masonry  dams ;  that  has  been  done  in  the  special  reports  and  arti- 
cles referred  to  in  g  520,  page  334.  The  fundamental  principles 
Till  be  considered,  particularly  vith  reference  to  their  applica- 
tion in  the  subsequent  stady  of  retaining  walls,  bridge  abutments, 
bridge  piers,  and  arches.  The  discnasioDs  of  this  chapter  are 
applicable  to  masonry  dams,  reservoir  walls,  or  to  any  wall  wbioh 
counteracts  the  pressure  of  water  mainly  by  its  weight. 

There  are  two  ways  in  which  a  masonry  dam  may  resist  the 
thrust  of  the  water ;  viz.,  (1)  by  the  inertia  of  its  masonry,  and 
(ti)  as  an  arch.  1.  The  horizontal  thrust  of  the  water  may  be  held 
in  equilibrium  by  the  resistance  of  the  masonry  to  sliding  forward 
or  to  overturning.  A  dam  which  acte  in  this  way  is  called  a  gravity 
dam,  Z.  The  thnui  of  the  water  may  be  resisted  t^  being  trans- 
mitted laterally  to  the  side-hilU  (abutments)  by  the  arch-like  action 
of  the  masonry.  A  dam  which  acts  in  this  way  is  called  an  arched 
dam. 

Only  two  dams  of  the  pure  arch  type  have  ever  been  built.  The 
almost  exclusive  use  of  the  gravity  type  is  due  to  the  uncertainty 
of  onr  knowledge  concerning  the  laws  governing  the  stability  of 
masonry  arches.  This  chapter  will  be  devoted  mainly  to  gravity 
dams,  those  of  the  arch  type  being  considered  only  incidentally. 
Arches  will  be  diaouised  fully  in  Chapter  XVUL 

ni 


ovGoQi^lc 


MA80NET  DAlfS.  [CHAP.  XIU. 


AST,  1.  Stability  of  Gaatitt  Daub. 

481.  FsnoiTLXB.  By  the  prmciplee  of  hydroetatics  we  know 
(1)  that  the  preesure  of  a  liquid  upon  any  aurtaco  is  eqoal  to  the 
weight  of  a  Tolume  of  the  liquid  whose  base  is  the  urea  of  the  im- 
mersed  surface  and  whose  height  is  the  vertical  distance  of  the  center 
of  gravity  of  that  surface  below  the  upper  surfftc©  of  the  water  ;  (2) 
that  this  pressure  is  always  perpendicular  to  the  pressed  surface  ; 
and  (3)  that,  for  rectangular  surfaces,  this  pressure  may  be  con- 
sidered as  &  aiugle  force  applied  at  a  distance  below  the  upper 
surface  of  the  liquid  equal  to  f  of  the  depth. 

482.  A  gravity  dam  may  fail  (I)  by  sliding  along  a  horizontal 
joint,  or  (3)  by  overturning  about  the  front  of  a  horizontal  joint, 
or  (3)  by  crushing  the  masonry,  particularly  at  the  front  of 
any  horizontal  joint.  However,  it  is  admitted  that  by  far  the 
greater  number  of  failures  of  dams  is  due  to  defects  in  the  founda- 
tion. The  method  of  securing  a  firm  fonndation  has  already  been 
discussed  in  Part  III ;  and,  hence,  this  subject  will  be  considered 
here  only  incidentally.  There  is  not  much  probability  that  a  dam 
will  fail  by  sliding  forward,  but  it  may  fail  by  overturning  or  by  the 
crnehing  of  the  masonry.  These  three  methods  of  failure  will  be 
considered  separately  and  in  the  above  order. 

483.  In  the  discussions  of  this  article  it  will  be  necessary  to 
consider  only  a  section  of  the  whII  included  between  two  vertical 
planes — a  unit  distance  apart — perpendicular  to  the  face  of  the 
wall,  and  then  so  arrange  this  section  that  it  will  resist  the  loads  and 
pressure  put  upon  it ;  that  is,  it  is  sufficient,  and  more  convenient, 
to  consider  the  dam  as  only  a  unit,  say  1  foot,  long. 

484.  HO][Sircu.TVBE.  The  following  nomenclature  will  be  used 
throughout  this  chapter  : 

ff  =  the  horizontal  pressure,  in  pounds,  of  the  water  against  a 
section  of  the  back  of  the  wall  1  foot  long  and  of  a  height 
equal  to  the  height  of  the  wall. 
TTa:  the  weight,  in  pounds,  of  a  section  of  the  wall  1  foot  long. 
w  =  the- weight,  in  pounds,  of  a  cubic  foot  of  the  masonry. 
A  =  the  height,  in  feet,  of  the  wall ;  t.  e.,  h  =  EF,  Pig.  66. ' 
/  =  the  length  of  the  base  of  the  cross  section ;  i.  e.,  I  ^  A  it- 
Fig.  68. 
t  =  the  vridth  (rf  the  wall  on  top ;  i.  e.,t=I)E,  Fig.  68. 


ovGoQi^lc 


AKT.  1.]  8TA.BIIITT  OF  QBATITT  DAKB.  SI'S 

b  =  the  batter  of  the  wall,  i,  e.,  the  inclinatioQ  of  the  sar&ce 
per  foot  of  rise — b'  being  nsed  for  the  batter  of  the  op- 
stream  face  and  b,  for  that  of  the  down-stream  face. 
K  =  AC=  the  diatance  from  the  dowD-stream  face  of  any  joint  to 
the  point  in  which  a  Teitical  through  the  center  of  gran^ 
of  the  wall  pierces  the  plane  of  the  base, 
i  =  the  distance  the  center  of  pressure  deviates  from  the  center 
of  the  base. 
62.K  =  the' weight,  in  pounds,  of  a  cubic  foot  of  water. 

48fi.  Stasilitt  aoaivbt  Busnre.  The  horizontal  pressure  of 
the  water  tends  to  slide  the  dam  forward,  and  is  resisted  by  the 
friction  due  to  the  weight  of  the  wall. 

486.  Sliding  Foree.  The  horizontal  pressure  of  the  water 
against  an  elementary  section  of  the  wall,  by  principle  (1)  of  §  481, 
is  equal  to  the  area  of  the  section  multiplied  by  Imlf  the  height  of 
the  wall,  and  that  product  by  the  weight  of  a  cubic  nnit  of  water;  or 


ir=kx  ixihxe 


=  31.25  h'. 


•     (1) 


Notice  that  H  is  the  same  whether  the  pressed  area  is  inclined  or 
vertical ;  that  is  to  say,  H  is  the  horizontal  component  of  the  total 
pressure  on  the  surface. 

187.  Betisting  Fonwi.     The  weight  of  an  elementary  section  of 
the  wall  is  equal  to  the  area  of  the  vertical  ^ 

cross  section  multiplied  by  the  weight  of  s 
cubic  nnit  of  the  masonry.  The  area  of 
tha  cross  section,  ABED,  Fig.  68,  equals 

SFxJ)£+iBFxFS+iDOxA0 

=  ht+ih'b'+ih'b,   ...    (2) 

Then  the  weight  of  the  elementary  sec- 
tion of  the  wall  is 

W=v,(ht  +  ib'b'  +  ik'b,)    .    (3) ^^-jj- 

The  vertical  pressure  of  the  water  on  »io.  en. 

the  inclined  face  increases  the  pressure  on  the  foundation,  and, 
cousequeutly,  adds  to  the  resistance  against  slidiDg,  The  vertical 
pressure  on  EB  is  equal  to  the  horizontal  projectioQ  of  that  area 
multiplied  by  the  distance  of  the  center  of  gravity  of  the  surface 
below  the  top  of  the  water  and  by  the  weight  of  a  oubic  unit  of 


ovGoQi^lc 


SU  ItlSOKKT  DA.HB.  [cHAP.  XIII. 

water,  or,  the  Tertical  presBnre  =  FB  X  1  X  i  A  X  62.5  =  A  i'  x 
\h  X  62.8  =  31.25  A"  A'. 

488.  If  the  eartlt  reete  against  the  heel  of  the  dam  (the  bot- 
tom of  the  inside  face),  it  will  iacrease  the  preaanre  on  the  fonn> 
dation,  dace  earth  weighs  more  than  water ;  on  the  other  hand,  the 
horizontal  pressnre  of  the  earth  will  be  a  little  greater  than  that  of 
an  eqnal  height  of  water.  Howerer,  since  the  net  resistaDce  with 
the  earth  upon  the  heel  of  the  wall  is  greater  than  with  an  equal 
depth  of  water,  it  will  be  asenmed  that  the  water  extends  to  the 
bottom  of  the  walL 

If  the  water  finds  ita  way  under  and  around  the  foundation  tA 
the  wall,  even  in  very  thin  sheets,  it  will  decrease  the  preaaure  of 
the  wall  on  the  foundation,  and,  consequently,  decrease  the 
stability  of  the  wall.  The  effective  weight  of  the  submerged  por- 
tion of  the  wall  will  be  decreased  62^  lbs.  per  ca.  ft  However,  the 
assumption  that  water  in  hydrostatic  oonditiou  finds  its  way  under 
or  into  a  daxn  is  hardly  admissible ;  hence  the  effect  of  baoyanoy 
will  not  be  considered.* 

489.  Co-effl«]ent  of  Triotion.  The  Talnes  of  the  co-efficient  of 
friction  most  frequently  required  in  masonry  computations  are  given 
in  the  table  on  p^e  315.  There  will  be  frequent  reference  to  this 
table  in  subsequent  chapters ;  and  therefore  it  is  made  more  full 
than  is  required  in  this  connection.  The  raluee  have  been  collected 
from  the  best  authorities,  and  are  believed  to  be  &ir  averages.  See 
also  the  table  on  page  276. 

490.  Condition  for  Equilibrium.  In  order  that  the  wall  may 
not  elide,  it  is  necessary  that  the  product  found  by  multiplying  the 
co-efficient  of  friction  by  the  sum  of  the  weight  of  the  wall  and  the 
vertical  pressure  (rf  the  water  shall  be  greater  tluui  the  horisontal 
pressure  of  the  water.  That  is  to  say,  in  order  that  the  dam  may 
not  slide  it  is  necessary  that  /i  (TF-f  31.25  A*d')  shall  be  greater 
than  if;  or,  in  mathematical  language, 

S  81.25  A' 

f*>  w  +  31.25  A'  4'  -^  w  (A  f  -H  t  A'  A'  -f- 1  A'  ft,)  -|-  31.26  A'  V ' 

■  SliiM  the  above  wh  written,  Jas.  B.  Francla  prewDtsd  a  paper  (Mar  IB,  18B9 
before  tbe  American  Socielr  ot  CItII  Enftlneen,  wblcb  Metas  to  ahow  that  wata 
premire  la  oommiuilaated,  almoet  nndlTnlnlahed,  through  a  larer  of  PortJand  osotnt 
mortar  (I  part  cement  and  3  parta  eand)  1  toot  tblok. 


ovGoQi^lc 


BTABIIITT  Of  OBATITT  DAHS. 


TABLE  W. 
Co-amctEHTB  or  Fsiction  tob  Dbt  HAaasRi. 


Soft  liamtone  on  soft  llmMtone,  both  well  dreased 

Brick-work  OD  brick-work,  with  illghtlr  damp  morter 

Hard  brick-workoD  hard  brick-work,  with  allgbtlj  damp  morUur. 

PoiDt-dresaed  gnulte  on  like  naaite. 

"         "  "        "  well-arened  graolle 

Common  brick  on  common  tjrick 

"  "      "  hard  llmealniie 

Hard  llmmtoae  on  bard  llmesloDe,  with  moist  mortar 

BeloQ  bkxika  (preMed)  on  Ifke  beton  blocki 

Fiiiti-cut  grnnite  on  pressed         "  ■'      

Well  (Irewed  ffDinlte  on  well  drasned  gninite 

Polished  limestone  on  polished  limestone  

Well-dresxed  granite  on  like  prnntte.  with  rresh  mortat 

Common  brick  on  common  bnck,  with  wet  mortar 

Polished  marble  on  common  brick 

PolDt-drened  granite  on  Krarel 

'■  ■•  "        "  dry  clay. 

"        "sand 

'■         "  "        "  moist  claj. 

Wnwght  IroD  on  well-dreaaed  Umentone 

"         ••     •'  haid,  well  dressed  limeatoDe,  wet 

Oak,  flatwise,  on  limestone 

"     endwise,  on  limestone 


0.75 
0.7S 
0.70  . 
0.70 
0.60 

o.as 

0.6S 
0.«S 
O.flS 
0.60 

o.eo 
o.«o 
o.so 
o.so 

0.4S 


0.S5 

o.os 

0.40 


which  rednced  becomes 


o*.o  " * .\ 

'' -*  v,{2t  +  h{b'  +  A,))  +  62.5  A b''    •     '    ■     W 

The  weight  of  a  cubic  foot  of  masonry,  w,  Tariee  between  135  lbs. 
for  concrete  or  poor  brick-work,  and  160  Ibe,  for  granite  ashlar. 
Dams  are  asnally  boilt  of  mbble,  whrch  weighs  about  150  lbs,  per 
cu.  ft.  To  simplify  the  formula,  we  will  assume  that  the  masonry 
weighs  125  lbs,  per  oo.  ft.;  i.  e,,  that  the  weight  of  a  cubic  foot  of 
masonry  is  twice  that  of  water.  This  assumption  is  on  the  safe  side, 
whatever  the  kind  of  masonry.*     Making  this  snbstitntioD  in  (4) 


>  Imiiiaiiiiil  satetr  genenllf  reqniree  Increaaed  cost  of  cosBtrncitlon,  and  benoe 
It  Is  not  permlaslblti  to  nse  approximate  data  BlmpI;  beoanae  the  error  la  on  the  side 
toward  Mfet}.  It  will  be  shown  that  there  is  no  probabllltr  of  any  dam'i  falling  by 
dldlnc  and  that  the  Mae,  and  ooDaeqnenU;  the  Toloine  and  ooat,  are  detennlnod  tij- 


ovGoQi^lc 


H^BONBT   DAXB.  [CHAP.  XIII, 


Other  thiDga  being  the  same,  the  tbinner  the  vail  at  the  top, 
the  euier  it  will  slide.  If  the  section  of  the  wall  is  a  triangle,  t. «., 
if  ^  =  0,  then  b;  equation  (5)  ve  see  that  the  dam  ia  safe  against 
sliding  Then 

"^"((vV^) '°' 

An  examination  of  the  table  on  page  315  shows  that  there  is  no 
probability  that  the  co-efficient  of  friction  will  be  less  than  0.5 ;  and 
inserting  this  TcJne  of  m  in  (6)  shows  that  sliding  can  not  take 
place  if  {J  b'  +  ft,)  >  or  =  1.  To  prevent  oTertnming,  (ft'  +  S,) 
is  nsuall;  =  or  >  1  (see  Fig.  72,  page  338) ;  and,  besides,  a  con- 
siderable thickness  at  the  top  (see  §  509)  is  needed  to  resist  the 
shook  of  waves,  etc.  Hence  there  ia  no  probability  of  the  dam's 
failing  by  sliding  forward.  Farther,  the  co-efficient  of  friction  in 
the  table  on  page  315  takes  no  acoonnt  of  the  cohesion  of  the  mor- 
tar, which  may  have  a  possible  maximnm  value,  for  best  Portland 
mortar,  of  36  tons  per  sq.  ft.  (500  Iba.  per  sq.  in.);  and  this  gives 
still  greater  security.  Aj^in,  the  earth  on,  and  also  in  front  of,  the 
toe  of  the  wall  adds  greatly  to  the  resistance  against  sliding.  Fi- 
nally, it  is  customary  to  buUd  masonry  dams  of  uncoui-sed  rubble 
(gg  213-17),  to  prevent  the  bed- joints  from  becoming  channels  for 
the  leakage  of  water;  and  hence  the  stones  are  thoronghly  inter* 
locked, — which  adds  still  further  resistance.  Therefore  it  is  certain 
that  there  is  no  danger  of  any  masonry  dam's  failing  by  sliding  for- 
ward under  the  pressure  of  still  water. 

491.  It  has  occasionally  happened  that  dams  and  retaining  walls 
have  been  moved  bodily  forward,  sliding  on  their  base;  but  such  an 
occurrence  is  certainly  unusual,  and  is  probably  the  result  of  the 
wall's  having  been  founded  on  an  unstable  material,  perhaps  on  an 
inclined  bed  of  moist  and  nacertain  soil.  In  moet  that  was  said  is 
Part  UI  oosoeming  tonndatioQS,  it  was  amnmed  that  the  foand» 


ovGoQi^lc 


ART.  1.]    ,  BTAfllLITT   OP   GRAVITY   DAMS.  317 

tion  iras  required  to  support  only  &  vertical  load.  When  the  etraci- 
ore  is  enbjected  also  to  a  lateral  pressure,  as  in  dams,  additional 
means  of  security  are  demanded  to  prevent  lateral  yielding. 

When  the  foundation  reeta  upon  piles  a  simple  expedient  is  to 
drive  pUee  in  front  of  and  against  the  edge  of  the  bed  of  the  founda- 
tion; but  obvioUBly  this  is  not  of  much  value  except  when  the  piles 
reach  a  firmer  soil  than  that  on  which  the  foundation  dire^ly  reErts. 
If  the  piles  reach  a  firm  subsoil]  it  will  help  matters  a  little  if  the 
upper  and  more  yielding  soil  is  removed  from  around  the  top  of  the 
pile,  and  the  place  filled  with  broken  atone,  etc  Or  a  wall  of  piles 
may  be  driven  around  the  foundation  at  some  distance  from  it,  and 
timber  braces  or  horizontal  bnttreBses  of  masonry  may  be  placed  at 
intervals  from  the  foundation  to  the  piles.  A  low  masonry  wall  is 
sometimes  used,  instead  of  the  wall  of  piles,  and  connected  with  the 
foot  of  the  main  wall  by  horizonlal  buttresses,  whose  feet,  on  the 
counter-wall,  are  connected  by  arches  in  a  horizontal  plane  in  order 
to  distribute  the  pressure  more  evenly. 

In  founding  a  dam  upon  bed-rock,  the  resistance  to  sliding  on 
the  foundation  may  be  greatly  increased  by  leaving  the  bed  rough  ; 
and,  in  case  the  rock  quarries  out  with  smooth  surfaces,  one  or  more 
longitudinal  trenchesmaybeeicavated  in  the  bed  of  the  foundation, 
and  afterwards  be  filled  with  the  masonry. 

In  the  proposed  Quaker  Bridge  dam  the  maximum  horizontal 
thrust  of  the  water  is  equal  to  0.597  of  the  weight  of  the  masonry. 

492.  Stasiutt  AOAnrsT  OvEBTiruiniQ.  The  horizontal  pres 
sure  of  the  water  tends  to  tip  the  wall  forward  about  the  front  o. 
any  joint,  and  is  i-eaigted  by  the  moment  of  the  weight  of  the  wall. 
For  the  present,  it  will  be  assumed  that  the  wall  resta  upon  a  rigid 
base,  and  therefore  can  fail  only  by  overturning  as  a  whole. 

The  conditions  necessary  for  stability  against  overtuming  can  be 
completely  determined  either  by  considering  the  moments  of  the 
several  forces,  or  by  the  principle  of  resolution  of  forces.  In  the 
following  discussion  the  conditions  will  be  first  determined  by  mo- 
ments, and  afterward  by  resolution  of  forces. 

463.  A.  Br  Vokemte.  The  Orerturning  Xomsnt  The  pressure 
of  the  water  is  perpendicular  to  the  pressed  snr&ce.  If  the  water 
presses  against  an  inclined  face,  then  the  pressure  makes  the  same 
angle  with  the  horizontal  that  the  surface  does  with  the  verticaL 
Since  there  is  a  little  ditKcnlty  in  dnding  the  aim  of  this  force,  it  is 


ovGoQi^lc 


S18     -  IU80NBT  DAHS.  [cHAP.  ZUL 

more  convenient  to  deal  with  the  horizontal  and  vertical  componenti 
of  the  presanre. 

The  horizontal  preaanre  of  the  water  can  be  foand  b;  equation 
(1),  page  313.  The  arm  of  this  force  is  eqnal  to  '^  A  (principle  3, 
g  481).     Hence  the  moment  tending  to  overturn  the  wall  is  equal  to 

iHk  =  i  31.25  V  =  10.43  A',     .     .     .     .     (7) 

vhicb,  for  convenience,  represent  by  M, . 

494,  The  Heiisting  Xomenti.  The  forces  resisting  the  over- 
taming  are  (1)  the  weight  of  the  wall  and  (2)  the  vertical  pressure 
of  the  water  on  the  inclined  face. 

The  weight  of  the  wall  can  be  computed  by  equation  (3),  page 
313,  It  acts  vertically  through  the  center  of  gravity  of  the  cross 
section. 

The  center  of  gravity  can  be  fonnd  algebraically  or  graphically. 
There  are  several  ways  in  each  case,  but 
the  following  graphical  solution  is  the  sim- 
plest. In  Fig.  69,  draw  the  diagonals  D  B 
and  A  E,  and  lay  off  A  J  =  E I;  then 
draw  D  J,  and  mark  the  middle  of  it  Q. 
The  center  of  gravity,  0,  of  the  area 
A  B  E  D  \^a^&  distance  from  Q  towards 
B  equal  \a\Q  B.  This  method  ia  appli- 
cable to  any  four-sided  figure. 

The  position  of  the  center  of  gravity  can 
Q     F  also  be  fonnd  algebraically  by  the  principle 

Fio.  a*.  that  the  moment  of  the  entire  mass  about 

Any  point,  as  A,  is  eqnal  to  the  moment  of  the  part  ADO,  plus 
^he  moment  of  the  portion  D  E  F  0,  pins  the  moment  of  the  part 
E  B  F,— all  about  the  same  point,  A.  Stating  this  principle  alge- 
braically gives 

t  A  6,  (4  A*  S.)  +  A  /  (t  (  -I-  4  J,)  + 1  A'  J*  (J  A  6'  +  f  +  ft  5,) 

=  aA*&'  +  Af  +  JA'5.)i.     .         ...     (8) 

in  which  x  =  the  distance  A  C.     Solving  (8)  givee 

'=  14(S'  +  »,)  +  i  •       <"' 


jvGooi^le 


ABT.  1.]  BTABILIIT  OP  GBATITT  DAMB.  319 

The  arm  of  the  weight  a  A  C  {=  x),  and  therefore  the  mo- 
ment is 

WxAC=u[ht  +  ih'{i'  +  b,)}x..    .    .    (10) 

which,  for  conTenieace,  represent  by  JT, . 

496.  The  vertical  pressure  of  the  water  on  the  inclined  face, 
JS  B,  has  been  computed  in  g  487,  which  eee.  This  force  acts  ver- 
tically between  F and  B,  at  a  distance  from  B  equal  \a  \  F  B;  the 
armof  thi8forcoi8-a£-4^5  =  /  — iAJ'=  hb,-\- 1 -\-\hb'. 
Therefore,  the  moment  of  the  vertical  pressare  on  the  inclined 
face  is 

81J35  A*  S' (i  A, -I- *  +  I A  J'),     ....     (11) 

which,  for  convenience,  represent  by  M, .    Of  conree,  if  the  presaed 
face  is  vertical,  M^  will  be  eqoal  to  zero. 

496.  The  moment  to  resist  overturning  is  equal  to  the  sum  of 
(10)  and  (11)  above,  or  Jl^,  +  JT, . 

The  moment  represented  by  the  sum  of  Jtf,  and  M^  can  be  deter- 
mined directly  by  considering  the  pressure  of  the  water  as  acting 
perpendicular  ia  B  Ba,t\  E  B  from  B;  the  arm  of  this  force  is  a 
line  from  A  perpendicular  to  the  line  of  action  of  the  pressure.  If 
the  cross  section  were  known,  it  would  be  an  easy  matter  to  measure 
this  arm  on  a  diagram;  but,  in  designing  a  dam,  it  la  necessary  to 
know  the  conditions  requisite  for  stability  before  the  cross  section 
can  be  determined,  and  hence  the  above  method  of  solution  is  the 
better. 

497.  Condition  for  Equilibrium.  In  order  that  the  wall  may 
not  turn  about  the  front  edge  of  a  joint,  it  is  neceasary  that  the 
overtaming  moment,  JV, ,  as  found  by  equation  (7),  shall  be  less 
than  the  snm  of  the  resisting  moments,  M,  and  M^ ,  as  found  by  ■ 
equations  (10)  and  (II);  or,  in  other  words,  the  factor  against  over- 
^      .  M.+  M, 

turnmg  =        jy (13) 

498.  Factor  of  Saf^  againft  Orertuming.  In  computing  the 
stability  against  overturning,  the  vertical  pressure  of  the  water 
against  the  inside  face  is  frequently  neglected;  t.e.,  itls  assumed 
that  M,,  u  above,  is  zero.  This  assumption  is  always  on  the  safe 
side.  Computed  in  this  way,  the  factor  of  safety  against  overturn- 
ing for  the  proposed  Quaker  Bridge  dam,  which  when  completed 


ovGoQi^lc 


330  HASONBY   DAKS  [OHAP.  Zm. 

will  be  considerably  the  largest  dam  in  the  world,  Tariee  between 
3,07  and  3.68.  Krantz,*  who  included  the  vertical  component  in 
his  compatatione,  considera  a  factor  of  2.6  to  5.65  aa  safe,  the  larger 
value  being  for  the  largest  dam,  owing  to  the  more  seriona  conse- 
qnencea  of  failure.  The  greater  the  factor  of  safety  provided  for, 
the  greater  is  the  first  cost;  and  the  less  the  &ctor  of  safety,  the 
greater  the  expense  of  maintenance,  including  a  possible  reconstruc- 
tion of  the  structure. 

489.  A  Bt  ItSaOI.VTlOH  Of  TOBOBS.  In  Fig.  70,  f  is  the  center 
of  preseore  of  the  water  on  the  back  of 
the  wall.  K  B  =^\  E  B.  o  is  the  center 
of  gravity  of  the  wall, — found  as  already 
described.  Through  K  draw  a  line,  K  a, 
perpendicular  ta  E  S;  through  o  draw  a 
vertical  line  o  a.  To  any  convenient 
scale  lay  off  ab  eqnal  to  the  total  pressure 
of  the  water  against  E  B,  and  to  the 
same  scale  make  af  equal  to  the  weight 
of  an  elementary  section  of  the  wall. 
Complete  the  parallelogram  a  b  ef.  The 
'■"■  ™  diagonal  ae   intersects  the  base  of  the 

wall  at  N. 

500.  On  the  assumption  that  the  masonry  and  foundation 
are  absolutely  incompressible  (the  compressibility  will  be  considered 
presently),  it  is  clear  that  the  wall  will  not  overturn  as  long  as  the 
resultant  ae  intersects  the  base  AB  between  A  and  B.     The  factor 

against  overturning  is  -jj-pj,  which  b  the  equivalent  of  equation  (13), 

The  wall  can  not  slide  horizontally  on  the  base,  when  the  angle 
NaC  is  lees  than  the  angle  of  repose,  t.  e.,  when  tan  NaOit  less 
than  the  co-efficient  of  friction.  The  factor  against  sliding  is  equal 
to  the  co-efBcieut  of  friction  divided  by  Ian  XaC,  which  is  only 
another  way  of  stating  the  conclusion  drawn  from  equation  (4), 
page  315. 

501.  Btabuitt  AOAnrsT  CBirBHnrei.  The  preceding  diecnssion 
of  the  stability  against  overturning  is  on  the  assumption  that  the 
masonry  does  not  crush.     This  method  of  failure  will  now  be  oon- 


"  Stodr  of  Bnorrolr  Walla,"  Uahao'i  tmulMloii,  p.  68. 


ovGoQi^lc 


ABT.  1.J  I      fflABIUTT  OF  QBATITT  DAMS.  331 

Bidered.  WheD  the  reserroir  is  empty,  the  preeBiire  tending  to 
produce  cruBhing  is  the  weight  of  the  dam  alone,  which  pressure  is 
dietribnted  uniformly  over  the  horizontal  area  of  the  wkII.  When 
the  reservoir  is  full,  the  thruat  of  the  water  modifies  the  distribntioa 
of  the  pressare,  increasing  the  pressure  at  the  front  of  the  wall  and 
decreasing  it  at  the  back.  We  will  now  determine  the  law  of  the 
Tariation  of  the  pressure. 

Let  A  B,  Fig.  7L,  represent  the  base  of  a  vertical  section  of  the 
dam ;   or  A  S  may  represent  the  rect- 
aognlar  base  (whose  width  is  a  unit)  of 
any  two  bodies  which  are  pressed  against     <t^^-ir>H?j-j->;-yi 
each  other  by  any  forces  whatever.  ^*       ■    '       ^^ 

M  —  the  resulting  moment  (about  A'^  of 

alt  the  external  forces.     In  the 

caae  of  a  dam,  M=  M,  —  M„— 

equations  (7)  and  (11).  nan. 

W  =  the  total  normal  pressure  on  A  B. 

In  the  case  of  a  dam,  W  =  the  weight  of  the  masomy. 
P  =  the  maximum  pressure,  per  unit  of  area,  at  A. 
p  =  the  change  in  unit  pressure,  per  anlt  of  distance,  from  A 

towards  B. 
X  =  any  distance  from  A  towards  B. 
P  ~p  X  =  the  pressure  per  unit  at  a  distance  x  from  A. 
Y  ~ti  general  expression  for  a  vertical  force. 

The  remainder  of  the  nomenclature  is  as  in  g  484,  page  812. 
Taking  moments  about  A  gives 

M-  Wx  +  ^(P-px)dx.x  =  (ii.     .     .     (13) 

M-Wx  +  iPt'-ipr  =  0. (14) 

For  eqnilibrinm,  the  sum  of  the  forces  normal  io  A  B  most  also 
be  equal  to  aero ;  or 

sr  =  -w+(*{P-px)dx=so,  .  .  .   (18) 

from  which 

pr^iPl-iW. (16) 


ovGoQi^lc 


iZi  VASONBT   DAXB.  [CQAP.  XnL 

602.  IfwImiiBi  FxMsnrt.    Combining  (16)  iritli  (U)  and  i« 
daoing, 

y=*-f  _l^+.5^. (1,) 

[f  the  stability  agaioBt  overtaming  be  determined  algebmicall;,  t,  e., 
by  equation  (12),  then  J/'and  x  are  known,  and  P  can  be  compnted 
by  eqnatioD  (17). 

If  the  wall  is  Bymmetrical  x  =  il,  and  (17)  becomes 


^  =  -T+-r (") 

Equation  (18)  is  the  same  as  equation  (1),  page  209,  except  that 
the  latter  is  applicable  to  any  form  of  horizontal  section,  vhile  the 
former  is  applicable  to  only  a  reotangolar  cross  section. 

In  equation  (16),  notice  that  -j  is  the  noiform  presenre  onAB 
due  to  the  .weight  of  the  wall ;  also  that  —jj-  is  the  increase  of  pres- 
sure at  A  due  to  the  tendency  to  overturn,  and  that  consequently 
the  uniform  preBSure  at  £  Is  decreased  a  like  amount. 

503.  The  maximum  pressure  may  be  found  also  in  another  way. 
Assume  that  N,  Fig.  71,  is  the  center  of  pressore.  Let  p,  (=  B  L) 
represent  the  pressure  at  B,  and  p,(=  J  £')  that  at  A  ;  and  any 
intermediate  ordinate  of  the  trapezoid  .4  ^£f  will  represent  the 
pressure  at  the  corresponding  point.  Then,  since  the  forces  acting 
on  ^  .5  must  be  in  equilibrium  for  translation,  the  area  of  the 
trapezoid  will  represent  the  entire  pressure  on  the  base  A  B.  Stated 
algebraically,  this  is 

f^l=W. (19) 

Also,  since  the  forces  acting  qti  AB  must  be  in  equilibrium  for 
rotation,  the  moment  of  the  pressure  to  the  right  of  N  must  be 
equal  to  that  to  the  left ;  that  is  to  say,  the  center  of  gravity  of -the 
trapezoid  ABLK must  lie  in  the  line  NJ.  By  the  principles  of 
analytioal  meohauioi,  the  ordinate  AN  \a  the  center  of  gravi^ 
ABLK'ta 


jvGooi^le 


ABT.  1.]  BTABIUTT  OF  QBATUT  DAMB,  SS8 

SolTlng  (19)  and  (20)  gives 

P»  =  —i f-- (21) 

If  the  wall  ia  a  right-angled  triangle  with  the  right  angle  at  A, 
x  =  il,  which,  Babatittited  in  the  above  expression,  shows  that  the 

preesare  at  A  is  —t-,  »nd  al")  that  the  preasare  a.t  B  is  zero, — all 

of  which  is  as  it  should  be.  Equation  (21)  is  a  perfectly  general 
expression  for  thepressure  betmten  any  two  plane  turfacet  pressed 
together  by  norvial  forces.  Notice  that  equation  (31)  ia  identical 
with  the  first  two  terms  of  the  right-hand  side  of  equation  (17). 

The  form  of  (31)  can  be  changed  by  Bnbetitnting  for  x  its  valne 
il-d;  then 

A  =  ^+^. m 

Equation  (S2)  gives  the  pressure  at  A  due  to  the  weight  of  the 
wall ;  bnt  it  will  also  give  the  maximum  pressure  on  the  base  due 
to  both  tho  vertical  and  the  horizontal  forces,  provided  d  be  taken 
as  the  distance  from  the  middle  of  the  base  to  the  poiut  in  which 
the  resultant  of  all  the  forces  cuts  the  base.  Therefore  we  may 
write 

p=-5^+^. m 

&04.  Equation  (33)  is  the  equivalent  of  equation  (17),  page  333. 
It  is  well  to  notice  that  equation  (33)  is  limited  to  rectangular  kori- 
zontttl  cross-sections,  since  it  was  assumed  that  the  pressure  on  the 
section  varies  as  the  distance  back  from  the  toe.  If  the  stability 
against  overturning  ia  determined  algebraically,  as  by  equation  (12), 
then  eqnation  (17)  is  the  more  convenient ;  but  if  the  stability  is 
determined  graphically,  as  in  Fig.  70,  then  equation   (33)  is  the 

simpler.    Notice  that  it  d  =  ^l,  P  =  —j—,  which  is  in  accordance 

with  what  is  known  in  the  theory  of  arches  as  the  principle  of  the 
middle  third  ;  that  is,  as  long  as  the  center  of  pressure  lies  within 
the  middle  third  of  the  joint,  the  maximum  pressure  is  not  more 
than  twice  the  mean,  and  there  is  no  tension  in  any  part  of  the 
joint. 


ovGoQi^lc 


JUSONET  DAMS.  [CHAP.  SIII. 


ity  of  the  load.  It  ie  immaterial  whether  the  deviation  d  is  cansed 
by  the  form  of  the  wall  or  by  forces  tending  to  prodnce  overtnm- 
ing. 

505.  Tension  on  the  Xaaonry.  By  an  analyeia  similar  to  that 
above,  it  can  be  shown  that  the  decrease  in  pressure  at  B,  dne  to 
the  overturning  moment,  is  equal  to  the  increase  at  ^.  ltd  ^  \  I, 
then  by  equation  (23)  the  increase  at  A  and  decrease  at  B  is  W, 
that  is  to  say,  the  pressure  at  ^  is  2  ^  and  that  at  B  is  zero. 
Thereforej  if  the  center  of  pressure  departs  more  than  4 1  from  the 
center  of  the  base,  there  will  be  a  minus  pressure,  i.  e.  tension,  at 
B.  Under  this  condition,  the  triangle  A  YK',  in  Fig.  71,  page 
321,  represents  the  total  presetire,  and  the  triangle  £  TX' the  total 
tension  on  the  masonry, — A  IC  being  the  maximum  pressure  at  A, 
and  BL'  the  maximum  tension  at  B. 

If  a  good  quality  of  cement  mortar  is  used,  it  is  not  unreason' 
able  to  count  upon  a  little  resistance  from  tension.  As  a  general 
rule,  it  is  more  economical  to  increase  the  quantity  of  stone  than  the 
quality  of  the  mortar ;  but  in  dams  it  is  necessary  to  nse  a  good 
mortar  to  prevent  (I)  leakage,  (2)  disintegration  on  the  water  side, 
and  (3)  crushing.  If  the  resistance  due  to  tendon  is  not  included 
in  the  computation,  it  is  an  increment  to  the  computed  margin  of 
safety. 

506.  If  the  masonry  he  considered  as  incapable  of  resisting  by 
tension,  then  when  d  in  equation  (23)  exceeds  \l  the  total  pres- 
sure will  be  borne  on  A  Y,  Fig.  71.  In  this  case  A  W  (the  distance 
from  A  to  the  point  where  the  resultant  pierces  the  base)  will  be 
less  than  \l.  It  A K"  represents  the  maximum  pressure  F,  then 
the  area  of  the  triangle  A  YK"  will  represent  the  total  weight  W. 
The  area  at  A  YK"  =  \AK"xAY=\PyZAN',  Hence 
\Px^AN'  =  W,OT 

P-AJL 2ff_ 

^~3^JV'-3(ii-d) ^""^ 

To  illastrate  the  difierence  between  equations  (23)  and  (24), 


ovGoQi^lc 


ABT.  1.]  eXABILITT  OF  ORA.TITT  DAHS.  oSS 

assume  that  the  distacce  from  the  resultant  to  the  center  of  the  ban 
is  one  quarter  of  the  length  of  the  base,  i.  e.,  assume  that  d  =  \l. 
Then,  by  equation  (23),  the  maximum  pressure  at  A  is 

P  =  ^+2^  =  2i^, M 

and  by  equation  (24)  it  is 

^  =  3Tfr?iO  =  ^T- M 

That  is  to  say,  it  the  masonry  is  capable  of  resisting  tension,  equa- 
tion (25)  shows  that  the  maximam  pressure  isS^  times  the  pressnrg 
due  to  the  weight  alone-;  and  if  the  masonry  is  incapable  of  resist- 
ing tension,  equation  (26)  shows  that  the  maximum  pressure  is  3j 
times  the  pressure  due  to  the  weight  alone. 

Notice  that  equation  (24)  is  not  applicable  when  d  is  lesa  than 
^l;  in  that  case,  eqoation  (23)  must  be  used. 

607.  Limiting  Pressure,  As  a  preliminary  to  the  actual  design- 
ing of  the  section,  it  is  necessary  to  fix  upon  the  maximum  pressure 
per  square  foot  to  which  it  is  proposed  to  subject  the  masonry.  Of 
course,  the  allowable  pressure  depends  upon  the  quality  of  the 
masonry,  and  also  upon  the  conditioDs  assumed  in  making  the  com- 
putations. It  appears  to  be  the  custom,  in  practical  computations, 
to  neglect  the  vertical  pressure  on  the  inside  face  of  the  dam,  i.  e,, 
to  assume  that  M, ,  equation  (II),  page  319,  is  zero ;  this  assumption 
ie  always  on  the  safe  side,  and  makes  the  maximum  pressare  on  the 
outside  toe  appear  greater  than  it  really  is.  Computed  fn  this  way, 
the  maximum  pressure  on  rubble  masonry  in  cement  mortar  in 
some  of  the  great  dams  of  the  world  is  from  11  to  14  tons  per  sq. 
ft.  The  proposed  Qnaker  Bridge  dam  is  designed  for  a  maximum 
pressure  of  16.6  tons  per  sq.  ft  on  massiTO  rubble  in  Portland 
cement  mortar. 

For  data  on  the  strength  of  stone  and  brick  masoniy,  see  gg 
221-23  and  §§  246-48,  respectively. 

608.  The  actual  pressure  at  the  toe  will  probably  be  less  than 
that  computed  as  above.  It  was  assumed  that  the  weight  of  the 
wall  was  uniformly  distributed  over  the  base ;  but  if  the  batter  ia 
considerable,  it  is  probable  that  the  pressure  due  to  the  weight  of 
the  wall  will  not  vary  uniformly  from  one  side  of  the  base  to  the 


ovGoQi^lc 


826  VASONST  DAHS.  [cHAP.  XIIX. 

other,  bnt  will  be  greater  on  the  central  portions.  The  actual 
mazitnnm  will,  therefore,  probably  occnr  at  eome  distance  back 
from  the  toe.  Neither  the  actoal  maximom  nor  the  point  at  which 
it  oconra  can  be  determined. 

Frofeaeor  Rankine  claims  that  the  limiting  preasnre  tor  the  out- 
side toe  shonld  be  leas  than  for  the  inside  toe.  Notice  that  the 
preceding  method  determines  the  maximum  vertical  presents 
When  the  maximum  pressure  on  the  inside  toe  occurs,  the  only 
force  acting  is  the  vertical  pressure ;  bnt  when  the  maximum  on 
the  outside  occurs,  the  thrust  of  the  water  also  is  acting,  and  there- 
lore  the  actual  pressure  ie  the  resultant  of  the  two.  With  the  pres- 
ent state  of  our  knowledge,  we  can  not  determine  the  effect  of  a 
horizontal  component  upon  the  vertical  resistance  of  a  block  of  stone, 
bnt  it  must  weaken  it  somewhat 

Abt.  %.  Odtlines  or  the  Design. 

SOS.  Width  oh  Top.  As  far  as  the  forces  already  considered 
are  concerned,  the  widtlj  of  the  wall  at  the  top  might  be  nothing, 
since  at  this  point  there  is  neither  a  pressure  of  water  nor  any 
weight  of  DiaBOnry.  But  in  practice  we  mast  consider  the  shock  of 
waves  and  ice,  which  in  certain  cases  may  acquire  great  force  and 
prove  very  destructive  to  the  upper  portion  of  the  dam.  This  force 
can  not  be  computed,  and  hence  the  width  on  top  mnst  be  assumed. 
This  width  depends  to  a  certain  extent  upon  the  height  and  length 
of  the  dam.  The  top  of  large  dauia  may  be  used  as  a  roadway. 
Krantz  *  says  that  it  is  "  scarcely  possible  to  reduce  the  top  width 
below  3  metres  (6.5  ft.)  for  small  pouds,  nor  necessary  to  make  it 
more  than  6  metres  (16.4  ft.)  for  the  largest." 

Fig.  73,  page  .328,  gives  the  width  on  top  of  Krantz's  profile  type, 
and  also  of  the.  profile  recommended  by  the  engineers  of  the 
Aqueduct  Commission  for  the  proposed  Quaker  Bridge  dam. 

510.  The  FBOTILE.  In  designing  the  vertical  cross  section  of  a 
gravity  dam  to  resist  still  water,  it  is  necessary  to  fulfill  three  con- 
ditions: (1)  To  prevent  sliding  forward,  equation  (4),  page  315, 
must  be  satisfied;  (3)  to  resist  overturning,  equation  (li),  page  H19, 
must  he  satisfied ;  and  (3)  to  resist  crushing,  equation  (23),  page 
323,  or  (24),  page  334,  must  be  satisfied.     As  these  equations  really 

•  "  Stndf  of  RewTToIr  WkIIb,"  Hahu'B  tnnalaUoii,  p.  36. 


ovGoQi^lc 


ABT.  %.]  0TTTLINE6  OF  THE  DESIQK.  837 

lUTolTe  only  three  Tariablee,  viz.:  hi  in  and  b', — the  height  of  the 
dam  and  the  batter  ot  the  two  faces, — they  can  be  satisfied  exactly. 
It  has  been  shovn  that  there  is  no  danger  ot  the  dam'e  eliding  for- 
ward even  it  the  width  on  top  is  zero ;  and  hence  there  are  practi- 
■  cally  but  two  conditions  to  be  fulfilled  and  two  variables  to  be 
;  determined.  To  prevent  overtnrning  when  the  reservoir  ia  fnll, 
equation  (12)  mast  be  satisfied  ;  and  to  prevent  crashing,  equation 
(23)— or  (34)— must  be  satisfied  for  the  points  (Figs.  69,  70,  etc.) 
^!ien  the  reaervoir  is  full,  and  for  B  when  the  reservoir  is  empty. 

Although  it  is  possible  to  satisfy  these  conditions  exactly,  the 
theoretical  profile  can  be  obtained  only  by  successive  approxima- 
tions. This  is  done  by  dividing  the  profile  into  elementary  hori- 
zontal layers,  beginning  at  the  top,  and  determining  the  dimension 
of  the  base  of  each  layer  separately.  The  theoretical  width  at  the 
top  being  zero  and  the  actual  width  being  considerable,  a  portion  of 
the  section  at  the  top  of  the  dam  will  be  rectangular.  A  layer  being 
given,  and  the  profile  of  the  portion  above  it  being  known,  certain 
dimensions  are  assumed  for  the  lower  base  of  the  layer ;  and  the 
stability  against  overturning  is  then  determined  by  applying  equa- 
tion (13),  or  by  the  method  of  Fig.  70  (page  330).  ^Tfae  maximum 
pressure  at  A  is  then  found  by  applying  equation  (17)  or  (;'3),  after 
which  the  maximum  pressure  at  B  when  the  reservoir  is  empty 
must  be  deteimined  by  applying  equation  (23).  If  the  first  dimen- 
sions do  .not  give  results  in  accordance  with  the  limiting  conditions, 
others  must  be  assumed  and  the  compntations  repeated.  A  third 
approximation  will  probably  rarely  be  needed. 

It  is  not  necessary  to  attempt  to  satisfy  these  equations  precisely, 
since  there  are  a  number  of  unknown  and  unknowable  factors;  as  the 
weight  of  the  stone,  the  quality  of  the  mortar,  the  character 
of  the  foundation,  the  quality  of  the  masonry,  the  hydrostatic 
pressure  under  the  mass,  the  amount  of  elastic  yielding,  the 
force  of  the  waves  and  of  the  ice,  etc,  which  have  more  to  do 
with  the  ultimate  stability  of  a  dam  than  the  mathematically  exact 
profile.  It  is  therefore  sufficient  to  assume  a  trial  profile,  being 
guided  in  this  by  the  matters  referred  to  in  g  511  and  §  513,  and 
test  it  at  a  few  points  by  applying  the  preceding  equations  ;  a  few 
modifications  to  more  nearly  satisfy  the  mathematical  conditions  cr 
to  simplify  the  profile  is  aa  far  as  it  ia  wise  to  carry  the  theoretical 
determination  of  the  profile. 


ovGoo^^lc 


3S8  UASONBX   DAHB.  [CHAP.  XIII. 

511.  Erantz'a  Stndy  of  Eeeervoir  Walls,  translated  from  the 
French  by  Gapt.  F.  A.  Mahan,  U.  S.  A.,  gives  the  theoretical  pro- 
files for  dams  from  16.40  ft  (5  metrea)  to  164  ft  (50  metres)  high. 
The  faces  are  arcs  of  circles.  The  mathematical  work  of  determin- 
ing the  profiles  is  not  given  ;  but  it  ia  evident  that  the  polygonal 
profile  was  deduced  as  above  described,  and  that  an  arc  of  a  cirele 
vras  then  drawn  to  average  the  irregularitiee.  The  largest  of  these 
profiles  is  shown  in  Fig.  73  by  the  broken  line.  The  others  are 
simply  the  npper  portion  of  the  largest,  with  the  tbickness  and  the 
height  of  the  portion  above  the  water  decreased  somewhat  and  the 
radios  of  the  faces  modified  correspondingly. 


The  lu-ger  profile  of  Fig.  73  is  that  recommended  by  the  eof^- 
neers  of  the  Aqnednct  Commission  for  the  proposed  Quaker  Bridge 
dam.     The  profiles  of  most  of  the  high  masonry  dams  of  the  world 


ovGoQi^lc 


ABT.  2.]  OUTLIITBB  OF  THE  DEBIQIT.  33d 

are  exceedingly  extraTngant,  and  hence  it  is  not  wortli  while  to  give 
examples. 

612.  Prol.  Wm.  Cain  haa  shown  *  that  the  eqaatione  of  condi- 
tion are  nearly  satisfied  by  a  cross  section  composed  of  two  tra- 
pezoids, the  lower  and  larger  of  which  is  the  lower  part  of  a  triangle 
having  its  base  on  the  fonndation  of  the  dam  and  its  apex  at  the 
surface  of  the  water,  and  the  upper  trapezoid  having  for  its  top  the 
predetermined  width  of  the  dam  on  top  (g  509),  and  for  its  sides 
nearly  vertical  lines  which  intersect  the  sides  of  the  lower  trapezoid. 
The  width  of  the  dam  at  the  bottom  is  obtained  by  applying  the 
equations  of  condition  as  above.  The  relative  batter  of  the  np- 
stream  and  down-stream  faces  depends  upon  the  relative  factors 
of  safety  for  crashing  and  overturning.  This  section  gives  a 
factor  of  Btrfety  which  increases  from  bottom  to  top, — an  important 
feature. 

613.  Tbs  Puv.  If  the  wall  is  to  bs  one  side  of  a  rectangular 
reservoir,  all  the  vertical  sections  will  be  alike ;  and  therefore  the 
heel,  the  toe,  and  the  crest  will  all  be  straight.  If  the  wall  is  to  be 
a  dam  across  a  narrow  valley,  the  height  of  the  masonry,  and  cons» 
qnently  its  thickness  at  the  bottom,  will  be  greater  at  the  center 
than  at  the  sides.  Id  this  case  the  several  vertical  cross  sections 
may  be  placed  so  that  (1)  the  crest  will  be  straight,  or  (2)  so  that 
the  heel  will  be  straight  in  plan,  or  (3)  so  that  the  toe  will  be 
straight  in  plan.  Since  the  up-stream  face  of  the  theoretical  pro- 
file is  nearly  vertical  (see  Fig.  72),  there  will  be  very  little  difference 
in  the  form  of  the  dam  whether  the  several  cross  sections  are 
placed  in  the  first  or  the  second  position  as  above.  If  the  creat  ig 
straight,  the  heel,  in  plan,  will  be  nearly  so  ;  if  the  crest  is  straight, 
the  toe,  in  plan,  will  be  the  arc  of  a  circle  such  that  the  middle 
ordinate  to  a  chord  equal  to  the  span  (length  of  the  crest)  will  be 
equal  to  the  maximuni  thickness  of  the  dam ;  and  if  the  toe  ia 
made  straight,  the  crest  will  become  a  circle  of  the  same  radius. 
This  shows  that  strictly  speaking  it  is  Impossible  to  have  a  straight 
gravity  dam  across  a  valley,  since  either  the  crest  or  toe  must  be 
curved.  The  question  then  arises  as  to  the  relative  merits  of  these 
two  forms. 

S14.  Straight  Crest  vs.  Straight  Toe.    The  amount  of  masonry 

■  SaginteHng  JThm,  vol.  xlx.  pp.  BU-Ul 


ovGoQi^lc 


830  hajbonbt  daks.  [chap.  xiu. 

in  the  two  forma  is  the  same,  gince  the  vertical  sections  at  all  points 
are  alike  io  both.* 

The  stabilitj  of  the  two  lorniB,  considered  only  as  gravity  dams, 
is  the  same,  since  the  crosB  sections  at  like  distances  from  the  center 
are  the  same. 

The  form  with  a  carved  crest  and  straight  toe  will  have  a  slight 
advantage  due  to  its  possible  action  as  an  arch.  However,  it  is  not 
necessary  to  disonas  further  the  relative  advantages  of  these  two 
types,  since  it  will  presently  be  shown  that  both  the  toe  and  the  crest 
of  a  gravity  dam  should  be  curved. 

616.  Gravity  n.  Aroh  Dams.  A  dam  of  the  pure  gravity  type 
is  one  in  which  the  sole  reliance  for  stability  ia  tha  weight  of  the 
masonry.  A  dam  of  the  pnre  arch  type  is  one  relying  solely  upon 
the  arched  form  for  stability.  With  the  arched  dam,  the  pressure 
of  the  water  is  transmitted  laterally  thtough  the  horizontal  sections 
to  the  abutments  (side  hills).  The  thickness  of  the  masonry  is  so 
small  that  the  resultant  of  the  horizontal  pressure  of  the  water  and 
the  weight  of  the  masonry  passes  outside  of  the  toe ;  and  hence, 
considered  only  as  a  gravity  dam,  is  in  a  state  of  unstable  equilib- 
rium. If  such  a  dam  fails,  it  will  probably  be  by  the  crushing 
of  the  masonry  at  the  ends  of  the  horizontal  arches.  In  the 
present  state  of  our  knowledge  concerning  the  elastic  yielding  of 
masonry,  we  can  not  determine,  with  any  considerable  degree  of 
accuracy,  the  distribution  oC  the  pressure  over  the  cross  section  of 
the  arch  (see  Art.  I,  Chap.  XVIII). 

If  it  were  not  for  the  incompleteness  of  onr  knowledge  of  the 
laws  governing  the  stability  of  masonry  arches,  the  arch  dam  would 
doubtless  be  the  best  type  form,  since  it  reqaires  less  masonry  for 
any  particular  case  than  the  pure  gravity  form.  The  best  infor- 
mation we  have  in  regard  to  the  stability  of  masonry  arches  is  de- 
rived from  experience.  The  largest  vertical  masonry  arch  in  the 
world  has  a  span  of  only  220  feet.  There  are  but  two  dams  of  the 
pnre  arch  type  in  the  world,  viz. :  the  Zola  f  in  France  and  the 

*  IF  the  TftUsf  acroM  which  thedMU  U  built  haa  anr  considerable  longltadlnkl  slope. 
Be  It  iuuall]r  will  have,  there  will  be  a  sllgbt  difference  according  to  the  relattre  posi- 
tion of  the  two  forms.  If  two  ends  remain  at  the  same  place,  the  straight  toe  throws 
tbe  dam  (artber  ap  tbe  valler,  makes  the  base  higher,  and  conaeqnently  allghtly  de- 
oreaaes  the  amount  of  maaom?. 

t  For  description,  see  Repeat  on  Qnaker  Brld^  Dam,  Oigtiuwine  Mwt,  toL  xlx. 


ovGoQi^lc 


ABT.  3.]  OUTLINES  OF  THE  DESIGN.  331 

Bear  Valley*  in  Sonthem  California.  The  length  of  the  former  is  ' 
205  feet  on  top,  height  122  feet,  and  radiua  158  feet;  the  length 
of  the  latter  ib  230  feet  on  top,  height  64  feet,  radius  of  tup 
335  feet  and  of  the  bottom  226  feet.  The  experience  with  larffs 
arches  is  bo  limited  (see  Table  63,  page  502),  as  to  render  it  un< 
wise  to  make  the  stability  of  a  dam  depend  wholly  upon  itB  action 
as  an  arch,  except  under  the  moBt  favorable  conditions  as  to  rigid 
side-hills  and  also  under  the  most  unfavorable  conditions  as  to  cost 
of  masonry.  Kotioe  that  with  a  dam  of  the  pure  arch  typo,  the 
failure  of  one  part  is  liable  to  cause  the  failure  of  the  whole ;  while 
with  a  gravity  section,  there  ia  much  less  danger  of  thia.  Further, 
since  the  average  pressure  on  the  end  arch  stones  increases  with  the  - 
span,  the  arch  form  is  most  suitable  for  short  dams. 

ftlB.  Curved  Gravity  Dami.  Although  it  is  not  generally  wise 
to  make  the  stability  of  a  dam  depend  entirely  upon  its  action  as 
an  arch,  a  gravity  dam  should  be  built  in  the  form  of  an  arch,  /. «., 
with'  both  crest  and  toe  curved,  and  thus  secure  some  of  the  advan- 
tages of  the  arch  type.  The  vertical  cross  section  should  be  so  pro- 
portioned as  to  resist  the  water  pressure  by  the  weight  of  the 
masonry  alone,  and  then  any  arch-like  action  will  give  an  addi- 
tional margin  for  safety.  If  the  section  is  proportioned  to  resist 
by  its  weight  alone,  arch  action  can  take  place  ouly  by  the  elastic 
yielding  of  the  masonry  under  the  water  pressure  ;  but  it  is  known 
that  masonry  will  yield  somewhat,  and  that  therefore  there  will  be 
some  arch  action  in  a  curved  gravity  dam.  Since  but  little  is  known 
about  the  elasticity  of  stone,  brick,  and  mortar  (see  §  16),  and  noth- 
ing at  all  about  the  elasticity  of  actual  masonry,  it  is  impoesiblo 
to  determioe  the  amount  of  arch  action,  t.  e.,  the  amount  of  pres- 
sure ih&t  is  transmitted  latemlly  to  the  abutments  (side-hills). 

That  it  is  possible  for  a  dam  to  act  as  an  arch  and  a  gravity  dam 
at  the  same  time  is  shown  as  follows :  "  Conceive  a  dam  of  the 
pnre  arch  type,  of  thin  rectangular  cross  section  so  as  to  have  no 
appraciable  gravity  stability.  Conceive  the  dam  to  be  made  up  of 
successive  horizoutal  arches  with  key-stones  vertically  over  each 
other.  The  thrust  in  each  arch  will  increase  with  the  depth,  but 
the  spans  will,  under  the  ordinary  practical  conditions,  decrease 
with  the  depth,  so  that  the  tendency  to  'settle  at  the  crown'  (move 
horizontally)  will  be  approximately  equal  in  each.     If  now  we  adopt 

*  For  descTlpttOD,  eee  Englnarmg  Xau,  vol.  xlz.  pp.  618-16. 


ovGoQi^lc 


332  HA80NBT  DAKS.  [OHAP.   XIII, 

a  triangular  in  place  of  a  rectangalar  crose  section,  we  increase  the 
areas  and  decrease  the  unit  pressureB  from  arch-thmst  as  we  go 
down,  and  hence  decrease  compression  and  consequent  horizontal 
'  settlement '  of  the  arches ;  in  other  words,  we  introduce  a  tendency 
in  the  water  face  of  the  dam  to  rotate  about  its  lower  edge.  But 
this  is  precisely  the  tendency  which  results  from  the  elastic  action  ' 
of  the  mass  in  respect  to  gravity  stability,  which  latter  we  hare  at 
the  same  time  introduced  by  adopting  the  gravity  section.  Hence 
the  two  act  in  perfect  harmony,  and  there  will  be  a  certain  size  of 
triangular  section  (thecretically, — practically  it  could  not  be  exact) 
at  which  precisely  half  the  stability  will  be  due  to  arch  action  and 
half  to  gravity  action,  each  acting  without  any  appreciable  conflict 
or  interference  with  the  other."  • 

617.  In  addition  to  the  increased  stability  of  a  curved  gravity 
dam  due  to  arch  action,  the  curved  form  has  another  advantage. 
The  pressure  of  the  water  on  the  back  of  the  arch  is  everywhere 
perpendicular  to  the  up-stream  face,  and  can  be  decomposed'  into 
two  components — one  perpendicular  to  the  chord  (the  span)  of  the 
arch,  and  the  other  parallel  to  the  chord,  of  the  arc.  The  first 
component  is  resisted  by  the  gravity  and  arch  stability  of  the  dam, 
and  the  second  throws  the  entire  up-stream  face  into  compression. 
The  aggr^ate  of  this  lateral  pressure  is  equal  to  the  water  pressure 
on  the  projection  of  the  np-stream  face  on  a  vertical  plane  perpeu' 
dicular  to  the  span  of  the  dam.  This  pressure  has  a  tendency  to 
close  all  vertical  cracks  and  to  consolidate  the  masonry  traiiBversely, 
— which  effect  is  very  desirable,  as  the  vertical  joints  are  always  \ea» 
perfectly  filled  than  the  horizontal  ones.  This  pressure  also  pre- 
pares the  dam  to  act  as  an  arch  earlier  than  it  would  otherwise  do, 
and  hence  makes  available  a  larger  amount  of  stability  due  to  arch 
action. 

The  compression  due  to  these  lateral  components  Is  entirely  in* 
dependent  of  the  arch  action  of  the  dam,  since  the  arch  action 
would  take  place  if  the  pressure  on  the  dam  were  everywhere  per- 
pendicular to  the  chord  of  the  arch.  Further,  it  in  no  way  weaken.'; 
the  dam,  since  considered  as  a  gravity  dam  the  effect  of  the  thrust 
of  the  water  is  to  relieve  the  pressure  on  the  back  face,  and  con- 
sidered as  an  arch  the  maximum  pressure  occurs  at  the  sides  of  tha 
down -stream  face. 

*  Editorial  In  Av<>Mcrtiv  J^HM,  ToL  xlx.  p.  97S. 


ovGoQi^lc 


AST.  2.]  OCTLIlTEa  OF  THE   DB9I0K.  833 

The  curred  dam  is  a  little  longer  than  a  straight  one,  and  heoce 
would  cost  a  little  more.  The  difference  in  length  between  a  chord 
and  its  arc  is  given,  to  a  close  degree  of  approximation,  by  the  formula 

in  which  a  =  the  length  of  the  arc,  c  =  the  length  of  the  chord, 
and  r  =  the  radias.  This  shows  that  the  increase  in  length  due  to 
the  arched  form  is  comparatively  slight  ¥or  example,  if  the  chord 
is  eqiiaitotheradins,  the  arch  is  only  fy,  or  4  per  cent,  longer  than 
the  chord.  Furthermore,  the  additional  cost  is  leas,  proportionally, 
than  the  additional  quantity  of  maeonry  ;  for  example,  10  per  cent 
additional  masonry  will  add  less  than  10  per  cent  to  the  cost. 

518.  Of  the  twenty-five  moat  important  masonry  dams  in  the 
world,  two  are  of  the  pure  arch  type,  fifteen  are  of  the  curved 
gravity  type,  and  eight  are  of  the  straight  gravity  type.  The  eight 
highest  dams  are  of  the  curved  gravity  type,* 

619.  QVAUTT  OF  THE  KASOITBT.  It  is  a,  well  settled  principle 
that  any  masonry  structure  which  sustains  a  vertical  load  should 
have  no  coDtinuona  vertical  jointa.  Dams  support  both  a  horizontal 
and  a  vertical  pressure,  and  hence  neither  the  vertical  nor  the  hori- 
zontal joints  should  be  continuous.  This  requires  that  the  masonry 
shall  be  broken  ashhtr  (Fig.  39,  page  136)  or  random  sqnared-atone 
masonry  (Fig,  44,  p^e  137),  or  uncoursed  rubble  (Fig.  45,  page  137). 
The  laat  ia  generally  employed,  particularly  for  large  dams.  The 
joints  on  the  foces  should  be  as  thin  as  possible,  to  diminish  the 
effect  of  the  weather  on  the  mortar  and  also  the  coat  of  repointing. 
In  ordinary  walls  much  more  care  is  given  to  filling  completely 
the  horizontal  than  the  vertical  ones  ;  but  in  dams  and  reservoir 
walls  it  is  important  that  the  vertical  joints  also  shall  be  completely 
filled. 

To  prevent  leakage,  it  is  rery  important  that  all  spaces  between 
the  stones  should  be  filled  completely  with  good  mortar,  or  better, 
with  mortar  impervious  to  water  (see  §  141).  If  the  stone  itself  is 
not  impervious,  the  wall  may  be  made  water  tight  by  the  ap- 
plication of  Sylvester'e  washes  (§  263)  to  the  inside  Ukx  of  the 
dam. 


*  For  Mnrce  ot  InfonnaUon  oonoeming  Umm  dame,  Me  |  tOO—BOilioefhj  o( 


ovGoQi^lc 


33i  KABOKBT  DAMS.  [OHA.F.  Xm, 

680.  BnuoeKAFET  or  HAaoKKX  SaKL  Deaiffn  and  Conttrue- 
tion  of  Masonry  Dams,  "R&niLiae,  (MiscellnaeoDB  Scientific  Papen, 
pp.  550-61.)  iSudy  of  Reservoir  Walla,  Krantz,  (tniulstod  from 
the  French  hj  Capt  F.  A.  Afohan,  U.  S.  A.)  Frofles  of  High 
Masonry  Dams,  McMaster,  (published  io  Van  Xostrand's  Engineer- 
ing Hagaziae  and  also  aa  TSo.  6  of  Van  Noetrand's  Science  Series. ) 
Strains  in  High  Masonry  Dams,  £.  Sherman  Qonld,  (Van 
NoBtraad'B  Engineering  Magazine,  vol. 30,  p.  265  tt  seg,).  Hirtori' 
col  and  Descriptive  Review  of  Earth  and  Masonry  Dams,  teilh 
Plans,  David  Gravel,  (Scientific  American  Supplement,  No.  595 
(Ma;  S8,  1S87),  pp.  9496-9500.)  Wegmann's  Design  and  Ooit- 
struction  of  Masonry  Dams  gives  an  account  of  methoda  em- 
ployed in  determining  the  profile  of  the  propoeed  Quaker  Bridge 
dam,  and  also  contains  illnBtrations  of  the  high  masonry  dams 
of  the  world.  For  a  general  disonssion  of  high  masonry  dams, 
inclnding  a  consideration  of  the  best  form  for  the  horizontal 
cross  section,  a  full  description  of  the  proposed  Quaker  Bridge 
dam  and  a  comparison  of  it  with  other  great  dams,  and  many 
valuable  points'  concerning  practical  details,  see  numerous  re- 
ports,  correspondence,  and  editorials  in  Engineering  News,  Jan- 
uary to  June,  ld8S  (vol.  19).  The  above  articles  contain  many 
references  to  the  literature,  mostly  French,  of  high  masonry  dams. 

Akt.  3.  Rock  Fill  Daiis. 

521.  There  are  three  well-known  types  of  dams,  which  have 
been  in  nae  from  time  immemorial :  earth  bank,  timber  crib-work, 
and  masonry.  Recent  engineering  practice  on  the  Pacific  coast  has 
introduced  another  type,  viz.:  the  Rock  Fill  Dam,  which  is  of  too 
much  importance  to  pass  by  without  a  mention  here,  although 
strictly  it  can  not  be  classed  as  masonry  constrnction, 

A  rock  fill  dam  consists  of  an  embankment  of  irre^lar  stones 
thrown  in  loosely,  except  that  sometimes  the  faces  are  laid  by  hand. 
If  the  overflow  is  to  discharge  over  the  crest,  the  largest  stones 
should  be  placed  on  the  down-stream  slope.  The  dam  may  be  made 
praoticolly  water  tight  (1)  by  filling  the  voids  with  smaller  stones, 
gravel,  sand,  and  earth,  or  (2)  by  placing  any  desired  thickneas  of 
earth  and  pnddle  on  the  up-stream  &ce,  or  (3)  by  covering  the 
water  slope  with  one  or  more  thicknesses  of  planking,  which  is  calked 
ind  sometimee  also  pointed.    Either  the  first  or  second  method 


ovGoQi^lc 


ABX.  3.]  ODTLUTES  OS  THE  DBSI6H.  33S 

TOnId  make  a  dam  ptactically  water  tight  from  the  beginning,  and 
it  would  grow  tighter  with  age  ;  the  third  method,  if  carefully  exe- 
outed,  would  make  the  dam  absolutely  water  tight  at  the  beginning, 
bat  would  decay,  aioce  the  upper  part  of  the  sheeting  would  ordi- 
narily be  alternately  wet  and  dry. 

A  great  number  of  rock  fill  dams  hare  been  built  on  the  Pacific 
slope  in  the  past  few  years,  for  mining  and  irrigating  parposea.  A 
dam  of  this  character  has  recently  been  completed  on  the  Hassa- 
yampa  River  in  Arizona,  of  the  following  dimeneions  :  "  Height, 
110  ft.;  base,  136  ft.;  top  width,  10  ft.;  length  on  top,  400  ft.; 
water  filopo,  SK)  ft.  horizontal  to  4?  ft.  vertical  (^  to  1);  back  slopes, 
70 ft.  horizontal  to  180ft.  vertical  (f  to  1); contents,  46,000 en.  jda.; 
coat,  by  contract,  12.40  per  ca.  yd."  *  It  is  proposed  to  build  a  dam 
of  this  character  in  California  3fiO  feet  high,  which  is  about  80  feet 
higher  than  any  existing  masonry  dam,  and  practically  ia  nearly  the 
eame  amount  higher  than  the  proposed  Quaker  Bridge  dam 
(Fig.  78,  page  328). 

038.  "Earth  dama  ara  good  and  useful  when  only  atill  water  not 
running  over  the  crest  is  to  be  dealt  with.  Counting  reservoir  walls 
as  dams,  which  they  are,  earth  dams  aro  vastly  mora  used  than  any 
other.  They  must  be  made  with  the  greatcat  care,  and,  if  of  any 
considerable  height,  an  inner  wall  of  puddle  is  necessary  to  their 
integrity.  They  must  be  carried  down  to  firm  and  impervious  sub- 
soil of  some  kind,  or  they  are  worthless.  Any  considerable  leak  is 
at  once  fatal  to  them ;  and  they  ara  also  subject  to  serious  injury 
from  muskrats,  crabs,  etc.  Kevertbeleas,  many  earth  dams  of 
great  age  and  great  height  exist,  and  bid  fair  to  exist  for  ages, 
showiug  that  it  is  entirely  possible  to  make  them  secura." 

Stone-filled  timber  cribs  have  been  very  much  used  for  dams  ; 
bat  such  structures  ara  sure  to  rot  in  time,  since  the  timber  can  not 
always  be  kept  wet.  It  seeme  probable  that  in  moat  instances  where 
cribs  have  been  used  a  rock-fill  dam  would  have  been  better, 
cheaper,  and  more  dnrabfe. 

Masonry  dams  of  all  sizes,  proportions,  and  agee  exist  in  great 
abundance,  and  the  entire  snitability  of  masonry  for  the  construction 
of  dama  is  well  established.  This  class  of  dams  is  to  be  preferred 
where  large  quantities  of  stone  are  not  near  at  hand,  or  where  leak- 
age ia  undesirable  because  of  loss  of  water  or  of  injar;  to  land  be- 
Kim,  T<^  XX.  p.  MS. 


ovGoQi^lc 


836  VASONRT   DAJfS.  [CHA.P.  XIII. 

low,  or  where  space  is  valaable,  or  where  the  aurrouudingB  require 
a  dam  of  good  appearance. 

533.  "  These  three  types  afford  an  adequate  choice  for  nearly  all 
requirements,  but  it  is  obvioDS  that  they  aire  open  to  certain  com- 
tnon  objections  from  which  the  fourth  type — a  rock-fill  dam — is 
free.  They  are  all  comparatively  costly  ;  they  require  a  good  deal 
of  labor,  and  much  of  it  skilled  and  faithful  labor,  for  their  con- 
struction ;  they  can  only  with  great  inconvenience  be  constructed 
with  water  around  them,  which  for  the  most  part  must  be  kept  away 
by  costly  coSer-dams  or  diversions  of  channels  ;  above  all,  a  leak  is 
always  a  source  of  danger,  and  is  apt  to  be  destructive.  They  are 
all  of  them,  ae  it  were,  during  all  their  existence,  in  unstable 
eqnilibriam — all  right  so  long  ae  the  balance  of  forces  remains  un- 
disturbed, and  seriously  endangered  by  a  variety  of  causes  which 
may  disturb  it.  On  the  other  hand  a  rock-fill  dam  is  by  the  very 
process  of  its  construction,  if  conducted  with  reasonable  judgment, 
a  structure  which  tends  to  improve  with  time,  and  which  can  not 
be  injured  but  may  be  benefited  by  causes  which  threaten  the 
other  and  more  artificial  types  ;  in  other  words,  it  is  a  structure 
which  may  not  be  very  tight,  but  which  is  in  stable  equilibrium  as 
respects  all  disturbing  causes,  being  improved  and  never  injured  by 
them. 

"  A  rock-fill  dam  is  appropriate  where  the  bed  on  which  it  rests 
is  either  rock,  hard-pan,  stiff  clay,  or  some  other  impervious  and 
almost  unwashable  material.  The  bed  may  be  more  or  less  over- 
laid with  gravel  or  loose  material  without  barm,  if  it  be  possible 
to  remove  the  loose  material  in  advance,  and  if  there  be  current 
enough  to  remove  it  from  under  the  foot  of  the  dam,  as  the  work 
of  construction  progresses,  it  will  not  even  involve  extra  expense  or 
delay,  and  the  dam  may  be  begun  on  top  of  the  stratum  without 
apparent  regard  to  it ;  but  whenever  there  is  any  considerable 
stratum  of  loose  material,  a  rock-fill  dam  can  only  be  built  byback- 
ing  it  with  earth  or  puddle  as  a  timber  dam  would  be,  and  the 
necessity  of  providing  a  proper  apron  to  receive  the  overflow  may 
make  a  timber  or  crib  dam  the  more  economical.  It  is  obvioua 
that  the  place  of  all  places  for  the  proper  use  of  such  a  rock-fill 
dam  is  where  leakage  is  of  no  importance,  either  from  the  loss  ot 
water  or  from  injury  to  land  below  ;  where  skilled  labor  is  scarce 
Aod  costly,  and  simplicity  of  work  rather  than  aggregate  quantitiea 


ovGoQi^lc 


AET.  2.]  OUTLINEB  OP  THE  DE3I0K.  337 

the  important  coneideration  ;  where  good  materials  for  masonry  are 
scarce  or  absent ;  and  where  the  surroundings  do  not  demand  at- 
tention to  the  question  of  appearance."  • 

The  greatest  economy  in  this  form  of  dam  occnrs  when  the  fill 
ie  made  in  water ;  and  it  is  particularly  advantageous  In  the  canali- 
sation of  riyers,  i.  «,,  in  forming  pools  in  rivers  for  the  benefit  of 
navigation.  It  has  been  proposed  to  use  rock-fill  dams  ezcluBively 
in  the  coustruction  of  the  Klcaragua  canal. 

524.  In  California  the  cost  of  this  class  of  dams  varies  from  tft 
to  t3  per  oubic  yard,  including  all  accessories,  which  is  said  to  be 
«bout  50  per  cent,  cheaper  than  for  earth  dams  of  equal  area  of 
transverse  cross  section. 

"  EdlEOrlal  Id  Sngineeri^f  JTnw,  voL  sz.  p.  7U. 


D.qitizeabyG00l^lc 


CHAPTER  XrV. 
RETAINING  WALLS. 

625.  DeFUIIIOWI.  lietaining  wall  ie  a  wall  of  masonry  toi- 
fnstaining  the  pressure  of  earth  deposited  behind  it  after  it  is  bnilt. 
A  retaiDing  wall  is  Bometimes  called  a  snstairtirig  wall. 

Face  wail,  or  nlope  wall,  is  a  species  of  reiainiog  wall  built 
against  the  face  of  earth  iu  its  undisturbed  and  natural  position. 
Obviously  it  is  mnch  less  important  and  involves  Less  diSSculties 
than  a  true  retaining  wall. 

Buttresses  are  projections  in  the  front  of  the  wall  to  strengthen 
it.  They  are  not  often  used,  on  account  of  their  unaightliness,  ex- 
cept as  a  remedy  when  a  wall  is  seen  to  be  failing. 

Counterforts  are  projections  at  the  rear  of  the  wall  to  increase 
its  strength.  They  are  of  doubtful  economy,  and  were  much  more 
frequently  used  formerly  than  now. 

Land-ties  are  long  iron  rods  which  connect  the  face  of  the  wall 
with  a  mass  of  masonry,  a  large  iron  plate,  or  a  large  wooden  post 
bedded  in  the  earth  behind  the  wall,  to  give  additional  resistance  to 
overturning. 

Surcharge.  If  the  material  to  be  supported  slopes  up  and  back 
from  the  top  of  the  wall,  the  earth  above  the  top  is  called  the  sur- 
charge. 

Retaining  walla  are  frequently  employed  in  railroad  work,  on 
canals,  about  harbors,  etc.;  and  the  principles  involved  in  their 
construction  have  more  or  less  direct  application  in  arches,  in  tun- 
neling and  mining,  in  timbering  of  shafts,  and  in  the  excavation  of 
deep  trenches  for  sewers,  etc.,  and  in  military  engineering. 

fi2e.  Method  of  FAUintE.  A  retaining  wall  may  fail  (1)  by 
revolving  about  the  front  of  any  horizontal  joint,  or  (2)  by  sliding 
on  the  plane  of  any  horizontal  joint,  or  (3)  by  the  bnlging  of  the 
body  of  the  masonry.     The  first  is  mnch  the  most  frequent  mode  of 


ovGoQi^lc 


DIFFICULTIES.  339 

failure,  and  the  second  ie  the  least  frequent.  The  wall  can  not  fail 
by  the  center's  bulging  out,  unless  some  force  acta  to  keep  the  top 
from  moving  fomard, — as  in  a  cellar  wall,  the  abutments  of  arches, 
etc. 

637.  DITFICUITIEB.  In  the  discussion  of  the  stability  of  dams, 
it  was  shown  that  in  order  to  completely  determine  the  effect  of  the 
thrust  of  the  water  against  the  wall,  it  is  necessary  to  know  (1) 
the  amount  of  the  pressure,  (3)  its  point  of  application,  and  (3) 
the  direction,  of  its  line  of  action.  Similarly,  to  determine  the 
eSeot  of  the  thmst  of  a  bank  of  earth  against  a  wall,  it  is  necessary 
to  know  (1)  the  amonnt  of  the  pressure,  (2)  its  point  of  application, 
-and  (3)  its  line  of  action.  The  determination  of  these  three^quan- 
tities  requires  three  equations.  The  resistance  of  the  wall  both  to 
sliding  and  to  overturning' can  be  found  with  sufficient  accuracy,  as 
has  already  been  explained  in  Chapter  XIII — Dama; — but  the 
othei  elements  of  the  problem  are,  in  the  present  state  of  our 
knowledge,  indeterminate. 

The  origin  of  the  difficnlties  may  be  esplained  briefly  as  follows. 
A  B  represents  a  retaining  wall ;  AD  v&  the 

■  ,'/ 

break  away  and  come  down  some  line  as  CD.    The  a/       .» 


A 


face  of  the  ground.  The  earth  has  a  tendency  to 
break  away  and  come  down  some  line  as  CD.  The 
force  tending  to  bring  the  earth  down  is  its  weight ;  Ar^  J 
the  forces  tending  to  keep  it  from  coming  down  are 
the  friction  and  cohesion  along  the  line  CD.  The_ 
pressure  against  the  wall  depends  upon  the  form  of 
the  line  CD.     If  the  constants  of  weight,  friction,  Fio.  78. 

and  cohesion  of  anj-  particular  ground  were  known,  the  form  of  CD 
and  also  the  amount  of  the  thrust  on  th6>  wall  could  be  determined. 
Kot  with  standing  the  fact  that  since  the  earliest  ages  constructors 
have  known  by  practical  experience  that  a  mass  of  earthwork 
will  eiert  a  severe  lateral  pressure  upon  a  wall  or  other  retaining 
structure,  there  is  probably  no  other  subject  connected  with  the 
constmctor'a  art  in  which  there  exists  the  same  lack  of  exact  ex- 
perimental data.  This  lack  is  doubtless  due,  in  part  at  least,  to  a 
reliance  upon  theoretical  investigations.  Of  coarse,  mathematical 
investigstions  unsupported  by  experiments  or  experience  are  a  very 
uncertain  guide. 

This  subject  will  be   discussed   further  under  the  heads  (1) 
Theoretical  Formulas,  and  (2)  Empirical  Rales. 


ovGoQi^lc 


BETAININO    WALL3,  [CHAP.    IIV. 


Aet.  1.    Theoretical  Foemulas. 

628.  A  great  variety  of  theories  have  been  presented,  bat  all  rest 
upon  an  nncertain  fonndation  of  assumption,  and  all  are  more  or 
less  defective  and  self- contradictory.  All  theories  of  the  stability 
of  retaining  walls  involve  the  three  following  assumptions  : 

S29.  FIBST  AssuiIPTIOH,  All  theories  assume  that  the  surface 
of  rupture,  C  D,  Fig.  "3-,  is  a  plane.  This  is  equivalent  to  asaum- 
ing  that  the  soil  ia  devoid  of  cohesion,  and  is  inelastic  and  homo- 
geneous, and  also  that  if  a  mass  of  such  material  be  sustained  by  a 
wall,  there  is  a  certain  plane,  called  the  plane  of  rupture,  along 
which  the  particles  are  m  equilibrium,  i.  e.,  are  just  on  the  point  of 
moving.  This  assumption  would  be  nearly  correct  in  the  case  of 
clean,  sharp  sand,  but  would  be  considerably  in  error  with  a  tough, 
tenacious  soil. 

This  assumption  gives  the  data  by  which  the  amount  of  the 
thrust  of  the  earth  can  be  computed;  that  is  to  say,  this  assumption 
furnishes  the  conditions  from  which  one  of  the  equations  may  be 
established. 

930.  fiEOOini  ABBUitPTlOH.  A  second  assumption  which  is  always 
made  is  that  the  point  of  application  of  the  lateral  pressure  of  the 
earth  is  one  third  of  the  height  of  the  wall  from  the  bottom.  The 
total  pressure  on  the  wall  varies  as  some  function  of  the  height ; 
And  it  is  assumed  to  vary  ae  the  square  of  the  height,  and  that 
therefore  the  center  of  pressure  is  at  a  point  two  thirds  of  the 
depth  below  the  top.  This  is  equivalent  to  assuming  that  the  varia- 
tion of  the  pressure  in  a  mass  of  earth  is  the  same  as  in  a  liqnid, 
4.  «.,  that  the  material  is  devoid  of  internal  friction. 

This  assumption  furnishes  the  second  of  the  equations  required 
-to  determine  the  effect  of  the  thrust  of  earth  against  a  retaining 
-wall. 

K31.  TEIBD  ASBOKPnoir.  The  third  equation  is  obtamed  by 
assuming  the  direction  of  the  pressure.  There  are  different  theories 
ibaeed  on  different  assumptions  as  to  this  direction. 

The  theories  of  the  stability  of  retaining  walls  in  most  frequent 
use  will  now  be  stated,  and '  the  underlying  assumptions  and  the 
defects  of  each  will  be  pointed  out. 


ovGoQi^lc 


ABT.  1.]  TQEOBETICA.L  FOBUULAS.  341 

632.  CotrtOMB's  Theokt.  The  theory  advanced  bj  Conlomb  in 
1784  was  the  first  to  eves  approximate  the  actual  conditioDs,  and 
bis  method  is  the  basis  of  Dearly  all  formulas  used  by  engineera  at 
the  present  time.  It  haa  been  taken  up  and  followed  out  to  its 
consequences  by  Prony  (1802),  Mayniel  (1808),  Fran<jaiBe  (1830), 
Na?ier  (1826),  Audoy  and  Poncelet  (1840),  Hagen  (1853),  Scheffler 
(1857),  and  Moseley,  as  well  as  a  host  of  others,  in  recent  times. 

Coulomb  assumea  (1)  that  the  line  D  C,  Fig.  73  (page  339),  is 
a  straight  line,  down  which  the  prism  A  CD  tends  to  slide;  (2)  that 
the  resultant  pressure  is  applied  at  a  point  two  thirds  of  the  depth 
below  the  top;  and  (3)  that  the  pressure  exerted  by  this  mass  oa  the 
wall  is  normal  to  its  back  face,  which  is  equivalent  to  neglecting  the 
friction  of  the  earth  against  the  back  of  the  wall.  He  decomposed  the 
weight,  ff,  of  the  prisma  CD,  Pig.  74,  and  the 
reaction,  R,  of  the  wall  into  two  components 
respectively,  parallel  and  perpendicular  to  the 
surface  of  rupture,  D  C.  The  difference  of 
these  parallel  components,  P^~  P,,  he  placed 
eqnal  to  the  prism's  resistance  to  sliding;  and 
assumed  the  latter  to  be  equal  to  n  N^,  in  which 
H  is  the  co-efficient  of  friction.  There  is  some  prism,  A  CD,  the 
presBure  of  which  against  the  wall  is  just  sufficient  to  cause  sliding. 
The  amount  of  this  pressure  will  depend  upon  the  weight,  w,  of  a 
anit  of  volume  of  the  backing;  upon  the  height,  h,  of  the  wall; 
upon  the  co-efficient  of  friction,  /i,  of  earth  on  earth;  and  upon  the 
distance  A  D,  which  call  x. 

Under  the  conditions  assumed,  it  is  possible  to  state  a  value  of 
R  in  terms  of  h,  w,  ft,  and  x.  Coulomb  assumed  R  to  vary  as  x,. 
and  differentiated  the  value  of  ^  to  find  the  position  of  the  snrtace- 
of  rupture,  D  C,  for  a  Maximum  pressure  on  the  wall.  This  Jeads^ 
to  the  simple  conclusion  that  the  lateral  pressure  exertttd  by  a  bant 
of  earth  with  a  horizmital  top  is  simply  that  due  to  the  wedge-shaped' 
mass  included  between  the  vertical  back  of  the  wall  and  a  line  bi- 
secting the  angle  between  the  vertical  and  the  slope  of  repose  of  the^ 
material;*  that  is,  the  pressure  of  the  earth  against  the  wall  A  B, 


*  For  OD  algebraic  demonatntlon,  see  Hoselej's  Mechanios  of  EhiglDeeriDK  (Sd 
Amar.  Ed.),  pp.  11S-16;  for  a  graphical  demonstntloii.  Bee  Van  Nostrand's 
log  Magazine,  vol.  tx.  p.  302,  and  vol.  izll.  p.  387. 


jvGooi^le 


342  BBTA.ININQ  WALLS.  [CHAP.  ZIT. 

Fig.  74,  IB  equal  to  the  prcBeure  of  the  prism  A  CE  eliding  along  a 
perfectly  smooth  plane  C  E,  which  bisects  the  angle  of  repose,  A  CD. 
No  satisfactory  proof  has  been  given  of  the  correctneBB  of  this 
procedure  by  either  Coulomb  or  any  one  else;  and  no  defense  has 
ever  been  made  against  a  number  of  serious  objections  to 
^  it  which  have  been  raised.  Experiments  show  that  the 
lateral  pressure  of  the  prism  ABC,  Fig.  75,  between  two 
boards  A  B  and  A  C,  against  A  B,  "  is  quite  as  much  when 
the  board  ^  6*  is  at  the  slope  of  repose,  1^  to  1,  as  when  it 
is  at  half  the  angle;  and  there  was  hardly  any  difference 
whether  the  board  was  horizontal,  or  at  a  slope  of  )  to  1,  or  at 
any  intermediate  slope."* 

533.  By  this  theory  the  pressure  of  the  wedge  ACT)  (Fig. 
74)  is 

P  =  JwA'tan'i^CD, (1) 

in  which  to  ie  the  weight  of  a  unit  of  the  material  to  be  supported, 
aad  h  is  the  height  of  the  wall.  This  thrust  is  assumed  to  act  two 
thirds  of  A  C,  Fig.  74,  below  A.  Or,  in  other  words,  the  thrust  of 
the  prism  is  equivalent  to  the  pressure  of  a  liquid  whose  weight  per 
unit  of  volume  is  w  tan'  \  A  CD. 

Equating  the  moment  of  the  overturning  force  and  the  moments 
of  resistance  in  terms  of  the  unknown  thickness,  and  solving  the 
«quation,  gives  the  thickness  which  the  wall  must  have  to  be  on  the 
point  of  overturning.  For  example,  iissume  that  it  is  desired  to 
determine  the  thickness,  t,  of  a  vertical  rectangular  wall.  Kepre- 
aent  the  weight  of  a  cubic  foot  of  the  masonry  by  IF.  Then  placing 
the  moment  of  the  wall  equal  to  the  amount  of  the  thrust  of  the 
earth,  gives 

W1il.iit  =  P.^h (2) 

Solving  equations  (1)  and  (2)  gives 

t  -  h  i»nh ACD\ 


•  Benj.  Baker,  an  eminent  Engllab  engineer,  In  a  yety  IntereaHng  and  Inatnictlve 
article  on  "  The  Actual  Lateral  Pressure  of  Earthwork,"  reprinted  in  Van  Noetrand's 
EngtoeeriDg  Magulne,  vol.  iiv.  pp.  388-12,  35&-n,  and  492-609,  from  Proc.  ol  tlia 
lost,  ot  C,  E.,  vol.  Iiv.  pp.  140-Ml, 


ovGoQi^lc 


ABT.  I.]  TBBORETICAL  POBMrLAS.  343 

KumerooB  tables  have  been  computed  which  give,  to  a  great 
number  of  decimal  places,  the  thickness  of  a  rectangular  wall  in 
terms  of  its  height,  the  arguments  being  the  ratio  of  the  weights  of 
a  unit  of  volume  of  the  wall  and  backing,  and  the  angle  of  repose. 
Snch  tables  are  of  but  Httle  practical  value,  as  will  appear  presently. 

S34.  Surcharged  Walls.  The  rule  that  the  plane  of  rupture 
bisects  the  angle  between  the  natural  slope  of  the  earth  and  the  back 
■of  the  wall,  holds  good  only  when  the  top  surface  of  the  bank  is 
horizontal  and  the  back  of  the  wall  vertical.  The  formula  for  a 
surcharged  wall,  or  for  the  case  in  which  the  back  is  not  vertical, 
■or  for  both  combined,  may  be  deduced*  in  the  same  general  way  as 
above;  bat  the  results  for  each  case  are  too  complicated  for  ordinary 
use,  and  each  is  subject  to  the  same  errors  as  the  formula  for  a  ver- 
tical wall  and  level  top  surface.  There  are  a  number  of  exceedingly 
Ingenious  graphical  solutiotui  of  the  resulting  equations,  f 

fi36.  Beliability  of  Coulomb's  Theory.  It  is, generally  conceded 
that  the  results  obtained  by  this  method  have  but  little  practical 
valne.  "  Experiments  and  practical  experience  show  that  walls, 
which  according  to  this  theory  are  on  the  point  of  overturning, 
possess  on  the  average  a  factor  of  safety  of  about  tjco."  I  One  of 
the  author's  students  experimented  with  fine  shot,  which  appear  to 
falfill  the  fundamental  assumptions  of  this  theory,  and  found  that 
the  observed  resistance  was  1.97  times  that  computed  by  Coulomb's 
formuIa.§  The  uncertainties  of  the  fondamental  assumptions  and 
the  qneBtionablenesB  of  some  of  the  mathematical  processes  are 
eafficient  explanation  of  the  difierence  between  the  theory  and 
practice. 

636.  WSTBAirOH'B  THEOBT.  This  is  the  latest  one,  having  bnen  j 
proposed  in  1878.  It  was  first  brought  to  the  attention  of  American 
engineers  by  Professor  J.  A.  Du  Bois's  translations  of  Winkler's 
•'  Neue  Theorie  dea  Erddruckes,"  and  Weyraiich's  paper  on  retain- 
ing walla  published  in  "Zeitschrift  fiir  Baukunde,"  1878,  Band  i. 
Heft  2,  which  translation  was  published  in  the  Journal  of  the  Frank- 

■  See  Moseley'B  Mechaolcs  ot  En^ueerinK,  pp.  4S4--3G. 

i  See  Van  Nostraud's  Eai^neeriDg  Magazine,  vol.  U.  p.  SD4 :  aod  do.,  voL  ixv. 
p.  3SS.  For  releranoea  to  elaborale  gmpbical  treatises  od  retaining  walls,  see  Dn. 
Bola's  Graphical  Slatlca.  pp.  Ir-M  of  Introdnctton. 

I  Beoj.  Baker  \a  "  The  Actual  Lateral  Pressure  ot  Earthwork."  See  loot-note  on 
psffeSia. 

S  See  M.  Fargnaeon'B  Bachelor's  Thesla,  University  of  Illinois. 


ovGoQi^lc 


344 


BETAINIirO  WALLS. 


[chap.  XIT. 


lin  Institute,  vol.  eviii,  pp.  361-87.    The  following  preseotation  ot 
tbiB  theory  is  drawo  mainly  from  that  article. 

This  theory  assumes  (1)  that  the  enrface  of  rupture  ia  a  pIaDe> 
(2)  that  the  point  of  application  of  the  resultant  of  the  latenj. 
pressare  of  the  eM-th,  is  at  a  point  one  third  of  the  height  of  the 
wall  from  the  bottom,  and  (3)  that  there  is  no  friction  between  the 
earth  and  the  back  of  the  widl.  It  ie  claimed  that  these  three  are, 
the  only  assumptions  involved  in  this  theory,  and  that  the  direction, 
of  the  resultant  pressure  is  deduced  from  the  fundameutal  rela- 
tions necessary  for  equilibrium  under  the  conditions  assumed. 

The  analysis  to  establish  the  equations  fobthe^ount  and  direc- 
tion of  the  thrust  of  the  earth  is  too  long  and  too  complicated  to  be 
attempted  here;  couBequently,  only  the  final  equations  will  be 
given. 

F  Let  S  =  the  thrust  of  earth  against 
the  wall. 
w  =  the  weight  of  a  nnit  of  the 

earth. 
h  =  the  height  of  the  walL 
a  =  the  angle  the  back  of  wall 

makes  with  the  vertical. 
6  =  the  angle  which  E  makes 
with   the  normal  to  the 
Fib.  Tt.  back  of  the  wall. 

6  =  the  angle  of  the  upper  surface  with  the  horizontal. 
fi  =  the  angle  of  the  plane  of  rapture  with  the  vertical. 
0  =  the  angle  of  repoee  with  the  horizontal. 
637.  General  Pormulaa.     For  a  plane  earth-surface,  horizontal 
or  eloping  up  at  any  angle,  and  the  back  of  the  wall  vertical  or 
leaning  forward  at  any  angle,  the  general  relations  are  * 


p-  rcoB(0-«)~l' 


2  COS  (a  +  Sy 


(*> 


_  i/aiP  (0  +  tf)  sin  (0— ~e) 
■*  '  cos  («  +  <J)  COS  (or  —  €)' 


(«) 


jvGooi^le 


T.  1.J  THBOfiETICAL  POBHULAS.  34j>> 

The  valne  oi  S  required  in  (5)  can  be  deduced  from 

-  flin  (3  or  —  e)  —  Kim  2  (a  —  e)  ,„. 

in  which 

__    COfl  6  —  V  COB*  £  —  cob'  0  .  , 

cos' 0       ~ '  '■ 

538.  Horiiontal  Earth-wfiiice.    If  the  upper  snr&oe  iit  the 
earth  is  horizontal,  then  £  =  0,  and 

P^       tana  Vw 

^-flin(a  +  tf)*^^' (^> 

and  S  can  be  found  from 

,       -  sin  0  sin  8  a:  „^ 

,tan  S  = r^--7 =— (9> 

1  —  Bin  0  cos  2  «  •    '    \'r 

If  the  back  of  the  wall  is  Tertical,  a  =  0;  aod  eqaation  (9)< 
gives  S  =  0.    Therefore 


=  tan*   46' 


E: 


639.  Bnroha^e  at  the  Hatnral  Slope.  If  the  upper  surface  of 
earth  has  the  natural  slope,  6  =  0;  and  therefore 

.  fcos  (0  -  a)-V         h'  w 

'L      cos«      j2coe(a  +  tf)*     ■    •    '     •     ^"' 

and  6  is  determined  from 

"      tan  tf  -    sin  0  COS  (0  -  2  «) 

**°*-l-Bin08in{0-2«) <*^> 

If  the  back  of  the  wall  is  vertical,  rt  =  0,  and  5=0,  which 
ahowB  that  E  acts  parallel  to  the  top  Borface  of  the  earth.  In  this 
case 

J?  =  iCOB0A'«. (13) 

*  Coippaie  with  eqwUlon  (1),  pige  848. 


ovGoQi^lc 


346  HETAIMING   WALL3,  [CHAP.   XIV. 

640.  The  general  eqaationa  for  Weyrsuch'a  theory,  viz.,  equa- 
tions (4),  (5),  (6),  and  (7),  have  not  been  solved  for  any  special 
•caae,  except  for  e  =  0,  and  e  =  0.  The  redaction  is  very  long  and 
tedious. 

641.  The  formulas  for  each  of  the  above  cases  may  be  solved 
graphically,*  but  the  explanations  ar£  too  long  to  be  given  ber«. 

542.  Heliability  of  Weyrauoh'B  Theory.  On  behalf  of  this 
theory  it  is  claimed  f  that  the  only  errors  in  it  are  those  due  to  the 
neglect  of  the  cohesion  of  the  backing,  and  to  assuming  that  the 
surface  of  niptare  is  a  plane  ;  and  also  that  "  it  is  free  from  all  the 
objections  which  may  be  urged  against  all  others,  and  can  be  used 
Vith  confidence."    These  claims  are  not  supported  by  the  facts. 

Weyrauch's  theory  is  unquestionably  subject  to  any  errors  Thich 
may  be  involved  in  the  aBsamptions  that  the  surface  of  rupture  is  a 
plane  (see  §  529),  and  that  the  point  of  application  of  the  resultant 
pressure  of  the  earth  is  at  two  thirds  of  the  height  of  the  wall  from 
the  top  {see  §  530).  Second,  the  analysis  purports  to  be  perfectly 
general ;  I  but  it  is  evidently  ina|^licable  to  a  wall  inclined  toward 
the  earth  to  be  supported,  since  the  formulas  make  the  thrust  of 
the  earth  increase  with  the  backward  inclination  of  the  wall.  Ir 
fact  the  theory  makes  no  difference  between  a  wall  leaning  forward 
and  one  leaning  backward.  For  a  wall  inclining  at  the  angle  of 
repose,  it  gives  a  very  great  lateral  pressure — see  eqs.  (S)  and  (9). 
Third,  the  mathematical  process  of  determining  the  position  of  the 
earface  of  rupture  is  at  least  questionable.  Fourth,  the  theory  errs 
on  the  safe  side,  becauee  it  neglects  a  vertical  component  of  the 
«arth  pressure  which  is  independent  of  friction.  § 

Weyrauch's  theory  differs  from  Coulomb's  only  in  the  form  of 
the  results  and  in  the  manner  of  deducing  them  ;  |  and  hence  is  of 
no  pi-actical  value. 

643.  Weyrauch's  method  of  deducing  the  direction  of  the  earth 

*S«e  Jonr.  Frank.  Inst.,  vol.  cvltl.  pp.  880-85;  Vui  Noatntnd'E  EDglneerfng 
Hag&zine,  vol  xiU.  pp.  366-78 ;  Howe's  ReUUnliig  W&lla  for  EBith,  pp.  7-l-i. 

t  Bf  IIS  antbor,  'Prot.  Werraucli,  and  also  by  Uie  tmoBlator,  Prol.  Du  BoIb,— ms 
Jonr.  Frank,  InjW.,  vol.  cvliL  pp,  48IS-87. 

t  See  Jonr.  Frank.  Inst.,  vol.  cvUi.  p.  3T7 ;  and  also  Howe's  Retaining  Walls  for 
Garth,  p.  a. 

i  In  proof  that  aach  a  component  exists,  see  experiments  tiy  Staler  In  Annalei  dm 
fbnliil  C/iatma,  reprinted  in  Selentiflc  Amirlatn  Supplentaii.  vol.  xxlv.  pp.  9I31-2S. 

I  Van  NoBtroDd's  Engineering  Magazine,  vol  nil,  pp.  SCC-TT. 


ovGoQi^lc 


ABT.    t.J  THEOEETICAL  F0BMULA8.  347 

pressure  assamoB  that  there  is  no  friction  betveen  the  earth  and  the 
back  of  the  vail,  or,  in  other  worda,  that  the  angle,  d,  vhich  the 
thrnst  of  the  earth  makes  with  the  back  of  the  wall,  does  not  de- 
pend upon  the  structure  of  the  wall  for  its  value.  The  formula  in 
this  form  faila  to  agree  with  ordinary  experience ;  and  hence  it 
hoe  been  proposed  *  to  modify  the  general  formula  by  considering 
that  the  angle  between  the  resultant  pressure  of  the  earth  and  the 
back  of  the  wall  is  never  less  than  the  angle  of  friction  between  the 
earth  and  the  wall.     The  method  of  doing  this  ie  as  follows : 

If  0*  represents  the  co-efBcient  of  friction  between  the  earth 
and  the  wall,  then  the  direction  of  E  must  make  an  angle  with  the 
normal  to  the  back  face  of  the  wall  eqnal  at  least  to  0'.  To  intro- 
doce  0'  into  Professor  Weyrauch'a  theory,  it  is  necessary  to  find  the 
valae  of  <J  aa  given  by  his  formula,  and  see  if  it  is  greater  or  less  than 
4^.  If  it  is  loss,  use  the  value  of  0'  to  determine  the  direction  of 
£;  if  greater,  nse  the  value  of  S  and  omit  0'  altogether.  The 
value  of  0'  can  not  be  determined  accurately ;  but  unless  the  back 
of  the  wall  is  exceedingly  smooth,  0'  will  be  greater  than  0.  If 
the  back  of  the  wall  is  rough  rubble  {§  213)  or  is  stepped,  0*  will  be 
considerably  larger  than  0.  If  the  friction  between  the  earth  and 
the  wall  be  neglected,  »',  c,  if  it  is  assumed  that  0'  =  0,  then  when 
rough  rubble  i;ctaining  walls  are  proportioned  according  to  Wey- 
raueh'a  theory,  they  will  have  a  factor  of  safety  considerably  larger 
than  appears  from  the  computations. 

This  modification  is  inconsistent  with  the  general  the  try,  since 
the  fundamental  equations  were  established  for  that  value  of  6  which 
would  produce  equilibrium,  and  the  corresponding  value  of  the 
thrust  was  deduced  accordingly.  It  is  certainly  incorrect  to  use  one 
direction  in  determining  the  value  of  the  thrust  and  another  in 
applying  it.  Further,  it  is  not  reasonable  to  believe  that  the  thrust 
ever  makes  an  angle  with  the  normal  to  the  back  of  the  wall 
greater  than  the  angle  of  friction,  since  one  of  the  fundamental 
conditions  of  statics  is  that  if  the  resultant  pressure  makes  an  angle 
with  the  normal  greater  than  the  angle  of  repose,  motion  takes 
place.  This  modification  of  Weyranch's  theory  purports  to  give  the 
relations  forastateof  eqnilibrinm,  and  yet  violates  the  fundamental 
condition  necessary  for  equilibrium.  Neither  the  original  theory 
aor  the  above  modification  of  it  are  of  any  practical  value. 

*  Br  Prof.  Cain  Id  Van  NoatnDd'B  Engineering  Magasine,  vol.  iiv.  p.  93. 


ovGoQi^lc 


348  BETAINIKO  WA13LS.  [CHAP.  IIV. 

544.  SAMEDn'fl  ThzobT.  There  is  a.iiother  class  of  theories, 
irhich,  in  addition  to  the  asenrnptiona  of  §  530  and  §  531,  aeantne! 
that  the  thrust  of  the  earth  makes  an  angle  with  the  hack  of  the. 
wall  eqaal  to  the  angle  of  repose  of  the  earth.  Different  writera 
arrive  at  their  resntts  in  different  ways,  hut  most  of  them  proceed 
Irom  a  consideration  of  the  conditions  of  equiUbrium  of  the  earth 
particles,  and  arrive  at  their  resnlts  by  integration.  Of  the  formnlns 
dednced  in  the  latter  way,  Bankine's  *  are  the  best  known.  All  tlie 
theories  of  this  claes  have  eaaentially  the  same  limitations  and  de- 
fects as  Coulomb's  and  Weyranch's, 

545.  ApmCABUlTT  OF  THXOKSnoAL  TobihtlUl  It  la  generally- 
conceded  that  the  ordinary  theories — Coulomb's,  Weyranch's,  and 
Sankine's, — types  of  the  only  ones  for  which  there  is  any  consider- 
able show  of  reasonableness, — are  safe  ;  but  "  to  assnme  upon  theo- 
retical grounds  a  lateral  thrust  which  practice  shows  to  be  excessive,, 
and  then  compensate  for  it  by  giving  no  foctor  of  safety  to  the  wall,, 
although  the  common  way,  is  not  a  scientific  mode  of  procedure." 
Thb  is  col;  another  reason  for  the  statement,  already  made,  that 
theoretical  investigationa  are  of  but  little  value  in  designing  re- 
taining walls.  The  problem  of  the  retaining  wall  is  not  one  that- 
admits  of  an  esact  mathematical  solution;  the  conditions  can  not  b& 
expressed  in  algebraic  formulas.  Something  must  be  assumed  in 
any  event,  and  it  is  for  more  simple  and  direct  to  assume  the  thick- 
ness of  the  wall  at  once  than  to  derive  the  latter  from  equations 
based  upon  a  namber  of  uncertain  assumptions. 

Bear  in  mind  that  none  of  the  above  formulas  apply  if  the  back 
of  the  wall  inclines  towards  the  earth  to  be  supported,  or  if  the 
wall  has  a  curved  pro^e,  or  if  the  upper  surface  is  irregular.  It 
seems  to  be  conceded  that  in  these  cases  the  surface  of  rupture  i& 
not  a  plane,  and  hence  no  theory  yet  proposed  will  apply. 

In  this  connection  it  seems  necessary  to  warn  the  student  that  • 
not  all  theories  for  retaining  walls  are  as  nearly  correct  as  those 
referred  to  above.  Some  of  them,  although  having  all  the  prestige 
of  antiquity  and  offering  the  advantages  of  extended  table^for  their 
application,  are  totally  valueless,  being  based  upon  unwarranted 
assumptions,  and  violating  the  fundamental  principles  of  mechanics. 

548.  Theoretical  investigations  of  many  engineering  problems 
which  in  every-day  practice  need  not  be  solved  with  extreme  scuu- 


ovGoQi^lc 


.A£J.  2.]  £UPIBICAL  BULES.  349 

Tocy,  tire  nsefal  in  detormiDiDg  the  relations  of  the  varions  elementa 
involved,  and  thus  serve  as  a  skeleton  about  which  to  group  the 
reaulta  of  experience ;  but  the  preceding  discuBsion  shows  that  the 
present  theories  of  the  stability  of  retaining  walls  are  not  sufficiently 
exact  to  serve  even  as  a  guide  for  future  investigations.  Further- 
more, the  stability  of  a  retaining  wall  is  not  a  purely  mathematical 
problem.  Often  the  wall  is  designed  and  built  before  the  nature  of 
the  backing  is  known;  and  the  vifriation  of  the  backing,  due  to  rain, 
frost,  shock,  extraneous  loads,  etc.,  can  not  be  included  in  any 
formnla. 

Abt.  3.  Empimcal  Rules. 

547.  XVOUBH  EUUS.  The  eminent  English  engineer  Benjamin 
Baker,  who  has  bad  large  experience  in  this  line  in  the  coustrnc- 
tioQ  of  the  underground  railroads  of  London,  says,  "Experienca 
has  shown  that  a  wall  [to  sustain  earth  having  a  level  top  surface], 
whose  thickness  is  one  fourth  of  its  height,  and  which  batters  1  or 
2  inches  per  foot  on  the  face,  possesses  sufBcient  stability  when  the 
backing  and  foundation  are  both  favorable.  This  allows  a  factor  o{ 
.safety  of  about  two  to  cover  contingencies.  It  has  also  been  proved 
by  experience  that  under  no  ordinary  conditions  of  surcharge  oi 
lieavy  backing  is  it  necessary  to  make  a  retaining  wall  on  a  solid 
foundation  more  than  double  the  above,  or  one  half  of  the  height  in 
thickness.  Within  these  limits  the  engineer  must  vary  the  strength 
according  to  the  conditions  affecting  the  particular  case.  Outside 
of  these  limits,  the  structure  ceases  to  be  a  retaining  wall  in  the 
ordinary  acceptation  of  the  term.  As  a  result  of  his  own  experi- 
ence, the  author  [Benj.  Baker]  makes  the  thickness  of  retaining 
walls  In  ground  of  an  average  character  equal  to  one  third  of  the 
height  from  the  top  of  the  footings. 

"'Hundreds  of  revetments  have  been  built  by  royal  engineer 
officers  in  accordance  with  Gen.  Fanahawe's  rule  of  some  fifty  years 
ago,  which  was  to  make  the  thickness  of  a  rectangular  brick  wall, 
retaining  ordinary  material,  34  per  cent,  of  the  height  for  a  batter 
of  i,  25  per  cent  for  ^,  26  per  cent,  for  J,  27  per  cent,  for  ^,  28  per 
oent  for  ^,  30  per  cent,  for  ^,  and  33  per  cent,  for  a  vertical  wall.' "  • 

548.  TBAUTWnrs'B  Bule.     Trautwinef  recommends  that  "the 

*Tmi  NoBtMDd'H  Engtneerlng  Magazine,  vol  zxv.  p.  B70,  tram  Froc.  Inst  of 
t  Engineer's  Pockct-Book  {Ed.  188S),  p.  683. 


ovGoQi^lc 


350  BXIAISISQ  WALLS.  [OHAP.  XXT. 

thickness  oq  the  top  of  the  footing  coarse  of  a  vertical  or  nearly 
vertical  wall  which  is  to  eustaiii  a  backing  of  sand,  gravel,  or  e^th, 
level  top  surface,  when  the  backing  Ib  deposited  looeelj  (as  when, 
dumped  from  cars,  carts,  etc.),  for  railroad  practice,  should  not  be 
less  Ihan  the  following  : 
Wall  of  cul-stoDe,  or  of  flrst-Glasa  large-ranged  rubble  in  mortar,  S5  per  cent. 

"     "  good  common' Hcabbled  mortsr- rubble,  or  brick. 40  percent. 

"     "  well  sea bbled  dry  rubble , SOperceoL 

When  the  backing  ie  somewhat  consolidated  in  horizontal  layers, 
each  of  these  thicknesses  may  be  reduced;  but  no  rule  can  be  given 
for  this.  Since  sand  or  gravel  has  no  cohesion,  the  full  dimensions 
06  above  should  be  used,  even  though  the  backing  be  deposited  in 
layers.  A  mixture  of  sand,  or  earth  with  pebbles,  paving  etoaes, 
bowlders,  etc.,  will  exert  a  greater  pressure  gainst  the  wall  than 
the  materials  ordinarily  used  for  backing;  and  hence  when  Buch 
jbacking  has  to  be  used,  the  above  thicknesseB  should  be  increased, 
say,  about  ^  to  |  part." 

549.  Details  of  ConrsiroTioir.  The  arrangement  of  the  foun- 
dation of  a  retaining  wall  is  an  important  matter,  but  has  already 
been  sufiicientlj  discussed  (Bee  Part  III,  and  also  g§  491  and  551). 
It  is  univereally  admitted  that  a  large  majority — by  some  put  at 
nine  out  of  ten,  and  by  others  at  ninety-nine  out  of  a  hundred — of 
foilures  of  retaining  walls  are  due  to  defects  in  the  foundation. 

Retaining  walls  are  constructed  of  ashlar  or  brick,  or  of  either 
ashlar  or  brick  backed  with  rabble,  or  of  rubble  either  with  mortar 
or  dry.  Aa. the  pressure  at  each  bed-joint  is  concentrated  towards 
the  face  of  the  wall,  the  larger  and  most  regular  stones  should  be 
placed  on  the  front.  Occasional  stones  or  even  courses  should 
project  beyond  the  back  of  the  wall,  so  thiit  the  backing  can  rest 
upon  them,  thus  increasing  the  rusistauce  of  the  wall  to  overturn- 
ing. This  object  ib  also  promoted  by  building  the  back  in  steps. 
The  coping  should  consist  of  large  flat  stones  extending  clear  across 
the  wall. 

Aa  a  rule,  the  greatest  thrnst  comes  a^inst  retaining  walls  when 
the  mortar  is  green  and  least  able  to  resist  it,  which  is  a  reason  for 
preferring  cement  to  lime  mortar.  If  the  backing  is  to  be  filled  in 
before  tbe  mortar  hardens,  it  shonld  be  deposited  in  thin,  horizon- 
tfil  layers,  or  the  wall  should  be  supported  temporarily  by  shores. 

650.  Drainage.     Kext  to  a  faulty  foundation,  water  behind  the 


ovGoQi^lc 


ABT.  2.]  EHPIBICAL   RULES.  3S1 

wall  is  the  most  frequent  cauBe  of  the  failure  of  retaining  walls. 
The  water  not  only  adds  to  the  weight  of  the  backing  material,  hnt 
also  softens  the  material  and  changes  the  angle  of  repose  so  as  to 
greatly  increase  its  lateral  thrust.  With  clayey  soil,  or  any  material 
resting  upon  a  gtratum  of  clay,  this  action  becomes  of  the  greatest 
importance.  To  guard  against  the  possibility  of  the  backing's  be- 
coming satnrated  with  water,  holes,  called  weepers,  are  left  through 
the  wall.  One  weep-hole,  three  or  four  inches  wide  and  the  depth 
of  a  course'  of  masonry,  is  generally  sufficient  for  every  three  or 
four  square  yards  of  front  of  the  wall.  When  the  backing  is  clean 
sand,  the  weep-holes  will  allow  all  the  water  to  escape ;  but  if  the 
backing  is  retentive  of  water,  a  vortical  layer  of  stones  or  coarse 
gravel  should  be  placed  next  to  the  wall  to  act  as  a  drain.  An 
ordinary  drain  at  the  back  of  the  wall  is  often  useful. 

Wnen  the  backing  is  liable  to  be  reduced  to  quicksand  or  mud 
by  saturation  with  water,  and  when  this  liability  can  not  be  removed 
by  cffic-ent  drainage,  one  way  of  making  provision  to  resist  the 
additional  pressure  which  may  arise  from  such  saturation  is  to  cal- 
culate the  requisite  thickness  of  wall  as  if  the  earth  were  a  fluid. 
A  pnddle-wftll  is  sometimes  bnilt  against  the  back  of  dock-walls  to 
keep  out  the  water. 

The  resistance  of  the  wall  to  sliding  is  materially  increased  by 
laying  the  lower  courses  of  masonry  with  an  inclination  inward. 
An  objection  to  inclining  the  joints,  particularly  in  dry  masonry, 
is  that  the  water  will  enter  them  and  be  carried  to  the  backing. 
This  objection  is  sometimes  met  by  building  the  face  with  horizon- 
tal courses,  and  inclining  the  courses  in  the  back  of  the  wall.  The 
back  of  the  wall  for  2  or  3  feet  from  the  top  should  have  a  batter 
of  at  least  1  inch  in  1  foot,  in  order  that  the  frost  may  lift  the 
earth  and  not  break  the  joints  of  the  masonry. 

Walls  are  sometimes  built  with  both  faces  inclined  toward  the 
material  to  be  supported,  and  sometimes  with  a  curved  profile  ;  but 
it  is  generally  considered  unwise  to  do  either,  owing  to  the  extra 
expense  and  trouble  in  construction. 

661.  Land  Ties.  Retaining  walls  may  have  their  stability  in- 
creased by  being  tied  or  anchored  by  iron  rods  to  vertical  plates  of 
iron  or  blocks  of  stones  imbedded  in  a  firm  stratum  of  earth'  at  a 
distance  behind  the  wall.  "  The  holding  power,  per  foot  of  breadth, 
of  a  rectangular  vertical  anchoring  plate,  the  depth  of  whose  upper 


ovGoQi^lc 


"8o3  BETAINING    WALLS.  [CHAP.  XW. 

aad  lower  edges  below  the  surface  are  respectively  a;,  and  a:,,  may 
be  approximately  calculated  from  the  following  formula : 

„         V  ~  «,'  4  sin  0  ,_ , , 

^  =  "'-'-l-^Sr3^ M 

in  which  H  ia  the  holding-power  of  the  plate  in  pounds  per  foot  of 
breadth,  to  is  the  weight  in    pounds  of  a  cubic  foot  of  the  earth, 

■  and  0  its  angle  of  repose.  The  center  of  pressure  of  the  plate  ie 
about  two  thirds  of  its  height  below  its  upper  edge, — at  which  point 
the  tie-rod  should  be  attached. 

"If  the  retaining  wall  depends  on  the  tie-rods  alone  for  its 
eecurity  against  sliding  forward,  they  should  be  fastened  to  plates 
on  the  face  of  the  wall  in  the  line  of  the  resultant  pressure  of  the 
earth  behind  the  wall,  that  is,  at  one  third  [see  1 530]  of  the  height 
of  the  wall  above  its  base.  But  if  the  resistance  to  sliding  forward 
ia  to  be  distributed  between  the  foundation  and  the  tie-rods,  the 
latter  should  be  placed  at  a  higher  level.  For  example,  if  half  the 
horizontal  thrust  is  to  be  borne  by  the  foundation  and  half  by  the 
tie-rods,  the  latter  should  be  fixed  to  the  wall  at  two  thirds  of  its 
height  above  the  base."* 

662.  BelieTing  Arohei.  In  extreme  caaes,  the  pressure  of  the 
■•earth  may  be  sustained  by  relieving-arches.  These  consist  of  a  row 
of  arches  having  their  axes  and  the  faces  of  their 
piers  at  right  angles  to  the  face  of  a  bank  of  earth. 
There  may  be  either  a  single  row  of  them  or  several 
tiers;  and  their  front  ends  may  be  closed  by  a  ver- 
tical wall, — which  then  presents  the  appearance  ol 
a  retaining  wall,  although  the  length  of  the  arch- 
ways is  such  as  to  prevent  the  earth  from  abutting 
Tia.  73.  against  it.     Fig.  77  represents  a  vertical  transverse 

■  section  of  such  a  wall,  with  two  tiers  of  relieving  arches  be- 
iiind  it. 

To  determine  the  conditions  of  stability  of  such  a  strueture  aa  a 
whole,  the  horizontal  pressure  against  the  vertical  plane  OD  may  be 
determined,  and  compounded  with  the  weight  of  the  combined 
mass  of  masonry  and  earth  OAED,  to  find  the  resultant  pressare 
•on  the  foundation. 

p.  4U. 


ovGoQi^lc 


CHAPTER  XV. 

BRIDGE  ABUTMENTS. 

MS.  OlHXKlL  Foxm.  There  are  four  formB  of  abutments  in 
morfk  or  less  general  nae,  1.  A  plain  wall  parallel  to  the  current,' 
shown  in  elevation  at  Pig,  78,  with  or  without  the  wings  J  DFaaA 
BEG.  The  slopes  may  be  finished  with  an  inclined  coping,  as 
A  D,  or  offset  at  each  course,  as  B  E — usually  the  latter.  This  form 
may  appropriately  be  called  the  straight  aiutmeni.  2.  The  wings 
may  be  swang  around  into  the  bank  at  any  angle,  as  shown  (in  plan) 
in  Fig.  79.    The  angle  0  is  usually  about  30°.     This  form  is  known 


.^^^^.=^yA 


SB  the  wing  abutment.  3.  When  (f>  of  Fig.  79  becomes  90°,  we  have 
Fig.  80,  which  is  caUed  the  U  abutment.  4.  If  the  wings  of  Fig. 
SO  are  moved  to  the  center  of  the  head-wall,  we  get  Fig.  81,  vhich 
is  known  as  the  T  abutment. 

'  The  abutment  of  an  ordinary  bridge  has  two  offices  to  perform, 
-viz.,  (1)  to  support  one  end  of  the  bridge,  and  (2)  to  keep  the  earth 
embankment  from  sliding  into  the  water.  In  Fig.  78,  the  portion 
D  E  Q  F  serves  both  these  purposes,  while  the  wings  A  D  F  and 
B  E  0  act  only  as  retaining  walls.  In  Figs.  79  and  80,  the  portion 
D  E  perf  ormB  both  offices,  while  the  wings  .4  D  and  B  E  are  merely 
retaining  walla.  In  Fig,  81  the  "  head  "  D  E  supports  the  bridge, 
and  the  "  tail,"  or  "  stem,"  A  B  carries  the  train;  hence  the  whole 
Htructnre  acts  as  a  retaining  wall  and  also  supports  the  load.  The 
abutment  proper  may  fail  (1)  by  sliding  forward,  (2)  by  bulging,  or 
(3)  by  criishing;  however,  it  is  improbable  that  it  will  fail  by  sliding 
forward.  Its  dimensions  are  to  be  determined  as  for  a  retaining 
-wall  (Chap.  XIV);  but  the  mathematical  theory  of  the  lateral 


ovGoQi^lc 


864  BEIDQE  ABUTKENTS.  [CHAP.  XV.. 

pressnre  of  earth  is  a  much  less  perfect  guide  for  designing  bridge- 
abutmentB  than  it  iB  for  simple  retaining  walls.  The  weight  of  the 
bridge  helps  the  abutment  to  reeiat  the  thrust  of  the  earth;  bnt,  on 
the  other  hand,  the  weight  of  the  train  on  the  embankment  in- 
'  creases  the  lateral  pressure  against  the  abatment. 

854.  The  form  of  the  abutment  to  be  adopted  for  any  particular 
case  will  depend  upon  the  locality, — whether  the  banks  are  low  and 
flat,  or  steep  and  rocky;  whether  the  current  is  swift  or  slow;  and 
also  upon  the  relative  cost  of  earthwork  and  masonry.  If  the  shore 
ie  flat,  and  not  liable  to  be  cut  away  by  the  current,  an  abutment 
like  Fig.  78  will  be  sufficient  and  most  economical.  However,  this 
form  is  seldom  used,  owing  to  the  danger  of  the  water's  flowing^ 
along  immediately  behind  the  wall. 

The  form  of  Fig.  79  may  be  adopted  when  there  is  a  contraction 
of  the  waterway  at  the  bridge  site,  since  deflecting  the  wing  walla, 
above  and  below,  slightly  increases  the  amount  of  water  that  can- 
pass.  This  advantage  can  be  obtained,  to  some  degree,  with  the 
straight  abutment  (Fig.  78)  by  thinning  the  wings  on  the  front  and 
leaving  the  back  of  the  wings  and  abutments  in  one  straight  line. 
There  is  not  only  no  hydraulic  advantage,  bat  there  is  a  positive 
disadvantage,  in  increasing  the  deflection  of  the  wings  beyond,  say, 
10°  or  15°.  The  more  the  wing  departs  from  the  face  line  as  it 
swings  round  into  the  embankment,  the  greater  it«  length  and  also- 
the  greater  is  the  thrust  upon  it.  The  wings  are  not  nsually  ex- 
tended to  the  toe,  B,  of  the  embankment  slope,  but  stop  at  a  height, 
depending  upon  the  angle  of  deflection  and  the  elope,  such  that  the- 
earth  flowing  around  the  end  of  the  wall  will  not  get  into  the  chan- 
nel of  the  stream.  It  can  be  shown  mathematically  that,  if  the  toe 
of  the  earth  which  flows  around  the  end  of  the  wing  is  to  be  kept 
three  or  four  feet  back  from  the  straight  line  through  the  &ce  of 
the  abutment,  an  angle  of  35°  to  35°  is  best  for  economy  of  the 
material  in  the  wing  -wallB.  This  angle  varies  slightly  with  the  pro- 
portions adopted  for  the  wing  wall  and  with  the  details  of  the 
masonry.  This  form  of  construction  is  objectionable,  since  the 
foot  of  the  slope  in  front  of  the  wing  is  liable  to  be  washed  away ;. 
but  this  could  be  remedied  somewhat  by  riprapping  the  slope,  or, 
better,  by  making  the  wings  longer. 

Fig.  78  is  one  extreme  of  Fig.  79,  and  Fig.  80  is  the  other.  Aa 
the  wing  swings  back  into  the  embankment  the  thrust  upon  it  in- 


ovGoQi^lc 


WING  ABCTMEJJT.  Wf 

I,  reaching  ita  iiiaximam  at  an  angle  of  about  45°;  whea  tb» 
wiDg  is  thrown  farther  back  the  oatward  thrust  decreaBes,  owing  to 
the  filling  np  of  the  slope  in  front  of  the  wing.  Bringing  the  winga 
perpendicnlar  to  the  face  of  the  abatment,  as  in  Fig,  80,  also  de- 
creases the  lateral  pressure  of  the  earth,  owing  to  the  intersection  of 
the  surfaces  of  ruptui-e  for  the  two  sides,  which  is  equivalent  to  re- 
moving part  of  the  "prisni  of  maiiraum  thrust."  If  the  banks  of 
the  stream  are  steep,  the  base  of  the  wing  walls  of  Fig.  80  may  b© 
stepped  to  fit  the  ground,  thereby  saving  masonry.  Under  these 
conditions,  also  the  wing  abutment,  Fig.  79,  can  be  treated  in  the 
same  way;  but  the  saving  is  considerably  less.  When  the  masonry 
is  stepped  off  in  this  way,  the  angle  thus  formed  becomes  the  weak- 
est part  of  the  masonry;  but,  as  the  masonry  has  a  large  excess  of 
strength,  there  is  not  much  probability  of  danger  from  this  cause, 
provided  the  work  is  executed  with  reasonable  care. 

566.  Fig.  81  is  the  most  common  form  of  abutment.  For  equal 
amounts  of  masonry,  wing  abutments  give  better  protection  to  the 
embankments  than  T  abutments.  The  latter  are  more  stable,  be- 
cause the  center  of  gravity  of  the  masonry  Is  farther  back  from  the 
line  of  the  face  of  the  abutment,  about  which  line  the  abutment 
must  turn  or  along  which  it  will  first  crush.  The  amount  of  m*- 
sonry  in  tall  T  abutments  can  be  decreased  by  building  the  tail  wall 
hollow,  or  by  introducing  arches  under  it.  The  more  massive  the 
masonry,  the  cheaper  it  can  be  constructed;  and,  for  this  reason,  it 
is  probable  that  the  simple  T  abatment  is  cheaper  than  the  U  abut- 
ment, although  the  latter  may  have  less  masonry  in  it.  On  the  other 
hand,  the  opportunities  for  inspecting  the  masonry  during  construc- 
tion are  better  with  the  U  than  with  the  T  abutment,  and  hence  the 
former  is  usually  better  built  than  the  latter.  This  la  an  important 
item,  since  it  is  somewhat  common  tor  railroad  masonry  to  fail  by 
being  shaken  to  pieces  by  the  passage  of  trains. 

666.  WWO  ABtrtWEXT.  Fig,  82  shows  a  common  form  of  the 
wing  abutment.  This  one  is  finished  with  stone  pedestal  blocks — 
marked  B  in  plan,  A  in  elevation,  and  C  in  section, — which  is  not 
always  done.  The  thickness  of  pedestal  blocks  and  the  thickness. 
of  the  coping  under  the  pedestal  blocks  vary  slightly  with  the  span 
(see  g  558).  The  height  of  the  parapet  wall,  or  dirt  wall  (the  wall 
which  keeps  back  the  top  of  the  embankment,  marked  /*  H'  in. 
section),  will  vary  with  the  style  of  the  bridge,  but  should  not  have 


ovGoQi^lc 


366  BBIDQE   ABLTMENXa  [CUAP,  XV. 

a  thickness  less  than  four  tenths  of  its  height  (see  g§  547  and  548). 
The  bridge  often  rests  directly  upon  the  coping.  The  top  dimen- 
sions of  the  abutment  will  depend  somewhat  upon  the  size  and 
form  of  bridge  ;  but  for  railroad  bridges  it  will  usuatlf  not  be  less 
than  5  ft.  vide  by  20  ft.  long,  nor  more  than  6  ft.  by  22  ft. 


II 


The  nsnal  batter  is  1  in  13;  sometimes  1  in  2i.  For  heights 
tiader  about  30  ft.,  the  top  dimensions  and  the  batter  determine  the 
thlckneBS  at  the  bottom.     For  greater  heights,  the  quite  nniform 


ovGoQi^lc 


WING  ABUTMENT. 


TABLE  87. 

QoAKTRT  or  Hasonbt  in  Wins  Abutments  of  the  Qeneeai.  Fobk 

8BOWN  IN  Fio.  83.    See  g  557. 


AaiA  or  Lowrar 


p 

p 

^< 

/«(. 

/«(. 

sa.B 

/«(. 

/«(. 

108 

M  1 

75. a 

IflS.S 
301. c 


•  DJmeDsioll  iit«n«  In  tvopntestat  blnckg =    Mcu.  feBt. 

-' cuplng  of  one  Bbutmeut =  SS4   "      " 

Total  dimeniioD  stone  in   '■  "         =889   "      " 

rale  ie  to  make  the  thickness  four  tenths  of  the  height.  The  amoant 
of  masonry  in  the  abutment  is  computed  in  accordance  with  this 
rule,  although  the  actual  quantity  is  usually  more  than  that  required 
by  it     >jince  there  is  no  objection  to  the  wall's  being  rough,  no 


ovGoQi^lc 


368  BRIDGE    ABCTMENTS,  [CDAP,  XT. 

stones  are  cnt  out  to  eecnre  the  specified  thickness,  and  hence  the 
actual  quantity  of  masonry  nsually  exceeds  tlie  amount  required. 
The  spread  of  the  footiug  courses  and  foundation  will  depend,  of 
course,  upon  the  location. 

The  wings  should  be  proportioned  according  to  the  rules  for 
retaining  walla  (see  g§  547  and  548).  The  wings  are  not  always  pro- 
longed until  their  outer  ends  intersect  the  foot  of  tlie  embankment 
slope;  but  aro  frequently  stopped  with  an  end  height  of  3  to  5  feet 
above  the  footing.  The  thickness  of  the  wing  wall  decreases  from 
the  body  of  the  abutment  toward  the  tail  in  proportion  to  the  height. 
For  appearance,  the  top  of  the  wing  is  usually  made  uniform  from 
head  to  tail,  being  uHually  from  2i  to  SJ  feet,  according  to  the  size 
of  the  structure.  The  steps  should  be  capped  with  stones,  not  less 
than  1  foot  thick,  covering  the  entire  step  and  extending  under  the 
step  above  not  less  than  1  foot. 

657.  Content*  of  Wing  Abutments.  The  table  on  page  357 
gives  the  quantities  of  masonry  in  wing  abutments  of  the  form 
shown  in  Fig.  82.  Since  the  outlines  of  such  structures  are  not 
simple  geometrical  figures,  it  is  necessary  to  make  more  or  less  ap- 
proximations in  computing  the  cubical  contents.  For  eianple,  fh 
Fig.  82  the  wings  are  stepped  ofi  to  fit  the  slope  of  the  emba  jkment 
as  shown;  and  hence  the  comer  of  each  course  projects  bej  ond  the 
earthwork.  The  amount  of  masonry  in  these  projecting  corners 
varies  as  the  thickness  of  the  courses,  and  for  any  j,-irticular  abut- 
ment it  could  be  found  accurately;  but,  in  computing  a  table  of 
general  results,  it  is  necessary  to  assume  some  thickness  for  the 
courses.  In  this  case  the  courses  were  assumed  to  be  1  foot  thick. 
Thebackof  the  "head  "was  assumed  to  conform  strictly  to  the  batter 
line,  although  in  construction  itwould  be  stepped.  The  dimensions 
of  the  parapet  wall  will  vjiry  with  the  thickness  of  the  pedestal 
blocks  used,  and  also  with  the  style  of  tlie  bridge.  The  contents 
of  the  parapet  as  given  in  the  table  are  for  the  dimensions  shown  in 
Fig.  83.  .     _  _ 

Footing  courses  were  not  included  in  the  table,  since  they  vary 
with  the  nature  of  the  foundation.  The  area  o£  the  lowest  course 
of  masonry  is  given,  from  which  the  areas  of  the  footing  courses  and 
of  the  foundation  pit  may  be  determined.  The  thickness  at  the 
top  and  the  batter,  as  in  Fig.  82,  give,  for  any  height  found  in  the 
lable,  a  thickness  of  wall  at  the  bottom  of  at  least  four  tenths  of  its 


ovGoQi^lc 


V   ABUTMENT.  369 

heigbt  (see  §548);  for  heights  greater  than  in  the  tab)e,  the  back 
-of  the  wall  must  be  stepped  to  keep  the  thickneae  four  tenths  of  the 
height.* 

668.  U  AbutmehT.  Fig.  83  shows  the  standard  plans  of  the 
Atchison,  Topeka  and  Santa  Fe  R.  R.f  for  U  abutments.  Tbia  is 
the  only  form  of  bridge  abutment  used  on  this  road,  except  in 
-special  cases.  The  T  abutment  was  once  the  standard,  but  was 
abandoned  about  fifteen  years  ago.^ 

The  specifications  under  whicli  these  abntmenta  are  bnilt,  require 
as  follows  :  "  1.  Bed-plate  pedestal  blocks  to  be  3  feet  thick,  and 
placed  symmetrically  with  regard  to  the  plates.  2.  Coping  under 
pedestal  blocks  to  be  18  inches  thick  for  all  spans  exceeding  100 
feet,  16  inches  for  90  feet,  and  14  inches  for  spans  under  90 
feet, — said  coping  to  be  through  stones,  and  spaced  alike  from  both  , 
sides  of  abutment.  3.  Distances  from  front  of  dirt  wall  to  front 
of  bridge  seat,  and  from  grade  line  to  top  of  bridge  seat,  and 
thickness  of- dirt  wall,  to  vary  for  different  styles  and  lengths  of 
bridges.  4.  Front  walls  to  l>e  23  feet  wide  under  bridge  seat  for 
all  spans  of  100  to  160  feet  inclusive.  5.  Total  width  of  bridge 
seat  to  be  5J  feet,  for  all  spans.  6.  Steps  on  back  of  walls  to 
be  used  only  when  necessary  to  keep  thickness  -fg  of  the  height. 
'7.  In  case  piling  is  not  used,  footing  courses  may  be  added  to  give 
secure  foundation.  8.  Length  of  wing  walls  to  be  determined  by  a 
-slope  of  1-^  to  1  at  the  back  end  ot  the  walla — as  shown  by  dotted 
line  in  front  elevation, — thence  by  a  slope  of  1  to  1  down  the  outside 
— as  shown  on  side  elevation — to  the  intersection  of  the  ground  line 
with  face  of  abutment.  This  rule  may  be  modified  in  special  cases. 
9.  Dimeusious  not  given  on  the  drawing  are  determined  by  the 
style  and  length  of  bridge,  and  are  to  be  found  on  special  sheet." 

669.  Although  this  road  is  noted  for  the  excellency  of  its 
masonry,  this  design  could  be  improved  by  leaving  a  weep  hole  in 
the  side  walls,  2  or  3  inches  wide  and  the  depth  of  a  course  of 


•  In  computing  the  conlenta  ol  masonry  Btructares,  tt  U  uecesMUT  to  remember 
that  the  volame  of  any  mass  which  1b  made  up  of  priBma.  wedg:es,  and  pyramids — or 
conee—mnst  be  determined  by  the  prlsmoldal  fonnala :  but  It  the  mass  la  compoeed 
wholly  ot  prisms  and  wedges,  the  contenta  can  be  correctly  toand  b;  osliig  the  aver- 


ovGoQi^lc 


BKtDQE  ABtTTHENTS.  [CBAP.  XT. 


Fib.  eiL-U  ABimaiiT.-A.  T.  &  B.  F.  B.  B 


ovGoQi^lc 


n   ABCTUENT. 


r  Mabonut  in  U  Abotmentb  of  thk  Qenebal  Fork 
anowN  IN  Pio.  83.    See  §  060. 


Sri 

OF  TH« 

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ll 
11 

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w 

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1.338 

11      33  8 

5.9 

141 

4.4^ 

1.377 

76!8 

1 

:  ins  \  1 

12  ■    24-0 

6,0 

14* 

4.8| 

1,530 

86.0 

18 

34.3 

6,1 

147 

5.31 

1,665 

96.0 

i  i 
1  1 

i 

14 

348     6.3 

150 

5.8; 

1.814 

106.8 

;  ixx  ==  =  «;-;-.  ^ 

15 

24-5     6.2 

153 

6.0 

1,966 

118.4 

■  ss  "-"f^  --ti  i 

16 

34,7 

6.3 

156 

6.4 

3,130 

130.8 

g  «^  II  n  "sig;,  V 

17 

24.8 

6,8 

139 

6.8 

3.288 

144-0 

la 

35.0 

7.8 

180 

7.2 

2,478 

158.0 

19 

2S.2 

7,6 

191 

7.6 

3;688 

172.8 

S 

^  ■--  £~Jui;^Z   " 

ao 

35-3 

8,0 

20:( 

8.0 

2,9-20 

188.4 

t   '^', 

;  is  g    |:++  f 

21 

35.5 

8.4 

214 

8,4 

8.1741  204,8 

i  -S  ^    I^M  1 

23 

25.7 

8.8 

326 

8,8 

3.449   223,0 

i    : 

28 

35.8 

».2 

338 

9.2 

3,746   340,0 

^       :S 

SflfiH 

31 

26.0 

0.6 

350 

9  6 

4,066    258.8 

2^ 

26.2 

10.0 

203 

10. 0 

4.408    278. 4 

1      " 

20 

36.3 

!0.4 

374 

10.4 

4.772;  298.8 

l?f:|f 

37 

26.5 

10.8 

386 

10-8 

5,160 

330.0 

s 

38 

26.7 

n.3 

299 

11.3 

5,570 

342.0 

2» 

26.8 

11-6 

311 

11.6 

8.oo;t 

364-8 

il--'sl 

30 

27.0   13.0 

834 

12-0 

6.460 

388-4 

l^' 

r"  t 

SI 

37,3  il3.4 

337 

13.4 

6,941 

413.8 

33 

37.8  il2.6 

sm  . 

12.8 

7,445 

438-0 

.  J        gSa 

33 

87.5    13-2 

863 

13.3 

7.97:l 

464.0 

84 

37.7  ,13.6 

37« 

13.6 

asafl  490,8 

85 

27.8  |14-0 

390 

14.0 

9,103   518.4 

|i|. 

. . , , .        , , , 

•  F"r  riin.pnBlon« 

of  oopltitr  snd  pedesul  blocks. 

hot\m.         "^ 

* 

jvGooi^le 


'362  BBIDOE    ABCTHENTS.  [CSAP.  XT. 

maaonry,  for  each  4  or  5  square  yards  of  wing  wall.  Cinders,  or 
Band  and  gravel  are  Bometimes  used  to  fill  in  between  the  wing  walls 
to  give  a  better  drain^e,  and  also  to  decrease  the  lateral  thrust  of 
the  earth. 

560.  Content!  of  U  Abntments.     The  table  on  page  361  gives 
the  contents  of  U  abutments  of  the  form  shown  in  Fig.  83.     The 


_  J  ij  li  LI  Lf  U) 
1  n  n  "  n  n  n  r» 
V  v  y  I)  ^,'  U  0  1^ 


T    ABUTMENT 


quantities  were  computed  on  the  basis  that  the  thickness  of  the 
walls  was  four  tenths  the  height,  except  that  no  wall  was  taken  of  a 
loss  thickness  than  that  given  by  the  thickness  at  the  top  and  the 
batter  as  in  the  drawing. 

661.  T  ABnmitT.    Fig.  81  shows  the  ordinary  form  of  T  abnt- 


ovGoQi^lc 


T  ABUTMENT. 


QnAsmT  aw  Habonsy  in  T  Abuthrhts  of  thb  Oehxral  Fobh 
BBOWN  IN  Pio.  84.    Sbb  §563. 


^S 

:r?H°/H's,. 

(Wtitt  or  Hawhrt. 

|e 

_ 

■s 

s 
1 

'^ 

1 

1 

'R 

tc 

^ 

/•«'. 

/«.(. 

fttt 

/«( 

cu.ft. 

Cll.fl. 

CH.fl. 

|°SS!S=IEIS|SIE  1 

22.8 

S.8 

183 

607 

13,6 

60  I 

e 

28.0 

6.0 

188 

743 

18.0 

73 

7 

23.3 

8.3 

148 

888 

34.5 

84 

ft,      «*^^*S 
1      Sffiffig 

:I 

8 

23  3 

6.3 

148 

1,039 

33.0 

96 

^•a-> 

S 

23.5 

6.5 

168 

1.179 

40.5 

108 

;i 

:o 

38.7 

a. 7 

168 

1.BS4 

50,0 

130 

11 

28.8 

6.8 

168 

1,496 

60.5 

m 

1  l«; 

m 

12 

24.0 

7.0 

188 

1,660 

73,0 

144  1 

:  i 

13 

34.2 

7,2 

173 

1,831 

84,5 

166  ! 

T     .^oos 

22a 

14 

24.8 

7.8 

178 

2,006 

96,0 

188 

4m 

;  b 

15 

34.5 

7.5 

184 

2.188 

112.5 

180  ■ 

Soe 

18 

24.7 

7.7 

189 

3.374 ■  138.0 

193 

tiii 

£ 

II  II  ff 

34.8 

7.8 

195 

2,566    144.6 

304  1 

!ff';|, 

18 

25.0 

8.0  ,    300 

3,768    163.0 

318 

■^S.  -  «;d    !» 

IB 

35.3 

8.3      206 

2,968    180.5 

238 

»l«  sli.8=-;3 
sis;    i,5|-;""xx 

20 

■21 
23 

35.8 
25.5 
35.7 

8.3      311 

8.6  217 

8.7  323 

3.174 
3,8H8 
3,608 

300,0 
220,6 
343.0 

340  1 
352  1 
264  ; 

28 

35.8 

8.8       336 

8,833 

364.6 

376 

84 

26. 0 

9-0      284 

4,064 

288,0 

268 

BiZi:,%-,t.-i..". 

25 

26.3 

9,3  ,     340 

4,301 

313,5 

800 

nii.i-fi'j'i' 

H6.3 

9.8      246 

4,544 

888.0 

312 

27 

36.5 

9.5 

2.53 

4,7931  364,6 

334  i 

:ae 

26.7 

9.7 

258 

5,047'  893  0 

386 

29 

36.8 

9.8 

264 

5,308    430.5 

348 

m'MR 

30 

27.0 

10.0 

270 

5.675 ■  450,0 

360 

81 

37.3 

10.2 

276 

5,H48i  480.5 

372 

3-2 

87.3 

10.8 

382 

6,127|  512.0 

884 

83 

37.6 

10.6  1    289 

6,418,  544,6 

396 

34 

27.7 

10.7      395 

6.706'  578.0 

408 

3S 

37.8 

10,8  !    801 

7.008    613,5 

1 

430 

lii=. =.==,==,, 

Ar«orcopln( 

on  a  wing.,  per 

t.ofl«nBth=.     R 

•q.f(. 

fill 

^..-..^otcopfn* 

ODbrHge-Mkt 

=  188 

jvGooi^le 


864  BRIDOB  ABUTMEHTS.  LCHAP.  Xt- 

ment.  For  railroad  bridges  the  head  is  nsnally  Dot  lesB  than  5  ft. 
X  20  ft.,  nor  more  than  6  ft,  X  22  ft.,  under  the  coping,  according 
to  the  size  of  the  bridge.  The  tail  wall  is  UBually  10  or  13  ft.  wide, 
and  of  such  length  that  the  foot  of  the  ^lope  of  the  embankment 
will  juBt  reach  to  the  back  of  the  head  wall.  The  batter  on  the 
head  wall  is  1  to  13  or  1  to  24  all  around.  The  tail  wall  is  generally 
built  vertical  on  the  sides  and  the  end.  Notice  the  batter  at  the 
top  of  the  free  end  of  the  tail  wall.  This  is  known  as  the  "  frost 
batter,"  and  is  to  prevent  the  frost  from  dislocating  the  corner  of 
the  masonry.  The  drainage  of  the  ballast  pocket  should  be  pro- 
vided for  by  leaving  a  space  between  the  ends  of  two  atones. 
Formerly  the  tail  wall  was  sometimes  only  7  or  8  feet  wide,  in  which 
caae  the  ties  were  laid  directly  upon  the  masonry  without  the  inter- 
vention of  ballast ;  but  this  practice  has  been  abandoned,  as  being 
very  destructive  of  both  rolling  stock  and  roasonry. 

According  to  the  common  theories  for  retaining  walls,  T  abut- 
ments with  dimensions  as  above  have  very  large  factors  of  stability 
against  sliding,  and  overturning,  and  crushing. 

562,  Content!  of  T  Abatments.  The  table  on  page  163  gives  the 
contents  of  the  abutments  of  the  form  shown  in  Fig.  84.  The 
height  of  the  tail  above  the  under  aide  of  the  bridge-seat  coping  will 
vary  with  the  thickness  of  the  pedestal  blocks,  and  with  the  style  of 
the  bridge ;  and  hence  the  table  gives  the  quantities  in  the  abutment 
below  the  bridge-seat  coping  und  above  the  footing.  The  quantity 
of  masonry  above  this  line  will  vary  also  with  the  amount  of  ballast 
used.  The  term  "wedge"  in  the  table  is  used  to  designate  tliat 
part  of  the  tail  included  between  the  head  and  a  vertical  plane 
through  the  lower  edge  of  the  back  face  of  the  head, 

663.  FOUHDATIOB.  Usnally  but  little  difficulty  is  encountered 
in  securing  a  foundation  for  bridge  abutments.  Frequently  the 
foundation  is  shallow,  und  can  be  put  down  without  a  coffer-dam, 
or  at  most  with  only  u  light  curb  (see  g§  316-;'0).  Where  the  ground 
is  soft  or  liable  to  scour,  a  pile  foundation  and  grillage  is  generally 
employed.  For  the  method  of  doing  this,  see  Art.  3,  Chapter  XI ; 
and  for  examples  of  this  kind  of  foundntion,  see  Fig.  84  (page  362), 
Fig.  86  (page  380),  and  Fig.  90  (page  386). 

Where  there  is  no  danger  of  undei' washing,  and  where  the  fonu- 
dation  will  at  all  times  be  under  water,  the  masonry  may  be  started 
upon  a  timber  platform  consisting  of  timbers  from,  say,  8  to  13 


ovGoQi^lc 


QCALITT   OF  MABONBT.  365 

incheB  thick,  laid  side  by  side  upon  sills,  and  covered  by  one  or 
more  layers  of  timbers  or  thick  planks,  according  to  the  depth  of 
the  foundation  and  the  magnitude  of  the  structure.  For  an  exam- 
ple of  a  foundation  of  this  class,  see  Plate  II.  For  a  discussion  of 
the  method  of  failure  by  sliding  on  the  fonndation,  see  §  491. 

564.  auAUTT  or  HASontX.— Bridge  abutments  are  built  of 
first-class  masonry  (g  307)  or  of  second-class  (gg  209  and  213),  ac- 
cording to  the  importance  of  the  structure.  See  also  the  specifica- 
tions tor  bridge  pier  masonry  (^  591-600).  The  coping  should  be 
composed  of  as  large  stones  as  practicable — not  less  than  13  inches 
thick,  and  15  or  18  inches  thick  is  better  and  more  frequently  used. 

Sometimes,  the  bed  plates  of  the  bridge  rest  directly  upon  the 
coping,  but  usually  upon  a  stone  pedestal  block  (see  Figs.  82  and 
S3),  in  which  case  small  pedestals,  upon  which  the  rail  stringers 
rest  (see  Fig.  90,  page  386),  are  also  generally  need. 

666.  Con.    For  data  on  the  cost  of  masonry,  see  g§  233-38. 


ovGoQi^lc 


CHAPTER  XVL 
BRIDQE    PIE»S. 

566.  The  eelection  of  the  site  of  the  bridge  and  the  arrangemeDt 
of  the  sptuiB,  although  important  in  themselves,  do  not  properly  be- 
long to  the  part  of  the  problem  here  considered ;  therefore  they 
■will  be  discussed  only  briefly.  The  location  of  the  bridge  is  nsually 
a  compromiBe  between  the  intereste  of  the  railroad  or  highway,  and 
of  the  river.  On  navigable  streams,  the  location  of  a  bridgf,  itfr 
keight,  position  of  piers,  etc.,  are  subject  to  the  approval  of  engi- 
neers appointed  for  the  porpose  by  the  United  States  Government. 
The  law  requires  that  the  bridge  shall  cross  the  main  channel  nearly- 
at  right  angles,  and  that  the  abutments  shall  not  contract  nor  the 
piers  obstruct  the  water  way.  For  the  regulations  governing  tho- 
varioDS  streams,  and  also  reports  made  on  special  cases,  see  the 
various  annnal  reports  of  the  Chief  of  Engineers,  XS.  S.  A.,  partlcQ- 
larly  Appendix  X,,  of  the  Report  for  1878. 

The  arrangement  of  the  spans  is  determined  mainly  by  the  rela- 
tive expense  for  foundations,  and  the  increased  expense  per  linear 
foot  of  long  spans.  Where  the  piers  are  low  and  foundations  eoeily 
secured,  with  a  correspondingly  light  cost,  short  spans  and  an  in- 
creased number  of  piers  are  generally  economical,  provided  the  piers 
do  not  dangerously  obstruct  the  current  or  the  stream  is  not  navi- 
gable. On  the  other  hand,  where  the  cost  of  securing  proper  foun- 
dations is  great  and  much  difficulty  is  likely  to  be  encountered,  long 
spans  and  the  minimum  number  of  piers  is  best.  Sound  judgment 
and  large  experience  are  required  in  comparing  and  deciding  upon 
the  plan  best  adapted  to  the  varying  local  conditions. 

Within  a  few  years  it  has  become  necessary  to  build  bridge  pier» 
of  very  great  height,  and  for  economical  considerations  iron  has 
been  substituted  for  stone.  The  determination  of  the  stability  of 
Buch  piers  is  wholly  a  question  of  finding  the  stress  in  fmme  struc- 
tures,— the  consideration  of  which  is  foi-eign  to  our  subject. 


ovGoQi^lc 


ABT.  1.]  THEOBT  0?  STABILITT. 


Art,  1,  Theory  of  Stability. 

667.  ItETEOD  OF  Fauurz.  A  bridge  pier  may  fail  in  any  on»- 
of  three  waya :  (1)  by  alidiiig  on  any  section  on  account  of  the  ac- 
tion of  the  wind  against  the  train,  bridge,  and  exposed  part  of  the 
pier,  and  of  the  current  of  the  stream  against  the  immersed  part  of 
the  pier ;  or  (2)  by  overturning  at  any  section  when  the  moment  of 
the  horizontal  forces  above  the  sectioD  exceeds  the  moment  of  the 
weight  on  the  section  ;  or  (3)  by  crushing  at  any  section  nnder  tho- 
combined  weight  of  the  pier,  the  bridge,  and  the  train.  Tha^ 
dimensions  of  piers  are  seldom  determined  by  the  preceding  condi- 
tions ;  the  dimensions  required  at  the  top  (§  584)  for  the  bridge. 
seat,  together  with  a  alight  batter  for  appearance,  generally  give 
sufBcient  stability  a^inst  sliding,  overturning,  and  crushiug.  How- 
ever, the  method  of  determining  the  stability  will  be  briefly  out- 
lined and  illnstrated  by  an  example. 

568.  Stabiutt  AOAivbt  SuBIiie.  Effect  of  the  Wind.  The- 
pressure  of  the  wind  against  the  truss  alone  is  usually  taken  at  50- 
Ibs.  per  sq.  ft.  against  twice  the  vertical  projection  of  oue  tmss^ 
which  for  well-proportioned  iron  trusses  will  average  about  10  sq.  ft. 
per  linear  foot  of  span.  The  pressure  of  the  wind  against  the  truss 
and  train  together  is  usually  taken  at  30  Iba  per  sq.  ft.  of  truss  and 
train.  The  train  exposes  about  10  sq.  ft,  of  surface,  per  linear  foot. 
The  pressure  of  the  wind  against  any  other  than  a  flat  surface  is. 
not  known  with  any  certainty ;  for  a  cylinder,  it  is  usually  assumed 
that  the  pressure  is  two  thirds  of  that  against  its  vertical  projection. 

569.  Effect  of  Current  For  the  pressure  of  the  current  of" 
water  against  an  obstruction,  Weisbach's  Mechanics  of  Engineering 
(page  1,030  of  Coxe'a  edition)  gives  the  formula. 


(!)■ 


in  which  P  is  the  pressure  in  pounds,  s  the  exposed  surface  in 
sq.  ft.,  A  a  co-efiBcient  depending  npon  the  ratio  of  width  to  length 
of  the  pier,  w  the  weight  of  a  cubic  foot  of  water,  v  the  velocity  in 
ft  per  sec.,  and  g  the  acceleration  of  gravity.  For  piers  with 
rectangular  cross  section,  k  varies  between  1.47  and  1.33,  the  first 
being  for  square  piers  and  the  latter  for  those  3  times  as  long  as. 


ovGoQi^lc 


368  BBIDOE   FIEBS.  [CUAP.   ZVI. 

Wide ;  for  cyliaders,  i  =  about  0.T3.  The  law  of  the  Tarution  of 
the  yelocity  with  depth  U  not  certainly  known;  bnt  it  is  probable 
that  the  velocity  raries  as  the  ordioates  of  an  ellipee,  the  greatest 
velocity  being  a  little  below  the  enrface.  Of  coarse,  the  water  haa 
ita  maiimam  effect  when  at  its  highest  stage. 

S70.  Effect  of  Im.  The  pier  is  also  liable  to  a  horisontal  press- 
ure dne  to  floating  ice.  The  formnlaa  for  impact  are  not  applica- 
ble to  this  case.  The  assumption  is  sometimes  made  that  the  field 
of  ice  which  may  rest  against  the  pier,  will  simply  increase  the  sar- 
face  exposed  to  the  pressure  of  the  carrent  The  greatest  pressare 
possible  will  occnrwhen  a  field  of  ice,  so  large  that  it  is  not  stopped 
by  the  impact,  strikes  the  pier  and  plows  past,  crashing  a  channel 
throngh  it  eqnal  to  the  greatest  width  of  the  pier.  The  resulting 
horizontal  pressure  is  eqnal  to  the  area  crushed  multiplied  by  the 
cmsbiag  strength  of  the  ice.  I'he  latter  varies  with  the  tempera- 
ture; bnt  since  ice  will  more  down  stream  ih  fields  only  when 
melting,  we  desire  its  minimum  strength.  The  crushing  strength 
of  floating  ice  is  sometimes  put  at  20  tons  per  sq.  ft  (300  lbs.  per 
eq.  inch);  bnt  in  computing  the  stability  of  the  piers  of  the  St. 
Lonis  steel-arch  bridge,  it  was  taken  at  600  lbs.  per  sq.  inch  (43 
tons  per  sq.  ft.).  According  to  experiments  made  under  the 
author's  direction,*  the  crushing  strength  of  ice  at  23°  P.,  varies 
between  370  and  760  lbs.  per  sq.  in. 

Occasionally  a  gorge  of  ice  may  form  between  the  piers,  and 
dam  the  water  back.  The  resulting  horizontal  pressure  on  a  pier 
will  then  be  eqnal  to  the  hydrostatic  pressure  on  the  width  of  the 
pier  and  half  the  span  on  either  side,  dne  to  the  difference  between 
the  level  of  the  water  immediately  above  and  below  the  bridge 
opening.  A  pier  is  also  liable  to  blows  from  rafts,  boats,  etc ;  but 
as  these  can  not  occur  simnltaneously  with  a  field  of  ice,  and  will 
probably  be  smaller  than  that,  it  will  not  generally  be  necessary  to 
consider  them. 

A  lateral  pressure  on  the  pier  is  possible,  due  to  the  earth's  be- 
ing washed  away  from  one  side  and  not  from  the  opposite.  It  will 
be  on  the  safe  side,  and  near  enough  for  this  purpose,  to  assume 
that  this  effect  is  equal  to  the  pressure  of  a  liquid  whose  density  is 
the  difference  between  that  of  the  water  and  the  saturated  soil  dis- 
placed. Under  these  conditions,  the  actual  tendency  to  slide  is 
•  The  TacHHoaRlPH,  Ualvenlty  of  IHinols,  No.  9  (1894-96).  pp.  88-48. 


ovGoQi^lc 


ART.  1.]  THEORY    OF    STABILITT.  369 

«qnal  to  the  square  root  of  the  sum  of  the  squares  of  the  down-stream 
lorces  and  the  lateral  thrnst.  However,  this  refinement  is  unnecee- 
-saty,  particularly  since  a  pier  which  is  reasonably  safe  against  over* 
taminET  ond  crushing  will  be  amply  safe  against  eliding. 

671.  Seiuting  Force*.  The  resisting  force  is  the  friction  due  to 
the  combined  weight  of  the  train,  bridge,  and  the  part  of  the  pier 
above  the  section  considered.  For  the  greatest  i-efinement,  it  would 
be  necessary  to  compute  the  forces  tending  to  slide  the  pier  for  two 
conditions  :  viz.,  (1)  with  a  wind  of  50  lbs.  per  sq.  ft.  on  truss  and 
pier,  in  which  case  th<!  weight  of  the  train  should  be  omitted  from 
the  resisting  forces ;  and  {'i)  with  a  wind  of  30  lbs.  per  sq.  ft  on 
truss,  train,  and  pier,  in  which  case  the  weight  of  a  train  of  empty 
■box  cars  should  be  included  in  the  resisting  forces.  For  a  table  of 
we^hts  of  maeonry,  see  page  200.  If  the  water  can  find  its  way 
under  the  foundation  in  thin  sheets,  the  weight  of  the  part  of  the 
pier  that  is  immersed  in  the  water  will  be  diminished  by  62^  lbs. 
per  cu.  ft.  by  buoyancy  ;  but  if  it  finds  its  way  under  any  section 
by  absorption  only,  then  no  allowance  need  be  made  for  buoyancy. 

The  resisting  force  is  equal  to  the  product  of  the  total  weight 
and  the  co-eflBcient  of  friction.  For  values  of  the  co-eflBcient  of 
friction,  see  the  table  on  page  315.  The  tenacity  of  the  mortar  is 
usually  n^lected,  although  it  is  a  \evj  considerable  element  of 
strength  (see  §  137). 

672.  SluniTT  AQADTBT  OviBTtrxitnro.  The  forces  which  tend 
to  produce  eliding  also  tend  to  produce  overturning,  and  the  forces 
■which  resist  sliding  also  resist  overturning ;  hence,  there  remains  to 
determine  only  their  points  of  application.  The  stability  can  be 
■determined  either  by  moments  or  by  resolution,  as  was  explained  for 
dams ;  but  in  this  case,  it  is  easier  by  moments,  since  there  are  sev- 
eral horizontal  forces,  and  it  requires  considerable  work  to  find  their 
resultant  as  demanded  by  the  method  by  resolution  of  forces. 

673.  A.  By  Xoments.  By  this  method,  it  is  necessary  to  find 
the  arm  of  the  forces,  i.e.,  the  perpendicular  distance  from  the  line 
of  action  of  the  forces  to  a  point  about  which  the  pier  tends  to  turn. 
This  is  the  same  method  as  that  used  in  §§  493-98,  which  see. 

The  center  of  pressure  of  the  wind  on  the  truss  is  practically  at 
the  middle  of  its  height ;  that  of  the  wind  on  the  train  is  7  to  9 
feet  above  the  top  of  the  rail ;  and  that  of  the  wind  on  the  pier  ie 
»t  the  middle  of  the  exposed  part    The  arm  for  the  pressure  of  the 


ovGoQi^lc 


370  BRIDGE    PIEBS.  [CHAP.  XTU 

ice  abould  be  measured  from  high  water.  The  center  of  pressnre- 
of  the  ciirreDt  ia  not  easily  determiaed,  since  the  law  of  the  Taria- 
tion  of  the  velocity  with  the  depth  is  not  Icuovn ;  but  it  will  proba- 
bly be  safe  to  take  it  at  one  thinl  the  depth.  Finally,  the  downward 
forces  will  usnally  act  vertically  throagh  the  center  of  the  pier. 

From  these  data  the  overturning  and  resisting  moments  am. 
easily  be  computed.  For  equilibrium,  the  summation  of  the  former 
must  be  less  than  the  latter.  The  above  principles  will  be  further 
elucidated  in  g§  579-8l>  by  an  example. 

674.  B.  By  BeiolDtlon  of  Foroet.  This  is  the  method  explained 
in  g  499  (page  3^0).  In  that  case  the  problem  was  ^ery  sim- 
ple, since  there  were  but  two  forces ;  but  in  the  present  case  there 
are  several  horizontal  forces  and  also  several  vertical  ones.  The  first 
step  is  to  find  a  single  force  which  is  equivalent  in  every  respect  to 
the  combined  effect  of  all  the  horizontal  forces ;  the  second  is  to 
find  an  xijuiralont  for  all  of  the  vertical  forces ;  and  the  third  is  to 
find  the  resultant  of  these  two  forces. 

The  horizontal  distance,  x,  of  the  point  of  application  of  the  re- 
snltant  of  all  the  vertical  forces,  back  from  the  toe  of  the  pier,  is 
found  by  the  equation, 

_  gum  of  the  momenls  of  the  vertical  forces  .  , 

~  sum  of  the  vertical  forces 

The  weight  of  the  train  and  bridge  act  vertically  through  the  center 
of  the  pier ;  and  if  the  pier  is  symmetrical,  as  it  usually  is,  the 
weight  of  the  pier  will  also  act  through  its  center.  Therefore,  x  in 
equation  (3)  will  usually  be  half  the  length  of  the  pier. 

The  vertical  distance,  y,  of  the  point  of  application  of  the  re- 
sultant of  all  the  horizontal  foi'cos  above  any  horizontal  joint  is 
found  by  the  equation, 

_  sum  of  the  moments  of  the  fiomoiifttl  forces  ,„. 

sum  of  the  horizontal  forces  '     "     ^  ' 

Having  found  x  and  y,  as  above,  draw  a  vertical  line  at  a  distance 
*  back  from  the  down  stream  end  of  the  pier ;  on  this  line  lay  off  a 
distance  y  above  the  horizontal  joint  under  consideration.  The 
point  thns  determined  corresponds  to  «  of  Fig.  TO  (page  3'iO).  Con- 
struct the  parallelogram  of  forces  by  laying  off,  to  any  convenient- 


ovGoQi^lc 


ART.   i-l  THEORY    OF   STABILITY.  371 

scale,  (1)  a.  horizontal  line  equal  to  the  sum  of  all  the  horizontal 
forces  acting  on  the  pier,  and  (2)  ii  vertical  line  equal  to  the  sum  of 
all  the  vertical  forcfs  ;  and  complete  the  diagram  by  drawing  the 
reBultaot.  The  stability  of  the  pier  is  determined  by  the  ratio  of 
A  C  to  iV  C,  Fig.  70. 

S7&.  StaBILITT  AGAIKBT  CBITSHIItO.  HepreBont  the  maximum 
pressure  by  P,  the  total  weight  on  the  section  by  W,  thearea  of  the 
section  by  S,  the  moment  of  inertia  of  the  section  by  /,  the  length 
of  the  section  by  I,  and  the  overturning  moment  by  M;  then  from 
equation  (1),  page  305,  we  have 

For  the  particular  case  in  which  the  pier  has  a  rectangular  horizon- 
tal cross  Ecctlon,  the  above  formula  becomes  the  same  b&  equation 
(18),  (page  aJ2,)  as  deduced  for  an  element  of  a  masonry  d&m. 

The  method  of  applying  the  above  equation  vrill  be  explained  in 
§  581  by  an  example. 

576.  ExAXFLE  OF  Method  or  Cokfutiito  8tabilitt.  Fig.  85 
shows  the  dimensions  of  the  channel  pier  of  the  Illinois  Central  R. 
R.  bridge  over  the  Ohio  River  at  Cairo,  111,  This  pier  stands  be- 
tween two  533-foot  spans.  Its  stability  will  now  be  tested  by  the 
preceding  principles. 

677.  Stability  against  Sliding.  Wo  will  examine  the  stabil- 
ity against  sliding  on  the  top  footing  course.  The  wind  surface  of 
the  truss  =  10  sq.  ft.  X  523  =  5,230  sq.  ft.  The  wind  pressure 
(^inst  the  truss  at  30  lbs.  per  sq.  ft.  =  30  lbs.  X  5,230  =156,900 
lbs.  -=  78  tons ;  and  the  wind  pressure  on  the  truss  at  50  lbs,  = 
50  lbs.  X  5,230  =  261,500  lbs.  =  131  tons. 

The  wind  pressure  on  train  at  30  lbs.  per  sq.  ft.  ,=  30  lbs.  X 
533  X  10  =  156,900  lbs  =  78  tons. 

The  pressure  of  the  wind  against  a  section  of  the  pier  52  fL 
long,  is  20  lbs.  x  52  X  14  =  14,560  lbs.  =  7  tons. 

The  pressure  doe  to  the  ice  is  found  as  follows:  Assume  the 
thickness  to  be  1  foot ,  and  also  assume  the  crushing  strength  of 
ice  to  be  200  lbs.  per  sq.  in.  =,  say,  15  tons  per  sq.  ft.  The  pier  is 
16  ft.  wide  at  the  high-water  line.  Hence  the  resistance  required  in 
the  pier  to  crash  its  way  through  a  field  of  ice  is  IS  tone  X  16  X  1 
^  240  tons. 


ovGoQi^lc 


BBIDOE    FIEBS.  [CHAF.  STI, 


ovGoQi^lc 


ART.  1.]  THBOBT  OP  STABILm.  873 

The  preesore  due  to  the  current  is  fooiid  as  follows:   From 


19  ft.  =  1,330  sq.  ft.,  which  valno  is  equivalent  to  asanming  that 
the  riTer  may  scour  to  the  top  of  the  footing  conrsea.  *  represents 
a  co-efficient,  which,  if  the  pier  were  rectangular,  would  be  about 
1.4,  and  if  the  pier  were  cylindrical  would  equal  about  0.73.  We 
will  asBume  it  to  be  1.1, — a  trifle  more  than  the  mean  of  tbese  two 
Talues.  to  =  62.5  lbs.  per  cu.  ft.  The  surface  velocity  at  the 
bridge  site  was  measured*  "  when  the  Mississippi  and  the  Ohio 
were  at  about  the  same  stage,"  and  found  to  be  4  miles  per  hour 
(=  6  ft  per  second);  but  as  high  water  may  occur  in  the  Ohio  at 
the  time  of  moderately  low  water  in  the  Mississippi,  the  possible 
mazimnin  velocity  is  greater  than  the  above,  and  bence  we  will  as- 
sume that  it  is  10  ft  per  second.  The  velocity  of  the  water  at 
various  depths  below  the  surface  of  a  stream  varies  as  the  ordinate 
of  an  ellipse;  but  the  effect  of  the  mean  velocity  is  approximated 
with  sufficient  accuracy  for  this  purpose  by  assuming  that  the  mean 
pressure  is  half  of  that  due  to  the  surface  velocity.  Substituting 
these  numbers,  the  above  equation  becomes  P  =  1,330  x  1.1  X 
6S.5  X  Vtf  =  ''0-5  tons  =  70  tons  with  sufficient  accuracy.  Divid- 
ing this  by  2  to  get  the  pressure  corresponding  to  the  mean  velocity* 
we  have  the  pressure  of  the  current  equal  to  35  tons. 
<Jollecting  the  preceding  results,  we  have: 

Wind  Ml  tnuB, 78  tons. 

"      "  Inia, 78    " 

"  pier, 7    " 

Pressure  of  ice, 8*)    " 

"       "  water 86    " 

Total  force  tendlcg  to  slide  the  pier  od  the  foot- 
ing      =    488t<»w. 

578.  The  weight  of  the  bridge  will  be  assumed  at  3  tons  per 
lineal  foot;  and  hence  the  total  weight  is  2  tons  X  533  =  1,046 
tons. 

The  weight  of  a  train  of  empty  cars  is  about  0.5  ton  per  lineal 

•  Thlid  Atmnal  Report  of  the  Uhnoii  Sodet;  of  Eagliiaeia,  p.  78. 


ovGoQi^lc 


374  BBIDOE    PIEBS.  [CHAP.  SVt. 

foot;  and  hence  the  total  weight  of  the  train  ie  0.5  tons  x  523  = 
261  tons. 

The  amonnt  of  masonry  below  the  high-water  line  =  67,946  ca. 
ft.;  the  amount  above  the  high  water  lino  =  24,534  en.  ft.;  and 
hence  the  total  masonry  =  93,480  cu.  ft.  We  will  assume  the 
weight  of  the  masonry  to  be  150  lbs.  per  cubic  foot.  Then  the 
weight  of  the  masonry  is  150  lbs.  X  93,480  =  6,936  tons. 

OoUecting  these  results,  we  have: 

Weight  of  the  bridge 1,046  tona. 

"      "    "    train  of  empty  cars, 361    " 

"      "    "    masonry, 6,986    " 

Total  weight  to  resUt  sliding =    S,248  toua. 

Sliding  cannot  take  place,  if  the  co-eEBcient  of  friction  ie  eqnal 
to  or  greater  than  438  -i-  8,243  =  0.053.  For  values  of  the  co-ef- 
ficients of  friction,  see  the  table  on  page  315.  In  the  above  ex- 
ample, .the  factor  of  safety  against  sliding  is  at  least  12  to  15. 

679.  Stability  against  Overtaming.  We  will  coneider  the 
stability  against  overturning  about  the  top  of  the  upper  footing 
course.  The  wind  on  the  trass  =  78  tons;  the  arm  of  this  force  = 
height  of  the  pier  {Vid  it)  +  half  the  depth  of  the  trass  {ZO  ft.)  = 
153  ft.;  and  therefore  the  moment  of  this  force  =  78  tons  X  153 
ft.  =  11,934  foot-tons. 

The  pressure  of  the  wind  on  the  train  =  78  tons;  and  the  arm 
of  this  pressure  =  distance  from  footing  tn  top  of  pier  (123  ft.)  -|- 
dislance  from  top  of  pier  to  top  of  rail  (8  ft.)  -\- distance  from  top 
af  rail  to  center  of  train  {8  ft.)  =  139  ft.  Therefore  the  moment 
at  this  pressure  is  78  tons  X  139  ft.  =  10,842  foot-tons. 

The  pressure  of  the  wind  against  the  pier  is  7  tons  (§  577);  the 
arm  of  this  force  =  i  (302  + 150)  —  79  =  97  ft. ;  and  the  moment  of 
this  force  =  679  foot-tons. 

The  pressure  of  the  ice  is  340  tons,  the  arm  is  70  ft.,  and  the 
moment  is  16,800  foot-tons. 

The  pressure  of  the  water  is  35  tons.  The  center  of  pressure 
lies  somewhere  between  one  third  and  one  half  of  the  depth  from 
the  top;  and-as  the  increased  area  at  the  base  of  the  pier  compen- 
sates in  part  for  the  deerease  of  velocity  with  the  depth,  we  will  as- 
sume that  it  is  at  half  the  depth.  The  arm  then  is  36  ft.,  and  the 
moment  is  35  tons  x  36  ft.  =  1,260  foot-tons. 


ovGoQi^lc 


ABT.  1.]  THEOKT  OF  STABILITY. 

Collecting  theBe  resnlta,  tee  have: 
it  of  the  wind  on  the  trun. 


"    "  pressure  of  the  ice, 


Total  OTertumIng  momeot  . 


11,884  fc- 

Dt-tons. 

.    10,842 

679 

.    16,800 

,      1,260 

=  41,015  foot-b>D>. 

580.  The  total  weight  aboTO  the  joint  considered  is  (§  678) 
S,343  tons.  This  force  acts  vertically  down  through  the  center  of 
the  pier;  hence  the  ami  iB  3I.fi  ft.,  aad  the  total  moment  resisting 
OTertuming  is  8,343  X  31.5  =  359,654  foot-tons.  The  factor  of 
safety  against  overturning  about  the  top  of  the  upper  footing 
course  ia  259,654  -f-  41,515  =  6.3. 

Assuming  the  traiu  to  be  o9  the  bridge,  and  that  the  vind 
pressure  on  the  tmsB  is  50  lbs.  per  sq.  ft.,  and  following  the  method 
pursned  above,  it  ie  found  that  the  factor  of  safety  against  over- 
turning under  thnse  conditions  is  6.4. 

581.  Stability  against  Cnuhing.  The  maximum  pressure  on 
the  section  will  occur  when  the  loaded  train  is  on  the  bridge  and 
all  the  horizontal  forces  are  acting  with  their  full  intensity.  The 
load  when  an  evipty  train  ia  on  the  bridge  is  (§  578)  8,243  tons. 
Assuming  that  a  loaded  train  will  weigh  li  tons  per  lineal  foot,  we 
must  add  (0.75  tons  x  533  =)  392  tons  to  the  above  for  the 
-difference  between  a  loaded  and  an  unloaded  train.  Then  the  total 
■direct  pressure  is  8,343  +  392  =  8,635  tons.  The  area  of  the  sec- 
tion at  the  top  of  the  footing  course  is  1,160  sq.  ft.  Hence,  the 
maximum  direct  pressure  is  8,635  -;- 1,160  =  7.4  tons  per  sq,  ft. 

The  moment  to  overturn,  M,  =  41,515  foot-tous.  The  greatest 
length  of  the  section  =  63  ft.  The  moment  of  inertia  of  the  sec- 
tion about  an  axis  through  its  center  and  perpendicular  to  ita 
length  =  287,917  (ft.).     Prom  §  575,  the  maximum  pressure 

s  ^si 

Substitating  the  sbore  qaaotities  in  this  equation  givee 

•^  =  '■*  +  Iw^sn  =  '•*  +  ■'■5  =  llil  '!»»  pel  •!■  ft- 
Since  it  is  highly  improbable  that  all  the  forces  will  act  at  the 
«ame  time  with  the  intensity  assumed  in  the  preceding  compnto- 


ovGoQi^lc 


3?t!  BBIDQB  PIEBS.  [CHAP.  ZVt^ 

tioDB,  we  may  eonolade  that  tbe  presenre  will  never  exceed  11.9 
tons  per  Bq.  ft.  A  compariBon  of  tbia  with  the  Taluee  of  the  com- 
pressive strength  of  masonry  as  given  in  g  233  (p^^  l^^)  shows 
that  this  presBure  is  entirely  safe. 

Since  this  is  ao  unusually  high  pier  under  an  nnnsnally  long 
span,  and  since  the  overturning  and  resisting  moments  and  also  the 
top  dimensions  of  the  pier  vary  with  the  span,  we  may  draw  the 
conclusion  that  any  pier  which  has  sufficient  room  on  top  for  the 
bridge  seat  (§  584)  and  which  has  a  batter  of  1  in  13,  or  1  in  34,  it 
safe  against  any  mode  of  failure. 

683.  FreniiTe  on  the  Bed  of  the  Foondation.  The  caisson, 
is  70  feet  long,  30  feet  wide,  and  50  feet  high.  The  load 
on  the  base  is  eqnal  to  the  weight  on  the  top  of  the  footing  ptttt- 
the  weight  of  the  footings  plus  the  weight  of  the  caisson. 
The  weight  above  the  footing  =  8,636  tons  (§581).  The  weight- 
of  the  footings  =  1,300  sq.  ft.  X  4  ft.  X  150  lbs.  =  390  tons.  Tbe. 
weight  of  the  caisson  =  70  ft.  X  30  ft.  X  50  ft.  X  100  lbs.  =  6,360 
tons.  The  total  weight  on  the  bed  =  8,635  +  390  +  6,250  =  14,- 
275  tons.  Tbe  area  =  70  ft.  x  30  ft.  =  3,100  sq.  ft.  The  direct 
pressure  per  nuit  of  area  =  14,375  -i-  3,100  =  6.8  tons  per  sq.  ft. 

The  overturning  moment,  M,  is  eqnal  to  the  moment  about  tb&; 
top  of  the  footing  (g  661)  plus  the  product  of  tbe  sum  of  the  bori- 
tontal  forces  and  the  distance  from  the  footing  to  tbe  base  of  the 
caisson;  or,  tbe  moment  about  the  base  =  41,515  foot-tons  -)-  438 
tons  X  54  ft.  =:  65,167  foot-tons.  The  moment  of  inertia,  I,  = 
^30(70)' =857,500  (ft.),  i  =  70  ft.  The  concentrated  preaaare 
caosed  by  the  tendency  to  overtam  is 

Ml      65,167  X  70      „„^ 
3T  =  2^857:500  =*-^'«^ 

The  caisson  was  sunk  all  the  way  through,  and  rests,  on  sand  ; 
consequently  the  water  will  find  its  way  freely  under  the  entire 
foundation,  thus  causing  bnoyaucy  to  act  with  its  full  force.  This 
upward  force  of  the  water  will  be  equal  to  the  volume  of  the  im- 
mersed masonry  multiplied  by  tbe  weight  of  a  cubic  foot  of  water;, 
or  tbe  buoyancy  =  (67,946  +  5,300  + 105,000)  X  62.4  =  5,558  tons. 
The  lifting  effect  of  buoyancy  is  (5,558  -r-  2,100  =)  2.62  tons  per 
sq.  fi 

Therefore,  the  total  pressure  is  not  greater  than  6.8  +  8.7  —  3.  ft 
,  =  6.9  tons  per  sq.  ft. 


ovGoQi^lc 


AET,  3.]  DETAILS   OP   COHSTBUCTION.  877" 

The  preaanre  voaM  oever  bo  so  mach,  for  the  following  reaeona  : 
1.  There  is  no  probability  th&t  both  spAas  will  be  covered  hy  s  train 
of  msximnm  weight  at  the  eame  time  that  the  mssitnum  effects  of 
the  wind,  of  the  current,  and  of  the  ice  occnr.  Z.  The  friction  oa 
the  sides  of  the  caisson  will  sustain  part  of  the  load.  A  friction  of 
600  lbs.  per  sq.  ft.,  which  was  about  the  amount  experienced  in 
sinking  these  piers  (see  g  455),  wonld  decrease  this  pressure  about. 
1^  tons  per  sq.  ft. 

Therefore,  we  conclude  that  the  pressure  on  the  sand  will  be  at. 
least  as  tnuch  as  6.8  —  1.5  —  2.6  =  2.7  tons  per  sq.  ft.;  and  that  it. 
may  possibly,  but  not  probably,  amount  to  6.8  +  3.7  —  3.6  —  1.5  = 
5.4  tons  per  sq.  ft.  The  larger  value  was  taken  at  the  greatest  pos- 
sible one  for  the  sake  of  establishing  the  conclusion  stated  in  th» 
last  paragraph  of  g  581. 

683.  Other  Examplta.  At  the  St.  Louis  steel-arch  bridge- 
tfae  greatest  pressure  possible  on  the  deepest  foundation  (bed- 
rock) is  19  tons  per  aq.  ft.  The  pressure  at  the  base  of  the 
New  York  tower  of  the  East  River  suspension  bridge  is  about. 
7^  tons  per  sq.  ft.  upon  a  stratum  of  sand  2  feet  thick  overlying^ 
bed-rock ;  and  at  the  base  of  the  masonry  the  pressure  is  about  11^ 
tons  per  sq.  ft.*  The  corresponding  qnantities  for  the  Brooklyn 
tower  were  a  little  over  a  ton  less  in  each  case.  At  the  Plattamonth 
bridge  f  the  maximum  pressure  caused  by  the  weight  of  train,  bridge, 
and  pier  ia  3  tons  per  sq.  ft,  At  the  Bismarck  bridge  f  the  pressure- 
due  to  the  direct  weight  is  3  tons  per  sq.  ft.  on  clay. 

Aet.  2.  Details  of  CoHSTECcnoN. 

684.  TOI  DncIHBIOni  The  dimensions  on  the  top  will  depend 
somewhat  upon  the  form  of  the  cross  section  of  the  pier,  and  also 
upon  the  style  and  span  of  the  bridge;  but,  in  a  general  way,  it  may 
be  stated  that,  for  trussed  spans  of  100  ft.  or  over,  the  dimenaiona 
under  the  coping  will  not  bo  less  than  5  ft.  X  20  ft. ;  for  250-ft. 
spans,  8  ft.  X  30  ft.;  and  for  500-ft  spans,  10  ft.  X  40  ft.  Appar- 
ently 6  ft.  X  22  ft.  nnder  the  coping  is  the  favorite  size  for  spans  of 
100  to  200  ft 

*  7.  ColltDffwood,  Mristant  engineer,  In  Tan  Noitrand'i  Engfn'K  >U8->  voL  xvL 
p.  «S1. 

t  Beport  of  Oea  B.  Koricon,  chief  engineer. 


ovGoQi^lc 


3*8  BBIDOE   PIEES.  [CHAP.  XVI, 

5S5.  BOTTOX  SuiEltslolts.  Theoretically  the  dimeusioDsat  the 
bottom  are  determined  by  the  area  necessary  for  stability;  bnt  the 
top  dimensions  required  for  the  bridge  seat,  together  with  a  slight 
batter  for  the  sake  of  appearance,  gives  sufficient  stability  (g  581). 
Only  high  piers  for  short  spans — a  combination  not  likely  to  occur 
in  practice — ^are  liable  to  fail  by  overturning  or  crushing. 

686.  Batteh.  The  nsnal  batter  is  1  inch  to  a  foot,  althoagh  l 
-an  inch  to  a  foot  is  very  common.  In  high  piers  it  is  customary  to 
use  a  batter  of  1  to  24,  and  offset  the  masonry  and  introduce  a  water- 
table  at  the  high-water  Hue,  so  as  to  give  an  average  batter  of  about 
1  to  13.  This  construction  very  much  improves  the  appearance, 
«nd  does  not  add  materially  to  the  cost. 

A  corbel  course,  or  "belt  course,"  is  sometimes  introduced  im- 
mediately under  the  coping  for  appearance's  sake.  For  an  exam- 
ple, see  Fig.  85  (p^e  372),  Fig.  87  (pa^  383),  and  Fig.  88  (page 
384). 

6S7.  Cbobb  Sectimi.  The  up-stream  end  of  a  pier,  and  to  a 
considerable  extent  the  down-stream  end  also,  should  be  rounded 
or  pointed  to  serve  as  a  cut-water  to  turn  the  current  aside  and  to 
prevent  the  formation  of  whirls  which  act  upon  the  bed  of  the 
«tream  around  the  foundation,  and  also  to  prevent  shock  from  ice, 
logs,  boats,  etc.  In  some  respects  the  semi-ellipse  is  the  best  form 
for  the  ends ;  but  as  it  is  more  expensive  to  form,  the  ends  are 
usually  finished  to  intersecting  arcs  of  circles  (see  Figs.  85,  87,  and 
89 — pages  372,  383,  and  385,  respectively),  or  with  semi-circulai 
ends.  Above  the  high-wat«r  line  a  rectangular  cross  section  is  as 
good  as  a  curved  outline,  except  possibly  for  appearance. 

A  cheaper,  but  not  quite  as  efficient,  construction  is  to  form  the 
two  ends,  called  starlings,  of  two  inclined  planes.  As  seen  in 
plan,  the  sides  of  the  starlings  usually  make  an  angle  of  about  45° 
with  the  sides  of  the  pier  (see  Fig.  90,  page  386).  A  still  cheaper 
construction,  and  the  one  most  common  for  the  smaller  piers,  is  to 
finish  the  up-stream  end,  below  the  high-water  line,  with  two  in- 
clined planes  which  intersect  each  other  in  a  line  having  a  batter  of 
from  3  to  9  inches  per  foot,  and  build  the  other  three  sides  and  the 
part  of  the  up-stream  face  above  tJie  high-water  line  with  a  batter 
cf  1  in  12  or  1  in  24.  Of  course  the  simplest  construction  is  to 
make  the  pier  rectangular  in  horizontal  cross  sections  and  give  it  the 
■same  batter  on  ill  faces. 


ovGoQi^lc 


ART.  2.]  DXTAIL8  OF   COKSTBUCTION.  379 

Occasionally,  tor  economy,  piere,  particularly  pivot  piers,  are 
built  hollow — sometimea  with  and  sometimes  without  interior  cross 
walls  (see  Fig.  86,  page  380).  The  piers  of  the  bridge  across  the 
'  Missouri  River  at  Glasgow,  Mo.,  are  solid  ap  to  the  high-water  line, 
and  above  that  each  pier  consists  of  two  stone  columua.  The  piers 
of  the  bridge  over  the  Missouri  at  St.  Charles,  Mo.,  have  a  somewhat 
similar  construction,  except  that  the  secondary  piers  are  connected 
by  a  comparatively  thin  wall. 

With  piers  subjected  to  a  severe  pressure  from  ice,  it  is  customary 
to  protect  the  edge  of  the  noee  with  an  angle-iron  or  a  railroad  rail. 

689.  Pivot  Fixbs.  These  differ  from  the  ordinary  piers  only 
in  that  they  are  circular,  are  larger  on  top,  and  have  plumb  sides. 
Pivot  piers  are  about  25  to  30  feet  in  diameter,  under  the  coping, 
for  spans  of  250  to  360  feet,  respectively. 

Fig.  86  shows  the  pivot  pier  for  the  Northern  Pacific  R.  R 
bridge  over  the  Bed  River  at  Grand  Forks,  Dakota.  The  specifica- 
tions for  the  grillage  were  as  follows:  "Fasten  the  first  course  of 
timbers  together  with  f-inch  x  20-inch  drift  bolts,  18  inches  apart; 
iasten  second  course  to  first  course  with  drift  bolts  of  same  size  at 
every  other  intersection.  Timbers  to  be  laid  with  broken  joints. 
Pat  on  top  course  of  4-inch  X  12-inch  plank,  nailed  every  2  feet 
with  jV'i^'^'i  X  S-inch  boat  spikes.  The  last  course  is  to  be  thor- 
oughly calked  with  oakum." 

Pivot  piers  are  protected  from  the  pressnre  of  ice  and  from 
shock  by  boats,  ejc,  by  an  ice  breaker  which  is  entirely  distinct 
from  the  pier.  The  ice  breaker  is  usually  constructed  by  driving  a 
group  of  60  or  70  piles  in  the  form  of  a  V  (the  sharp  end  np  stream), 
at  a  short  distance  above  the  pier.  On  and  above  these  piles  a 
strong  timber  crib-work  is  framed  so  as  to  form  an  inclined  ridge 
up  which  the  cakes  of  ice  sjide  and  break  in  two  of  their  own  weight 
Between  the  ice  breaker  and  the  pier  two  rows  of  piles  are  driven, 
on  which  a  comparatively  light  crib  is  constrncted  for  the  greater 
security  of  the  pier  and  also  for  the  protection  of  the  river  craft. 

68S.  QlFALITT  Ot  HABOITBT.  Bridge  piers  are  usually  quarry- 
foced  ashlar,  i.  e. ,  first-class  masonry  (see  §  207)  backed  with  rubble. 
Good  concrete,  if  made  with  reasonable  care,  is  equally  aa  good  as 
ordinary  rubble  masonry,  and  is  sometimes  cheaper, — since  it  affords 
an  opportunity  to  use  up  the  refuse  from  the  quarry. 


ovGoQi^lc 


BBIDOB   PIERS.  [CHAP.  Z7I. 


7crib;G00l^lc 


ABT.  2.]  DETAILS  OF  CONSTRL-CTIOS.  381 

For  an  iUuBtrated  description  of  the  method  of  building  concreta 
bridge  piera,  see  Engineering  News,  vol.  xix.  pp.  443-44. 

690.  BPlcincATlolls.  The  follnwing  specificationa  for  the  ma- 
sonry of  the  railroad  bridge  over  the  ^f  iseouri  River  near  Sibley,  Mo., 
^Octave  Channte,  engineer)  may  be  taken  as  an  example  of  the  best 
practice.* 

S81.  0«a«rftl  aaqnlnmuit*.  "  The  stone  to  be  used  Id  tbeee  pieia  must  be 
of  what  is  kuowD  M  the  best  qualltj  of  Cottonwood  llmeHtoiie,  or  otber  stoue 
wbicb.  Id  tbe  opiuioa  of  the  eugineer,  Is  of  equally  good  quality  and  in  every 
way  suil&ble  for  the  purpose  for  which  it  is  to  be  used.  It  must  be  aoucd  and 
durable,  free  from  all  drys,  Bhakes,  or  flaws  of  any  kind  »h»teser,-end  must 
be  of  such  a  character  as  will,  in  the  opTnTou  of  the  engineer,  withstand  the 
action  of  the  weather.  No  alone  o(  an  ipferior  quality  will  be  accepted  or 
«veD  permitted  to  be  delivered  upon  tlie  ground.  The  masonry  in  the  bridge 
piers  must  be  of  tbe  Ijest^nd  largest  atones  that  the  qunrry  will  afford,  and 
muat  l>e  quarried  in  time  to  aeoaoii  again  at  froat  before  being  used. 

"  The  face  stonescompoaing  the  starling,  and  the  ends  and  aides  of  the  river 
piera  from  the  neat  line  alxiut  low  water  up  for  a  distance  of  twelve  (18j  feet, 
Uid  also  the  pedestal  blocks  of  the  main  piera  will  be  of  Uinneaota  granite, 
or  a  granite  of  equal  quality  approved  by  the  engineer.  ' 

"  All  masonry  of  the  main  piers  shall  be  regular  coursed  ashlar  of  the  best 
ieacrlptioD,  and  muat  be  laid  in  mortar  of  the  proportions  of  sand  and  cement 
hereinafter  specified. 

"  All  stones  must  tie  so  shaped  that  the  bearing  beds  abail  be  parallel  to  tbe 
natural  beds,  and  be  prepared  by  dressing  and  bammering  before  they  are 
brought  on  tbe  walls,  as  tooling  and  hammering  will  not  be  allowed  after  the 
Stones  are  in  place.  They  are  to  be  laid  to  a  firm  bearing  on  their  natural  beds 
In  a  full  bed  of  mortar,  without  the  uae  of  chips,  pinnera,  or  leveiers.  No 
shelving  projections  will  tw  allowed  to  extend  beyond  the  under  bed  on  either 
side.  The  stone  and  work  are  to  be  kept  free  from  all  dirt  that  will  interfere 
with  the  adhesion  of  mortar.  Stones  must  be  sprinkled  with  water  before 
being  placed  in  poaiiton  on  ihe  wall.  In  laying  stone  in  mortar,  their  beds  are 
to  be  so  prepared  that  when  settled  down  they  may  rest  close  and  full  on  tbe 
monar.  In  handling  tbe  stones  care  must  be  used  not  to  iujure  the  joints  of 
those  already  laid;  and  in  case  a  stone  is  moved  after  being  set  and  tbe  joint 
broken.  It  must  be  taken  out,  tbe  mortar  thoroughly  cleaned  from  tbe  beds, 
and  then  reset, 

"  Wherever  the  engineer  shall  so  require,  atones  shall  have  one  or  two  1^- 
tnch  iron  dowels  passing  through  them  and  iuto  tbe  stones  below.  The  holes 
for  tbe  dowels  shall  be  drilled  through  such  stones  Ijefore  they  are  put  In 
position  on  the  walls.  After  the  stones  are  in  place  the  boles  shall  be  con- 
tinued down  into  the  under  stones  at  least  six  (6|  inches ;  tbe  dowel  pins  will 
then  be  set  In  and  tbe  holes  filled  with  neat  cement  grout.     Cramps  binding 

♦ywpeeifleaaotMforflrst-clawmBSOPrr,  seejao?;  see  also  Appendix! 


ovGoQi^lc 


BSIDOE    FIEBS.  [cHAP.  XTI. 


the  seTeral  atones  of  a  course  togeiber  may  be  inserted  when  required  by  the 
eDgineer  ;  !d  such  caae  tbey  will  be  couater-suck  into  tbe  stones  wtiicb  they 
fastCD  together. 

S0S.  7km  ftonai.  "  Tbe  face  stones  must  be  accurately  squared,  jointed, 
and  dreaacd  uii  their  beds  and  builds ;  and  tbe  Joints  must  be  dressed  back  at 
least  twelve  inches  (13j  from  tbe  face.  FacestoueBare  to  be  brought  to  s  Joint, 
wheo  laid,  of  not  more  IhaQ  three  quarters  (})  of  an  inch  nor  less  than  one 
half  (ii  inch.  The  courses  shall  not'be  leas  than  eighteen  (18)  inches  In  thick- 
ness, decreasing  from  bottom  lo  top  of  the  wall.  Courses  to  be  well  bonded. 
The  face  stones  shall  break  joints  at  least  twelve  (12)  inches.  The  face  stones 
may  be  left  rough,  except  the  stones  forming  the  starting,  which  must  be  care- 
fully dressed  to  a  uniform  surface.  The  eAgts  of  face  stones  shall  be  pitched 
true  and  full  to  line,  and  on  corners  of  all  piers  a  chisel  draft  one  and  a  half 
(li)  inches  must  be  carried  up  from  base  to  tbe  under  side  of  the  coping.  No 
projection  of  more  than  three  (3)  inclii^s  from  the  edge  of  face  stones  will  be 
allowed.     No  s-toue  with  a  hollow  face  will  be  allowed  in  the  work. 

69S.  Stntoher*.  "Xacb  stretcher  shall  have  at  least  twenty  (SO)  Incfaeb 
width  of  bed  for  all  course?  of  from  eighteen  (IB)  to  twenty  (20)  inches  rise, 
and  for  all  thicker  courses  at  least  as  much  bed  as  rise ;  and  shall  have  an 
averse  length  of  ai  least  three  and  one  half  (8^)  feet,  and  no  stretcher  aliall  be 
less  than  three  (8)  feet  in  length. 

SH.  Hsadan.  "Each  header  shall  bavc  a  width  of  not  lees  than  eighteen 
Inches  (IS)  and  shall  hold,  back  into  the  heart  of  the  wnll,  tbe  size  that  It  shows 
on  tlie  face.  The  headers  bLhU  occupy  at  least  one  fifth  1^^  of  the  whole  face 
of  the  wall,  and  be,  as  nearly  as  practicable,  evenly  distributed  over  it,  and  be 
80  placed  that  tbe  headers  in  each  course  shall  divide  equally,  or  nearly  so,  the 
■paces  Iwlween  the  headers  in  the  course  directly  below.  In  walls  over  six 
feet  vO)iu  thickness,  the  headers  shall  in  no  case  be  leas  than  three  and  out'  lialf 
feet  (3J)  long;  and  in  walls  over  nine  (9)  feet  thick,  the  headers  shall  be  equal 
in  length  to  one  third  the  thickness  of  the  wall,  except  when  this  length  of 
bender  exceeds  six  (6)  feet.^uo  header  over  e\x  (6)  feet  long  being  required. 

S9B.  Ba«ldng.  "  Tbe  headers  must  alternate  front  and  back,  and  their 
binding  effect  be  carried  through  the  wall  by  inleniiediale  stones— not  less  in 
length  and  thickness  than  the  headers  of  tbe  same  course^laid  crosswise  !□ 
the  interior  of  the  wall.  Tbe  slrelcbers  and  all  stones  In  tbe  heart  of  the  wall 
shall  be  ot  the  same  general  dimensious  and  proportions  us  the  face  stones, 
aud  shall  have  equally  good  bed  and  bond,  but  may  have  less  nice  vertical 
Joiola,— although  no  space  greater  than  Ave  (5)  inches  in  width  shall  be  left  be- 
tween stones.  All  stones  in  the  backing  must  be  well  fitted  to  their  plAces, 
and  carry  the  course  evenly  quite  through  the  wall. 

5M.  Coping.  "  The  tops  of  the  bridge  piers,  cap  stones  of  tbe  pedestals, 
and  such  other  ports  of  the  masonry  as  the  engineer  shall  direct,  shall  be  cov- 
ered with  coping  of  such  dimensions  as  prescribed.  A.1I  coping  stones  shall 
be  neatly  bush-hammer  dressed  on  the  face,  bed,  top,  and  Joints;  and  shall  be 
well  and  carefully  set  on  the  walls,  brought  to  one  quarter  (i)  inch  joints,  and. 


ovGoQi^lc 


ABT,  a.]  DETAILS  OF  CONSTRUCTION. 


Tia.  ffl. — Sbore  Pnn.  Buir  Bridoi. 


jvGooi^le 


SSi  BBIDGE   FIEBS.  [chap.  ZTT. 

If  required,  be  doweled,  the  dowels  being  well  secured  in  twd  to  the  coping 
iritlt  grout.    No  coping  Btone  sLall  be  Icbs  (ban  nine  (9|  equare  feet  on  top, 

097.  FolDtimg.  "  All  maBOnr)'  is  to  be  pobited  bo  as  to  fill  the  Joints  solid, 
fbc  surface  of  the  wall  is  to  be  scraped  clean  and  the  ^ints  freed  of  all  loose 
raortar  aad  refilled  solid  by  using  proper  ramming  tools.  Joints  must  be  well 
wet  before  being  pointed.  Hortar  used  in  pointing  is  to  be  composed  of  one 
part  Portland  cement  and  one  part  sand. 

SOS.  Osnient.  "  llie  cement  used  iti  the  work  shall  be  equal  in  quality  to 
the  best  brands  of  Milwaukee  or  Louisville  cement,  and  shall  be  ground  so 
tbnt  at  least  90  per  cent.  In  weight  will  pass  a  standatd  sieve  of  3,500  mesbes 
(c  the  square  Inch,  iind  shall  have  a  lensile  strength— afler  being  exposed  one 
hour,  or  until  set,  in  air,  and  the  balance  of  the  twenty- four  hours  in  water  not 


Tia.  88.— Top  or  Piut,  Hi 


TwIowW"  F— of  at  least  40  pounds  per  square  inch;  and,  after  being  exposed 
-one  day  in  air  and  six  days  in  water,  from  60  to  100  pounds  per  square  inch. 

"  All  cemenia  shall  be  furnished  by  llie  contractor  subject  to  approval  by 
the  engineer.  The  contractor  shsU  provide  a  suitable  building  for  storing  the 
cement,  in  which  the  same  must  be  placed  before  being  tested.  The  engineer 
shall  be  notified  of  tbe  receipt  of  cement  at  least  three  days  before  it  is  required 
for  use.  and  the  inspector  may  take  a  sample  from  each  package  for  testing. 

600.  Xortar.  "The  mortar  shall  be  composed  of  tbe  above  cement  and 
clean,  dry.  sharp  sand  Id  the  proportion  of  one  part  cement  to  two  parts  of 
sand  by  weight.*  The  sand  and  cement  shall  be  Ihoroughly  mixed  dry,  and, 
after  adding  sufficient  water  to  render  Ibe  mass  plastic,  shall  be  mixed  and 
worked  until  of  uniform  consistency  throughout. 

"  Hortar  remaining  unused  so  long  as  to  have  taken  an  initial  set  shall  not 
be  used  in  the  work. 


ovGoQi^lc 


a-] 


DETAILS  OF  COKSTRUCTION. 


eoo.  FtdMtel  KaMmTj.  "  The  pedestals  shall  be  founded  upon  t,  bed  of 
'Concrete  or  upon  piles,  ae  may  be  directed  by  the  engineer.  The  masonry  In 
the  pedestals  shall  be  of  the  best  de- 
scription of  couiwd  aahhu- composed  of 
the  ItmeHtooe  and  the  mortar  described 
above,  the  stimea  U>  be  not  less  than 
twelve  (13)  inches  thick,  and  to  have 
horizontal  beds  and  vertical  Joints  on 
the  face.  When  the  walls  do  not  ex- 
ceed three  and  one  half  (81)  feet  in 
thtclcnesB,  the  headers  shall  run  entirely  J 
through,  or  a  single  stone — square  and 
of  the  proper  thichuen— may  be  used. 
In  walls  over  three  and  one  half  (8^) 
feet  in  thickness,  and  not  over  seven 
<7)  feet  in  thiobnesi,  headers  and 
^stretchers  shall  alternate,  and  there 
mtuil  be  aa  many  headera  aa  stretchers. 
The  space  in  the  Interior  of  the  walls 
■hall  be  fliled  with  a  single  stone 
to  fit  such  space,  and  said  stone  shall 
be  of  the  same  heiglit  as  the  headers 
»ndatretchenof  thecourse.  In  all  the 
masonry  of  these  pedestals  the  slope 
must  be  carried  up  by  steps  and  in  a 
-cordance  with  the  plans  of  theengineer. 
All  the  quoins  must  have  hammer- 
dressed  beds,  builds,  and  joints,  and 
draft  comets." 


601.       •gfSlfPT.M       ffg 

Puss.  Fig.  8S  (page  372)  shows 
the  channel  pier  of  the  IHinois 
Central  B.  B.  bridge  over  the 
Ohio  at  Cairo,  IlL 

Fig.  86  (page  380)  shows  the 
pivot  pier  of  the  Northern  Pacific 
B.  R.  bridge  over  the  Red  River 
■at  Grand  Forks,  Dakota. 

Fig.  87  (page  383)  shows  one 
of  the  two  shore  piers  of  the 
bridge  over  the  Missouri  River, 
near  Blair,  Neb.*    This  pier  stands  between  two 


)-ft.  spans. 


•  From  tlie  Report  of  Geo.  8.  MorUon,  chief  engineer  of  the  bridge. 


ovGoQi^lc 


BSIDQE  PlEBa  [CHAP.  XT^ 


"aK.      't'<.'— -I 


Fn.  (0.— Pin  or  Bi.  Cwuz  Kitib  Bi 


jvGooi^le 


ABT.  2.]  DETAILS  OP  CONBTEUCTION.  387 

"  The  Tertical  joints  are  shown  as  they  actually  are  in  the  stmot- 
nre."    The  masonry  ia  145  It  from  top  to  bottom. 

Fig.  88  (page  384)  shows  the  top  of  the  pier  between  two  525-ft 
channel  spans  of  the  LouisTille  and  Nashville  B.  R  bridge  across 
the  Ohio  River  at  Henderson,  Ey. 

Fig.  69  (page  385)  shows  the  actual  arrangement  of  the  stones  in 
one  of  the  courses  of  one  of  the  channel  piers  (Fig.  86)  of  the  Blinois 
Central  R.  R.  bridge  over  the  Oliio  River,  at  Cairo,  JR. 

80S.  Fig.  90  (page  386)  shows  the  river  pier  of  the  Chicago,  Bur- 
lington and  Northern  R.  R.  bridge  across  the  St.  Croix  River.  This 
pier  stands  between  a  draw  of  370  feet  and  a  fixed  span  of  153  foet. 
The  thickness  of  the  courses  is  as  follows,  in  order  from  the  bottom 
ap :  Two  conrses,  including  the  footing,  28  inches;  two  26  inches ; 
one  each  34,  22,  21,  19,  and  17  inches;  two  15  inches;  four  14 
inches ;  one  13  inches ;  one  13  inches ;  and  the  coping  18  inches. 

The  following  table  givestheqnantityof  masonry  in  the  pier  and 
illnstrates  the  manner  of  computing  the  contents  of  such  stractnies. 
Notice  tha*  the  order  in  the  table  is  the  same  as  that  in  the  pier  ■ 
1.8.,  the  top  line  of  the  table  relates  to  the  appermost  masonry,  etc. 

TABLE  40. 
CoNTBSTS  or  THE  PiER  sEowH  EH  FiQ.  W  (page  8S6). 


Btringer  ResU. 
Bridge  Seaia. . . 
Coping. 


ax3.75'X8.(r  XS-lff... 
8  X  3.75' X  B-ff  Xl.«'.. 
7.6' X  ai-C  X  1.5' 


Ice  Bnaker. . . . 
Footing  Course. 


f(3xM'  +  8.6)88'  +  cax8.6'  +  «.5')ae.l'l~-. 

(3x8.a'  +  7.1')8.8'xi^ 

,  [8.6'x8.«)(— -t-l.c) 

i(8.6X8.«'+4.8'x4.8-)iaiT 

B,6-  X  89.4'  X  3.88' 

"       4.8' X  8.88' 

Total  =  880.89  cubic  yards  = 


608.  Iron  Tubular  Pien.  For  a  description  of  an  iron  tubular 
pier,  see  g  415  ;  and  for  a  description  of  a  pier  founded  upon  screw 
piles,  see  Engineering  Newa,  vol.  xiii.  pp.  210-12. 


ovGoQi^lc 


388  BBIDGK   PIEBS.  [CHAP.   XTI. 

604.  Timber  Barrel  Piers.  The  Chicago,  Burlington  and  Qnincy 
E.  R.  has  constructed  a  few  "barrel  piers"  as  an  experiment,  the 
object  being  to  reduce  the  cost  of  foundations,  and  also  to  find  some 
cheap  anbstitate  foi  masonry.  The  barrels  are  cjUndrioal,  8  feet  ia 
diameter,  and  30  to  30  feet  in  length.  The  stares  are  10  inches 
thick,  8  inches  wide  on  the  outside,  and  are  dressed  to  fit  together 
to  form  a  cylinder.  Tlic  staves  are  bolted  at  the  top  and  bottom 
to  two  inside  rings  made  of  I-beams,  aud  are  further  held  in  place 
by  strong  outside  hoops  of  iron.  These  caissons  or  barrels  are  sunk 
by  excavating  the  soil  from  the  inside.  The  bottom  and  top  por- 
tions of  the  caisson  are  filled  with  concrete,  and  the  intermediate 
portion  with  saud.  On  top  of  the  wooden  barrel,  an  iron  frame  is 
placed,  upon  which  the  truss  rests.  Two  barrels  constitute  a  pier. 
The  advantages  claimed  for  the  wooden  caissons  are  that  they  can 
be  put  in  witho.ut  interfering  with  traffic,  or  without  loss  of  time  in 
sinking  by  the  passive  of  trains.  The  objection  to  them  is  that  they 
Are  not  durable. 

605.  COHTSirrB  or  B&IDOX  FlESa.  The  table  on  page  389  gives 
the  quantity  of  masonry  in  bridge  piera  having  rectangular  cross 
sections  and  such  dimensions  on  top  and  hatters  as  occur  most 
frequently  (see  g§  584-67).  The  quantities  in  the  first  four  columns 
cover  most  of  the  eases  for  highway  and  single  track  railway  bridges; 
and  the  quantities  in  the  last  two  columns  are  applicable  to  double 
track  railway  bridges.  Since  that  portion  of  the  pier  below  the 
water  should  have  more  or  less  pointed  ends,  and  since  there  is 
likely  to  be  an  offset  in  the  profile — particularly  of  high  piers, — 
the  quantities  in  the  table  (being  for  a  rectangular  cross  section)  are 
mainly  useful  in  milking  preliminary  estimates. 

Thecontentsof  piersof  other  dimensioni  than  those  in  the  table 
may  be  computed  by  the  following  formula :  • 

confenfs  =  thl  + b(l  +  Ijh'  +  lil^h?, 
in  which  /  =  the  length  on  top  under  the  coping, 

t="   thickness  on  top  under  the  coping, 
h  =   "   height  to  the  under  side  of  the  coping, 
5  =   "   batter — i.  e.,  b  =  -^  or  ^, 
The  length  on  the  bottom  =  I  +  2bh;  and  the  thickness  on  tho 
bottom  =  t-\-Zbh.     To  illustrato  the  method  of  applying  this  for- 


ovGoQi^lc 


ART.  2.] 


DETAILS  OF   CONSTKCCTION. 


I   BkCTIOS  AMD 


'S%- 

DnDDiwoN  or  TBI  Pub  oi 

«TOPU«.« 

IHSCOFDra. 

Fmotwo 

Btt.  X 

-B. 

arc.. 

8»(C. 

8  ft.. 

Mft. 

noPIBB. 

BUUr  1 :  IE 

Bauerl^iM 

B..^rni. 

B«HePl;M 

BMIerliU 

Batl«rl:M 

rati. 

CB-Vd.. 

cu.v<i<. 

c».Vd». 

™-lrfi. 

CU.IKI". 

».  V<I>. 

s 

80. « 

19.49 

36.64 

35.58 

40.90 

89.88 

0 

25.07 

23.68 

83.51 

80.90 

49.84 

47.67 

7 

20.68 

37.85 

88.57 

86.86 

59.06 

65.98 

8 

34.74 

83.18 

44.81 

41.90 

68.53 

64.48 

9 

89.84 

88.62 

51.24 

47.55 

78  28 

78.0* 

10 

46-09 

40.97 

67.86 

68  38 

88.33 

81.8ft 

11 

80.53 

45.61 

64.67 

69.09 

98.50 

90.88 

12 

66.14 

60.14 

71.69 

65.03 

1U9.03 

99.68 

18 

61.98 

54.85 

78.89 

71.03 

119.88 

108.83 

14 

67.01 

69.64 

86.81 

77.18 

180.90 

118.09 

15 

74.07 

64, S3 

93.93 

88.83 

142-25 

137.49 

16 

80,40 

69.48 

101.73 

89.61 

158-88 

187.08 

17 

86.98 

74.58 

109.75 

96.00 

165,79 

146.69 

18 

93.65 

79.66 

117.98 

103.49 

177.99 

186.49 

1» 

100.58 

S4.87 

136,43 

109.06 

190.45 

166.40 

ao 

ior.6« 

90.18 

186,07 

115.72 

208.22 

178.47 

31 

114.96 

95,57 

148  94 

123.49 

216.28 

188.67 

32 

133.46 

101  06 

158.01 

139.36 

229.80 

198.98 

38 

130,15 

106.83 

162,38 

136.34 

243.24 

207.46 

34 

138,04 

112.27 

171.84 

148.89 

257.17 

318.05 

25 

146,14 

118.03 

181.66 

150.58 

271-39 

36 

154,45 

128.86 

191.63 

157.79 

380.91 

239! 85 

27 

163,96 

139.79 

aoi,74 

165-17 

.     300.74 

2.W.67 

38 

171.69 

185,81 

212-16 

173  68 

[     815,87 

381.62 

29 

180,62 

141.93 

332.79 

180.18 

881.27 

273.09 

80 

189.77 

148.13 

283.68 

187.85 

347,01 

284.51 

S3 

308-73 

160.81 

256  19 

208.47 

879.43 

807.78 

S4 

328.64 

178.86 

279.58 

319,53 

413.06 

881.69 

86 

848,36 

187.30 

303.98 

285,98 

447.99 

855.99 

38 

270.91 

301.13 

329.86 

2.*i2.84 

484.17 

480.92 

40 

293.47 

2I.i.33 

■855.74 

370.13 

■     531.86 

406.43 

13 

316.98 

239.98 

388.17 

287.88 

560.61 

432.57 

41 

841.46 

344.91 

411.59 

306.03 

600.64 

469.32 

4e 

866.00 

260.29 

441.05 

324,60 

643.15 

486.47 

•«' 

8B!1.86 

3T6.09 

471.66 

843.66 

1     684,99 

S14.S3 

80 

420.83 

293.29 

503.83 

368.13 

739  34 

542-78 

53 

449.33 

308.90 

686.07 

774,88 

671.80 

M 

478.86 

335.93 

569.96 

403.45 

831.98 

801.47 

56 

509.45 

348.38 

604.96 

424.39 

870.45 

681.71 

58 

541.13 

361.34 

641.11 

445.57 

930.41 

663.37 

SO 

678.85 

879.62 

878.48 

467.43 

1     971.78 

694.02 

jvGooi^le 


390  BBIDOB  PIBBS.  [CHAP.  XVL 

mala,  aasume  that  it  is  required  to  find  the  coutenta  of  a  pier  4  leet 
thick,  20  feet  long  on  top,  and  30  feet  high,  having  a  batter  on 
all  fonr  faces  of  1  inch  per  foot.  Then  I  =  20,  t  =  i,  b  =  -^j  and 
the  preceding  formula  becomes 

eonienta  =  4  X  20  X  30  +  V.  (20  +  *)   (30)'  +  |  x  yir  X  (30)' 
=4,450  cubic  feet. 

606.  Co§T.  For  a  general  discussion  of  the  cost  of  masonry,  see 
gg  226-38  (pp.  153-60) ;  and  for  data  on  the  cost  of  bridge  pier 
maaonij,  see  §  235  (p.  157). 


ovGoQi^lc 


CHAPTER  XVa 


Aet.  1.    Watee  Wat  BEQUlBElk 

607.  The  determinstioD  of  the  amount  of  water  wayreqaired  in 
007  given  ca^  is  a  problem  that  does  not  admit  of  an  exact  matlie- 
matical  Bolacion.  Although  the  proportioniog  of  culverts  is  in  a 
measure  indeterminate,  it  demands  an  inbelliguit  treatment.  If 
the  culvert  is  too  small,  it  is  liable  to  cauee  a  washout,  entailing 
possibly  loss  of  life,  intermptions  of  traffic,  and  cost  of  repairs. 
On  the  other  band,  if  the  culvert  is  made  unnecessaril;  large,  the 
■cost  of  construction  is  needlessly  increased.  Any  one  can  make  a 
culvert  large  enough  ;  but  it  is  the  province  of  the  engineer  tc 
design  one  of  sufficient  bat  not  extravagant  size. 

BOB.  The  Faotobb.  The  area  of  water  way  required  depends 
npon  (I)  the  rate  of  rain-fall,  (2)  the  kind  and  condition  of  the 
soil,  (3)  the  character  and  inclination  of  the  surface,  (4)  the  condi- 
tion and  inclination  of  the  bed  of  the  stream,  (6)  the  shape  of  the 
area  to  be  drained  and  the  position  of  the  branches  of  the  stream, 
(6)  the  form  of  the  mouth  and  the  incliQation  of  the  bed  of  the 
-culvert,  and  (7)  whether  it  la  permissible  to  back  the  water  up  above 
the  culvert,  thereby  causing  it  to  discharge  nnder  a  head. 

1.  It  is  the  maximum  rate  of  rain-fall  during  the  severest  stomu 
which  is  required  in  this  connection.  This  certainly  varies  greatly 
in  different  aectiona  ;  but  there  are  almost  no  data  to  show  what  it  ia 
for  any  particular  locality,  since  records  generally  give  the  amount 
per  day,  and  rarely  per  hour,  while  the  duration  of  the  storm 
is  seldom  recorded.  Further,  probably  the  longer  the  series  of 
observations,  the  larger  will  be  the  maximum  rate  recorded,  since 
the  heavier  the  storm  the  less  frequent  its  occurrence  ;  and  bence  a 
record  tor  a  short  period,  however  complete,  is  of  but  little  value 
in  this  connection.  Further,  the  severest  rain-falls  are  of  company 
lively  limited  extent,  and  hence  the  smaller  the  area,  the  larger  the 

Ml 


ovGoQi^lc 


898  CULVERTS.  [chap,  xvii^ 

possible  maiimnm  precipitation.  Finally,  the  effect  of  the  rain-fall 
in  melting  snow  would  have  to  be  considered  in  determining  the- 
mtuimnm  amount  of  water  for  a.  gi^en  area, 

2.  The  amount  of  water  to  be  drained  off  will  depend  upon  the. 
permeability  of  the  surface  of  the  ground,  which  will  vary  greatly 
with  the  kind  of  soil,  the  degree  of  saturation,  the  condition  of 
oultiTation,  the  amount  of  vegetation,  etc. 

3.  The  rapidity  with  which  the  water  will  reach  the  water 
courses  depends  upon  whether  the  surface  is  rough  or  smooth,  steep 
or  flat,  barren  or  covered  with  vegetation,  etc. 

4.  The  rapidity  with  which  the  water  will  reach  the  culvert, 
uepends  upon  whether  there  is  a  well-dedned  and  unobstructed 
channel,  or  whether  the  water  finds  its  way  in  a  broad  thin  sheet. 
If  the  water  course  is  unobstructed  and  has  a  considerable  inclina- 

'  tion,  the  water  may  arrive  at  the  culvert  nearly  as  rapidly  as  it 
falls ;  but  if  the  channel  is  obstructed,  the  water  may  be  much, 
longer  in  paesitig  the  culvert  than  in  falling. 

5.  Of  course,  the  water  way  depends  upon  the  amount  of  area- 
to  be  drained:  but  in  many  cases  the  shape  of  this  area  and  the 
position  of  the  branches  of  the  stream  are  of  more  importance  than 
the  amount  of  the  territory.  For  example,  if  the  area  is  long  and 
narrow,  the  water  from  the  lower  portion  may  pass  through  the 
culvert  before  that  from  the  upper  end  arrives  ;  or,  on  the  other 
hand,  if  the  upper  end  of  the  area  is  steeper  than  the  lower,  the 
water  from  the  former  may  arrive  eimultaneouBly  with  that  from 
the  latter.  Again,  if  the  lower  part  of  the  area  is  better  supplied 
with  branches  than  the  upper  portion,  the  water  from  the  former 
will  be  carried  past  the  culvert  before  the  arrival  of  that  from  the- 
latter;  or,  on  the  other  hand,  if  the  upper  portion  is  better  supplied 
with  branch  water  courses  than  the  lower,  the  water  from  the 
whole  area  may  arrive  at  the  culvert  at  nearly  the  same  time.  In 
lai^e  areas  the  shape  of  the  area  and  the  position  of  the  water 
■lourses  are  very  important  considerations. 

6.  The  efQciency  of  a  culvert  may  be  materially  increased  by  so 
lOranging  the  upper  end  that  the  water  may  enter  it  without  being 
retarded  (see  §  639).  The  discharging  capacity  of  a  culvert  can 
also  be  increased  by  increasing  the  inclination  of  ite  bed,  provided 
the  channel  below  will  allow  the  water  to  flow  away  freely  after 


ovGoQi^lc 


ART.   1.]  WATER   WAY    REQUIRED.  393 

hariog  passed  the  culTert.  The  last,  although  very  important,  ia 
frequeatly  overlooked. 

7.  The  discharging  capacity  of  a  culvert  can  be  greatly  increased 
by  allowing  the  water  to  dam  up  above  it.  A  culvert  will  discharge 
twice  as  much  under  a  head  of  4  feet  as  undei'a  head  of  1  foot. 
This  can  only  safely  be  done  with  a  well-conetructed  culvert. 

009.  FOBKHLAB.  The  determination  of  the  values  of  the  difFer- 
ent  factors  entering  into  the  problem  is  almost  wholly  a  matter  of 
judgment.  An  estimate  for  any  one  of  the  above  factors  is  liable 
to  be  in  error  from  100  to  300  per  cent.,  or  even  more,  and  of 
course  any  result  deduced  from  such  data  must  be  very  uncertain. 
Fortunately,  mathematical  exactness  is  not  required  by  the  problem 
nor  warranted  by  the  data.  The  question  is  not  one  of  10  or  30 
per  cent,  of  increase ;  for  if  a  2-foot  pipe  is  insufficient,  a  3-foot 
pipe  will  probably  be  the  next  size — an  increase  of  335  per  cent., — 
and  if  a  6-foot  arch  culvert  is  too  small,  an  S-foot  will  be  used — 
an  increase  of  180  per  cent.  The  real' question  is  whether  a  3-foot 
pipe  or  an  8-foot  arch  culvert  is  needed. 

Numerous  empirical  formulas  have  been  proposed  for  this  and 
similar  problems ;  *  but  at  best  they  are  all  only  approximate,  since 
no  formula  can  give  accurate  results  with  inaccurate  data.  The 
several  formulas,  when  applied  to  the  same  problem,  give  very 
discordant  results,  owing  (1)  to  the  sources  of  error  already  re- 
ferred to  and  (3)  to  the  formulas'  having  been  deduced  for  localities 
differing  widely  in  the  essential  characteristics  npon  which  the 
results  depend.  For  example,  a  formula  deduced  for  a  dry  climate, 
as  India,  b  wholly  inapplicable  to  a  humid  and  swampy  region,  as 
Florida;  and  a  formula  deduced  from  an  agricultural  region  is 
inapplicable  in  a  city. 

However,  an  approximate  formala,  if  simple  and  easily  applied, 
may  be  valuable  as  a  nucleus  about  which  to  group  the  results  of 
personal  experience.  Such  a  formula  is  to  be  employed  more  as  a 
guide  to  the  judgment  than  as  a  working  rule ;  and  its  form,  and 
also  the  value  of  the  constants  in  it,  should  be  changed  as  subse- 
quent experience  seems  to  indicate.  With  this  use  in  view,  a  few 
formulas  will  be  referred  to  briefly. 

There  are  two  classes  of  these  formulas,  one  of  which  purports 

*  For  a  general  note  ou  empirical  lonmilaa,  «ee  |  m. 


ovGoQi^lc 


394  CDLVERTS.  [chap.  XVII. 

to  give  the  quantitj  of  water  to  be  diecharged  per  nnit  of  drainage 
area  and  the  other  the  area  of  the  water  way  in  terms  of  the  area  of 
the  territory  to  be  drained.  I'he  former  giTes  the  amoant  of  water 
sappoBed  to  reach  the  culvert;  and  the  area,  elope,  form,  etc.,  of 
the  culvert  mast  be  adjusted  to  allow  this  amount  of  water  to  pass. 
There  are  do  reliable  data  by  which  to  determine  the  discharging 
capacity  of  a  culvert  of  any  given  form,  and  hence  the  use  of  the 
formulas  of  the  first  class  adds  complicatioa  without  securing  any 
-compensating  reliability.  Most  of  the  formulas  in  common  use  for 
proportioning  water  ways  belong  to  this  class.  Such  formulas  will 
not  be  considered  here. 

The  two  following  formulas  belong  to  the  second  class. 

610  Hysr'i  Formala.  Of  the  formulas  giving  a  relation  be- 
tween the  area  of  water  way  and  the  area  to  be  drained,  Myer's  is 
the  one  most  frequently  need.     It  is 

Areatf  water  way,  in  tgy^M'e  feet  ■:=  C  ^Drainage  area,  in  aeret, 
in  which  C  is  a  variable  co-efficient  to  be  assigned,  for  slightly 
rolling  prairie,  0  is  usually  taken  at  1;  for  billy  ground  at  1.5;  and 
for  mountainous  and  rocky  ground  at  4.  For  most  localities,  at 
least,  this  formula  gives  too  large  results  for  small  drainage  areas. 
For  example,  according  to  the  formula,  a  culvert  having  a  watei 
way  of  one  square  foot  will  carry  the  water  from  a  single  acre  only. 
Further,  if  the  preponderance  of  the  testimony  of  the  formulas  for 
the  quantity  of  water  reaching  the  culvert  from  a  given  area  can 
be  relied  upon,  the  area  of  water  way  increases  more  rapidly  than 
the  square  root  of  the  drainage  area  as  required  by  this  formula. 
Hence,  it  appears  that  neither  the  constants  nor  the  form  of  this 
formula  were  correctly  chosen;  and,  consequently,  for  small  drainage 
areas  it  gives  the  area  of  waterway  too  great,  and  for  large  drain- 
age areas  too  small. 

611.  Talbot's  Pormnla.  Prof.  A.  N.  Talbot  proposed  the  fol- 
lowing formula,  "more  as  a  guide  to  the  judgment  than  as  a  work- 
ing rule :"  * 

Area  itf  water  wag,  in»guaTefeet=  C  •^(Drainage  area,  in  aertt)*, 
in  which  (7  is  a  variable  co-efficient.    Data  from  various  States  gave 
values  for  C  as  follows:    "For  steep  and  rocky  ground,  Cvariea 


ovGoQi^lc 


AST.  1.]  WATER  WAT    BEQUIBED.  395 

from  f  to  1.  For  rolling  agiicQlttiral  country  subject  to  floods  at 
times  of  melting  of  edow,  and  with  the  length  of  valley  three  or 
four  times  its  width,  C  is  about  \;  and  if  the  stream  ia  longer  in 
proportion  to  the  area,  decrease  C.  In  districts  not  affected  by 
accumulated  snow,  and  where  the  length  of  the  valley  is  several 
times  the  width,  \  or  \,  or  even  less,  may  be  need,  ^should  be 
increased  for  steep  side  slopes,  especially  if  the  upper  part  of  the 
valley  has  a  much  greater  fall  than  the  channel  at  the  culvert." 

The  author  has  tested  the  above  formula  by  numerous  culverts 
and  small  bridges  in  a  small  city  and  also  by  culverts  nnder  high- 
ways in  the  country  (ail  slightly  rolling  prairie),  and  finds  that 
it  agrees  fairly  well  with  the  experience  of  fifteen  to  twenty  years. 
In  these  teats,  it  was  found  that  water  ways  proportioned  by  this 
formula  will  probably  be  slightly  flooded,  and  consequently  be  com- 
pelled to  discharge  under  a  small  head,  once  every  four  or  five 
jears. 

612.  In  both  of  the  preceding  formulas  it  will  be  noticed  that 
the  large  range  of  the  "  constant "  C  affords  ample  opportunity  for 
ihe  exercise  of  good  judgment,  and  maJtes  the  results  obtained  by 
the  formulas  almost  wholly  a  matter  of  opinion. 

613,  Practical  Hethod.  Valuable  data  on  the  proper  size  of 
«ny  particular  culvert  may  be  obtained  (1)  by  observing  the  existing 
openings  on  the  same  stream,  (S)  by  measuring — preferably  at  time 
-of  high  water — a  cross  section  of  the  stream  at  some  narrow  place, 
■and  (3)  by  determining  the  height  of  high  water  as  indicated  by 
iirift  and  the  evidence  of  the  inhabitants  of  the  neighborhood. 
With  these  data  and  a  careful  consideration  of  the  various  matters 
referred  to  in  g  608,  it  is  possible  to  determine  the  proper  area  of 
water  way  with  a  reasonable  degree  of  accuracy. 

Ordinarily  it  is  wise  to  take  into  account  a  probable  increase  of 
flow  as  the  country  becomes  better  improved.  However,  in  con- 
structing any  structure,  it  is  not  wise  to  make  it  absolutely  safe 
^against  every  possible  contingency  that  may  arise,  for  the  expen- 
diture necessitated  by  such  a  course  wonld  be  a  ruinous  and  un- 
justifiable extravagance.  Washouts  can  not  be  prevented  altogether, 
oor  their  liability  reduced  to  a  minimum,  without  an  unreasonable 
expenditure.  It  has  been  said — and  within  reasonable  limits  it  ia 
^e — that  if  some  of  a  number  of  calverte  are  not  carried  awa^ 


ovGoQi^lc 


896  CUL7EBTB.  [cHAP.  XTII. 

each  year,  they  are  not  well  deBigned;  that  is  to  say,  it  is  only  a 
qneetion  of  time  when  a  properly  proportioned  colTert  will  periBlL 
in  some  excessiTe  flood.  It  is  easy  to  make  a  culvert  lai^  enoqgii 
to  be  safe  under  all  circumBtances,  but  tlie  difCerenoe  in  cost  be- 
tween such  a  structure  and  one  that  would  be  reasonably  safe  would 
probably  much  more  than  overbalance  the  losses  from  the  washing 
out  of  an  occasional  cnlrert.  It  is  seldom  justifiable  to  provide  for 
all  that  may  possibly  happen  in  the  course  of  fifty  or  one  hundred 
years.  One  dollar  at  5  per  cent,  compound  interest  will  amount  to 
tll.47  in  50  years  and  to  $131.50  in  100  years.  Of  course,  the 
question  is  not  purely  one  of  finance,  but  also  one  of  safety  to  human 
life;  but  even  then  it  logically  follows  that,  unlese  the  engineer  is 
prepared  to  spend  ti:U.50  to  avoid  a  given  danger  now,  he  is  not 
justified  in  spending  $1  to  avoid  a  similar  danger  100  years  hence. 
This  phase  of  the  problem  is  very  important,  but  is  foreign  to  the 
subject  of  this  volame. 

614.  In  the  construction  of  a  new  railroad,  considerations  of 
first  cost,  time,  and  a  lack  of  knowledge  of  the  amonnt  of  fnture 
traffic  as  well  as  ignorance  of  the  physical  features  of  the  country, 
usually  require  that  temporary  structures  be  first  put  in,  to  be  re- 
placed by  permanent  ones  later.  In  the  mean  time  an  incidental 
hut  very  'mportant  duty  of  the  engineer  is  to  make  a  careful  study 
of  the  requirement  of  the  permanent  structures  which  will  ulti- 
mately replace  the  temporary  ones.  The  high-water  mark  of  streams 
and  the  effect  of  floods,  even  in  water  courses  ordinarily  dry,  should 
be  recorded.  With  these  data  the  proper  proportioning  of  the 
water  way  of  the  permanent  Btnictures  becomes  a  comparatively  easy 
task.  Upon  the  judgment  and  ability  displayed  in  this  depends 
most  of  the  economical  value  of  the  improvements;  for,  aa  the  road 
will  have  fixed  or  standard  plans  for  culverts,  abutments,  piers, 
etc.,  the  supervision  of  the  construction  will  not  be  diflScult, 

Art.  3.  Box  and  Pipe  CcLvEirra. 
616.  Stofe  Box  Cvitiet.  This  culvert  consists  of  vertical  side 
walls  of  masonry  with  flag  stones  on  top  from  one  wall  to  the  other. 
Masonry  box  culverts  were  constructed  much  more  frequently  for- 
merly than  at  the  present  time.  The  lack  of  suitable  stone  in  many 
parts  of  the  West  led  to  the  adoption  of  vitrified  pipes  (§  637)  and 
iron  pipes  (§  631)  instead  of  masonry  box  culverts.     However,  in 


ovGoQi^lc 


ART.  2.]  BTONB  BOX  CDLTBETS.  397 

many  localities  they  are  built  frequently  enoagh  to  warrant  a  brief 


616.  Fonndatioit  A  common  foandstion  for  masonry  box  ciil< 
Terts  is  a  stone  pavement  (§  319)  under  tbe  entire  culvert,  npon 
which  the  side  walls  rest  (see  Fig.  91a).  This  is  not  good  practice ; 
for,  sinca  the  paving  is  liable  to  be  washed  oat,  it  endangers  tho 


wall.  The  tendency  of  the  pavement  to  undermine  may  be  dimin- 
ished (1)  by  driving  sheet  piling  or  by  setting  deep  curb-stones  at 
both  ends,  or  (2)  by  extending  the  paving  to  a  considerable  distance 
beyond  bo^-h  ends.  The  first  is  the  better  method ;  bnt  nsnally 
these  devices  only  postpone,  and  do  not  prevent,'final  failure.  The 
water  is  nearly  certain  to  carry  the  soil  away  from  ander  the  pave- 
ment, even  if  the  curb-stones  or  sheet  piles  remain  intact. 

Sometimes  culvert  foundations  are  paved  by  laying  large  stones 
flatwise.  This  practice  is  no  better  than  ordinary  st^ne  paving,  un- 
ices the  flags  are  large  enough  to  extend  under  both  walls ;  but 
atones  large  enongh  for  this  can  seldom  be  obtained. 

A  much  better  method  is  to  give  each  side  wall  an  independent 
ioundation  and  to  pave  between  the  walls  only  (see  Fig.  Qlb).  Am 
important  advantage  of  this  method  is  that  each  wall  can  be  placed 
separately,  which  facilitates  the  keeping  of  the  water  away  from  the 
foundation  pit.  Indeed,  if  the  foundations  are  deep,  or  if  there  is 
not  much  current,  the  paving  may  be  entirely  omitted.  If  the  cur- 
rent is  only  moderate,  it  is  sufficient  to  build  in,  at  each  end  of  the 
culvert,  between  the  ends  of  the  side  walls  with  solid  masonry  up 
to  the  bed  of  the  stream  ;  but  if  the  culvert  is  long,  it  is  wise  to 
build  one  or  more  intermediate  cross  walls  also.  If  the  current  is 
strong,  the  cross  walls  at  the  ends  should  be  carried  down  deep, 
and  the  space  between  the  side  walls  should  be  paved  with  large 
stones  closely  set  and  deeply  bedded.  The  beet  job  possible  is  se- 
cured by  setting  the  paving  in  cement  mortar.  In  this  connection, 
see  Figs.  94,  95,  and  96  (pages  403,  iOi,  and  406). 


ovGoQi^lc 


[CHAP,  xra^ 

alle^jp&rticnlarly  at  the  end  of  the 
tions  b^riow  the  effect  of  frost. 
f  box  culT6>rts  are  nsoally  finished 
iular  to  the  axViB  of  the  culvert  as 
7  stepping  the  eVids  off  as  shown 
B  to  become  clogget^l  and  to  have 
,  and  probably  its  oWl^esistence 
i  its  upper  end.     ThiB  a*«Miger  la 


ig  the  Bide  walla  at  the  upper  end] 
)4  (page  403).  If  the  month  of' 
L  with  drift,  the  open  top  is  a  well 
In  this  way  the  full  discharging- 
atained.     The  lower  end  niay  be 

linner  at  the  outer  end,  thus  pro^  I 
effect  as  is  obtained  in  splaying  \ 


,.  96  (page  406). 

)  a  relatiouBhip  between  the  thiolc-    | 

ad  to  be  supported,  let  t 


\ 


ibove  the  top  of  the  culyert ; 
7ounds  per  square  inch  ; 
strength  (§  15) ; 
over  the  cover  stone,  in  pounds. 


N 


jvGooi^le 


AKT.  8.]  8T0NB  BOX  CULTEBTS.  SSft"- 

For  simplicity,  consider  a  section  of  the  cnlTert  only  a  foot  long. 

The  coTer  atones  are  in  the  condition  of  a  beam  supported  at  the 
ends  and  loaded  uniformly.  By  the  principles  of  the  resistance  of 
materials,  one  eighth  of  the  uniform  load  multiplied  by  the  span  ig 
equal  to  one  sixth  of  the  continued  product  of  the  modulus  of  rup- 
ture, the  breadth,  and  the  square  of  the  thickness.  Expressing, 
this  in  symbols  as  above,  and  reducing,  gives 

^^ (i>. 


=  / 


Ordinarily,  earth  weighs  from  80  to  100  lbs.  per  en.  ft,  bnt  for 
convenience  ve  wiU  assnme  it  at  100  lbs.  per  cu.  ft,  which  is  on 
the  safe  side ;  then  W  =  100  S  S.  The  maximnm  moving  load  for^ 
railroad  bridges  may  be  taken  at,  say,  2  tons  per  foot  of  track. 
This  is  distributed  over  at  least  8  square  feet ;  and  hence  the  liva- 
load  is  eqn&l  to  one  quarter  of  a  ton,  or  500  poands,  per  square  foot* 
i.  e.  the  live  load  is  equal  to  an  embankment  &  feet  high.  Therefore., 
the  maximum  live  load — a  locomotive — ia  provided  for  by  adding  5 
■  feet  to  the  actual  height  of  the  embankment  The  table  on  pag&- 
13  shows  that  for  limestone  R  =  1,500.  Substituting  these  values, 
in  equation  (1),  above,  gives  for  limestone 

T=0.Z0SVH+5, (2). 

By  substituting  the  corresponding  value  of  R  from  the  table  on 
page  12,  we  have  for  Bandtt&ne 

r=0.355Vir+6, (8> 

For  hightaat/s,  it  is  sufficiently  exact  to  drop  the  6  under  the 
radical,  i.  e.,  to  neglect  the  live  l(»d ;  and  equation  (1)  then  becomes, 
for  limestone 

T=0:208VH,' (4), 

and  for  sandatone 

I'  =  0.25S/ff. (5> 

The  preceding  formulas  give  the  thickness  which  a  stone  of 
average  quality  must  have  to  be  on  the  point  of  breaking;  and  henc«- 


ovGoQi^lc 


400  CCLVEBTS.  [CHAP.  XVIL. 

in  applying  them  it  will  be  necessary  to  allow  a  margin  for  safety, 
cither  by  selectiog  the  stone  or  by  increasing  the  computed  thick- 
ness. If  reasonable  care  is  used  in  selecting  the  stones,  it  is  probably 
safe  to  double  the  thickness  found  as  above.  To  allow  for  any  given 
fiictor  of  safety,  multiply  the  thickness  found  by  applying  the  above 
formulas  by  the  square  root  of  the  factor  of  safety.  Thus,  to  allow 
for  a  factor  of  4,  multiply  the  thickness  found  as  above  by  2  ;  for  a 
factor  of  6,  mnltipty  by  2J  ;  and  for  a  factor  of  9,  multiply  by  3. 

619.  The  thickness  of  the  cover  stones  does  not,  however,  de- 
pend alone  upon  the  depth  of  the  earth,  the  live  load,  and  the  span. 

In  the  first  place,  the  pressure  on  the  cover  stone  does  not  vary 
directly  as  the  depth  of  the  earth  above  it.  {a)  The  earth  itself 
acts  more  or  less  as  a  beam  to  support  part,  at  least,  of  the  weight 
over  the  opening.  That  earth  may  act  thus  is  proven  by  the  fact 
that  an  excavation  can  be  carried  Iiorizontally  into  an  embankment 
<ir  side  hill  without  supporting  the  roof.  '  The  beam  strength  of  tht 
earth  increases  with  the  compactness  and  the  tenacity  of  the  soil 
and  with  the  square  of  the  height  of  the  embankment  above  the 
roof.  This  effect  would  be  zero  with  clean  sand  ;  but,  owing  to  the 
nature  of  that  material,  it  would  seldom  be  employed  for  filling  over 
A  culvert.  Hence,  under  ordinary  conditions,  part  of  the  load  is 
BUpportfld  by  the  beam  strength  of  the  earth  itself.  Therefore,  a 
low  embankment  may  produce  a  greater  strain  in  the  cover  than  a 
much  higher  one.  (5)  The  prism  of  earth  directly  over  the  culvert 
will  be  partially  supported  by  the  adjacent  soil ;  that  is  to  say,  the 
particles  of  earth  directly  above  the  culvert  will  act  more  or  less  as 
arches  resting  upon  the  earth  at  the  sides  of  the  culvert,  thus  par- 
tially relieving  the  c<Jver  stones.  This  effect  would  be  greater  with 
sharp  eand  than  with  clay,  but  would  be  entirely  destroyed  by  shock, 
aa  of  passing  trains,  (c)  The  stones  at  the  center  of  the  culvert 
would  be  relieved  of  part  of  their  load  by  an  action  similar  to  that 
mentioned  above,  whereby  the  weight  over  the  center  of  the  culvert 
is  transferred  towards  its  ends.  However,  the  relief  caused  by  this 
action  is  but  slight. 

In  the  second  place,  the  pressure  due  to  the  live  load  is  trans- 
mitted downward  in  diverging  lines,  thus  distributing  the  weight 
over  a  considerably  larger  area  than  that  assumed  in  deducing  eqoar- 
tioDs  (3)  and  (3)  above. 

In  the  third  place,  the  cover  most  be  thick  enough  to  resist  the 


ovGoQi^lc 


-ABT.  2.]  8T0KE  BOX  CULVERTS.  401 

■eftbct  of  frost,  as  well  as  to  support  the  earth  and  live  load  above  it. 
The  freezing,  and  consequent  ezpausiOD,  of  the  earth  is  a  force 
tending  directly  to  break  the  cover  stones.  That  this  is  an  impor- 
tant consideration  is  proved  by  the  fact  that  tliese  stones  break 
near  the  ends  of  culverts  as  frequently  as  near  the  middle,  although 
the  weight  to  be  supported  is  greater  at  the  latter  place. 

620.  It  is  impossible  to  compute,  even  approximately,  the  effect 
of  the  preceding  factors ;  but  experience  shows  that  the  thickness 
is  independent  of  the  height  of  the  embankment,  provided  there  is 
sufBcient  earth  over  the  cover  stones  to  prevent  serious  shock, — say 
3  feet  for  railroads  and  1  to  2  feet  for  highways. 

The  thickness  employed  on  the  railroads  in  States  along  the 
fortieth  parallel  of  latitude  is  generally  about  as  foUovfs,  irrespec- 
tive of  the  height  of  the  bank  or  of  whether  the  cover  is  limestone 
■or  sandstone :  ' 

8PAH  or  CDI.TMBI.  Thickness  or  Corn, 

a  feet 10  Inches. 

S  feet 12  laches. 

A  feet 15  inclies. 

On  the  Canadian  Pacific  R.  R.,  the  minimum  thickness  of  cover 
atones  for  spanB  of  3  feet  is  16  inches,  and  under  3  feet,  14  inches. 

621.  Quality  of  Masonry.  Box  culverts  are  usually  built  of 
rubble  masonry  (§  313)  laid  in  cement  mortar.  Formerly  they  were 
■often  built  of  dry  rubble,  except  for  3  or  t  feet  at  each  end,  which 
was  laid  in  mortar.  It  is  now  generally  hold  that  box  culverts 
■should  be  so  built  that  they  may  discharge  under  a  head  without 
damage.  It  is  usually  specified  that  the  cover  stones  must  have  a 
solid,  well-leveled  bearing  on  the  side  walls  of  not  leas  than  15 
inches.  The  most  careful  constructors  close  the  joints  between  the 
cover  stones  by  bedding  spalls  m  mortar  over  them. 

63S.  Speeifieatiotu.'  A11  atose  box  culverta  shall  bavea  wnterwnjat  l«sat 
2iX.S  feet.  The  side  walls  sbiOl  not  be  less  than  two  feet  <2')  thick,  and 
shall  be  built  of  aound,  durable  stouca  not  less  thaa  six  inches  (6")  thick,  laid 
In  cement  mortar  [usually  1  part  Rosendale  cement  to  3  parts  sand].  Tbe 
walla  must  be  laid  in  true  horizontHi  courses,  but  in  case  the  thicknCBs  of  the 
course  Is  greater  than  12  Intbea  (IS"),  occasionatly  two  stones  may  be  uied  to 
make  up  the  thickness.  The  walls  must  oe  laid  so  as  to  be  thoroughly  bonded, 
and  at  least  one  fourth  of  the  area  of  each  course  must  be  headers  going  en- 

*F«nnsrlvBi)ia  Railroad. 


ovGoQi^lc 


4ff4  COLTEET3.  [CSAP.  STTL 

tlrely  through  the  wall.  The  top  course  must  have  one  half  its  area  of  througb. 
(rlones,  and  ibe  remaioder  of  thla  course  must  consist  of  sloue  go\ng  at  least 
one  half  of  the  way  across  the  wall  from  tbc  inside  face.  Tbe  face  stones  ot 
each  course  must  tie  dressed  to  a  straight  edge,  and  pitched  off  to  a  true  line. 
All  of  the  coping  stones  of  head  walls  must  lie  througlis,  and  must  have  the 
upper  surface  hammer-dressed  to  a  straight  edge,  and  the  face  pitched  off 
to  a  line  with  margin  draft.  Cbver  stones  shall  have  a  thickness  of  at  least 
twelve  inches  <13  "J  for  opening  of  three  feet  (3'),  and  at  leaslUinches  (14")  for 
opening  of  four  feet  (4') ;  and  must  be  carefuUj  selected,  and  must  be  of  such 
length  as  to  have  a  tiearing  of  at  least  one  foot  (1)  on  either  wall. 

The  beds  and  vertical  joints  of  the  face  stones  for  a  distance  of  six 
Inches  (6")  from  the  face  of  the  wall  shall  be  so  dressed  as  to  require  a  mortar 
Joint  not  thiclier  than  tbree  fourths  of  an  inch  ({").  Joints  between  the  cov- 
ering stones  must  be  not  wider  than  three  fourths  of  an  inch  <{"),  and  the 
bearing  surface  of  cover  stones  upon  side  walls  must  be  ao  dressed  as  to 
require  not  more  than  a  one-inch  (1")  mortar  joint. 

The  paving  sliiill  consist  of  flat  stones,  set  on  edge,  at  right  angles  with  the 
line  of  the  culvert,  not  less  than  twelve  inches  (12 ')  deep,  and  shall  be  laid  in 
cement  mortar  and  grouted.  , 

623.  ExampleB.    The  box  colvert  shown  in  Fig.  94  (page  403), 

JB  presented  as  being  on  .the  whole  the  beet  (see  §  617).  The  table 
sccompanjing  the  diagram  gives  the  various  dimensions  of,  and  also 
quantities  of  masonry  in,  bos  culveii^s  for  different  openings.  The 
former  data  and  the  diagrams  are  ample  (or  the  construction  of  any 
box  culvert ;  while  the  latter  data  will  be  useful  in  making  esti- 
mates of  cost  (§  636).  In  the  headings  of  the  colums  under  "  Size 
of  the  Openings,"  the  first  number  is  the  span  of  the  culvert,  and 
the  second  is  the  clear  height  of  water  way.  The  quantities  of 
masonry  in  the  table  were  computed  for  a  cross  wall  at  each  end  of 
the  culverts,  of  the  section  s'lowu  in  Fig.  94 ;  but  in  many  cases, 
this  should  be  3  feet  deep  instead  of  2,  as  shown.  In  using  the 
table  this  correction  is  easily  iipplied. 

824.  The  box  culvert  shown  in  Fig.  95  is  the  one  employed  in 
the  construction  of  the  !'Weet  Slioro  R.  E." — New  York  City  to 
Buffalo.  The  data  in  the  table  accompanying  tlie  dii^ram  give  the 
dimensions  and  qnantities  of  masonry  of  various  sizes.  In  the  head- 
ings under  "Size  of  the  Openings,"  the  first  number  is  the  span  of 
the  opening  and  the  second  is  its'height. 

Box  culverte  of  the  general  form  show*  in  Fig.  95  are  sometimes 
built  double;  i.e.,  two  culverts  are  built  side  by  side  in  such  a 
maimer  as  to  have  o^e  side  wall  in  common.     The  following  table 


ovGoQi^lc 


LBT.  2.] 


STONE   BOX  CULVBHIB. 


p: 

> 


E-i 


g       ^ 


£>%&&&^    s  S  ^ 


5-1 

ill 


irf.|| 


jvGooi^le 


CCLVEBIB. 


[chap.  im. 


EC 

p: 

g 

£ 

(  i 

"= 

X 

CQ 

D 

E-i 

s 

^ 

'1 

1 

|fI 

'  s 

f^   DC 

K 

1^1 

I   ^• 

1 

|r  "1 

1 

•^  X 

1       X 

O 

m 

i 

ir> 

^ 

s   d 

s 

1  E 

i 

£ 

8SS 

I 

s 

s 

d 

7 

T 

1 

3- 

^!-i.i.S 

^iS 

d 

s 

!!| 

JS2 
Iff 

-h 


m 


^1    , 


15! 

lis  I 

si. ^'8  ,til 

SI- -la  fill 


jvGooi^le 


ART.  2.]  STONE  BOX  CULVBRTS,  405 

gives  the  dimeiiBionB  and  qaantities  for  such  box  culverts.  The 
dimensions  not  given  in  the  following  table  ore  the  same  as  in  the 
table  accompanying  Fig.  95. 

TABLE  44. 
DniKNBionB  aus  ConTBiiTfl  of  Doijbib  Box  Ctn-vxRii. 


Sum  Of  THi  OPENtm. 

'&? 

v.* 

lOi." 

'£! 

i^^ 

I>M™«™! 

wv 
w 

IS.1S 
0.8M 

0.407 

rv 

U.1S 
0.W1 
0.444 

yo" 

Sl.DO 

i.m 

0.481 

»'0" 

at.  IS 

l.JW 

o.ut 

OtannmK 

Muoiii7lntw<i<iDilwa1I«.liieiLJd«. 

a—oarr  la  tniok,  per  toot  of  lenctb  from  bi- 
■Jde  to  Ipslde  DfeDd  walJi,  in  oD.  rda.  .  . 

9.S» 

The  standard  double  box  culvert  employed  in  the  eotiBtmctioa 
of  the  Canadian  Pacific  B.  S.  differed  from  the  form  described 
abore  in  having  (1)  shorter  end  walls,  and  wings  at  an  angle  of  30*^ 
■with  the  axis  of  the  colTwt,  and  (2)  a  triangular  cat-water  at  the 
upper  end  of  the  dlTision  wall. 

625.  The  culvert  shown  in  Pig.  96  is  the  standard  on  the  Inter- 
colonial Bailway  of  Canada,  and  is  very  substantially  constrncted. 

626.  Cost.    With  the  data  accompanying  Figs.  94  and  95  (pages 
\    403  and  40i),  and  the  table  of  cost  of  masonry  on  page  160,  it  is 

an  easy  matter  to  make  an  estimate  of  the  .cost  of  a  box  culverts 
For  example,  assume  that  it  is  proposed  to  build  a  culvert  30  feet 
long — out  to  out  of  culvert  proper — having  a  water  way  3  feet  wide 
and  4  feet  high,  and  that  estimates  of  the  cost  of  the  general  forms 
shown  in  Fig.  94  and  ateo  of  that  of  Fig.  95  are  desired. 

StUmaUifor  o  8  X  tjt.  Box  Culvert  qfOie  Q«neral  Form  ifuwn  in  S\g.  M. 

Huonryln   «eTid  wbIIr— IB.ffi  cu.  fda ....(^  $S.GOpeTCU.  ;d.  =    tU.OB 

"  EG  feet  of  trunk  (1444  >»=)Se.I0car(li.O*^B0       "        "    ■•     US.» 

PartDR     "  85    "     "       "       (0.111  ■»=)  S.JS  ■•      "    at!.«l      •'        '■    -        B.W 

Total  cHHt SlKl.ie 

BttimaUtfor  aiy.Aft.  Box  OultartqfAe  Oerteral  Firrm  Aoan  in  Fig.  OSl 


7  in   Sendiralli 


i_S4.aOcu.Td» a  »S  SO  per  OIL  yd,  =    $84.70 

-UDk(»<  1.14B=)3T.Wim.]'d>.$WiO       "       "     =>      8e.4S 
"      (81  X  O.S70=)   8.88  "     ■■     ®  tt.00       ■'        '■     =       1179 


ovGoQi^lc 


CULTEETB.  [CHAP.  XTII. 


'I 

i 
i 


jvGooi^le 


4RT.  3.]  VITRIFIED   PIPE   CCLVERTS.  407 

If  the  price  for  the  masonry  does  not  include  the  expense  for 
the  neceseKrj  ezcaTation,  the  above  estimates  should  be  increased 
by  the  coat  of  excavation,  which  will  vary  with  the  situation  of  the 
culvert. 

To  make  a  comparison  of  the  relative  coat  of  the  two  types 
of  culverts  just  mentioned,  we  may  proceed  as  follows :  The  coat 
per  foot  of  the  trunk  of  a  3  X  4  culvert  of  the  form  shown  in 
Fig.  94  is  (1.444  cu.  yds.  of  masonry  @  13.50  plus  0.111  cu.  yds. 
of  paving  ®  13.00)  15.28;  and  the  corresponding  cost  for  Fig. 
95  is  (1.148  CO.  yds.  of  masonry  @  t3.50  plus  0.370  cu.  yds. 
of  paving  @  )2.00)  $4.76.  The  difference,  in  cost  per  foot 
is  {$5.28- J4. 76)  $0.52  in  favor  of  Fig.  95.  The  cost  of  the 
cnd.wallsforFig.  94  is  (16.88  cu.  yds.  @  $3.50)  $59.08;  and  the 
corresponding  cost  for  Fig.  95  is  (34.30  cu.  yds.  @  $3.50)  $84.70. 
The  difference  is  $25.62  in  favor  of  Fig.  94.  Since  in  the  former 
the  cross  wall  extends  but  3  feet  below  the  floor  of  the  culvert, 
irhile  in  the  latter  the  end  walls  extend  3  feet,  the  difference  tn  cost 
shonld  be  decreased  by  the  cost  of  the  difference  of  the  f  oundationa. 
If  the  cross  walls  of  Fig.  94  be  carried  down  another  foot,  the 
amount  of  masonry  will  be  increased  3  cu.  yds.  and  the  cost  $7.00; 
and  the  difference  in  coat  of  the  end  walls  will  be  ($35.63  —  $7.00) 
$18.62  in  favor  of  Fig.  94.  Under  these  conditions,  for  a  culvert 
'40  feet  long,  the  two  types  will  cost  the  same;  for  lengths  less  than 
■40  feet  Fig.  94  is  the  cheaper,  and  for  lengths  greater  than  40  feet 
Fig.  95  is  the  cheaper.  If  the  end  walls  of  Fig.  95  are  carried 
down  only  2  feet,  the  amount  of  masonry  will  he  decreased  by  3. 4 
en,  yds.  and  the  cost  by  $11.90;  and  then  the  difference  of  cost  will 
l>e($25.63  — $11.90)  $13.73.  Under  this  condition,  for  a  culvert 
30  feet  long,  the  two  types  will  cost  the  same;  for  lengths  less  than 
30  feet  Fig.  94  is  the  cheaper,  and  for  lengths  greater  than  30  feet 
Fig.  95  is  the  cheaper.  We  may  conclude,  therefore,  that  for 
lengths  under  35  or  40  feet  the  type  shown  in  Fig.  94  ia  a  little 
cheaper,  while  for  greater  lengths  than  35  or  40  feet  that  in  Fig. 
95  is  slightly  cheaper.  For  the  smallest  size  the  length  of  equal 
cost  is  abont  10  feet. 

There  is  no  material  difference  in  the  first  coat  of  the  two  types; 
but  the  culvert  shown  in  Fig.  94  is  the  more  efScient. 

627.  TnaiTIED  Pipe  CtllTZBTt.  During  the  past  lew  years 
vitrified  sewer  pipes  have  been  extensively  employed  for  small  col- 


ovGoQi^lc 


408  CULVEETS.  [chap,  xvir 

verts  tmder  both  highvaye  and  railroads.  The  pipe  generally- 
employed  for  this  pnrpoae  is  that  known  to  the  trade  as  culrert 
pipe  or  "ertra  heavy"  or  "double  strength"  sewer  pipe,  which  is 
20  to  40  per  cent,  (varying  with  the  maker  and  the  size)  heavier  than 
the  quality  ordinarily  employed  for  sewers. 

Apparently  the  heavier  pipe  is  need  on  the  supposition  that  the 
lighter  is  not  strong  enough  for  cnlverts.  In  moet  cases,  at  least, 
this  is  an  erroneous  assumption.  1.  With  the  same  depth  of  earth 
over  the  pipe,  there  is  but  little  more  pressure  on  the  pipe  when 
jused  as  a  culvert  than  when  employed  in  a  sewer.  At  moet,  the- 
difference  of  pressure  is  that  due  to  the  live  load,  which  can  not 
exceed  the  weight  of  an  additional  5  feet  of  earth  (see  g  618),  and. 
will  generally  he  much  less  (see  the  second  paragraph  of  g  619). 
8.  Experience  demonstrates  that  the  lighter  pipes  are  not  deficient 
in  strength  when  used  in  sewers,  however  deep  they  are  laid. 
According  to  experiments  made  by  bedding  the  lower  half  of  the 
pipe  in  sand  and  applying  a  pressure  along  a  comparatively  ftarrov^ 
area,  the  average  cmahing  strength  of  ordinary  sewer  pipe  was- 
;i,400  Iba.  per  sq.  ft.  of  horizontal  section,  and  (or  culvert  pipe 
12,000  lbs.  per  sq.  fi*  .  If  the  pressure  had  been  applied  more 
nearly  as  in  actual  practice,  the  pipes  would  have  borne  consider- 
ably more.  The  firat  of  the  above  results  is  equal  to  the  weight  of 
24  feet  of  earth,  and  the  second  to  that  of  130  feet,  although  actual 
embankments  of  these  heights  would  not  give  anything  like  ih&- 
abovti  pressures  (see  g  619). 

There  is  a  little  difference  between  culverts  and  aewers  in  the- 
exposure  to  frost;  but  no  danger  need  be  apprehended  from  this. 
cause,  provided  the  culverts  are  so  constructed  that  the  water  is 
carried  away  from  the  lower  end,  since  ordinary  soft  drain  tile  are 
not  in  the  least  injured  by  the  expansion  of  the  frost  in  the  earth, 
around  them. 

62S,  Constmction.  In  laying  the  pipe,  the  bottom  of  the  trench.  . 
should  be  rounded  out  to  fit  the  lower  half  of  the  body  of  the  pipe,. 
with  proper  depressions  for  the  sockets.  If  the  ground  is  soft  or 
sandy,  the  earth  should  bo  rammed  carefully,  but  solidly,  in  and 
around  the  lower  part  of  the  pipe.  On  railways,  three  feet  of  earthi 
between  the  top  of  the  pipe  and  the  bottom  of  the  tie  has  been 
found  anfScient.  On  highways  pipes  have  stood  from  10  to  Ifi 
years  under  heavy  loads  with  only  8  to  13  inches  of  earth  over- 
*  For  addJtloDol  data,  see  Note  7,  pt^e  617. 


jvGooi^le 


ART.  3.]  VITEiriED    PIPE   CULVBKTB.  Wftt 

them;  but  as  a  rule  it  is  not  wise  to  lay  them  vith  less  than  12  to- 
18  inches  of  earth  covering. 

In  many  cases — perhaps  in  most — the  joints  are  not  calked.  If 
this  is  not  done,  there  is  liability  of  the  water's  being  forced  out  at 
the  joints  and  washing  away  the  soil  from  aronnd  the  pipe.  Even 
if  the  danger  is  not  very  imminent,  the  joints  of  the  larger  pipes, 
at  least,  should  be  calked  with  hydraulic  cement,  since  the  coat  is. 
very  Bmall  compared  with  the  insurance  of  safety  thereby  secured.. 
Sometimes  the  joints  are  calked  with  clay.  Every  cnlvert  should 
be  built  so  that  it  can  discharge  water  under  a  head  without  damage- 
to  iteelf. 

The  end  sections  should  be  protected  with  a  timbet  or  masonry- 
bnlkhead,  althongh  it  is  often  omitted.  Of  course  a  parapet  wait 
of  rubble  masonry  or  brick-work  laid  in  cement  is  best  (see  Fig.  97)^ 


Bio.  7T.  Fio.  98. 

The  fonndation  of  the  bnlkhead  should  be  deep  enough  not  to  ho- 
disturbed  by  frost  In  constructing  the  end  wall,  it  is  well  to  in- 
crease the  ^11  near  the  outlet  to  allow  for  a  poesible  settlement  of 
the  interior  sections.  When  stone  and  brick  abntments  are  too 
expensive,  a  £iir  aubetitute  can  be  made  by  setting  poets  in  the 
ground  and  spiking  plank  on  as  shown  in  Fig.  98.  When  planka 
are  used,  it  is  best  to  set  them  with  considerable  inclination  towards 
the  road  bed  to  prevent  their  being  crowded  outward  by  the  pressure 
of  the  embankment.  The  upper  end  of  the  cnlvert  should  be  so 
protected  that  the  water  will  not  readily  find  its  way  along  the  out- 
side of  the  pipes.  In  case  the  mouth  of  the  culvert  shonld  become 
submerged. 

The  freezing  o!  water  in  the  pipe,  particularly  if  more  than 
half  full,  is  liable  to  burst  it;  eonse<|uently  the  pipe  should  have  a. 
sofBcient  fall  to  drain  itself,  and  the  outlet  should  be  so  low  that. 


ovGoQi^lc 


410  CCliVERTS.  [chap.  XTir. 

there  is  no  danger  of  back-water's  reaching  the  pipe.     If  properly 
drained,  there  is  no  danger  from  froet. 

When  the  capacity  of  one  pipe  is  not  sufficient,  two  or  more 
may  be  laid  side  by  side.  Although  two  Bmall  pipes  do  not  hare 
tm  much  discharging  capacity  as  a  single  large  one  of  eqoal  cross 
section,  yet  there  is  an  advantage  in  laying  two  small  ones  side  by 
side,  since  then  the  water  need  not  rise  so  high  to  utilize  the  full 
capacity  of  the  two  pipes  as  would  be  uecessary  to  discharge  itself 
throngh  a  single  one  of  larger  size, 

629.  Examplea.  Fig.  99  (page  411)  shows  the  standard  yitri- 
£ed  pipe  culrerts  employed  on  the  Kansas  City  and  Omaha  B.  B. 
This  construction  gives  a  strong,  durable  cuhert  which  passes  water 
freely.  The  dimensions  of  the  masonry  end  walls  and  of  the  con- 
crete bed  for  the  intermediate  sizes  are  nearly  proportional  to  those 
«hown  in  Fig.  99,  Table  46  (page  411)  shows  the  quantities  of 
masonry  required  for  the  principal  sizes. 

630.  Cost.  Prices  of  vitrified  pipe  vary  greatly  with  the  con- 
ditions of  trade,  and  with  competition  and  freight.  Current  (1888), 
non-competitive  prices  for  ordinary  sewer  pipe,  in  car-load  lots 
/.  0.  b.  at  the  factory,  are  about  as  in  the  table  below. 

TABLE  «. 
Cost  ahd  Weight  of  Vitbitibd  Seweb  Pipb. 


PucinsFooT. 

Abu. 

WCIOHT  PCB 

'SJZS.* 

12  lucbea. 

15  ceots. 

.78  aq.  fl. 

45  1be. 

500  feet 

28      " 

56  " 

400    ■' 

18      " 

80      " 

1.40   •'     '■ 

63   " 

860    ■' 

18      '• 

88      ■' 

1.76  ■•     '■ 

75  " 

800    " 

20      " 

63      " 

2.18  "     " 

90  •' 

260    " 

83      " 

67      " 

2.64   •■     ■■ 

110  ■■ 

280    " 

34      " 

87      " 

8.14   ■•     •' 

140  " 

200    •' 

Culvett  pipe  costs  about  20  to  25  per  cent,  more  than  as  above, 
and  second  quality  sewer  pipe  about  30  to  25  per  cent,  less.  The 
latter  difiers  from  first  quality  in  being  less  perfectly  glazed,  less 
perfectly  burned,  or  not  perfectly  round,  or  in  having  fire  cracks  in 
the  glazing,  blisters  on  either  surface,  eicrescences  or  pimples  on 
the  inside,  or  a  piece  broken  out  of  the  end.  Frequently  such 
pipe  ie  as  good  for  calverts  as  first  quality  seWer  pipe. 


ovGoQi^lc 


ABT.  ».J  TITBIPIED  PIPE  CULVEKIB. 


TiTBirtm  Fin  CCLvnti.— K.  C.  &  0,  K.  B. 


U&soHRT  Rbqdibed  fob  YmuriKD  Pipe   Cultkbtb  or  thb   Qsuxjui, 

TOBM   HHOWM  ABOVE. 


ITM*. 

DUKCTKB 

ofPtpi. 

14  IncbM. 

IB  inches. 

a)  Inches 

Mlnobta. 

n«h.    t« 

If 

ir 

"til?- 

Total  Uauorr 

S.4T 

BIB 

7fl5 

G.H 

Concrete,  per  lineal  too».. 

O.CCT 

o.ioa 

0,,» 

...» 

jvGooi^le 


413  CULVERTS.  [chap.  XVII. 

631.  iBOir  Pips  Cultebtb.  In  recent  yeara,  iron  pipes  have 
been  much  need  for  culvert*.  In  tnanj  localities  good  stone  is  not 
available,  and  hence  stone  box  culverts  (|§  615-26)  can  not  be  need. 
In  such  localities  vitrified  stoneware  pipes  are  nsed ;  but  as  thej 
are  not  made  larger  than  3  feet  in  diameter,  iron  or  stone  is  the  only 
material  available  for  permanent  culverts  requiring  a  greater  water 
way  than  that  obtained  by  using  one  or  two  of  the  largest  vitrified 
pipes.  Apparently,  stone  culverts  if  well  built  should  last  forever; 
but,  as  constructed  in  the  paat,  they  have  been  found  to  lest  rela- 
tively only  a  short  time.  Hence,  with  the  increasing  cheapness  of 
iron,  there  has  been  an  increasing  tendency  to  use  iron  pipe  for  even 
large  cnlverta,  Caet-iron  pipes  from  12  to  48  inches  in  diameter 
and  1'4  feet  long  are  in  common  use  by  all  of  the  prominent  roada 
of  the  Mississippi  Valley.  Some  of  the  roads  cast  their  own,  while 
others  buy  ordinary  water  pipe.  The  lightest  water  pipes  made,  or 
even  such  as  have  been  rejected,  are  sufficiently  strong  for  use  in 
culverts.  The  dimensions  used  on  the  Chici^,  Milwaukee  and  St. 
Paul  R.  B.  are  about  as  follows : 

TABLE  47, 

DiMSNBIONH   OF   CAST-IaOH   Cni.TSBT  PiFE. 


iKODEDuMCm. 

w„„™^. 

r.„„. 

Wbidbt  pn  LnmiL  Four 

A  iDch. 

16 

88  " 

88    •■ 

ao 

118  •■ 

69    ■' 

u 

175  •' 

66    •' 

80 

" 

86 

820  " 

i    ■■ 

«    " 

4a 

400  " 

\-- 

42    " 

48      " 

510   " 

41    " 

632.  Cosfltrnotioii.  In  constructing  a  culvert  with  cast  iron, 
the  points  requiring  particular  attention  are  (1)  tamping  the  soil 
tightly  around  the  pipe  to  prevent  the  water  from  forming  a  clian- 
nel  along  the  outside,  and  (2)  protecting  the  ends  by  suitable  head 
walls  and,  when  necessary,  laying  riprap  at  the  lower  end.  The 
amount  of  masonry  required  for  the  end  walls  depends  upon  the 
relative  width  of  the  embankment  and  the  number  of  eections  of 
pipe  used.  For  example,  if  the  embankment  is,  say,  40  feet  wide 
at  the  base,   the  culvert  may  consist  of  three  12-foot  lengths  of 


ovGoQi^lc 


JUff.  S.]  IKOlf   PIPE   CULVEUT8.  413 

pipe  and  a  light  end  wall  near  the  toe  of  the  bank ;  bnt  if  the 
embankment  ia,  aay,  33  feet  wide,  the  culvert  may  consist  of  two 
12-foot  lengths  of  pipe  and  a  eomparatiyelj  heavy  end  wall  well 
back  from  the  toe  of  the  bank.  The  smaller  sizes  of  pipe  usoally 
jome  in  13-foot  lengths,  but  sometimes  a  few  G-foot  lengths  are 
included  for  use  in  adjuetlug  the  length  of  culvert  to  the  width  of 
bank.     The  larger  sizes  are  generally  6  feet  long. 

Fig.  100  (page  414)  shows  the  method  employed  on  the  Atchi- 
son, Topeka  and  Santa  F^  B.  R.  in  putting  in  coet-iron  pipe 
^ulvertB.  Table  48  (page  414)  gives  the  dimensions  for  the  end 
walls  for  the  various  sizes.  The  length  of  pipe  is  determined  by 
taking  the  multiple  of  6  feet  next  larger  than  the  length  given  by 
the  position  slope  as  in  Fig.  100.  To  allow  for  settling,  the  pipe  is 
laid  to  a  vertical  curve  having  a  crown  at  the  center  of  1  inch  for 
-each  5  feet  in  vertic^  height  from  bottom  of  pipe  to  profile  grade. 

Where  the  soil  is  treacherous,  it  would  be  wise  to  lay  the  pipes 
■on  a  bed  of  broken  stone  to  prevent  undue  settling.  In  this  con- 
nection, see  Figs.  96  and  99  (pages  406  and  411). 

633.  Fig.  101  (page  415)  shows  the  method  employed  on  the 
Chicago,  Burlington  and  Quincy  R.  H.  of  putting  in  cast-iron  pipe 
'Culverts.     This  conatmction  has  given  entire  liatisf action. 

The  same  road  has  recently  commenced  the  use  of  iron  for  cul- 
verte  up  to  12  feet  in  diameter.  For  diameters  greater  than  4  feet, 
the  pipes  are  cast  in  quadrants  3,  4,  6,  and  8  feet  long,  which  are 
afterwards  bolted  together,  through  outside  flanges,  to  form  a 
cylinder  of  any  desired  length.  The  different  segments  are  so  com- 
bined as  to  break  joints  around  and  also  along  the  pipe.  The  body 
-of  the  pipe  was  formerly  1|  inches  thick  ;  but  is  now  IJ,  etiSened  on 
the  outside  by  ribs.  The  sections  are  put  together  without  any  chip- 
ping, drilling;  or  other  skilled  labor.  Between  the  different  sec- 
tions is  a  recess  in  which  a  tarred  rope  smeared  with  neat  cement 
mortar  is  placed  before  bolting  the  segments  together,  which  makes 
tne  joints  tight.* 

634.  Cost.  The  cost  of  cast-iron  pipe  varies  greatly  with  com- 
petition and  the  conditiona  of  trade.  The  price  ranges  from  #36  to 
$36  per  ton  for  firat  quality  water  pipes,/,  o.  b.  at  the  foundry;  or 
approximately,  say,  IJ  cents  per  pound. 

'  For  innatntloD  of  deUUs,  ue  ^Uroad  Qaatu,  voL  zlx.  pp.  123-34. 


ovGoQi^lc 


[chap.  XVII. 


i 

\ 

a  I, 


1 

s 

I 

i 

if:::: 

1 

i 

1 

! 

SVSBS 

\ 

jvGooi^le 


ART.  3.]  IROS  PTPB  CCLVERTB. 


n*.  101,— Cmt-Uom  Pira  CuLrna.^C,  B.  A  ^  &  & 


ovGoQi^lc 


■416  CCLVERTS.  [chap.  XYU, 

Table  47  (ptige  412)  shows  that'  the  average  weight  of  the  pipe 
per  foot  per  square  foot  of  water  way  ia  about  60  pounds ;  ana 
hence  the  cost  of  the  trunk  of  a  cast-iron  pipe,  exclusive  of  trans- 
portation and  labor,  is  about  (60  X  li)  90  cents  per  lineal  foot  per 

■  sq.  ft.  of  area.  The  cost  of  sewer  pipes  ia,  from  Table  46  (page 
411),  about  22  cents  per  foot  per  square  foot  of  water  way ;  and  for 
culvert  pipe  about  30  cents. 

Assuming  the  cost  of  rubble  masonry  to  be  $3.50  per  cubic  yard 
and  of  paving  to  be  $^.00  per  cubic  yard,  the  averse  cost  of  the 
masonry  in  the  trunk  of  the  box  culvert  ehown  in  Fig.  95  (page 
404)  is  40  cents  per  lineal  foot  for  each  square  foot  of  water  way  ; 
and  the  corresponding  cost  for  the  culvert  of  Fig.  94  (page  403)  is 
46  cents.  The  end  walls  required  for  these  different  forms  of  cul- 
verts are  essentially  the  sanift;  and  hence  the  above  comparison 

■  shows  approximately  t  .e  relative  cost  of  the  different  forms  of  cul- 
verts. According  to  this  showing,  cast-iron  pipe  is  the  most  ex- 
pensive ;  but  this  difference  is  partly  neutralized  by  the  greater 

■ease  with  which  the  iron  pipe  can  be  put  into  place  either  in  new 
work  or  in  replacing  a  wooden  box-Kiulvert, 

635.  The  following  figures  give  the  cost  of  a  7-foot  cast-iron 
^iulvert  of  the  form  referred  to  in  §  633,  which  see. 

43  ((.  body      ®  136.55  per  foot  (I.M  ceots  per  pouod) ILIU-Sa 

8  It.  speciala  @  ta9.48    "     "      ' aas.BS 

Bolts  and  washers 29.81 

Unloading IT..™ 

Putting  (n  place I4H.95 

Stone  for  end  walls,  70cu.  yds.,                ®  tl.QO 105.00 

Stone  forriprap  fouudation,  60cu.  yda.,  ®  tlOO 60.00 

BflmoTiDg  temporary  bridge 235.63 

Total 11.947.15 

Excluding  the  cost  of  removing  the  temporary  bridge — which 
is  not  a  part  of  the  culvert  proper, — and  of  the  riprap  foundation — 
which  the  anusnal  conditions  required, — the  cost  of  the  culvert  was 
433.03  per  foot,  or  83  cents  per  lineal  foot  for  each  square  foot  of 
water  way. 

636.  TmBB  Box  Ctltebts.  Timber  box  calvertB  should  be 
used  only  where  more  substantial  material  is  not  attainable  at  a 
reasonable  cost.      Many  cnlverts  are  constructed    of  timber  an^ 


ovGoQi^lc 


AET.  2.]  BOX  AND   PIPE  CULVERTS.  417 

periodically  renewed  with  the  same  material,  and  many  are  con- 
strncted  of  wood  and  replaced  with  stone,  or  sewer  or  iron  pipe. 

The  latter  is  an  example  of  what  may  be  called  the  standard 
'  practice  in  American  railroad  building ;  i.  e.,  constructing  the  road 
as  quickly  and  cheaply  as  possible,  asiug  temporary  BtmctuTes,  and 
-completing  with  permanent  ones  later  as  the  finances  of  the  company 
will  allow  and  as  the  requirements  of  the  situation  become  better 
understood.  After  the  line  is  open,  the  permanent  atructures  can 
be  built  in  a  more  leisurely  manner,  at  appropriate  seasons,  and 
thus  insure  the  maximum  durability  at  a  minimum  cost. 

There  is  a  great  variety  of  timber  box  culverte  in  common  use, 
but  probably  there  are  none  more  durable  and  efficient  than  those 
tised  on  the  Chicago,  Milwaukee  and  St.  Paul  H.  R., — shown  in 
Pig.  102  (page  418).*  On  this  road,  it  is  the  custom  to  replace  the 
wooden  boxes  with  iron  pipes  before  the  timber  has  seriously  de- 
cayed. If  experience  has  shown  the  size  of  the  wooden  box  to  be 
about  right,  the  timbers  are  cut  out  a  little  and  an  iron  pipe  is 
placed  inside  of  the  box  without  disturbing  the  earth. 

For  timber  bos  culverts  of  sizes  larger  than  can  be  made  of 
plank,  the  Atchison,  Topeka  and  Santa  'Ek  R  R.  employs  bridge- 
tie  box  cnlTerte.  These  are  made  by  laying  6x8  inch  abwed 
bridge  ties  flatwise,  in  contact,  to  form  a  floor.  These  ties  are 
gained  at  the  ends  so  as  to  leave  a  shoulder  1  inch  deep  against 
which  the  inside  of  the  side  walls  bears.  Upon  this  floor,  vertical 
side  walls  are  constructed  by  laying  ties  flatwise,  one  on  top  of  the 
other ;  the  lowest  timber  in  each  side  wall  is  fastened  to  each  tie  in 
the  floor  by  a  drift-bolt  12  inches  long,  and  each  timber  in  the  side 
wall  is  fastened  to  the  one  below  it  by  a  12-inch  drift-bolt  every  3 
feet.  The  lengths  of  the  ties  employed  in  the  side  walls  are  so  ad- 
justed as  to  make  the  exposed  ends  conform  closely  to  the  slope  of 
the  embankment.  Thereof  consists  of  6-  x  8-inch  ties  set  edgewise, 
in  close  contact,  with  a  shoulder  1  inch  deep  on  the  inside,  both  ' 
ends  of  each  piece  being  also  drift-bolted  to  the  side  wall. 

637.  TIHBEB  BA£S£L  CmTXSTB.  For  a  number  of  years  past 
the  Chicago,  Burlington  and  Qnincy  R.  R.  has  found  it  desirable, 
in  view  of  the  absence  or  poor  quality  of  the  stone  along  its  lines,  to 
use  a  timber  "barrel-culvert"  when  the  opening  is  too  large  for  a 

*  From  SaOrvad  CkuMt. 


ovGoQi^lc 


CULVERTS.  [chap.  xtii:. 


m 


iim 


"^f 

$ 


vm 


xS 


iGooi^le 


IXt.  3.]  ARCH  CULTSBIS.  419 

timber  box-culvert.  The  staves  are  10  or  12  inches  thick,  accord- 
ing to  the  size  of  the  culvert,  and  8  inches  wide  on  the  outside, 
dressed  to  form  a  circle  4^  or  6  feet  in  diameter.  Iron  rings — made 
of  old  rails — spaced  about  10  feet  apart,  are  used  as  a  form  upon 
which  to  construct  the  culvert  aud  also  to  give  it  strength.  The 
staves  break  joints  and  are  drift-bolted  (g  381)  together.  M  soon 
as  the  timber  is  thoroughly  seasoned,  the  culverts  are  lined  with  a 
single  ring  of  brick,  and  concrete  or  stoue  parapet  walla  are  built. 
If,  at  any  time,  the  timber  fails,  it  is  the  intention  to  put  iron  pipe 
through  the  present  opening. 

The  timber  costs  about  $13  per  thousand  feet,  board  measure, 
at  the  MisaiBBippi  Biver ;  and  the  cost  of  dressing  at  the  company's 
shops  is  about  tl.50  per  thousand. 

Abt.  3.  Abce  Culvebts. 

638.  In  this'  article  will  be  discussed  what  may  be  called  ths 
theory  of  the  arch  culvert  in  contradistinction  to  the  theory  of  the 
arch.     The  latter  will  be  considered  in  the  next  chapter. 

By  the  theory  of  the  arch  culvert  is  meant  an  exposition  of  the 
method  of  disposing  a  given  quantity  of  masonry  so  as  to  secure  (1) 
maximum  discharging  capacity,  (2)  minimum  liability  of  being 
choked  by  drift,  and  (3)  maximum  strength.  Attention  to  a  few 
points,  which  are  often  neglected  in  the  design  of  culverts,  will  se- 
cure these  ends  without  additional  cost. 

639.  OiaXBAL  FOBII  OF  CVLTBKT.  Splay  of  Wingfl.  There 
are  three  common  ways  of  disposing  the  wing  walls  for  finishing 
the  ends  of  arch  culverts.  1.  The  culvert  is  finished  with  a  straight 
wall  at  right  angles  to  the  axis  of  the  culvert  (see  Fig.  103).     3.  The 


JLM 


wings  are  placed  at  an  angle  of  30°  with  the  axis  of  the  culvert 
(see  Fig.  104).  8.  The  wing  walls  are  built  parallel  to  the 
axis  of  the  culvert,  the  back  of  the  wing  and  the  abutment 
being  in  a  straight  line  aud  the  only  splay  being  derived  from  thia- 


ovGoQi^lc 


420  CULVERTS.  [CHAP.  XVll. 

ning  the  wings  at  their  outer  ends  (see  Fig.  105).  The  first  method 
ia  shown  on  a  larger  scale  in  Plate  II,  the  third  in  Plate  III,  and 
the  second  in  Plate  IV. 

The  quantity  of  masonry  required  for  these  three  forms  of  wings 
does  not  differ  materially,  Fig.  105  requiring  the  least  and  Fig.  103 
the  most  The  most  economical  angle  for  the  wings  of  Fig.  104  is 
abont  30°  with  the  axis. 

The  position  of  the  wings  shown  in  Fig.  104  is  much  the  most 
common  and  is  better  than  either  of  the  others.  Fig.  103  is  ob- 
jectionable for  hydraulic  considerations  which  will  be  considered 
in  the  nest  section,  and  also  because  it  is  more  liable  to  become 
choked  than  either  of  the  others.  Fig.  105  does  not  have  splay 
enough  to  admit  the  natural  width  of  the  stream  at  high  water, 
and  does  not  gire  snflScient  protection  to  the  toe  of  the  embankment. 
610.  Junction  of  Wings  and  Body.  With  a  calvert  of  the 
general  form  outlined  in  Fig.  104, 
there  are  two  methods  of  joining 
the  wings  to  the  body  of  the  cul- 
vert. The  more  common  method 
is  shown  in  Figa.  106  and  108;  and 
.  the  better,  but  less  common,  one  is 
^  shown  in  Figs.  107  and  109. 
""''"'  ""■""■  ^^^  j^^^  shown  in  Figs.   106 

and  108  is  very  objectionable  because  (1)  the  comers  reduce  the 
o»pacity  of  the  culvert,  and  (2)  add  to  its  cost. 


/  \/  \ 


,',  I     I 


^ 


Fio.  :<».  Fid.  10ft. 

1.  The  sharp  angles  of  Fig.  106  materially  decrease  the  amount 
oi  vater  which  can  enter  under  a  given  head  and  also  the  amount 


ovGoQi^lc 


ART.  3.]  ARCH  CCLVEHTS.  421 

which  can  be  discharged.  It  is  a  well-eBtabliahed  fact  in  hydraulics 
that  the  discharging  capacity  of  a  pipe  can  be  increased  200,  or 
eren  300,  per  cent,  simply  by  giving  the  inlet  and  outlet  forms  some- 
what similar  to  Fig.  107.  Although  nothing  hie  this  increase  can 
be  obtained  with  a  culvert,  one  finished  at  both  the  apper  and  the 
lower  end  like  Fig.  107  will  discharge  considerably  more  water  than 
one  like  Fig.  106.  The  capacity  of  Fig.  107  decreasee  as  the  angle 
between  the  wing  and  the  axis  increases ;  hence,  the  less  splay  the 
better,  provided  the  outer  ends  of  the  wings  are  far  enough  apart 
to  accommodate  the  natural  width  of  the  stream  at  high  water. 
Also  the  less  the  splay,  the  less  the  probability  of  the  culvert's  being 
choked  with  drift.  Fig.  106  is  very  bad  for  both  the  admission  and 
the  discharge  of  water,  and  also  on  account  of  the  great  liability 
that  drift  and  rolling  stones  will  catch  in  the  angles  between  the 
wings  and  the  end  walls.  In  this  latter  respect  Fig.  108  is  slightly 
better  than  Fig.  106. 

2.  Every  angle  adds  materially  to  the  cost  of  the  masonry.  In 
a  culvert  like  Fig.  106,  there  are  fonr  unnecessary  comers.  This 
form  probably  owes  its  prevalence  to  the  desire  to  have  a  uniform 
batter  on  the  face  of  the  wing,  and  to  have  the  face  of  the  wing 
wall  intersect  the  end  wall  back  of  the  arch  stones.  Satisfying  both 
of  these  conditions  gives  a  culvert  in  ground  plan  like  Fig.  106; 
and  satisfying  the  second  one  only,  gives  Fig.  108.  Practically 
there  is  but  little  difference  between  these  two  forma — both  are 
objectionable,  as  already  explained.  If  the  wing  of  Fig.  108  is 
moved  inward,  and  the  corner  of  the  wing,  which  would  other- 
wise project  into  the  water  way,  is  rounded  off  to  a  gentle  curve, 
Fig.  109  is  obtained.  This  form  is  simple,  efficient,  aud,  on  the 
whole,  the  best. 

Plate  III  shows  another  method  of  joining  the  wing  to  the 
end  wall  without  having  an  unnecessary  angle.  In  this  case,  the 
face  of  the  wing  up  to  the  springing  line  of  the  arch  is  a  warped 
surface,  which  is  in  some  respects  undesirable,  although  it  saves 
a  little  masonry.  However,  the  face  of  the  wing  wall  could  be 
built  vertical  up  to  the  springing  line  and  then  battered;  or 
the  wing  could  be  moved  forward  and  the  comer  be  rounded  off 
as  in  Fig.  io9. 

641.  8«mi-ciroalar  vs.  Segmental  Arohei.  There  are  two 
classes  of  arches  employed  for  culverts,  viz.,  the  semi-circular  and 


ovGoQi^lc 


488  CDLTBRTS.  [CHAP.  IVII. 

the  eegmental.     The  first  ia  by  far  the  more  common;  but  neverthe- 
lesB  the  latter  is,  on  the  whole,  much  the  better. 

1.  For  the  same  span,  the  segmental  arch  reqairea  a  shorter  iD- 
tradoB  (the  inside  cnrve  of  a  section  of  the  arch  perpendicular  to 
its  axis).  For  example,  the  culverts  shown  in  Plates  IV  and  V 
have  the  same  span,  hat  the  intrados  of  the  semi-circular  arch  is 
15.71  ft.,  while  that  of  the  segmental  arch  is  10. 73  ft. ;  that  is,  the 
intrados  of  the  segmental  is  only  68  per  cent,  of  the  intrados  of  the 
semi-circular  arch.  ■  This  difference  depends  upon  the  degree  of 
fiatucss  of  the  segmental  arch.  The  above  example  is  an  extreme 
case,  since  the  segmental  arch  is  unnsiially  flat,  the  central  angle 
being  only  73°  44'.  (The  rise  is  one  sixth  of  the  span.)  With  a 
central  angle  of,  120°,  the  intrados  of  the  segment  is  77  per  cent,  of 
the  semi -circle. 

Or,  to  state  the  above  comparison  in  another  and  better  form,  for 
the  same  length  of  intrados  the  segmental  arch  gives  the  greater 
span.  For  example,  a  segmental  arch  on  the  same  general  plan  as 
that  of  Plate  V,  but  having  an  intrados  equal  to  that  of  Plate  lY, 
would  have  a  span  of  14.64  ft.,  which  is  46  per  cent,  greater  than 
the  span  of  the  semi-circnlar  arch  shown  in  Plate  IV.  A  segmental 
arch  with  a  central  angle  of  130°  has  a  span  33  per  cent,  greater 
than  a  semi-circular  arch  having  the  same  length  of  intrados.  This 
difference  constitutes  an  important  advantage  in  favor  of  the  seg- 
mental arch  cnlvert,  since  the  wider  the  span  the  lees  the  danger  of 
the  culvert's  being  choked  by  obstrnctions,  and  because  it  will  pass 
considerably  more  water  for  the  same  de[)th. 

2.  For  the  same  length  of  intrados,  the  segmental  arch  gives  the 
greater  water  way.  The  water  way  of  the  culvert  shown  in  Plate 
IV  is  87.6  square  feet ;  hut  the  same  length  of  intrados  in  a  seg- 
mental arch  culvert  having  73°  44'  central  angle  (the  same  as  Plato 
V)  would  have  a  water  way  of  98.3  square  feet;  and  with  a  central 
angle  of  120°  would  have  a  water  way  of  99.5  square  feet.  In  both 
examples  the  increase  ia  one  eighth. 

3.  On  the  other  hand,  the  segmental  culvert  will  require  a 
thicker  arch.  It  will  he  shown  in  the  next  chapter  that  arches 
can  not  be  proportioned  strictly  in  accordance  with  mathematical 
formulas ;  and  hence  the  exact  difference  in  thickness  of  arch  which 
should  exist  between  a  semi-circular  and  a  segmental  arch  can  not 
be  computed.    According  to  estahlished  rules  of  practice,  small 


ovGoQi^lc 


ART.  3.j  ARCH  CULVERTS.  423 

"Segmental  arches  are  from  10  to  25  per  cent,  thicker  than  semi- 
oircalar  ones.  Thia  difference  is  not  very  great,  and  its  effect  upon 
the  006L  of  the  cnlvert  is,  proportionally,  still  less,  since  the  coat 
per  yard  of  arch  masonry  is  leas  for  the  thiciier  arches.  Then,  we 
may  couclade  that,  aince  for  the  same  apan  the  intrados  of  seg- 
mental arches  is  from  20  to  40  per  cent,  shorter  than  the  semi- 
circle, the  segmental  arch  requires  a  less  volume  of  arch  masonry 
than  the  semi- circular,  and  also  costs  less  per  cubic  yard.  The  arch 
masonry  per  foot  of  length  of  the  segmental  arch  culvert  shown  in 
Plate  \'  is  only  71  per  cent,  of  that  in  the  semi-ciroalar  one  shown 
in  Plate  IV.  The  dimensions  and  contents  of  arch  culverts  of  the 
general  forms  shown  in  Plates  IV  and  V  are  given  in  Tables  51 
and  53  (pp.  430  and  431  respectively),  from  which  it  appears  that 
the  segmental  arch  contains  only  from  60  to  76  per  cent,  ae  much 
masonry  as  the  semi-circular,  the  average  for  the  six  spans  being 
almost  exactly  70  per  cent.  The  coat  of  these  two  classes  is  shown 
in  Tables  56  and  57  (pages  437  and  438),  from  which  it  appears  that 
the  average  coat  of  segmental  culverts  20  feet  long  and  of  different 
spans  is  only  59  per  cent,  of  the  cost  of  aemt-circnlar  ones  of  the 
same  length  and  span;  and  the  average  cost  of  an  additional  foot 
in  length  for  the  segmental  is  only  86  per  cent,  of  that  for  a  circnlar 
one.  The  water  ways  of  the  semi-circular  culverts  are  a  little  the 
greater,  and  hence  the  difference  in  cost  per  square  foot  of  water 
way  is  not  as  great  as  above;  but,  on  the  other  hand,  the  form  of 
water  way  of  the  segmental  culvert  is  the  more  efficient,  and  hence 
the  above  comparison  is  about  correct. 

4.  Will  the  segmental,  i.  e.,  the  flatter,  arch  require  heavier  abut- 
ments (side  walls)?  Unquestionably  the  flatter  the  arch  the 
greater  the  thrust  upon  the  abutment;  but  the  abutment  not  only 
resists  the  thrust  of  the  arch  which  tends  to  turn  it  over  outwards, 
but  also  the  thrust  of  the  embankment,  which  tends  to  push  it  in- 
wards. It  is  impossible  to  compute,  with  any  degree  of  accuracy, 
■either  the  thrust  of  the  arch  or  of  the  embankment;  and  hence  it  is 
impossible  to  determine  either  the  relative  value  of  these  forces  or  the 
thickness  which  the  two  abutments  should  have.  Experience  seems 
to  indicate  that  the  thrust  of  the  earth  is  greater  than  that  of  th« 
arch,  as  is  shown  by  the  fact  that  nearly  all  semi-circular  culverts 
have  abutments  of  much  greater  thickness  than  are  required  to  n- 
.eist  the  thnut  of  the  arch;  and  hence  we  may  conclude  that  ezp»- 


ovGoQi^lc 


424  CL'LTEBTS.  [CHAP.  ZVU. 

rienoe  has  shovii  tliat  tbe  thrust  of  the  earth  neceBBitates  a  heavier 
ftbutmeDt  than  does  the  thrust  of  the  arch.  If  this  be  true,  then 
the  abutment  for  aegmeotal  arches  may  be  thinner  than  thoae  for 
semi-circular  ones;  for,  since  the  thrust  of  the  former  is  greater- 
thsD  the  latter,  it  ezerts  a  greater  force  ontvard,  which  counter- 
balances a  larger  part  of  the  inward  thrust  of  the  embankment,  and 
thus  leaves  a  less  proportion  of  the  latt«r  to  be  resisted  by  the  mass 
of  the  abatment.  Segmental  arch  culverts  are  not  often  built;  and 
designers  appear  to  have  overlooked  the  thrust  of  the  earth,  since 
the  side  walls  of  segmental  arches  are  generally  thicker  than  for' 
semi-circular  ones  (compare  Plates  IV"  and  V).  • 

The  conclnsions  may,  therefore,  be  drawn  that  segmental  arch 
culverts  are  both  cheaper  and  more  efficient  than  semi-circular  ones. 

642.  As  built,  many  semi-circnlar  arches  are  practically  seg- 
.  mental;  that  is,  the  side  walls  are  built  so  high,  or  the  backing  is 

made  so  heavy,  that  practically  the  abutments  are  less  than  130° 
apart,  and  hence  the  two  lower  ends  of  the  arch  are  really  only  a. 
part  of  the  side  wall,  and  should  be  built  square. 

Further,  it  is  shown  in  §§  681-82  that  a  trne  arch  of  more  thaa 
about  90  to  130  degrees  is  impossible. 

643.  EXUCPUES.  Under  this  head  will  be  ^ven  a  brief  descrip- 
tion of  four  series  of  arch  culverts  which  are  believed  to  be  repre- 
sertative  of  the  best  practice.   , 

644.  niinois  Central  Arch  Cnlrerts.  Plate  II  shows  the  gen- 
eral plan  of  the  standard  arch  culvert  employed  in  the  construction 
(1852-53)  of  tlie  Chicago  branch  of  the  Illinois  Central  Railroad.* 
While  the  timber  iu  the  foundation  is  apparently  still  in  good  con- 
dition, the  use  of  timber  for  such  shallow  foundations  can  not  be 
considered  as  the  best  construction.  However,  many  of  the  con- 
ditions, particularly  drainage,  have  greatly  changed  since  this  road 
waa  built,  and  it  is  by  no  means  certain  that  this  use  of  timber 
was  not  good  practice  at  that  time  (see  §  636). 

Tablu  49   (page  425)  gives  the  dimensions  and  contents  for  the; 

several  spans  of  this  form  of  culvert.     The  contents  of  the  end 

walls  were  computed  on  the  assumption  that  the  off-set  at  the  back 

■  Tvas  6  inches  for  each  foot,  counting  from  the  top,  until  the  fall 

thickness  at  the  bottom  was  obtained  (see  Section  £-F,  Plate  II). 

*  PabUsbed  by  peraission  of  J.  H.  Ilealeri  DlvUlon  Engineer. 


ovGoQi^lc 


Jbt.  3.] 


ABCH  0CLVERT8. 


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'486  ccLVEBTS.  [chap,  ivil 

645.  Example  of  the  Use  of  Table  49.  To  illastrate  the  Baethod 
of  using  the  above  table,  asenme  that  an  eetimate  of  the  amoant  of 
material  in  an  8-ft.  arch  culvert  of  the  preceding  form  is  required. 
Assume  that  the  top  of  the  coping  is  3  feet  below  sub-grade,  i.  e., 
that  there  is  4. 25  feet  of  earth  above  the  crown  of  the  arch.  Assume 
also  that  the  road  bed  is  16  feet,  and  that  the  slope  of  the  embank- 
ment is  li  to  1.  Then  the  length  of  the  culvert  from  inside  to  in- 
side of  the  end  walls  will  be  16-1-2  (I  X  3)  =  16 -f  9  =25  feet;  and 
'  from  out  to  out  of  end  walls,  the  length  will  be  25  -(-  2  X  3.5  =  3U 
feet. 

Assuming  that  the  timbers  under  the  planking  are  8x10  inches, 
the  305  aq.  ft.,  as  per  the  table,  will  leqoire  1,422  ft.  6.  M.  of  tim- 
ber, or  9  pieces  24  ft.  long.  Xotice,  however,  that  in  practice  10 
pieces  would  be  used — 5  at  each  end  of  the  culvert.  The  length  of 
the  trunk  of  tho  foundation  is  30  —  2  (4-|-  J^  -|-  1)  =  IS  ft  Hence 
the  area  under  the  trunk  of  the  foundation  to  be  covered  with  tim- 
ber is  19  X  8  (see  table)  =  153  sq.  ft. ;  and  if  S  X  10-inch  timbers 
are  used,  this  will  require  1,216  ft.  B.  M.,  or  12  pieces  14  feet  long. 
The  plank  under  the  wings  and  in  the  sheet  piling  is  1,493  feet  (see 
table),  and  that  in  the  trunk  is  32  (see  table)  X 19  =  608  ft.  B.  M. ; 
hence  the  total  plank  is  1,493  +  608  =  2,101  ft.  B.  M. 

The  masonry  in  the  end  wall  is  32.97  cu.  yds.,  as  in  table.  The 
masonry  in  I  foot  of  arch  is  (see  table)  0.673  -|-  0.284  =  0.957;  and 
in  30  ft.  it  is  0.957x30  =  28.71  cu.  yds.  The  masonry  in  the  side 
walls  (abutments  of  the  arch)  is  0.444  (see  table)  x30  =  13.32  cu. 
jds.     The  coping  is  117.0  cu  ft.  (see  table)  =  4.33  cu.  yds. 

Collecting  and  tabulating  the  preceding  results,  we  have  the 
following : 

Timber:— 10  pieces.  8  X  10  laches,  S4  ft  long 1,600  ft.  B.  H. 

13 14  ■■     " 1,180"     ■■ 

a-inchplank 2,101  "     " 

ToUl  timber  In  culvert  26  ft.  long....    4,681  "     " 

MmouT:— 3  eod  walls SS.Ocu.  yds. 

coping 4,8  ■'      '■ 

■Ide  WKllB  (abutments). 13.8  "      " 

arch  masonry 28.7  "      " 

Total  maaouryiD  culvert  86  ft,  long..     10.8  "      " 


ovGoQi^lc 


^ST.  3.J  ABCH  CULVERTS.  437 

646.  Chicago,  EansaaandHebraaka  Arch  Culverts. — The  culvert 
shown  in  Plate  III  is  the  standard  form  employed  oo  the  Chicago, 
Kansas  and  Nebraska  Bailroad.*  Notice  that  the  slope  line  inter- 
sects the  inside  face  of  the  end  wall  at  a  considerable  diatance  above 
the  back  of  the  crown  of  the  arch  (see  Side  View,  Plate  III).  This 
is  sometimes  urged  as  an  objection  to  this  form  of  construction,  on 
account  of  the  supposed  liability  of  the  top  of  the  end  wall  being 
pushed  outward;  but  there  is  no  danger  of  this  method  of  failure, 
since  the  height  of  the  end  wall  above  the  crown  of  the  arch  ia,  ex- 
clusive of  the  coping,  only  oqnal  to  its  thickness,  and  in  addition  it 
is  buttressed  on  the  outside  by  the  wings.  The.  advantage  of  this 
construction  is  that  it  requires  less  masonry  and  also  less  i&bor. 

Concerning  the  manner  of  joining  the  wings  to  the  body,  see  the 
last  paragraph  of  §  640  (page  4S1). 

Table  50  (page  428)  gives  the.  dimensions  and  contents  for 
various  spans.  The  contents  of  the  wings  above  the  springing  line 
of  the  arch  were  computed  for  courses  1  foot  thick  and  for  an  earth 
slope  of  IJ  to  1  (see  §557). 

647.  Example  of  the  Use  of  Table  50.  Assume  the  same  depth 
'Of  earth  over  the  crown  of  the  arch  as  in  the  example  in  §645,( 

t.  e.,  4.25  ft.;  and  assume  also  that  the  slope  line  strikes  the  upper 
comer  of  the  coping  instead  of  the  lower  &a  shown  in  Plate  III. 
The  top  of  the  coping  will  be  0.75  ft.  below  sub-grade;  and,  for  a 
16-ft.  road-bed,  the  length  of  the  arch — inside  to  inside  of  end  " 
walls— is  16  +  2(f  X  0.75)  =  18.25  ft.  With  the  above  data  and 
'Table  50,  we  have  the  following  for  an  Sfoot  culvert : 

Four  wing  walls,  including  one  footing  course,     .    .      40.5  cu.  jda. 
Two  head     "  "  "       "  " 

Coping, 

Two  side  walls,  18}  ft.  @  l.SSa  cu.  yds.  per  foot, 

Arcb  mtuonry,    ■'    "    "1.184"     "      "      " 

PftvlDg,  38.08  ft.  igi  0.272  cu.  yd.  pet  ft.,      .    . 

Total  masoDiy  in  culvert  18}  ft.  long. 

In  attempting  to  make  comparisons  between  the  above  total  and 
that  of  §645,  notice  that  the  culverts  are  of  very  different  style  (see 
;S§  638  and  639)  and  that  the  water  ways  are  of  different  areas. 


*  FnbUilied  br  permlMioii  of  H.  A.  Parker,  Chief 


ovGoQi^lc 


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«BT.  3.]  ABCH   CULYBBTS.  429 

648.  AtahiHn,  Topeka  and  Santa  F4  Aroh  ColvertB.  Fktes 
IV  and  V  show  the  standard  eemi-eircular  and  segmental  arch  cul- 
verts used  by  the  Atchison,  Topeka  and  Santa  Fe  Railroad.* 

Tables  51  and  53  give  the  dimensions  and  contents  for  the 
several  spans.  Kotice  that  the  heights  of  the  end  walls  do  not  Tary 
uniformly,  that  for  the  12-foot  span  being  proportionately  too  great; 
and  consequently  the  contents  of  the  end  walls  and  of  the  wings  do 
not  vary  uniformly.  The  contents  of  the  facing  of  the  wings  were 
computed  for  courses  18  inches  thick  (see  §  557),  and  the  backing 
was  computed  on  the  assumption  that  the  back  surface  was  a  plane 
snch  that  the  dimension  at  the  outer  end  and  also  where  a  plane 
parallel  to  the  section  E~F  passes  through  the  corner  of  the  end 
wall  is  as  in  the  diagram. 

In  computing  the  masonry  in  a  given  culvert,  these  tables  are  to 
be  employed  ae  already  explained  for  Tables  49  and  50 — see  §g  645 
and  647. 

649.  Standard  Arch  CiLlT«rt.  The  culvert  shown  in  Plate  VI 
has  been  designed  in  accordance  with  the  principles  laid  down 
in  the  preceding  diacuseion  (§§  638-41).  The  wings  are  joined  to 
the  body  in  such  a  manner  as  to  offer  the  least  possible  resistance 
to  the  passage  of  water  and  drift.  If  the  current  is  slow  and  not 
liable  to  scour,  the  paving  may  be  omitted,  since  the  end  walls,  being 
continuous  under  the  ends  of  the  water  way,  will  prevent  under- 
mining of  the  side  walls;  or,  in  long  culverts,  one  or  more  inter- 
mediate cross  walls  may  be  constructed.  But  ordinarily  the  money 
paid  for  paving  is  a  good  investment.  If  the  current  is  very  rapid, 
it  is  wise  to  grout  the  paving, — and  also  to  inspect  the  structure 
frequently. 

The  arch  ring  is  amply  strong  to  support  any  bank  of  earth  (see 
Table  63,  page  502,  particularly  Nos.  9,  12,  18,  53,  54,  and  61). 
The  strains  in  a  masonry  arch  can  not  be  computed  exactly;  but  the 
best  method  of  analysis  (§  688)  shows  that  if  the  earth  is  10  feet 
thick  over  the  crown,  the  maximum  pressure  is  not  more  than  55 
pounds  per  square  inch  (compare  with  §  222  and  also  ,§§  246-48), 
A  greater  thickness  of  earth  at  the  crown  would  doubtless  increase 
the  maximum  pressura  in  the  arch;  but  proportionally  the  pressure 
would  increase  much  less  rapidly  than  the  height  of  the  bank  (see 

•  Pabllshed  by  pennusioD  of  A.  A.  Boblsaon,  Chief  EngluMr. 


jvGooi^le 


cnLVBETs.  ,      [chap.  xtii. 


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ARr.  3.] 


ABCH  CCLTEKTS. 


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482  cnLVERTS.  [chap.  itii. 

§  619).  The  arch  ie  also  stable  under  anj  position  of  tlie  morlQg 
load,  with  either  a  heavy  or  a  light  embankment.  The  joints  of 
the  abutment  are  radial,  to  prevent  any  poasibility  of  fi^lure  by 
the  sliding  of  one  course  on  another  (see  §  674). 

Table  53  (page  433)  gives  the  dimensions  and  contents  of  various 
sizes.  In  each  case  the  rise  is  one  fifth  of  the  span,  the  central 
angle  is  87°  V2',  and  the  height  of  the  opening  is  equal  to  half  the 
epan.  The  paving  and  coping  were  eac^  assumed  to  be  1  foot  thick; 
but  for  any  other  thickness  it  is  only  neoeBsary  to  increase  or  de- 
-crease  the  tabular  numbers  proportionally.  The  contents  of  the 
Tings  were  compnted  on  the  assumption  that  all  the  courBes  were  I 
foot  thick  (see  §  557). 

690.  ftVUJTT  OF  HAaomT.  The  masonry  of  arch  cnlverta  is 
usually  divided  into  two  classes;  the  first  consists  of  the  masonry  in 
the  wings  and  end  walls  (parapet),  and  the  second  of  the  arch 
etonea.  The  former  is  classified  as  first-clasa  or  second-class  ma- 
sonry (see  §225).  Only  the  maaonry  in  the  arch  stones  is  called 
arch  masonry.  The  arch  stones  which  show  at  the  end  of  the  arch 
«re  called  ring  stones,  and  the  remainder  of  the  arch  stones  the 
■arcA  iheeting.  The  arch  masonry  proper  is  usually  classified  as 
first-class  or  secoud-closs  arch  masonry.  The  distinction  between 
these  two  classes  is  usually  about  as  in  the  specifications  below. 

eSl.  BpMlflwtloiu.*  Ffmndatioju.  "When  the  bottom  of  the  pit  is 
common  earth,  gravel,  etc.,  the  foundations  of  arch  culverts  will  generally 
-conaiat  of  B  pavement  formed  of  stone,  not  less  than  twelve  incbea  (13")  in 
depth,  set  edgewise,  and  secured  at  the  ends  by  deep  curbslouee  whicb  must 
be  protected  from  uadermlning  by  broken  atoue  placed  In  such  quantity  and 
position  as  the  engineer  may  direct.  When  the  bottom  upon  which  a  culvert 
is  to  be  built  is  soft  and  compressible,  and  where  \%  will  at  all  times  be 
covered  with  water,  timber  well  hewn,  and  from  eight  (81  to  twelve  Inchet 
fl8")  In  thickness,  according  to  the  span  of  the  culvert,  shall  be  laid  side  by 
■side  crosswise  upon  longitudinal  ailU;  and  when  Ihe  position  of  the  culvert  ii 
such  that  a  strong  current  will  be  forced  through  during  floods,  three  courses 
of  sheet  piling  shall  be  placed  across  the  foundation— one  course  at  each  end, 
«nd  one  in  the  middle,— which  ahall  be  sunk  from  three  (3)  to  sii  feel  (6') 
below  the  top  of  the  timber,  according  as  the  earth  is  more  or  less  compact,  "t 

6aS.  Finl-Ctau  Arch  MatOTify.  "  Firat-class  arch  masonry  shall  be  buUt 
in  accordance  with  the  speclflcalions  for  flrst-class  masonry  [§  325],  with  the 
exception  of  the  arch  sheeting  and  the  ring  stones.    The  ring  stones  shaU  be 

•  See  also  SpeclflcatJons  for  Railroad  Maaonrr,  Appendix  1. 
t  PennarlvanlB  Railroad. 


ovGoQi^lc 


AST.  3.] 


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434  CCLTEKCS.  [chap.  XTIL 

dressed  to  such  alutpe  as  the  engineer  shall  direct.  The  ring  atones  snd  the 
arch  sbeeling  Btaall  be  of  stooe  not  less  than  ten  Inches  (10")  thick  on  the 
inindos,  shall  be  dressed  with  three  eighths  oF  an  inch  (|"). joints,  and  shall 
be  of  the  full  depth  specified  for  the  thickness  of  the  arch;  and  the  Joint* 
shall  be  at  right  angles  to  the  surface  of  the  iutradoe.  The  face  of  sheeting 
stones  shall  be  dressed  to  nuke  e.  close  centering  joint.  The  ring  stones  utd 
the  sheeting  shall  break  joints  not  leas  than  one  foot  (1 '). 

"  The  wtugfi  shall  be  neatly  stepped  with  selected  stones  of  the  full  width 
of  the  wing  and  of  not  lessthun  ten  Inches  (10")  in  thickness,  which  shall 
oveiisp  by  not  less  than  eighteen  inches  (18");  or  shall  be  finished  with  a 
neatly-capped  newel  at  the  free  end,  and  a  coping  coium  on  the  wing.  The 
parapets  shall  be  finished  with  a  coping  course  not  less  than  ten  inches  (10") 
thick  and  of  the  full  width  of  the  parapet,  which  shall  project  sis  inches  (6*'), 

US.  Sieond-Olau  AreK  Itatanry.  "Second-class  arch  masonry  is  tlia 
same  ss  second-class  mssonry  [§223],  with  the  exception  of  the  arch  sheeting. 
The  stones  of  the  nrch  sheeting  shall  have  a  good  bearing  throughout,  and 
shall  be  well  bonded  and  of  the  full  depth  of  the  thickness  of  the  arch.  No 
stone  shall  be  less  than  four  inches  (4")  in  thickness  on  the  intiadoa.  Ring 
stones  of  all  arches  over  eight  feet  (8')  span  shall  be  dressed  according  to 
specifications  for  first-class  arch  mssoniy  [g  601]."  * 

6U.  Fating.  For  specifications  for  Paving,  see  g  319  (page  148),  and 
also  Spedfic&tloos  for  Railroad  Masonry,  Appendix  I. 

665.  Com.  §§  226-38  contain  data  on  the  coat  of  maBOury,  of 
which  the  last  is  a  summary.  Table  17  (page  1S9)  contains  a  de- 
tailed statement  of  the  actual  cost  of  the  masonry  in  an  arch 
cnlyert;  and  below  are  the  items  of  the  total  cost  of  that  cnlvert. 

S18  cu.  yds.  of  masonry  ®  f  S.SQ 94,088.85 

Ezcavations— foundations  and  drainage, S6S.H 

Sheet  piling 19.60 

Concrete 48.75 

Extra  allowance  on  sheeting  stones, 20.00 

Total  oost  of  culvert (4,888.65 

The  total  cost  of  the  cnlvert  per  yard  of  masonry  is  17.16, — which 
is  QnnBaally  low. 

Below  is  the  total  actnal  cost  of  the  8-ft.  culvert  (length  out  to 
out  of  end  walls  =30  ft)  for  which  the  quantities  were  estimated 
in  g  645  (page  426). 

•  Atoblacn,  Topeka  and  Bonta  N  B.  K. 


ovGoQi^lc 


AET.  3.] 


ABCH  CDLVEBT8. 


Wallmwonry— 48.7cn.  y(U.a«7.00, 1840.90 

Archmasonry— 38.7  -     "     "     8.S0, 348.95 

Timber— 5.M7n.,B  M.,@  $40.00. 309.88 

ExcKTHting  fotiDdations  and  stnlgbtenlng  stream  168  cu. 

yda.  ®60c 79.00 

Total  coat  of  culvert $878.78 

The  total  coat  of  this  culvert  per  cnbic  yard  of  masonry  is  til. 29. 
The  average  total  cost  of  a  number  of  representative  culverts  of 
this  style  was  111.46  per  cubic  yard  of  masonry,  being  practically 
constant  for  all  spaDS. 

656.  Illinois  Central  CnlTerti.  Table  54  gives  the  cost  of  cal- 
verts  25  feet  long— out  to  out  of  end  walls — of  various  spans  of  the 
general  plan  shown  in  Piute  II,  iind  will  be  very  nseful  In  estimat- 
ing the  cost  of  such  culverts.  The  quantities  of  masonry  necessary 
to  compute  Table  54  were  taken  from  Table  49  (page  425).  The 
prices  are  believed  to  be  fair  averages  (see  page  160)  for  the  first- 
class  masonry  described  in  §  651.  The  prices  are  the  same  as 
actually  paid  by  the  Illinois  Central  Railroad,  except  for  arch 
masonry  and  excavation,  for  which  $8,50  and  50c.  respectively  were 
paid.  The  prices  used  in  deducing  the  table  are  given  therein,  and 
hence  the  results  can  be  modified  for  prices  difFering  from  those 
there  employed  by  simply  taking  proportional  parts  of  the  tabulated 

TABLE  64. 

Cost  or  Illihoib  CsimiALi  Abcb  CDLTsaTs  36  Ft.  Lono  fbom  Out  to 

Oet  of  Ekd  Walls,  akd  also  of  kach  Additional  Foot. 

iroR  DEBCRIPTION  BEE  PAGE  4S4. 


Itww. 

Sfam. 

Bft. 

Bfl. 

10  ft. 

an. 

XZSS^S'S''^"!'-^^ 

HI 

*^-i 

I9.« 

ttss.ns 

SSSSwAJSs::;;:-:; 

■S!:S 

Total  cort  or  oolTertSS  ft.  long 

PI>irm«otir)ra»mpet«i.7_d 

tmw 

.as 

ITW.M 
.40 

VMM 
tSIl 

10.  ei 

(1,100. 10- 

!3.Sf 

Si(.e4 

tlB.OO 

$1B.M 

SM.tt 

jvGooi^le 


430  OULTEBTB.  [OHAP.  XTII. 

qoantitiee.  The  amonat  of  exoavstion  used  in  computing  the  table 
is  the  mean  of  the  actual  quantities  for  a  number  of  representative 
culrerte  as  constructed  on  the  above  road. 

607.  Chicago,  Kansas  and  Hebraaka  Colverts.  Table  65  is  girea 
to  facilitate  estimating  the  cost  of  culverts  of  the  general  form 
showQ  in  Plate  III.  The  prices  are  about  the  average  for  the 
respective  kinds  of  work;  but  in  case  ib  is  desired  to  determine  the 
cost  for  other  prices,  it  is  only  neoeseary  to  increase  or  decrease  the 
tabular  numbers  proportionally.  The  quantities  of  excavation  are, 
approximately,  averages  of  the  actual  amounts  for  a  number  of 
similar  culverts,  and  are  equivalent  to  a  pit  2  feet  2  inches  deep  and 
of  an  area  eqnal  to  the  area  of  the  foundation.  The  table  includes 
only  oue  footing  course,  but  in  so  doing  it  is  not  intended  to  imply 
that  one  is  always,  or  even  generally,  enough.  Notice  that  the  cul- 
Tert  in  Table  55  is  25^  feet  long  from  outside  to  outside  of  end 
walls,  and  hence  is  oue  third  of  a  foot  longer  than  that  presented  ia 
Table  54. 

668.  A.,  T.  and  8.  F,  Beioi-elnniUr  Calvertt.  Table  56  is  similar 
to  the  two  preceding  ooes,  and  shows  the  cost  of  the  Atchison, 

TABLE  5S. 

Con  or  C    E.  ixo  N.  Arch  Cdi.vkktb  90  Pr.  Loire  raoM  iHsms  to 
Insidb  or  CoFino,  anu  alm  of  each  Additiokai.  Foot  or  Lehots. 

FOS  DBSCBIPTIOM  SEE  FAOB  427. 

This  table  Includes  oue  tooting  coune. 


Itma. 

Sruf. 

tft. 

4ft. 

en. 

en. 

»ft. 

X=;?n:Si"^*;::::;: 

p«Ti«K          &  a.00  "    "    - 

"it 

4.41 

11 

ITOS.M 
11 

11 

Tot.]  eM(orcul««aft.  long  .. 

SL«oa   1  *;S  ::  "  ::;::;::: 

'.at 

"•'s 

'.Wl 

lato.w 

•071.M 

•l!E 

.St 

H.M 

flO.TB 

•ia.80 

ttO.M 

•K.M 

jvGooi^le 


ABT.  3.]  A.ItCH  ODLTBBTS,  437 

Topeks  and  Santa  F4'b  standard  semi-circular  arch  culvert  as  given 
in  Plate  IV  and  Table  51  (pi^e  430).  The  excavation  is  only  ap- 
proximate, and  is  computed  on  the  assaroption  of  a  pit  2  feet  2 
inches  deep  for  the  entire  fonndation  including  the  paved  area;  /.  e., 
the  excavation  is  computed  on  the  same  basis  ae  the  two  preceding. 
Notice  that  this  culvert  ie  23  feet  between  the  outer  faces  of  the 
end  walls,  and  hence  is  1  foot  shorter  than  that  of  Table  54  and  2) 
feet  shorter  than  that  of  Table  55. 

TA^ia  se. 

Cost  or  A.  T.  tSD  B.  F.  8Bia-ciBCUi.AB  Axcb  Cui.vkbtb  SO  Pr.  Lous 
FROM  Ikbtdb  to  Inside  op  thb  Corisa.  axd  also  of  each  Addi- 
tional Foot  or  Lksgth. 

FOR  DBSCIUPTIOII  BKB  PAOE  439. 

Thia  table  doe*  not  include  the  maaoatj  In  the  footlDgs. 


Brut. 

en. 

StL 

10  ft. 

l»ft. 

Mft. 

ISfb 

PliUn  mMonrr  a  KM  per  c«.  yd 

Il 

11 

KO.W 
IB.«t 

"«;g 

|i.M.ia 

HUM 

•■ss 

14  44 

ToUl  COM  or  oulTert  10  ft.  Iodk. 

»tW.S8 

"'1 

two.w 

« 

.80 

'lire 

fl.«5.» 

»I3.4. 

$I,TI».«I 

ll^.«l 

%l»M 

»18.08 

%t*.K 

•(B.tO 

SM.e. 

•4>.BB 

669.  A.,  T.  and  8.  7.  Segmental  Cnlverti.  Table  57  is  similar  to 
the  three  preceding,  and  is  given  to  facilitate  estimating  the  cost  of 
segmental  arch  culverts  of  the  standard  fonn  employed  by  the 
Atchison,  Topeka  and  Santa  F&  Bailroad,  as  shown  in  Plate  V  and 
Table  53  (page  431).  The  excavation  is  only  approximate,  and  is 
computed  on  the  assumption  of  a  pit  2  feet  2  inches  deep  over  the 
entire  foundation,  including  the  paved  area.  Notice  that  this 
culvert  is  23  feet  between  the  outer  faces  of  the  end  walls,  and  is 
therefore  the  same  length  as  that  of  Table  66. 


ovGoQi^lc 


438 


CULTEBTS. 


[chap.  XTir. 


TABLE  87. 
Con  OF  A.  T.  Am)  S.  F.   Sbomkntai.  Arch  Cultertb  SO  Ft.   hova 
TBoii  Inside  to  Ihbide  of  the  CoPtNO.  aus  also  of  kach  Addi- 
noNAi.  Foot  of  Lekoth. 

FOR  DBacRimoB  SEE  page  420. 
This  table  doet  not  tDclude  the  inuoDT7  In  the  footiugi. 


,™ 

SfAH. 

tn. 

8tt. 

10  ft. 

uft.  1  utt. 

JO  ft 

BS=?!^ST??:::::; 

i>:ii 

•aoi.M 

si 

IB. 17     ie.4a 

•ss 

tS.M 

TolAlcort  of  culTurtM  real  long.  ... 

Com  or  AH  Ansimniu.  Foot  or 

nAnnu,»jBrT^VM^im.j;A 

ATc^^™«.r7^  100  ■■  ■;  *■::::: 

El«T>tloa        *■       JB    "    "     " 

.It 

la.Tt 

1 

•wi.eo 

•14.4^ 

11.087  OB 

Total  ooM  of  laddlUooal  foot 

no.ss 

•17.SS 

Sn.H 

•».ii 

tx.ti 

»IM 

660.  Btand&rd  Aroli  CQlvert    Table  56  is  given  to  facilitate  the 

estimation  of  the  cost  of  culverts  of  the  general  form  shomi  in  Plate 

VI.     The  prices  are  about  the  average  for  the  respective  kinds  of 

work ;  but  in  case  it  is  desired  to  determine  the  cost  for  other  prices, 

TABLE  08. 


The  muonrj  In  the  footiags  Is  not  Included  in  this  table. 


8ruf. 

Oft. 

.«. 

10  ft.       ,«B. 

14ft.     1     l»ft. 

^:S    1S:S 

ills 

so.n 

TolAl  ™c  of  culwrtso fe«« toOB  . . . 

PWn  mjBcmry  O*^  pjr  ott.  7,?- ■  ■ 
FBTinK                "     Sloo    "    "     "'..'.'. 
SiOTMIon        ■•       .» 

tn*M 

If 

>t4S.BI 

•S4B.1>  1886.44 
tO.BS    914.00 

S    1 

»1.«!7,70 
1 

li.aw.«r 

•S;S 

TotalcoMotlBddldOnalloot 

»7« 

Iii.r 

■ia.»r  v».i7 

KO.GO 

•».14 

jvGooi^le 


ABT.  S.]  iBOH  CULTEBTS.  439 

it  is  only  neeeSBary  to  increase  or  decrease  the  tabnlar  nninbera 
proportionally.  The  qnantitiee  of  eicaTatioQ  are,  approximately, 
averages  of  the  actual  amotrntB  for  a  number  of  similar  cnlrerta, 
and  are  equivalent  to  a  pit  2  feet  2  inches  deep  and  of  an  area  equal 
to  the  area  of  the  foundation.  Notice  that  the  culvert  in  Table  58 
is  23  feet  between  the  outer  faces  of  the  end  walls;  and  is  therefore 
the  same  length  as  that  in  Tables  56  and  57,  and  is  l.foot  shorter 
than  that  of  Table  54  and  2i  feet  shorter  than  that  of  Table  55. 
Notice  also  that  in  Table  58  the  height  of  the  opening  is  in  each 
case  half  of  the  span  (see  Table  53,  page  433),  while  in  Tables  56 
and  67  the  height  of  the  opening  is  nearly  the  same  for  all  spans 
(see  Tablet  61  and  52,  pages  430,  431). 


ovGoQi^lc 


CHAPTER  XVm. 


861.  DMruiTUm.  Fmrtt  of  an  Anh.  Vougsoirt.  The  wedge- 
sDsped  Btones  of  which  the  arch  is  composed ;  also  called  the  ard- 

ttOM*. 

Keyttone.     The  center  or  highest  TonsBoir  or  arch-etone. 

8o£it.    The  inner  or  concaye  mirface  of  the  arch. 

Iiilrados,  The  concave  line  of  intersection  of  the  soffit,  with  a 
rertical  plane  perpendicalar  to  the  axis  or  len^  of  the  arch.  See 
Fig.  110. 

Extradot.  The  convex  curve,  in  the  same  plane  as  the  intrados, 
which  Vmnds  the  enter  extremities  of  the  joints  between  the 
voasfloirs. 

Crown.  The  highest  part 
of  the  arch. 

Skewback.  The  inclined 
surface  or  joint  upon  which 
the  end  of  the  arch  rests. 

Abutment.  A  skewback 
and  the  masonr;  which  sup- 
ports it. 

Springing  Line.  Thein- 
ner  edge  of  the  skewback. 

Upmiger.     The  lowest  vonssoir  or  arch-atone 

ffaunek.  The  part  of  the  arch  between  the  orown  and  the 
Bkewbaok. 

Spandrel.  The  space  between  the  eztrados  and  the  roadway. 
The  material  deposited  in  this  space  is  colled  the  spandrel  jiUing, 
and  may  be  either  masonry  or  earth,  or  a  oombination  of  them.  Id 
large  arches  it  often  consists  of  several  walls  mnning  parallel  with 
the  roadway,  connected  at  the  top  by  small  arches  or  covered  with 
flat  stonea,  which  support  the  material  of  the  roadway. 


ovGoQi^lc 


KINDS   OF    ABCHEB.  441 

Span.  The  pttpendionlw  liateooo  ^wtweeo  the  •pringing 
lines. 

Rito.  The  vertical  dietanoe  between  the  highest  part  of  the 
intrados'  and  the  plane  of  the  springing  lines. 

Ring  Stones.  The  Tonssoirs  or  arch-stonea  which  show  at  the 
ends  of  the  arch. 

Arch  Sheeting.  The  TOUBSoirs  which  do  not  show  at  the  end 
of  the  arch. 

Backing,  Masonry,  nsnally  with  joints  horizontal  or  nearly 
so,  carried  above  the  skewbacks  and  ontside  of  the  extrados. 

String  Course.  A  course  of  vonssoirs  extending  from  one  end 
of  the  arch  to  the  other. 

Coursing  Joint.  The  joint  between  two  adjoining  string 
courseB.  It  is  continnous  from  one  end  of  the  arch  to  the 
other. 

Heading  Joint.  A  joint  in  a  plane  at  right  angles  to  the  axis 
cKC  the  arch.     It  is  not  continnons.  * 

Ring  Course.  The  stones  between  two  consecutive  series  of 
heading  joints. 

662.  Kindi  of  Arohei.  Circular  Arch.  One  in  which  the 
intrados  is  a  part  of  a  circle. 

Semi-circular  Arch.  One  whose  intrados  is  a  eemi-circle;  also 
called  a  full-centered  arch. 

Segmental  Arch,  One  whose  intrados  is  less  than  a  semi- 
circle. 

Elliptical  Arch.  One  in  which  the  intrados  is  a  part  of  an 
ellipse. 

Bashet-Handle  Arch.  One  in  which  the  intrados  resembles  a 
semi-elliptie,  but  is  composed  of  arcs  of  circles  tangent  to  each 
other. 

Pointed  Arch,  One  in  which  the  intrados  consists  of  two  arcs 
of  equal  circles  intersecting  over  the  middle  of  the  span.  For  ex- 
ample, see  Figs.  115  and  117,  page  447. 

Hydrostatic  Arch.  An  arch  in  equilibrium  under  the  yertical 
pressure  of  water. 

Geo'tatic  Arch,  An  arch  in  equilibrium  under  the  vertical 
pressure  of  an  earth  embankment. 

Catenarian  Arch,     One  whose  intrados  is  a  catenary. 

668.  Right  Arch.    A  cylindrical  arch,  either  oiroolar  or  el- 


ovGoQi^lc 


442  ABCHBa.  [chap,  ztiii. 

liptical,  termiiuttod  b;  two  planes,  termed  heads  of  the  arch,  at 
right  angles  to  the  axis  of  the  atoh.    '^^e  Fig.  111. 


Fig.  III.— RiBHT  Abok 

Skew  Arch.  One  whose  beads  are  oblique  to  the  axis.  See 
Pig.  112.  Skew  arches  are  quite  common  in  Enrope,  bnt  are 
rarely  employed  in  the  United  States ;  and  in  the  ktter  when 
an  oblique  arch  is  required,  it  is  nsually  made,  not  after  the 
European  method  with  spiral  joints  as  shown  in  Fig.  112,  but 
by  building  a  number  of  short  right  arches  or  ribs  in  contact 
with  each  other,  each  snccessiTo  rib  being  placed  a  little  to  one 
Eide  of  its  neighbor,' 

Groined  and  Cloistered  Arckes.  Those  formed  by  the  in- 
tersection of  two  or  more  cylindrical  arches.  The  spans  of 
the  intersecting  arches  may  be  different,  but  the  rise  must  be 
the  same  in  each;  and  their  axes  must  lie  in  the  same  plaue, 
but  may  intersect  at  any  angle.  The  groined  arch  is  formed 
by  removing  those  portions  of  each  cylinder  whirfi  lie  under 
the  other  and  between  their  common  curves  of  intersection, 
thus  forming  a  projecting  or  salient  angle  on  the  soffit  along 
these  curves.  The  cloistered  arch  is  formed  by  removing  those 
portions  of  each  cylinder  which  are  above  the  other  and  exterior 
to  their  common  intersection,  thus  forming  re-entrant  angles 
along  the  same  lines. 

Dome  and  Vault.  If  an  arch  revolves  around  a  vertical 
through  the  keystone,  a  dome  is  produced ;  and  if  it  moves  in 
a  straight  line  on  the  springer,  a  vault  is  produced.  Hence 
there  are  essentially  the  same  kinds  of  domes  and  vaults  as 
arches. 

Only  right  archee  will  he  considered  in  this  chapter. 


ovGoQi^lc 


LHTE  or  BB8ISTANCB. 


443 


661.  Line  of  Reiiitasm.  If  the  action  and  reaction  between 
each  pair  of  adjacent  aceh-Btouap  be  replaced  by  single  forces  bo 
sitnated  aa  to  be  in  e^ry  way  the  eqaivalent  of  the  diatribnted 
preasnres,  the  line  connecting  the  points  of  application  of  these 
seTeral  forces  is  the  Hne  of  resistance  of  the  arch.  For  example, 
assmne  that  the  half  af'cl^  shown  in  Fig.  113  is  held  in  eqailibriam 
by  the  horizontal  thmst  3^°-i)te'reactioD  of  the  right-hand  half  of  the 
arch— applied  at  some  point  a  in  the  joint  CF.   Aseome  also  that  the 


sereral  arch-stones  fit  mathematicaUy,  and  that  there  is  no  adhesion 
of  the  mortar.  The  forces  F^,  F,,  F,,  and  F^  represent  the  result- 
ants of  all  the  forces  (including  the  weight  of  the  stone  itself)  acting 
upon  the  several  TOnssoira.  The  arch-stone  CIBF  is  in  eqnililK 
rinm  under  the  action  of  the  three  forces,  T,  F, ,  and  the  reaction 
of  the  TOUBSoir  IHEO.  Hence  these  three  forces  must  intersect 
in  a  point,  and  the  direction  of  R, — the  resultant  pressure  be- 
tween the  TouHBoirs  CIHF  and  IHEO — can  be  found  gtaphioally 
as  shown  in  Fig.  113.  The  point  of  application  of  fi,  is  at  fr— - 
the  point  where  R,  intersects  the  joint  HI.    The  Tonssoir  OEHX 


ovGoQi^lc 


U4  ARCHES.  [chap,  xthl 

ia  in  eqnilibrinm  under  the  action  of  fl, ,  F,,  and  S, — the  reealtant 
rtectioD  between  QEHl  and  QEDH, — and  hence  the  direction, 
the  amoaot,  and  the  point  of  application  (c)  of  if,  can  be  deter- 
mined m  ehowQ  in  the  figure.  B^  and  B,  ore  determined  in  the  same 
manner  aa  B,  and  B^ . 

The  points  a,  i,  c,  d,  and  e,  called  centers  of  pressure,  are  ths 
points  of  application  of  the  reBnltants  of  the  preBsare  on  the  several 
jointe  i  or  they  may  be  regarded  aa  the  centers  of  rexistance  for  the 
Bevenl  joints.  In  the  latter  case  the  line  abcds  would  be  called 
the  line  of  resisianee,  and  in  the  former  the  line  of  pressure. 
Strictly  speaking,  the  line  of  resistance  is  a  continuoas  cnrve  cir- 
cumscribing the  polygon  abciie.  The  greater  the  number  of 
joints  the  nearer  the  polygon  abcde  approaches  this  curve.  Occa- 
sionally ths  polygon  mnop  is  called  the  line  of  resistance.  The 
greater  the  number  of  joints  the  nearer  this  line  approaches  the 
line  of  resistance  as  defined  above.  For  an  infinite  number  of  joints 
the  polygons  abcde  and  mnop  coincide  with  the  curved  line  of  t6- 
sistance,  a,  b,  c,  d,  and  e  being  common  to  all  three. 

Notice  that  if  the  four  geometrical  lines  ab,  be,  cd,  and  de  were 
placed  in  the  relative  position  shown  in  Fig.  113,  and  were  acted 
upon  by  the  forces  T,  F,,  F,,  F^,  F^,  and  R,  us  shown,  they  would 
be  in  equilibrium;  and  hence  the  line  abcde,  or  rather  a  curve 
passing  through  the  points  a,  b,  c,  d,  and  e,  is  Bometimee  called  a 
linear  arch. 

Akt.  I.    Thkobt  op  the  Asch. 

606.  The  theory  of  the  masonry  arch  is  one  of  great  com- 
plexity. KumerouB  volumes  have  been  written  on  this  subject,  and 
it  still  occupies  the  attention  of  mathematicians.  No  attempt  will 
be  made  here  to  give  an  exhaustive  treatise  on  the  arch  ;  but  the 
fundamental  principles  will  be  stated  as  clearly  as  possible,  and  the 
principal  solutions  of  the  problem  which  have  been  proposed  from 
time  to  time  will  be  explained  and  their  underlying  assumptions 
pointed  out. 

666.  Thx  XzTUUr&I  FOBCW.  It  is  clear  that  before  we  can 
find  the  strains  in  a  proposed  arch  and  determine  its  dimensions, 
we  must  know  the  load  to  he  supported  by  it.  In  other  words, 
the  strength  and  stability  of  a  masonry  arch  depend  upon  the 


ovGoQi^lc 


AST.  ].]  THEOST  OF  THE  AECH.  440 

position  of  the  lice  of  reeistauce ;  and  before  this  can  be  deter- 
mined, it  is  necessary  that  the  external  forces  acting  upon  the  arch 
shall  be  fully  known,  i.  e.,  that  (1)  the  point  of  application,  (2)  the 
direction,  and  (3)  the  intensity  of  the  forces  acting  upon  each 
vonssoir  shall  be  knovn.  Unfortunately,  the  accurate  determina- 
tion of  the  outer  forces  is,  in  general,  an  impossibility. 

1.  If  the  arch  supports  a  fiuid,  the  pressnre  upon  the  several 
voussoirs  is  perpendicnlar  to  the  eitrados,  and  can  easily  he  found ; 
and  combining  this  with  the  weight  of  each  Toussoir  gives  the 
several  external  forces.    This  case  seldom  occurs  in  practice. 

2.  If  the  arch  is  surmounted  by  a  masonry  wall,  as  is  frequently 
the  case,  it  is  impossible  to  determine,  with  any  degree  of  accuracy, 
the  effect  of  the  spandrel  walls  upon  the  stability  of  the  arch.  It 
is  usually  assumed  that  the  entire  weight  of  the  masonry  above  the 
soffit  presses  vertically  upon  the  arch;  but  it  is  known  certainly 
that  this  is  not  the  case,  for  with  even  dry  masonry  a  part  of  the 
wall  will  be  self-supporting.  The  load  supported  by  the  arch  can 
be  computed  roughly  by  the  principle  of  g  250  (p.  168) ;  hut,  as  this 
gives  no  idea  of  the  manner  in  which  this  pressure  is  distributed,  it 
is  of  but  little  help.  The  error  in  the  assumption  that  the  entire 
weight  of  the  masonry  above  the  arch  presses  upon  it  is  certainly  on 
the  safe  side;  bat  If  the  data  are  so  rudely  approximate,  it  is  use- 
less to  attempt  to  compute  the  strains  by  mathematical  processes. 
The  inability  to  determine  this  pressure  constitutes  one  of  the  limi- 
tations of  the  theory  of  the  arch. 

Usually  it  is  virtually  assumed  that  the  extradoeal  end  of  each 
Toussoir  terminates  in  a  horisontal  and  vertical  surface  (the  latter 
may  be  zero);  and  therefore,  since  the  masonry  is  assumed  to  press 
only  vertically,  there  are  no  horizontal  forces  to  be  considered.  But 
as  the  extrados  is  sometimes  a  regular  curve,  there  would  be  active 
horizontal  components  of  the  vertical  pressure  on  this  surface;  and 
thi»  would  be  true  even  though  the  spandrel  masonry  were  divided 
by  vertical  joints  extending  from  the  extrados  to  the  upper  limit  of 
the  masonry.  Further,  even  though  no  active  horizontal  forces  are 
developed,  the  passive  resistance  of  the  spandrel  masonry — either 
spandrel  walls  or  spandrel  backing — materially  afFects  the  stability 
of  an  arch.  Experience  shows  that  most  arches  sink  at  the  crown 
and  rise  at  the  haunches  when  the  centers  are  removed  (see  Fig. 
116,  p.  447),  and  hence  the  reedstance  of  the  spandrel  masonry  will 


ovGoQi^lc 


446  AECHES.  [CHJIP.  xmL 

materully  aaeiBt  in  preventing  the  most  common  form  of  &ilar& 
The  efScienc;  of  this  renstance  vill  depend  ufoa  the  execution  of 
the  spandrel  mitsonr;,  and  vill  increase  as  the  deformation  of  the 
arch  ring  increases.  It  is  impoesible  to  compote,  even  ronghly,  the 
borisontal  forces  due  to  the  spandrel  masonry. 

Farther,  in  compating  the  strains  in  the  lach,  it  is  nsnallj 
assnmed  that  the  arch  ring  alone  sapporta  the  masonry  above  it ; 
while,  as  a  matter  of  fact,  the  entire  masonry  from  the  intiados  to 
the  top  of  the  wall  acts  somewhat  as  an  arch  in  snpporting  its  own 
weight. 

3.  If  the  arch  sopports  a  mass  of  earth,  we  can  know  neither  the 
amount  nor  the  direction  of  the  earth  pressare  with  any  degree  of 
accuracy  (see  Chap.  XIV — Retaining  Walla, — particolarly  §  527, 
page  339).  We  do  know,  however,  that  the  arch  does  not  anpport 
the  entire  mau  above  it  (see  g  619).  No  one  ever  thinks  of 
trying  to  make  a  tunnel  arch  strong  enongb  to  sustain  the  weight  of 
the  entire  mass  above  it. 

In  the  theory  of  the  masonry  arch,  the  pressnre  of  the  earth  is 
nenally  assnmed  to  be  wholly  vertical.  That  the  pressure  of  earth 
gives,  in  genera),  active  horizontal  forces  appears  to  be  nnqnestion- 
able.  An  examination  of  Fig.  113  (page  443)  will  show  how  the 
horizontal  forces  add  stability  to  an  arch  ring  whose  rise  is  equal  to 
or  less  than  half  the  span.  It  is  clear  that  for  a  certain  position 
and  intensity  of  throst  T,  the  line  of  resistance  will  approach  the 
extrados  nearer  when  the  external  forces  are  vertical  than  when 
they  are  mclined.  We  know  certainly  that  the  passive  reEOstance  of 
the  earth  adds  materially  to  the  Btability  of  masonry  arches^  for  the 
arch  rings  of  many  sewers  which  stand  without  any  evidence  of 
weakness  are  in  a  state  of  unstable  eqailibrium,  if  the  vertical  press- 
ure of  the  earth  immediately  above  it  be  considered  as  the  only 
external  force  acting  upon  it. 

667.  KlTHim  OF  TAnttSB  OF  AxcExa.  A  masonry  arch  may 
yield  in  any  one  of  three  ways,  viz. :  (I)  by  the  croshing  of  the 
stone,  or  (3)  by  the  sliding  of  one  vonssoir  on  another,  or  (3)  by 
rotation  abont  an  edge  of  some  joint.  1.  An  arch  will  fail  if  the 
pressure  on  any  part  is  greater  than  the  crushing  strength  of  the 
material  composing  it.  2.  Figs.  114  and  115  represent  the  second 
method  of  failure ;  in  the  former  the  haunches  of  the  arch  slide 


ovGoQi^lc 


(T.  1.] 


IHBOBT  OF  IHB  ABOH. 


447 


ont  and  the  orown  Blips  down,  and  in  the  latter  the  rererse  ia 
Bhown.  If  the  rise  is  leas  than  the  span  and  the  arch  fails  by  the 
diding  of  one  Toosaoir  on  the  other,  the  crown  will  nsually  ank; 
bnt  if  the  rise  is  more  than  the  span,  the  hannohes  will  generally 


be  pressed  inward  and  the  crown  will  rise.     3.  Figs.  116  and  117 
show  the  two  methods  by  which  an  arch  may  give  way  by  rotation 


aboat  the  joints.  As  a  mle  the  first  case  is  most  freqnent  tor  flai 
arches  and  the  second  for  pointed  ones.  ' 

However,  more  arches  fail' on  account  of  nneqnal  settlement  of 
the  fonndation  than  because  of  a  faulty  design  of  the  arch  proper. 

668.  Cbtrbia  of  Satett.  There  are  three  criteria,  corre- 
spending  to  th'e  three  modes  of  failure,  by  which  the  stability  of  an 
arch  may  be  judged.  (1)  To  prevent  overturning,  it  is  necessary 
that  the  line  of  resistance  shall  everywhere  lie  between  the  intrados 
and  the  extrados.  (2)  To  prevent  crushing,  the  line  of  resistance 
should  intersect  each  joint  far  enough  from  the  edge  so  that  the 
maximum  pressure  will  be  less  than  the  crashing  strength  of  the 
masonry.  (3)  To  prevent  sliding,  the  angle  between  the  line  of 
resistance  and  the  normal  to  any  joint  should  be  less  than  the  angle 
of  repose  ("angle  of  friction  ")  for  those  surfaces ;  that  is  to  say, 
the  tangent  of  the  angle  between  the  line  of  resistance  and  the 
normal  to  any  joint  should  be  leas  than  the  co-efficient  of  friction 
(I  489). 


jvGooi^le 


448  ARCE^  [OHA.P.  ZTIII. 

669.  Stability  agaisit  Sotatioo.  An  arch  composed  of  incom- 
pressible  vonssoira  can  not  fail  by  rotation  as  shown  in  Fig,  116, 
tuJees  the  line  of  resistance  tonches  the  intrados  at  two  points  and 
the  extradoB  at  one  higher  intermediate  point  (see  Fig.  120,  page 
454);  and  an  arch  can  not  fail  by  rotation  as  shown  in  Fig.  117, 
nnless  the  line  of  reBistance  touches  the  estradoB  at  two  points 
and  the  intrados  at  one  higher  intermediate  point  (see  Fig.  1^0). 
The  factor  of  safety  against  rotation  about  any  point  is  eqnal 
to  half  the  length  of  the  joint  divided  by  the  distance  between 
the  center  of  pressure  and  the  center  of  the  joint ;  that  is  to 
eay, 

the  factor  of  safely  ~^' (^) 


in  which  I  is  the  length  of  the  joint  and  d  the  distance  between 
the  center  of  preesnre  and  the  center  of  the  joint.  For  example,  if 
the  center  of  pressure  is  at  one  extremity  of  the  middle  third  of  tlie 
joint,  tl  =  il ;  and,  by  equation  (1),  the  factor  of  safety  is  three. 
If  the  center  of  pressure  is  ^2  from  the. middle  of  the  joint,  the 
factor  of  safety  is  two. 

It  is  customary  to  require  that  the  Ime  of  resistance  shall  lie 
within  the  middle  third  of  the  arch  ring,  which  is  equivalent  to 
specifying  that  the  minimum  factor  of  safety  for  rotation  shall  not 
be  less  than  three. 

670.  Stability  against  Cnuhing.  The  method  of  determining 
the  pressure  on  any  part  of  a  joint  has  already  been  discussed  in  tlie 
chapter  on  masonry  dams  (see  pp.  320-28).  When  the  total  presa- 
nre  and  its  center  are  known,  the  maximum  pressure  at  any  part 
of  the  joint  is  given  by  formula  (33),  page  333.    It  is 


in  which  P  is  the  maximum  pressure  cu  the  joint  per  unit  of  ai-ea ; 
W  is  the  total  normal  pressure  on  the  joint  per  unit  of  length  of  the 
arch  ;  I  is  the  depth  of  the  joint,  i.  e.,  the  distance  from  intrados  to 
extrados  ;  and  d'ia  the  distance  from  the  center  of  pressure  to 
the  middle  of  the  joint.     This  formula  is  general,  provided  the 


D.qitizeabyG00l^lc 


AKT.  l.J  THEOBY  OF  THE  A.UCH.  449 

masonr;  is  capable  of  resisting  tension  ;  and  if  the  masonry  ii 
assamed  to  be  incapable  of  resisting  tension,  it  is  still  general,  pro- 
vided d  does  not  exceed  ^  I. 

For  the  case  in  which  the  masonry  is  incapable  of  retisting  ten- 
sion and  d  exceeds  ^  /,  tbe  maximum  pressure  is  given  by  formula 
(21),  pt^e  334.    It  is 


Z{il-d)- 


(3) 


If  the  line  of  resistance  for  any  arch  can  be  drawn,  the  maximum 
pressure  can  be  found  by  (1)  resolving  the  resultant  reaction  per- 
pendicular to  the  given  joint,  and  ('^)  measuring  the  distance  d  from 
a  dif^ram  of  the  arch  similar  to  Fig.  113  (page  443),  and  (3)  sub- 
stituting these  data  in  the  proper  one  of  the  above  formulas  (the 
one  to  be  employed  depends  upon  the  value  of  dj,  and  computing 
P.*  This  pressnre  should  not  exceed  the  compressive  strength  of 
the  masonry. 

It  is  customary  to  prescribe  that  the  line  of  resistance  shall  lie 
within  the  middle  third  of  each  joint,  and  also  that  the  result 
obtained  by  dividing  the  total  pressure  by  the  area  of  the  joint  shall 
not  be  more  than  one  twentieth  of  the  ultimate  crashing  strength 
of  the  stone.  Under  these  conditions  the  maximum  pressure  is 
twice  the  mean,  and  hepce  using  the  above  limits  is  equivalent  to 
saying  that  the  maximum  pressure  shall  not  be  more  than  one  tenth 
of  tbe  ultimate  crushing  strength  of  the  stone.  The  mean  pressure 
in  ai-ches  is  usually  not  morR  than  one  fortieth  or  one  fiftieth,  and 
sometimes  only  one  hundredth,  of  the  ultimate  compressive  strength 
of  the  stone  or  brick  of  which  it  is  constructed. 

871.  Unil  Pressure.  In  the  present  state  of  our  knowledge  it 
is  not  possible  to  determine  the  value  of  a  safe  and  not  extravagant 
unit  working-pressure.  The  customary  unit  appears  less  extrava- 
gant, when  it  is  remembered  (1)  that  the  crusfaing  strength  of 
masonry  is  considerably  less  than  that  of  the  stone  or  brick  of  which 
it  is  composed  (see  gg  321-3^  and  §§  346-47  respectively),  and  that 
we  have  no  definite  knowledge  concerning  cither  the  ultimate  or 
the  safe  crushing  strength  of  stone  masonry  (§  223)  and  but  little 

*  F<»  a  numerical  ez&mple  ot  tbe  method  ol  doing  thta,  see  2,  J  ABO. 


ovGoQi^lc 


450  ABCHXS.  [RUAP.  ZTIII. 

concerning  that  of  brickwork  (g  249) ;  and  (Z)  that  all  the  data  we 
have  on  crashing  atrengtb  are  for  a  load  perpendicular  to  the 
pressed  surface,  while  we  have  no  experimental  knowledge  of  the 
effect  of  the  component  of  the  pressure  parallel  to  the  surface  of  the 
joint,  althongh  it  is  probable  that  this  component  would  have  eome- 
wbat  the  same  effect  npon  the  strength  of  the  Ton^^soirs  as  a  sheet 
of  lead  has  when  placed  next  to  a  block  of  stone  subjected  to  com- 
pression (§12). 

On  the  other  band,  there  are  some  considerations  which  still 
further  increase  tbe  degree  of  safety  of  the  usual  working-pressnre. 
(1)  When  the  ultimate  crusbing  strength  of  stone  is  referred  to,  tbe 
crushing  strength  of  cubes  is  intended,  although  the  blocks  of  stone 
employed  in  actual  masonry  have  less  thickness  than  width,  and 
hence  are  much  stronger  than  cubes  (see  g  15,  paragraph  2  §  60,  and 
g  273).  To  prevent  the  arch  stones  from  faking  ofi  at  the  edges, 
the  mortar  is  sometimes  dug  out  of  the  outer  edge  of  the  joint. 
This  procedure  diminishes  the  area  under  pressure,  and  hence 
increases  the  unit  pressure  ;  but,  on  the  other  hand,  the  edge  of 
the  stone  which  is  not  under  pressure  gives  lateral  snpport  to  the 
interior  portions,  and  hence  increases  the  resistance  of  that  portion 
(see  §  373).  It  is  impossible  to  compute  the  relative  effect  of  these 
elements,  and  hence  we  can  not  theoretically  determine  tbe  efficiency 
of  thus  relieving  the  extreme  edges  of  tbe  joint.  (2)  The  preceding 
formulas  (2  and  3)  for  the  maximum  pressure  neglect  the  effect  of 
the  elasticity  of  the  stone ;  and  hence  the  actual  pressure  must  be 
less,  by  some  unknown  amount,  than  that  given  by  either  of 'the 
formulas. 

672.  \otice  that  the  distance  which  the  center  of  pressnre  may 
vary  from  the  center  of  the  joint  without  the  masonry's  being 
crushed  depends  upon  the  ratio  between  the  ultimate  crushing 
strength  and  the  mean  pressure  on  the  joint.  In  other  words,  if 
the  mean  pressure  is  very  nearly  equal  to  the  ultimate  crushing 
strength,  then  a  slight  departure  of  the  center  of  pressure  from  the 
center  of  the  joint  may  crush  the  voussoir ;  bat,  on  the  other  hand, 
if  the  mean  pressnre  is  small,  the  center  of  pressure  may  de- 
part considerably  from  the  center  of  the  joint  without  the  stone's 
being  crushed.     This  can  be  shown  by  equation   (2),  page  448. 

If  both  F  and  -j-  are  large,  d  must  be  small ;  bnt  if  jP  ia  large  and 


ovGoQi^lc 


iKT.  I.]  THBOay  OF  THB  ABCH.  461 

2^  email,  then  d  may  be  large.    Esaentially  the  same  reenlt  can  be 

dedaced  from  equation  (3),  page  449. 

Even  though  the  line  of  resiatance  approaches  ao  near  the  edge 
of  the  joint  that  the  atone  is  crushed,  the  stability  of  the  arch  is  not 
necessarily  endangered.  For  example,  conceive  a  bloclt  of  stone 
rescinj;  upon  an  incompressible  plane, 
AB,  Fig.  118,  and  assume  that  the 
center  of  pressure  is  at  iV'.  Then  the  /i 
pressure  is  applied  over  an  area  pro- 
jected ia  A  V,  such  that  AN=  iAV. 
The  pressure  at  A  is  represented  by  k 
AK,  and   the  area  of   the  triangle  Fn>.  iis. 

jJffT  represents  the  total  pressure  on  the  joint.  Asenme  that 
AK  is  the  ultimate  crushing  strength  of  the  stone,  and  that  the 
center  of  pressure  is  moved  to  JV'.  The  pressure  is  borne  on  an 
area  projected  in  A  V.  The  pressure  in  the  vicinity  qI  A  Sa 
uniform  and  equal  to  the  crushing  strength  AK;  and  the  total 
pressDre  on  the  joint  is  represented  by  the  area  of  the  figure 
A  KQ  V't  which  has  its  center  of  gravity  in  the  vertical 
through  N'.  Eventually,  when  the  center  of  pressure  approaches 
so  near  A  that  the  area  in  which  the  etone  is  crushed  becomes 
too  great,  the  whole  block  will  give  way  and  the  arch  will 
fall.* 

673.  Op6n  Jointg.  It  ia  frequently  prescribed  that  the  line  of 
resistance  shall  pass  through  the  middle  third  of  each  jcint,  "  so 
that  the  joint  may  not  open  on  the  side  most  remote  from  Ihe  line 
of  resistance."  If  the  line  of  resistance  departs  from  the  middle 
third,  the  remote  edge  of  the  joint  will  be  in  tension  ;  bnt  since 
cement  mortar  is  now  quite  generally  employed,  if  the  masonry  is 
laid  with  ordinary  care  the  joint  will  be  able  to  bear  considerable 
tension  (see  Table  13,  page  94);  and  hence  it  does  not  necessa- 
rily  follow  that  the  joint  will  open. 

*  RanklDe  sSfH :  "  It  Is  trae  that  arches  have  stood,  and  stlU  itaod,  In  whl<^  the 
cent«n  of  reelstance  of  JolntB  faH  beyond  the  middle  Ihlid  of  the  depth  of  Ihe  arch 
ring  1  bnt  the  stabtlltr  of  snch  arcbei  fa  either  now  precarloos,  or  innst  have  been 
precariona  wbUe  the  mortar  was  freah."  The  above  la  one  reason  whr  the  stabillt; 
of  tbe  aich  la  not  necsBaarllr  precatloOB,  and  other  reasons  are  found  In  t  666  and 
also  In  the  snbeeqaent  dlscnaalon.  A  reasonable  tfaeorr  of  tbe  arch  will  not  make  a 
•tractan  qtpear  Instable  which  shows  ererr  evidence  of  secnritr. 


ovGoQi^lc 


4SS  ABCHES.  [CHAP.  XVIIL 

If  the  line  of  preesnre  departs  from  the  middle  third  and  the 
mortar  ia  incapable  of  reeiBting  teneion,  the  joint  will  open  on  the 
Bide  farthest  from  the  line  of  resistance.  For  example,  if  the 
center  of  pressure  is  at  iV,  Fig.  118,  then  a  portion  of  the  joint 
A  V  {=  3  A  N)  is  in  compression,  while  the  portion  VB  has  no  force 
acting  upon  it ;  and  hence  the  yielding  of  the  portion  A  Fwill  cauae 
the  joint  to  open  a  little  at  £.  Thia  opening  will  increase  as  the 
center  of  pressnre  approaches  J,  and  when  the  material  at  that 
point  begins  to  crush  the  increase  will  become  comparatively  rapid. 

Notice  tliat  if  there  are  open  joints  in  an  arch,  it  is  certain 
that  the  actual  line  of  resistance  does  not  lie  witbin  the  middle 
third  of  SDch  joints.  Notice,  however,  that  the  opening  of  a  joint 
does  not  indicate  that  the  stability  of  the  arch  is  in  danger.  In 
moat  oases,  an  open  joint  is  no  serious  matter,  particularly  if  it  is  in 
the  BofRt.  If  in  the  cxtrados,  it  is  a  little  more  aeriona,  since  water 
might  get  into  it  and  fre«ze.  To  guard  against  this  danger,  it  is 
customary  to  cover  the  estrados  with  a  layer  of  puddle  or  some 
coating  impervious  to  water  (§  364). 

674.  Stability  against  Sliding.  If  the  effect  of  the  mortar  is 
neglected,  an  arch  is  stable  against  sliding  when  the  line  of  resist- 
ance makes  with  the  normal  an  angle  less  than  the  angle  of  friction. 
According  to  Table  36  (page  315)  the  co-efficient  of  friction  of 
masonry  under  conditions  the  most  unfavorable  for  etahility — f.  e., 
while  the  mortar  is  wet — is  about  0.50,  which  corresponds  to  an  angle 
of  friction  of  about  25°.  Hence  if  the  line  of  pressure  makes  an 
angle  with  the  normal  of  more  than  25°,  there  is  a  possibility  of 
one  Toussoir's  sliding  on  the  other.  This  possibility  can  be  elimi- 
nated by  changing  the  joints  to  a  direction  more  nearly  at  right 
angles  to  the  line  of  pressure. 

However,  there  is  no  probability  that  an  arch  will  receive  its  full 
load  before  the  mortar  has  begun  to  set ;  and  hence  the  angle  of 
friction  is  virtually  much  greater  than  25°.  It  is  customary  to 
arrange  the  joints  of  the  arch  at  least  nearly  perpendicular  to  the 
line  of  resistance,  in  which  case  little  or  no  reliance  is  placed  on  the 
resistance  of  friction  or  the  adhesion  of  the  mortar. 

676.  Gonoliuion.  From  the  preceding  discussion,  it  will  be 
noticed  that  the  factors  of  stability  for  rotation  and  for  crushing 
are  dependent  upon  each  other ;  while  the  factor  for  sliding  is 
independent  of  the  other  conditions  of  failure,  and  is  dependent 


ovGoQi^lc 


ABT.  1.]  THEORY   OF  THE   ARCH.  453 

only  upon  the  direction  given  to  the  joints.  A  theoreticull;  perfect 
deuigu  for  an  arch  would  be  one  in  which  the  thi'ee  factors  of  Bafety 
were  equal  to  each  other  and  uniform  throughout  the  arch.  As 
arches  are  ordiaaril;  built,  the  factor  tor  rotation  is  about  three,  or 
a  little  more  ;  the  nominal  factor  for  crushtDg  ia  ten  to  forty ;  and 
the  nominal  factor  for  sliding  is  one  and  a  half  to  two. 

It  is  evident  that  before  any  conclusions  can  be  drawn  concern- 
ing the  strength  or  stability  of  a  masonry  arch,  the  position  of  the 
line  of  resistance  mnst  be  known ;  or,  at  least,  limits  roust  be  found 
within  which  the  true  line  of  resistance  must  be  proved  to  lie. 

676.  LOOATIOII  OF  THE  TBVE  IihB  OT  BSHUTAaOE.  The  de- 
termination of  the  line  of  resistance  of  a  semi-arch  requires  that  the 
external  forces  shall  be  fully  known,  and  also  that  (1)  the  amount, 
(2)  the  point  of  application,  and  (3)  the  direction  of  the  thrust  at 
the  crown  shall  be  known.  The  determination  of  the  external 
forces  is  a  problem  independent  of  the  theory  of  the  aith  ;  and  for 
the  present  it  will  be  assumed  that  they  are  fully  known,  although 
as  a  matter  of  fact  they  can  not  be  known  with  any  considerable 
degree  of  accuracy  (see  g  666). 

Each  value  for  the  intensity  of  the  thrust  at  the  crown  gives  a 
different  line  of  resistance.  For  example,  in  Fig,  113  (page  443), 
if  the  thrust  The  increased,  the  point  b — where  R^  intersects  the 
plane  of  the  joint  Ifl — will  approach  I;  and  consequently  c,  d, 
and  e  will  approach  0,  H,  and  A  respectively.  If  7*  be  increased 
sufficiently,  the  line  of  pressure  will  pass  through  A  or  H  (usually 
the  former,  this  depending,  however,  upon  the  dimensions  of  the 
arch  and  the  values  and  directions  of  F, ,  F,,  and  F,),  and  the  arch 
will  he  on  the  point  of  rotating  about  the  outer  edge  of  one  of  these 
joints.  This  value  of  T  is  then  the  maximum  thrust  at  a  consistent 
with  stability  of  rotation  about  the  outer  edge  of  a  joint,  and  the 
corresponding  line  of  resistance  is  the  line  of  resistance  for  maxi- 
mum thrust  at  a.  Similarly,  if  the  thmst  7'be  gradually  decreased, 
the  line  of  i-esistance  will  approach  and  finally  intersect  the  intradoa, 
ill  which  case  the  thrust  is  the  least  possible  consistent  with  stabil- 
ity of  rotation  about  some  point  in  the  intrados.  The  lines  of 
resistance  for  maximum  and  minimum  thrust  at  a  are  shown  in 
Fig.  119  (page  454). 

If  the  point  of  application  of  the  force  Tbe  gradually  lowered 
ftud  at  the  same  time  its  intensity  be  increased,  a  line  of  resistance 


ovGoQi^lc 


454 


[chap.  iTin. 


may  be  obtained  vhich  will  hare  one  point  in  common  with  the 
intmdos.  This  is  the  line  of  reaiBtance  for 
mazimnm  thrust  at  the  crovn  joint.  Simi- 
larly, if  the  point  of  application  of  7"  be 
gradually  raised,  and  at  the  same  time  its 
intensity  be  decreased,  a  line  of  resistance 
may  be  obtained  which  will  have  one  point 
in  common  with  the  extrados.  This  is  the 
line  of  reeistanoe  for  minimum  ihrnst  ut 
the  crown  joint.  The  lines  of  resistance 
for  maximum  and  minimum  thrust  at  the  crown  are  shown  in 
Fig.  ]iO. 

Similarly  each  direction  of  the 
thrust  T  will  give  a  new  line  of  re- 
Bistanoe,  In  short,  every  different 
falne  of  each  of  the  several  factors, 
«nd  also  every  combination  of  these 
raluea,  will  give  a  different  position 
for  the  line  of  resistance.  Hence,  the 
problem  is  to  determine  which  of  the  / 
infinite  number  of  possible  lines  of  t 
rcsistanct  is  the  actual  one.  This 
problem  is  indeterminate,  since  there  are  more  unknown  quantities 
than  conditions  (equations)  by  which  to  determine  them.  To 
meet  these  difficulties  and  make  a  solution  of  the  problem  possible, 
various  hypotheses  have  been  made  ;  but  there  is  no  unanimity  of 
opinion  among  authorities  regarding  the  position  of  the  true  line 
of  resistance.  Some  of  these  hypotheses  will  now  he  considered 
briefly. 

677.  HypothesiB  of  Least  Prennre.  Some  writers  have  assumed 
the  true  line  of  resistance  to  be  that  which  gives  the  smallest  abso- 
lute pressure  on  any  joint.  This  principle  is  a  m eta-physical  one. 
and  leads  to  resnJts  unquestionably  incorrect.  Of  the  font  hypo- 
theses here  discussed  this  fa  the  least  satisfactory,  and  the  least 
frequently  employed.     It  will  not  be  considered  further. 

For  an  explanation  of  Claye's  method  of  drawing  the  line  of 
pressure  according  to  this  theory,  see  Van  JTostrand's  Engineering 
Magazine,  vol.  xv,  pp.  33-B6.  For  a  general  discussion  of  the 
theory  of  the  arch  founded  on  this  hypotheds,  see  an  article  by  Pro- 


ovGoQi^lc 


iBT.  1.]  THIOST  OP  THE  ABOH.  45B 

feasor  Dn  Bois  in  Van  Nostrand'e  En^neering  Magazine,  toI.  xiii, 
pp.  341-46,  and  also  Du  Bois's  "Graphical  Statics,"  Chapter  XV, 

678.  HTpothesis  of  Leait  Thnut  at  the  Crown.  According  to 
this  hypothesis  the  tnie  line  of  resistance  is  that  for  which  the 
tbruM  at  the  crown  is  the  least  possible  consistent  with  eqnilibriam. 
This  asBumee  that  the  thrnst  at  the  crown  is  a  passive  force  called 
into  action  by  the  external  forces  ;  and  that,  since  there  ie  no  need 
for  a  fnrther  increase  after  it  has  caased  stability,  it  will  be  the  least 
possible  consistent  with  equilibriam. 

This  principle  alone  does  not  limit  the  position  of  the  line  of 
resistance;  but,  if  the  external  forces  are  known  and  the  direction 
of  the  thrnst  is  aaaumed,  this  hypothesis  famishes  s  condition  by 
which  the  line  of  resistance  corresponding  to  a  minimam  thrust  can 
he  found  by  a  tentative  process.  The  principle  of  least  crown 
thrust  was  first  proposed  by  Moseley,*  was  amplified  by  Scheffler,f 
and  has  been  adopted  more  generally 
by  writers  and  engineers  than  any  W  J*^  n 
other.  *        \r:X, 

678,  The  portion  of  the  arch  shown  V"v^\! 

in  Fig.  121  is  held  in  equilibrium  by  (1)  Px  kjJ^ 

the  vertical  forces,  to,,  w,,  etc.,  (2)  by    h/t"  X\        ' 

the  horizontal  forces  A,,  A„  etc.,  (3)  by  /^jf^/C..X !„ 

the  reaction  R  at  the  abutment,  and  (4)     /i)ih t^ — ^ 

by  the  thrust  T  at  the  crown.    The         I* '*•'*" 

direction  of  R  is  immaterial  in  this 

discossion.  Let  a  and  h  represent  the  points  of  application  of  T 
and  R,  respectively,  although  the  location  of  these  points  is  yet  un- 
determined.    Let 

T=  the  thrust  at  the  crown; 

a:,  =  the  horizontal  distance  from  b  to  the  line  of  action  of  u\; 
X,  =  the  same  for  w„  etc. ; 

■  Phllosopblcal  Magsztae,  Oct..  188S — see  Moseler's  Mechanical  Principles  ol  En- 
glneering,  2d  American  ed.,  p.  130. 

t  "  Theoris  der  GenClbe,  Fntiermsaern,  und  slsemen  Brllcken,"  BranuBChwelg, 
1S6T,  A  French  tnuiBlallon  of  this  work  U  entlUed  "  Tralt4  du  la  StabUitd  dm  con- 
Btrnctlotu ;  Ire  partie,  Tbdorle  dea  Vontcs  et  dee  Mure  de  Soatenement,"  Paris,  1864. 
Cain's  "  A  Practical  Tbeorr  ot  VousMlr  Arches  "—No.  13  of  Van  yostrand'e  Science 
8erie«— New  Tork,  ISTi,  la  an  exposition  of  a  theory  of  the  srch  baasd  npon  this 
hfpothsds. 


ovGoQi^lc 


466  ABCHBS.  [CHAF.  XTHI. 

y  =  the  perpendicalar  distance  from  b  to  the  line  of  action  of  Tj 
k^  =  the  perpendicn]ar  distance  from  J  to  the  line  of  action  of 

h,;  i,  =  the  same  for  k,;  etc. 
Then,  by  taking  moments  abont  h,  we  hare 

Ty=w,z,  +  w,x,  +  eic.  +  A,  i,  +  A,  *,  +  etc ;    .     (4) 
hence 

r=l£f+^A^ (5) 

1.  The  Talne  of  T  depends  apon  S  A  k — the  enm  of  the 
moments  of  the  horizontal  component  of  the  external  forces; — bnt 
we  know  neither  the  nature  of  the  material  over  the  arch  nor  the 
Talne  ot  Shk for  any  particular  material  (see  g§  527-31).  In 
diEicnssing  and  applying  this  principle,  the  term  ^  A  it  is  asnally 
neglected.  Ordinarily  this  gives  an  increased  degree  ot  stability; 
but  this  is  not  Qecessarily  the  case.  The  omission  of  the  eflect  of 
the  horizontal  component  makes  the  computed  value  of  Tless  than 
it  really  is,  and  causes  the  line  of  resistance  found  on  this  assump- 
tion to  approach  the  in'rados  at  the  haunches  nearer  than  it  does  in 
fact;  and  hence  the  conditions  may  be  such  that  the  actual  line  of 
resistaDce  will  be  anduly  near  the  extrados  at  the  haunches,  and 
consequently  endanger  the  arch  in  a  new  direction, 

3.  For  simplicity  of  discussion,  and  because  the  error  involved  in 
the  discussion  immediately  to  follow  is  immaterial,  we  will  tempo- 
rarily omit  the  effect  of  the  horizontal  components  of  the  external 
forces.  If  the  horizontal  forces  are  disregarded,  equation  (5) 
becomes 

T=1J^ (6) 

From  equation  (6)  we  see  that,  other  things  remaining  the  Eame. 
the  larger  )/  the  smaller  T;  and  hence,  for  a  minimum  value  of  T, 
a  should  be  as  near  (7 as  Js  possible  without  crushing  the  stone  (see 
gg  670-73).  Usually  It  is  assumed  that  aC  ia  equal  to  one  third  of 
the  thickness  of  the  arch  at  the  crown ;  and  hence  the  average 
pressure  per  unit  of  area  is  to  be  equal  to  one  half  of  the  assumed 
unit  working  pressure ;  or,  in  other  words,  twice  the  thrust  T 
divided  by  the  thickness  of  the  crown  is  to  be  equal  to  the  unit 
working  pressure. 


ovGoQi^lc 


*  A 


ABT.  1.]  THEOBI  OF  THE  AECH.  457 

3.  To  determine  y,  it  is  nccesBary  that  the  direction  of  Tshonld 
be  known.  It  is  naually  aseumed  that  T  ia  horizontal.  If  the  arch 
is  eymmetrical  and  is  loaded  nniformly  over  the  entire  span,  this 
asBumption  is  reasonable  ;  but  if  the  arch  is  subject  to  heavy  moTing 
loads,  as  most  are,  the  thrust  at  the  crovn  is  certainly  not  hori- 
zontal, and  can  not  be  determined. 

1.  If  the  joint  A  B  '\^  horizontal,  then  J  is  to  be  taken  as  near 
j1  as  is  consistent  with  the  crnshing  strength  of  the  stone,  or  at. 
Bay,  one  third  of  the  length  of  the  joint  A  B  from  A.  Notice  that 
if  the  springing  line  is  inclined,  as  in  general  it  will  be  (see  last 
two  paragraphs  of  §  683,  p.  463),  moving  i  toward  A  decreases  x, 
and  will  at  the  same  time  increase  y.  Hence  the  position  of  h  cor- 
responding to  a  minimum  value  of  T  can  be  found  only  by  trial. 
It  is  usual,  however,  to  assume  that  Ah  is  one  third  of  AB,  what- 
ever the  inclination  of  the  joint, 

680.  Joint  of  Rupture.  The  joint  of  rupture  ia  that  joint  lor 
which  the  tendency  to  open  at  the  extrados  is  the  greatest.  The 
joint  of  rupture  of  an  arch  is  analogous  to  the  dangerous  sectioD  of 
a  beam.  Practically,  the  joint  of  rupture  is  the  springing  line  of 
the  arch,  the  arch  masonry  below  that  joint  being  virtually  only  a 
part  of  the  abutment. 

That  no  joint  may  open  at  the  extradoe,  the  thrust  at  the  crown 
must  be  at  least  equal  to  the  maximum  value  of  7*  as  determined 
by  equation  (5),  page  456.  If  the  thruRt  is  less  than  this,  the  joint 
of  rupture  will  open  at  the  extrudes ;  and  a  greater  value  is  incon> 
sistent  with  the  hypothesis  of  minimum  crown  thmat.  Since  the 
moment  of  the  horizontal  components  of  the  external  forces  is 
indeterminable,  the  position  of  the  true  joint  of  rupture  can  be 
found  only  by  trial  for  assumed  values  and  positions  of  the  hori- 
zontal forces. 

881.  Aa  an  example,  assume  that  it  is  required  to  determine  the 
joint  of  rupture  of  the  16-foot  arch  shown  in  Fig.  122,  which  ia 
the  standard  form  employed  on  the  Chicago,  Kansas  St  Xebraska 
U.  R  (see  page  427  and  Plate  III).  Assume  that  the  arch  supports 
an  embankment  of  earth  extending  10  feet  above  the  crown,  and 
that  the  earth  weighs  100  pounds  per  cubic  foot  and  the  masonry 
160.  For  simplicity,  consider  a  section  of  the  arch  only  a  foot 
thick  perpendicular  to  the  plane  of  the  paper.  The  half-arch  ring 
uid  the  earth  embankment  above  it  are  divided  into  eight  aections. 


ovGoQi^lc 


458 


[chap.  iTm. 


which  for  a  more  accurate  determination  of  the  joint  of  rnptnre 
are  made  Bmaller  near  the  anpposed  position  of  that  joint.  The 
weight  of  the  first  Beetion  reatB  upon  the  first  joint,  that  of  the  first 
two  upon  the  eecond  joint,  etc.    The  values  and  the  positions  of 


the  lines  of  action  of  the  weights  of  the  several  sections  are  given  in 
the  second  and  third  columns  of  Table  59.* 


*  Tbe  center  of  gravity  o(  Ibe  arch  Btooe  ts  fontid  b;  Uie  method  explained  In 
}  494  (page  318) :  and  the  center  of  gravltj-  of  the  prism  of  earth  restlDg  npoa  each  arch 
stone  may,  wlchoat  sensible  error,  be  taken  aa  acting  through  its  medial  verKcal  line. 
Tbe  center  of  gravity  ol  tbe  coinbinad  weight  of  the  arch  stone  and  tbe  earth  reatlng 
npon  it  may  be  fonod  by  either  of  the  two  following  methods,  of  which  tbe  flrst  is 
the  shorter  and  more  accurate  : 

1.  Tbe  center  of  gravity  of  tbe  two  masses  may  befotiud  by  the  following  well- 
known  principle  of  aoalytlcal  mechanics : 


'  =  ■  'mI  +  ic, — ' *" 

in  which  z  Is  the  horizontal  distance  from  any  point,  aay  Uis  crown,  to  tbe  vertical 
thro3>[h  the  center  of  gravity  of  the  combined  masses,  w,  and  H|  are  the  weight*  of 
the  two  masses,  and  z,  and  x,  the  horltoutal  distances  from  soy  point,  say  tbe  crowu, 
to  the  Tenloato  throa«(h  the  centers  of  gravity  of  the  separate  masses  respectively. 
The  same  method  can  be  employed  for  finding  the  ceater  of  gtK7V,j  of  any  number 
of  masses,  by  simply  adding  the  corresponding  term  or  tenns  Id  the  numerator  and 
tbe  denominator  of  equation  <7). 

2.  Since  the  principles  employed  In  the  second  method  of  flikding  tfaeoenlcrot 
graritr  of  each  aioh  stone  and  Its  load  are  freqiiently  employed.  In  one  farm  or 


ovGoQi^lc 


ABT.  1.] 


THBOBT   OF  THE   ARCH. 


TABLE  69. 
To  nKD  THE  Joiin  of  Ruftukb  of  the  A.rcb  Rino  bhown  is  Fio.  133. 


ii 

DiT* 

1>1TA  FOR  HOU- 

CSNT«B  or 

THBmrr 

ATTUCBOWa. 

1 

- 

l 

• 

— 

|h  III 

1 

1 

?_"* 

",' 

ss. 

UM 

s«? 

« 

4.i»e 

i.m 

».S0    ,    ».» 

J,WO 

l.tlW 

anotber.  Id  dlacaaaloas  of  cbe  itabUlt]'  of  the  masoniT  arch,  this  method  will  be  ex- 
plained a  little  more  (Dlly  than  1b  reqnlrod  for  the  problem  In  band. 

The  first  step  la  to  reduce  the  actoiJ  load  upon  an  arcb  (Includins  the  Height  ol 
the  arch  ring  Itself)  to  an  equlralent  homofceneous  load  of  the  same  density  as  the 
arch  ring.  'Ilie  upper  limit  of  tbls  Im^nary  loading  la  called  the  nduoil-toatl  conJour. 
For  example,  suppoee  It  la  required  to  find  the  reduced-load  contour  tor  the  arch 
loaded  as  In  Fig.  llS.    Asaume  that  the  weight  of  the  arch  ring   la  160  pounds  per 


tbe  nibble  baching,  140:  and  that  of  the  earth,  100.  Then  the 
load  conlonr  of  uo  equivalent  load  ot  the  density  of  the  arch  ring 
66"  "*""''  I^  ^ '  say.ff/  The  valueof  j/Ululd  off  In  Fig.  124. 
Lonopntlng  the  ordinatea  for  other  polnla  In  Ihe  load  contour  giToa  the  line  EF.Tig. 
134,  which  la  the  reduced-load  contour  for  the  load  shown  In  Fig.  ViS.  The  area 
between  the  Intradoa  and  the  reduced-load  contour  U  proportional  to  the  load  on  the 
arch.  In  a  similar  manner,  a  live  load  |as.  tor  example,  a  train)  can  be  reduced  U> 
an  equivalent  load  of  jnasonry,— In  which  case  the  reduced-load  contour  would  con- 
sist ot  a  line  <t  H  above  and  parallel  u>  B I  tor  that  part  ot  ihe  span  covered  by  tbe 


ovGoQi^lc 


460  ABCHES.  [chap,  stiii. 

The  value  and  positiOD  of  the  horizontal  componenta  of  the 
external  forces  are  somewhat  indetenniuate  (see  §§  528-31).  Ac- 
cording to  BankJne's  theory  of   earth  pressure,*  the  horizontal 

pressure  of  earth  at  any  point  can  not  be  greater  than  ^-■--  ■ . — -r 

times  the  Tertioal   pressure  at   the   same    point,   nor   less    than 

^— jm_^  times  the  vertical  pressure, — d>  heing  the  angle  of 
1  +  Bin  ^ 

repose,  t  If  0  =  30",  the  above  expression  is  equivalent  to  saying 
that  the  horizontal  pressure  can  not  be  greater  than  three  times 
the  vertical  pressure  nor  less  than  one  third  of  it.  Evidently 
the  horizontal  component  will  be  greater  the  harder  the  earth 
spandrel-filling  is  rammed  into  place.  The  condition  in  which  tho 
earth  will  be  deposited  behind  the  arch  can  not  be  foretold,  but  it 
is  probable  that  at  least  the  minimum  value,  as  above,  will  always 
be  realized.  Hence  we  will  assume  that  the  horizontal  intensity 
is  at  least  one  third  of  the  vertical  intensity ;  that  is  to  say, 
h  =  ^edlfin  which  e  is  the  weight  of  a  cubic  unit  of  earth — which 
was  assumed  above  at  100  pounds, — d  the  depth  of  the  center  of 
pressed  surface  below  the  top  of  the  earth  filling,  and  /  the  vertical 
dimension  of  the  surface.  The  values  and  the  positions  of  the 
horizontal  forces  acting  on  tho  respective  sections  of  the  arch  ring 
are  given  in  the  second  double  column  of  Table  59. 

To  find  the  least  thrust  at  the  crown  consistent  with  stability  of 
rotation,  assume  that  the  center  of  pressure  on  any  joint  is  at  a 
distance  from  the  intrados  equal  to  one  third  of  the  length  of  the 
joint  (see  paragraph  4,  page  457).  Tbe  co-ordinates  to  the  several 
centers  of  pressures  are  given  in  the  third  double  column  of  Table 
59.  Notice  that  the  several  values  of  x  and  k  are  simply  the  differ- 
ences between  two  quantities  given  in  the  table.  The  thrust  at  the 
crown  is  supposed  to  be  applied  at  tlie  upper  limit  of  the  middle 
third  of  the  crown  joint.  The  length  of  the  crown  joint  is  1,25  feet ; 
and  hence  the  several  v^ues  of  y  are  the  respective  quautities  in  the 

trotD  1  whlls  for  the ramalnder  ot  the  span,  tbe  Una  IP  Is  the  rednced-load  contour. 
The  Becond  step  U  to  draw  the  srch  ring  and  Its  reduoed-load  contour  on  thick 
paper,  to  a  lurge  scale,  and  then,  irlth  a  sharp  koKe,  caretuUj-  cut  oat  the  area  Kpr»- 
«enting  the  load  on  each  arch  rtone.  TheceQter  of  gravity  of  each  piece,  asijt  I  mn, 
F1|^.  124,  can  be  found  by  balanclnic  It  oo  a  knife-edge  ;  and  then  the  position  ot  the 
center  of  gravlt;  is  to  be  transferred  to  the  drawing  ot  the  arcb. 

•  See  S  544,  page  348. 

t  Banklne's  Clrll  F.nirlneoring,  p.  tSO. 


ovGoQi^lc 


*ltT.  1,]  THEORY   OP  THE  ARCH.  461 

eeventh  column  of  Table  59  miTins  ^  of  1.20  feet.  The  last  three 
columns  of  the  table  contain  the  values  of  the  crown  thrust  as 
computed  by  equation  (5),  page  456. 

Au  inspection  of  the  results  in  the  last  column  of  Table  59 
shows  that  the  thrust  is  a  maximum  for  joint  4.  A  repetition  of 
the  computations,  using  smaller  divisions  of  the  arch  ring,  might 
show  that  the  abdoluti;  maximum  occurs  a  little  to  one  side  or  the 
other  of  this  joint;  but  the  uncertainty  in  the  data  for  both  the 
vertical  and  the  horizontal  forces  is  too  great  (see  §  619  and  §g  527-31 
reBpectively)  to  justify  an  attempt  at  absolute  accuracy,  and  hence 
we  will  assume  that  joint  4  is  the  true  joint  of  rupture.  The 
angular  distance  of  this  joint  from  the  crown  is  45°,  which  quantity 
is  termed  the  angle  of  rupture. 

Any  increase  in  the  assumed  intensity  of  the  horizontal  com- 
ponents increases  the  computed  value  of  the  angle  of  rupture. 
For  example,  if  the  quantities  in  the  next  to  the  last  column  of 
Table  59  bo  doubled,  the  thrust  for  joint  7  will  he  the  maximum. 
Probably  this  condition  could  be  realized  by  tightly  tamping  the 
earth  spandrel-filling. 

Notice  that  the  preceding  discussion  of  the  position  of  the 
joint  of  rupture  is  for  a  uniform  stationary  load.  The  angle  of 
rupture  for  a  concentrated  moving  load  will  diSer  from  the  results 
found  above;  but  the  mathematical  investigation  of  the  latter  ease 
is  too  complicated  and  too  uncertain  to  justify  attempting  it. 

682.  In  discussions  of  the  positiou  of  the  joint  of  rupture,  the 
horizontal  components  are  usually  neglected.*  This  phase  of  the 
subject  will  be  considered  only  briefly.  The  following  is  the 
method  usually  employed  f  in  investigating  the  position  of  the  joint 
of  rupture,  and  is  based  on  the  assumptioQ  that  the  crown  thrust  is 
correctly  given  by  equation  (6),  page  466. 

Let  If'=the  total  weight  resting  on  any  joint;  a;  =  the  hori- 
zontal distance  of  the  center  of  gravity  of  this  weight  from  the 
origin  of  moments;  and  ^  =  the  arm  of  tlie  crown  thrust.  Then 
equation  (6)  becomes 

^=f w 

•  So  br  u  obserred,  Ranklae's  Inveatlifatlon  Is  the  only  wceptlon;  and  it  ia.  la 
tact,  only  an  apparent  exception  taee  paragraph  3,  page  tilO)- 

tPor  eumide,  Me  Sonnet's  DlciioBiiftire  dw  MWWmatiqne  AppliqoieB,  pp. 
1064-85. 


ovGoQi^lc 


462  AECHBS.  —     [CHAP.   IVIIl. 

To  determine  the  condition  for  a  maximani,  it  ia  asBiimed  that  W, 
X,  ftnd  y  are  independent  Tariables.     Differentiating  equation  (6), 

dT_ld{W'i)       Wx^ 
dy     y     dy  y*  ' 

}ya.td{Wx)  =  Wdx+dW.  idx=  Wdz,  tmi  ibaa 

dT_W_^_Wx  ... 

^  dy~  y  dy     Y' ^  ' 

Hence  the  condition  for  a  maximnm  crown  thnut  li 


dx 


■  (10) 


The  aenal  interpretation  of  equation  (10)  is:  "The  joint  of  rap- 
ture is  that  joint  at  which  the  tangent  to  the  intrados  paaaea 
throngh  the  intersection  of  T  and  the  resoltant  of  all  the  vertical 
forces  above  the  joint  in  question." 

The  position  of  the  joint  of  mptnre  can  be  found  bf  the  above 
principle  only  by  trial.  This  method  posseeBea  no  advantage  over 
the  one  explained  in  the  preceding  section,  and  is  less  convenient  to 
apply.  The  preceding  investigation  ieapproximate  for  the  following 
reasons:  1.  The  eSect  of  the  horizontal  forces  ia  omitted.  2.  W, 
X,  and  y  are  dependent  variables,  and  not  independent  as  assumed. 
3.  In  the  interpretation  of  equation  (10),  instead  of  "the  tangent 
to  the  intrados,"  should  be  employed  the  tarijfmt  to  th«  hn9  of 
resistance. 

In  applying  this  method,  a  table,  computed  by  M.  Petit,  which 
gives  the  angle  of  rupture  in  terms  of  the  ratio  of  the  radii  of  the 
intrados  and  the  extrados,  is  generally  employed.  The  table  in- 
volves the  assumption  that  a.  Fig.  121  (p.  455),  is  in  the  extrados 
and  b  in  the  intrados;  and  also  that  the  intrados  and  extrados  are 
parallel.  According  to  this  table,  "a  semi-circular  arch  of  which 
the  thickness  is  uniform  throughout  and  equal  to  the  span  divided 
by  seventeen  and  a  Italf  is  the  thinnest  or  lightest  arch  that  can 
stand.  A  thinner  arch  would  be  impossible."  If  the  line  of  re- 
sistance is  restricted  to  the  middle  third,  then,  according  to  this 
theory,  the  thinnest  semi-circular  arch  which  can  stand  is  one 
whose  span  ia  jive  and  a  kalf  times  the  uniform  thicknees.     Many 


ovGoQi^lc 


AHT.  1.]  .        THBOBT  OF  TBB  AfiCH.  46S 

arches  in  vhich  the  thicknese  is  much  less  thao  one  aerenteeDth 
of  the  Bpan  Btand  and  carry  heavy  loads  without  showing  any  evi- 
dence  of  weakneea.  For  example,  in  arch  No,  26  of  Table  63  (pp. 
503-3),  which  is  frequently  cited  as  being  a  model,  the  average  thick- 
ness is  3.S5  ft.,  or  about  one  Iwmity-fiftk  of  the  span ;  and  since  no 
joints  open,  the  line  of  reeistance  must  lie  in  the  middle  third, 
even  though  the  thickness  is  only  one  fifth  of  that  required  by  the 
table.  Owing  to  the  approximations  involved,  and  also  to  the  limi* 
tations  to  arches  having  intrados  and,  extradoa  parallel,  the  ordi- 
nary tables  for  the  position-  of  the  joint  of  rupture  have  little,  if 
any,  practical  value.  The  only  satisfactory  way  to  find  the  angle 
of  rupture  is  by  trial  by  equation  (5),  aa  explained  in  g  681. 

According  to  M.  Petit's  table,  if  the  thickneea  ia  one  fortieth  of 
the  diiimeter,  the  angle  of  rapture  is  46°  13';  if  the  thickness  is  one 
twentieth,  the  angle  is  53°  15';  and  if  one  tenth,  59°  41'. 

In  conclusion,  notice  that  the  investigations  of  both  this  and  the 
preceding  section  show  that  an  arch  of  more  than  about  90°  to  130° 
central  angle  is  impossible. 

683.  Winkler's  HypotheilB.  Prof.  Winkler,  of  Berlin, — a  well- 
known  authority — published  in  1879  ia  the  "  Zeitschrift  das  Archie 
teklen  und  Iiigftiieur  Vereins  zu  Hannover,"  page  199,  the  follow- 
ing theorem  concerning  the  position  of  the  line  of  resistance :  "  For 
an  arch  ring  of  constant  cross  section  that  line  of  resistance  ia 
approximately  the  true  one  which  lies  nearest  to  the  axis  of  the 
arch  ring,  as  determined  by  the  method  of  least  squares."  * 

The  only  proof  of  this  theorem  is  that  by  it  certain  coDcluaions 
can  be  drawn  from  the  vouseoir  arch  which  harmonize  with  the 
accepted  theory  of  solid  elastic  arches.  The  demonstration  de- 
pends upon  certain  assumptions  and  approximations,  as  follows: 
1.  It  ia  assumed  that  the  external  forces  acting  on  the  arch  are 
vertical;  whereaa  in  many  eases,  and  perhaps  in  most,  they  are 
inclined.  2.  The  loads  are  assumed  to  be  uniform  over  the  entire 
span ;  whereas  in  many  cases  the  arch  is  subject  to  moving  con- 
centrated loads,  and  sometimes  the  permanent  load  on  one  aide  of 
the  arch  is  heavier  than  that  on  the  other.  3.  It  is  assumed  that 
the  load  included  between  the  lines  PGD  and  2fHC,  Fig.  12i 
(page  458),  is  equal  in  all  respects  to  that  included  between  P02 
•  Thli  tbeorem  wbb  Qnt  brought  Co  the  sttentloii  at  American  resdeis  In  1880,  bf 
pTofcMor  SwiUn  In  an  article  in  Van  Nogtrand'i  Engln'g  Uag.,  VOL  xxUl,  pp.  3K-n 


ovGoQi^lc 


16i  ABCHES.  [chap.  XVm. 

aDd  N  H\.  The  error  thus  involved  is  inapprociable  at  the  crown, 
but  at  the  springing  of  semicircakr  arches  is  considerable.  4.  "Vha 
conclusions  dmwn  from  the  voussoir  (masonry)  arch  only  approxi- 
mately agree  with  the  theory  o[  elastic  (solid  iron  or  wood]  arches. 
6.  Masonry  arches  do  not  ordinarily  have  a  constant  cross  section 
as  required  by  the  above  theorem ;  but  it  uenally,  and  properly, 
increases  toward  the  springing.  6.  The  phrase  "  as  determined  by 
the  method  of  least  squares "  means  that  the  true  line  of  resist- 
auce  is  that  for  which  the  sum  of  the  squares  of  the  vertical 
deviations  is  a  minimum.  Since  the  joints  must  be  nearly  perpen- 
dicular to  the  line  of  resistance,  the  deviations  should  be  meaenred 
normal  to  that  line.  For  a  uniform  load  over  the  entire  arch,  the 
lines  of  reBistanee  are  comparatively  smooth  curves;  and  hence,  if 
the  sum  of  the  squares  of  the  vertical  deviations  is  a  minimum, 
that  of  the  normal  also  would  probably  be  a  minimum.  But  for 
eccentric  or  concentrated  loads  it  is  by  no  means  certain  that  such  a 
relation  would  exist.  7.  The  degree  of  approximation  in  this  theorem 
is  le^s  the  flatter  the  arch. 

684.  To  apply  Winkler's  theorem,  it  is  necessary  to  (1)  con- 
struct a  line  of  resistance,  (3)  measure  its  deviations  from  the  axis, 
and  (3)  compute  the  sum  of  the  squares  of  the  deviations;  and  it  is 
then  necessary  to  do  the  same  for  all  possible  lines  of  resistances, 
the  one  for  which  the  sum  of  the  squares  of  the  deviations  is  least 
being  the  "  trne"  one. 

Instead  of  applying  Winkler's  theorem  as  above,  many  writers 
employ  the  following  principle,  which  it  is  asserted  follows  directly 
from  that  theorem;  "  If  any  line  of  resistance  can  be  constructed 
within  the  middle  third  of  the  arch  ring,  the  true  line  of  resistaace 
lies  within  the  same  limits,  and  hence  the  arch  is  stable."  This 
assertion  is  disputed  by  Winkler  himself,  who  says  it  is  not,  in  gen- 
eral, correct.*  It  does  not  necessarily  follow  that  becHUse  one  line 
of  resistance  lies  within  the  middle  third  of  the  arch  ring,  the 
"true"  line  of  resistance  also  does;  for  the  "trne"  line  may  coin- 
cide very  closely  with  the  axia  in  one  part  of  the  arch  ring  and 
depart  considerably  from  it  in  another  part,  and  still  the  sum  of  the 
squares  of  the  deviations  be  a  minimum.  This  method  of  applying 
Winkler's  theorem  is  practically  nothing  more  or  less  than  an  appli< 


ovGoQi^lc 


AST.   1,]  THEOET  OF  THE  ABCH.  465 

cation  of  the  coQcInsiona  derived  from  the  hjpothesia  of  leaet 

resistance  (g  677). 

685.  Hairier's  Principle.  It  is  well  known,  from  the  principles 
of  fiuid  pressure,  that  the  tangential  thrust  at  any  point  of  a  circle 
pressed  by  normal  forces  is  equal  to  the  pressure  per  unit  of  area 
multiplied  by  the  radius.  "  The  condition  of  an  arch  of  any  form 
Dt  any  point  where  the  pressure  is  normal  is  similar  to  that  of  a  cir- 
cular rib  of  the  same  curvature  under  a  normal  pressure  of  the  same 
intensity ;  and  hence  the  following  principle:  Ihe  thrust  at  any 
normally  pressed  point  of  a  linear  arch  is  the  prodvct  of  ihe  radius 
of  curvature  iy  the  intennity  of  the  pressure  at  that  point.  Or, 
denoting  the  radius  of  curvature  by  p,  the  normal  pressure  per 
unit  of  length  of  intrados  by  p,  and  the  thrust  by  T,  we  have 

T=pp." (11) 

The  above  relation,  due  originally  to  Navier,  has  in  itself  nothing 
to  do  with  the  position  of  the  line  of  resistance;  but  is  employed  by 
writers  who  assume  that  an  arch  is  stable  if  a  line  of  resistance  can 
be  drawn  anywhere  within  the  middle  third  of  the  arch  ring,'to 
determine  the  crown  thrust.  Notice,  however,  that  under  these 
conditions  the  radias  of  curvature  is  known  only  within  limits.  An 
example  of  its  application  will  be  referred  to  later  (§  704;  and  8, 
g  705;— pp.  482  and  486  respectively). 

686.  THE0BIE8  OF  THE  ABOH.  Various  theories  have  been 
proposed  from  time  to  time,  which  differ  greatly  in  the  fundamental 
principles  involved.  Unfortunately,  the  underlying  assumptions 
are  not  usaally  stated ;  and,  as  a  rule,  the  theory  is  presented  in  such 
a  way  as  to  lead  the  reader  to  believe  that  each  particular  method 
"  is  free  from  any  indeterminateuese,  and  gives  results  easily  and 
accurately."  Every  theory  of  the  masonry  arch*  is  approximate, 
owing  to  the  uncertainty  concerning  the  amount  and  distribution 
of  the  external  forces  (§  666),  to  the  indeterminateness  of  the  posi- 
tion of  the  true  line  of  resistance  (g§  676-85),  to  the  neglect  of  the 
infiuence  of  the  adhesion  of  the  mortar  and  of  the  elasticity  of  the 
material,  and  to  the  lack  of  knowledge  concerning  the  strength  of 
masonry;  and,  further,  the  strains  in  a  masonry  arch  are  indeter- 
minate owing  to  the  effect  of  variations  in  the  material  of  which  the 


ovGoQi^lc 


466  ASCHZa.  [chap.  ZTTn. 

arch  u  composed,  to  the  effect  of  imperfect  workmanship  in  dreiB- 
ing  and  bedding  the  Btones,  to  the  action  of  the  center — its  rigidilj, 
the  method  and  rapidity  of  striking  it, — to  the  spreading  of  th& 
ftbntmenta,  and  to  the  settling  of  the  fonndstioDs.  These  elementa 
are  indeterminate,  and  can  never  be  stated  accnrately  or  adequately 
in  a  mathematical  formula  ;  and  hence  any  theory  can  be  at  best 
only  an  approximation.  The  inflaence  of  a  variation  in  any  one  of 
these  factors  can  be  approximated  only  by  a  clear  comprehension  of 
the  relation  wliich  they  severally  bear  to  each  other ;  and  hence  a 
thorough  knowledge  of  theoretical  methods  is  necessary  for  the 
iDtclligent  design  and  construction  of  arches. 

A  few  of  the  most  important  theories  will  now  be  stated,  and 
the  fundamental  principles  involved  in  each  explained. 

687.  To  save  repetition,  it  may  be  mentioned  here,  once  for  all, 
that  every  theory  of  the  arch  is  bat  a  method  of  verification.  The 
first  step  is  to  assnme  the  dimensions  of  the  arch  ontright,  or  to 
make  tbem  agree  with  some  existing  arch  or  conform  to  some  em- 
pirical formula.  The  second  step  is  to  test  the  assnmed  arch  by  the 
theory,  and  then  if  the  line  of  resistance,  as  determined  by  the 
theory,  does  not  lie  within  the  prescribed  limits — usually  the  middle- 
third, — the  depths  of  the  voussoirs  mast  be  altered,  and  the  design 
mast  be  tested  again. 

688.  Katioval  Teeost.  The  following  method  of  determining 
the  line  of  resistance  is  based  upon  the  hypotheeis  of  least  crown 
thrust  (g  C78),  and  recognizes  the  existence  of  the  horizontal  com- 
ponents of  the  external  forces.  Unfortunately,  the  results  found 
by  this  method,  as  well  as  those  by  all  others,  are  rendered  some- 
what uncertain  by  the  indeterminateness  of  the  external  forces 
(S  6fi6). 

689.  Symmetrical  Load.  General  Solnlion.  As  an  example 
of  the  application  of  this  theory,  let  us  investigate  the  stability  of 
the  semi-arch  shown  in  Fig.  125  (page  467).  The  first  step  is  to 
determine  the  line  of  resistance.  The  maximum  crown  thrust  was 
computed  in  Table  59  (page  459),  as  already  explained  (§  681). 
To  construct  the  force  diagram,  a  line  BO  is  drawn  to  scale  to 
represent  the  maximum  thrust  as  found  in  the  fourth  line  of  the 
last  column  of  Table  59.  From  0,  w,  is  kid  off  vertically  upwards  j 
and  from  its  extremity,  k,  is  laid  off  horizontally  to  the  left.  Then 
the  line  from  0  to  the  left-hand  extremity  of  /(,  (not  shown  in  this 


ovGoQi^lc 


ABT.  l.J 


RATIONAL  THEOBY   OF  THE   AKCH. 


4er 


particular  case)  represents  the  directioD  and  amount  of  the  external 
force  F^  acting  upon  the  first  division  of  the  arch  stone ;  and  the 
line  B^  from  B  to  the  upper  extremity  of  F,  represents  the  resultant 
pressure  of  the  first  arch  stone  upon  the  one  nest  below  it.  Simi- 
larly, lay  off  to,  vertically  upwards  from  the  left-hand  extremity  of 
Ji,,  and  lay  oS  A,  horizontally  to  the  left;  then  a  line  F,  from  the 
upper  end  of  w,  to  the  left-band  end  of  /i,  represents  the  resultant 
of  the  external  forces  acting  on  the  second  dirisions  of  the  arch, 
and  a  line  Jl,  from  the  upper  extremity  of  F,  represents  the  resultant 
pressure  of  the  second  arch  stone  on  the  third.  The  force  diagram 
is  completed  by  drawing  lines  to  represent  the  other  values  of 
w,  7i,  F,  and  the  corresponding  reactions. 


In  the  diagram  of  the  arch,  the  points  in  which  the  horizontal 
and  vertical  forces  acting  upon  the  several  arch  stones  intersect,  are 
marked  g,,  g,,  etc.,  respectively  ;  and  the  oblique  line  through  each 
of  these  points  shows  the  direction  of  the  resultant  external  force 
acting  on  each  arch  stone. 

To  construct  the  line  of  resistance,  draw  through  C— the  upper 


ovGoQi^lc 


4G8  ABOHES.  [OHAP.  XTIII. 

limit  of  the  middle  third  of  the  crown  joint — a  horizontal  line  to  an 
intereection  with  the  oblique  force  through  g, ;  and  from  this  point 
draw  a  line  parallel  to  R, ,  and  prolong  it  to  an  intersection  with  the 
obliqne  fcrce  tbrongh  y, .  In  a  similar  manner  continue  to  the 
springing  line.  Then  the  intersection  of  the  Hoe  parallel  to  B^ 
with  the  first  joint  gives  the  center  of  pressure  on  that  joint ;  and 
the  intersection  of  E,  with  the  second  joint  gives  the  center  of 
pressure  for  that  joint,— and  so  on  for  the  other  joints.  Each 
center  of  pressure  is  marked  b;  a  circular  dot.  A  line  connecting 
these  centers  of  pressure  would  be  the  line  of  resistance ;  but  the 
line  is  not  shown  in  Fig.  125. 

690.  The  next  step  is  to  determine  the  degree  of  stability. 

1.  Since  the  line  of  resistance  lies  within  the  middle  third  of  the 
arch  ring,  and  touches  the  inner  limit  of  that  third  at  two  pointa 
and  its  ontbr  limit  at  an  intermediate  and  higher  point,  the  factor 
against  rotation  is  3  (see  §  669). 

2.  The  unit  working  pressure  is  found  by  applying  equation  (3), 

page  448.     At  the  crown,  rf  =  ^  /,  and  hence  P  =  —j— ;  or,  since 

W=  9,400  pounds  and  I  =  1.25  feet,  P  =  15,040  pounds  per  square 
foot  =  104  pounds  per  squuro  inch.  At  the  springing,  IT  =31,700 
pounds,  I  =  4.5  feet,  and  d  =  0.10  feet ;  and  therefore 

—iTm -"v-O  +  643  =  5,463. 

(4.5)' 

That  is,  P  =  5,463  pounds  per  square  foot,  or  38  pounds  per  sqnar, 
inch.  Except  for  a  particular  kind  of  stone  and  a  definite  quality 
of  masonry,  it  is  impossible  even  to  discuss  the  probable  factor  of 
3ufety ;  but  it  is  certain  that  in  this  case  the  nominal  factor  is 
excessive  (see  §  223),  while  the  real  factor  is  still  more  so  (see 
§§671-72). 

If  the  maximum  pressure  at  the  most  compressed  joint  had  been 
more  than  the  safe  bearing  power  of  the  masonry,  it  would  have 
been  necessary  to  increase  the  depth  of  the  arch  stones  and  repeat 
I  lie  entire  process.  ^Notice  that  the  total  pressure  on  the  joints 
increases  from  the  crown  toward  springing,  and  that  hence  the 
depth  of  the  arch  stones  also  should  increase  in  the  same  direo 
tion. 

3.  To  determine  the  degree  of  stability  against  sliding,  notiM 


ovGoQi^lc 


LBX.  1.]  KATIONAL  THEORY.  4S9 

that  the  angle  betweeD  the  resaltant  pressure  on  any  joint  and 
the  joint  is  least  at  the  Bpringing  joint ;  and  hence  the  stability 
ct  this  joint  against  sliding  is  less  than  that  for  any  other.  The 
nominal  factor  of  safety  is  equal  to  the  co-efficient  of  friction 
divided  by  tan  (90°  —  TS")  =  tan  18°  =  0.33.  An  examination  of 
Table  36  (page  315)  shows  that  when  the  mortar  is  still  wet  the 
co-efficient  is  at  least  0.50  ;  and  hence  the  nominal  factor  for  the 
joint  in  question  is  at  least  Ij,  and  probably  more,  while  the  real 
factor  is  still  greater.  The  nominal  factor  for  joint  7  is  at  least  IJj, 
and  that  for  joint  3  la  abont  5.  There  is  little  or  no  probability  that 
an  arch  will  be  fonnd  to  be  stable  for  rotation  ^d  crashing,  and 
unstable  for  sliding.  If  such  a  condition  should  occur,  the  direc- 
tion of  the  assumed  joint  could  be  changed  to  give  stability.*  The 
actual  joints  should  be  as  nearly  perpendicular  to  the  line  of  resist- 
ance as  is  consistent  with  simplicity  of  workmanship  and  with 
stability.  For  circular  arches,  it  is  ordinarily  sufficient  to  make  all 
the  joints  radlaL  In  Fig.  125,  the  joints  are  radial  to  the  intrados  ; 
bat  if  they  had  been  made  radial  to  the  extradoe  or  to  an  intermedin 
ate  curve,  the  stability  against  sliding,  particularly  at  the  springing 
joint,  would  have  been  a  little  greater, 

691.  Special  SoUition.  The  following  entirely  graphical  solution 
ia  useful  when  it  is  desired  to  find  a  line  of  resistance  which  will 
pass  through  two  predetermined  points. 

For  example,  assume  that  it  is  desired  to  pass  a  line  of  resistance 
through  U  and  a,  Fig.  126  (page  470),  the  former  being  the  upper 
extremity  of  the  middle  third  of  the  crown  joint  and  the  latter  the 
inner  extremity  of  the  middle  third  of  joint  4. 

The  value  and  positions  of  the  extei'nal  forces,  which  are  the 
same  as  those  employed  in  Fig.  125,  are  given  in  Table  59  (page 
459).  Construct  a  load  line,  as  shown  in  the  force  diagram,  by 
laying  off  w,  and  A, ,  and  w,  and  h, ,  etc.,  in  succession,  and  drawing 
F,,F,,  etc.  Since  the  load  is  Bymmetrical,  we  may  assume  that  the 
thrust  at  the  crown  is  i^orizontal ;  and  hence  we  may  choose  a  pole 
at  any  point,  say  P',  horizontally  opposite  0.  Draw  lines  from  P' 
to  the  extremities  of  P,,  P,,  etc.  Construct  a  trial  equilibrium 
polygon  by  drawing  through  F7aline  parallel  to  the  line  P'O,  of 
the  force  diagram,  and  prolong  it  to  d  where  it  intersects  P^ .    From 

*  Strlctlfuiy  cbacge  In  tbe  direction  ot  the  Joints  will  Dec«e8tt«te  a  recompataUoB 
«(  tlw  entire  probleni  i  bnt,  except  in  extreme  oasea,  snch  reTlnion  li  DoneccssaiT'. 

D.qilizMbvG00l^le 


470 


[chap.  XTin. 


i  draw  ft  line  be  parallel  to  Ji'^  of  the  force  diftgram  ;  from  c,  the 
point  where  be  intereectA  the  line  of  F,,  draw  a  line  cd  parallel  to 
B', ;  from  d,  the  point  where  cd  intereecta  F,,  draw  a  line  de 
parallel  to  Ji\ ;  and  from  e,  the  point  where  de  tnteraects  /*,,  draw 
a  line  e/  parallel  to  R\ .    Prolong  the  line  /e  to  g,  the  point  in 


which  it  intersects  the  prolongation  of  Ub;  and  then,  by  the  prin- 
ciples of  graphical  statics,  jr  is  a  point  on  the  reenltant  of  the  forces 
F,,F,,  F,,  and  F,. 

The  section  of  the  arch  from  the  crown  joint  to  joint  4  is  at 
rest  nnder  the  action  of  the  crown  thmst  T,  the  resultant  of  the 
external  forces,  and  the  reaction  of  joint  4.  Since  the  first  tvo 
intersect  at  y,  and  since  it  has  been  assnmed  that  the  center  of 
preesarefor  joiut  4  isatn — the  inner  extremity  of  the  middle  third, 
— a  line  ag  mnst  represent  the  direction  of  the  resnltant  reaction  of 
joint  4 ;  and  hence  the  line  R,,  in  the  force  diagram  drawn  from 
the  npper  extremity  of  /*, ,  parallel  to  a  ^,  to  an  intersection  with 
P'O,  represents,  to  the  scale  of  the  load  line,  the  amount  of  the 
reaction  of  joint  4.  Then  PO,  to  the  same  scale,  represents  the 
crown  thrust  corresponding  totheline  of  resistance  passing  through 
U  and  a ;   and  a  line — uot  shown  in  Fig.  126 — from  the  npper 


ovGoQi^lc 


AET.  1-]  BATIONAL  THEOBT.  471 

e^remity  of  /",  to  the  lower  extremity  of  F, ,  would  represent,  in 
both  direction  and  amount,  the  reBulUint  of  F,,  F,,  F,,  and  F^. 

Having  found  the  thrust  at  the  crown,  complete  the  force  dia- 
gram by  drawing  the  lines  i?,,  E,,  Ji,,  etc.  ;  and  then  construct  a 
new  equilibrium  polygon  exactly  as  was  described  above  for  the 
trial  eqailibrium  polygon.  The  construction  may  be  continued  to 
the  springing  line.  The  eqailibrium  polygon  shown  in  Fig.  126  by 
a  solid  lin>«  was  obtained  in  this  way. 

The  amount  of  the  pressure  on  any  joint  is  given  by  the  length 
of  the  corresponding  ray  in  the  force  diagram.  The  points  in  which 
the  sides  of  the  equilibrium  polygon  cut  the  joints  are  the  centers 
of  pressure  on  ihe  respective  joints.  The  stability  of  the  arch  may 
be  discossed  as  iu  g  690. 

692.  One  of  the  most  useful  applications  of  the  method  described 
in  the  preceding  seution  is  in  determining  the  line  of  resistance  for 
a  segmental  arch  hbfing  a  central  angle  so  small  aa  to  make  it 
obvious  that  the  joint  at  rupture  (§§  680-81)  b  at  the  springing. 

For  example,  assume  that  it  is  required  to  draw  the  line  of 
resistance  for  the  circnlar  arch  shown  in  Fig.  127  (p.  472).  The  span 
is  50  feet,  the  rise  10  feet,  the  depth  of  vouasoirs  2.5  feet,  and  the 
height  of  the  earth  above  the  summit  of  the  arch  ring  is  10  feet. 
The  angular  distance  of  the  springing  from  the  crown  is  43°  45' ; 
and  since  the  angle  of  rupture  is  nearly  always  more  than  45°,  it  is 
safe  to  assume  that  the  joint  of  rupture  is  at  the  springing. 

The  method  of  determining  the  line  of  resistance  is  the  same 
as  that  explained  in  §  691,  and  is  sufficiently  apparent  from  an 
inspection  of  Fig.  137. 

d93.  Uniymmetrioal  Load.  The  design  for  an  arch  ring 
should  not  be  considered  perfect  until  it  is  found  that  the  criteria 
of  safety  (§§  668-75)  are  satisfied  for  the  dead  load  and  also  for 
every  possible  position  of  the  live  load.  A  direct  determination  of 
the  line  of  resistance  for  an  arch  under  an  nnsymmetrical  load  is 
impossible.  To  find  the  line  of  resistance  for  an  arch  under  a 
symmetrical  load,  it  was  necessary  to  make  some  assumption  con* 
corning  (1)  the  amount  of  the  thrust,  (2)  its  point  of  application, 
and  (3)  its  direction  ;  but  when  the  load  is  nnsymmetrical,  we 
neither  know  any  of  these  items  nor  can  make  any  reasonable 
hypothesis  by  which  they  can  be  determined.  For  an  nnsymmetri- 
cal load  we  know  nothing  concerning  the  position  of  the  joint  of 


ovGoQi^lc 


[chap.  xTin. 


rapture,  sad  know  that  the  throat  at  the  crown  is  neither  horixoatal 
Dor  ^tplied  «t  one  third  of   the  depth  of   that  joint  from  tbs 


crown ;  and  hence  the  preceding  methods  can  not  be  employed. 
When  the  load  ia  not  Bymmotrical,  the  following  method  may  be 
employed  to  find  a  Hne  of  resistance  ;  bat  it  gives  no  indication  as 
to  which  of  the  many  possible  lines  of  resistance  is  the  true  one. 

Let  it  be  reqnircd  to  test  the  stability  of  a  symmetrical  arch  har- 
ing  a  uniform  lire  load  covering  half  the  span.  Divide  the  arch  and 
its  load  into  sections,  as  shown  in  Fig.  128.  The  live  load  is  a  ver- 
tical force,  and  the  earth  presenre  would  give  a  horizontal  compo- 
nent. The  approximate  reduced-load  contour  for  the  vertical  forces 
is  shown  in  Fig.  138,  and  the  horizontal  and  vertical  components 
are  laid  oS  in  the  force  diagram.  An  equilibrium  polygon  can  be 
made  to  pass  through  any  three  points ;  and  therefore  we  may  as- 
sume three  points  for  a  trial  equilibrium  polygon, — as,  for  example, 
(1)  the  lower  limit  of  the  middle  third  of  the  joint  at  the  abutment 
A,  (2)  the  middle,  C,  of  the  crown  joint,  and  (3)  the  upper  limit 
of  the  middle  third  of  the  joint  at  B, 


ovGoQi^lc 


AST.  1.]  aahonal  ihbobt.  473^ 

CoQBtract  a  force  digram  by  Isying  off  the  external  forces  anc- 
cessirely  from  O  m  the  usual  way  (§  689),  selecting  a  pole,  P',  at  any 
point,  and  drawing  lines  connecting  J"  with  the  points  of  division 
of  the  load  line.  Then,  commenoing  at  A,  construct  an  eqnilib- 
rium  polygon  through  A,  C,  and  S',  by  the  method  explained  in 
gg  691-92. 

It  is  then  necessary  to  move  the  pole  of  the  force  diagram  in 
such  a  way  that  the  equilibrium  polygon  will  pass  through  B  instead 
of  B\  To  do  this,  draw  a  line  through  the  pole  F',  parallel  to  A  B' 
— the  closing  Hue  of  the  trial  equilibrium  polygon, — and  then 
through  H — thu  intersection  of  the  preceding  line  with  the  load 
line — draw  HP  parallel  to  AB,     The  new  pole^  P,  is  at  a  point 


on  this  line  such  that  HP  is  to  the  horizontal  distance  from  P  to- 
tlio  load  line  as  CD'  is  to  CD.  From  P  dmw  lines  to  the  points 
of  division  of  the  load  line,  and  then  construct  an  equilibrium 
polygon  through  A,  C,  and  B.  If  the  resulting  line  of  resistance 
does  not  lie  within  the  middle  third,  try  some  othor  position  of  the 
three  points  A,  C,  and  B  instead  of  aa  above.  If  a  line  of  resistance 
can  not  be  drawn  (see  g  694)  within  the  prescribed  limits,  then  the 
section  of  the  arch  ring  must  be  changed  so  as  to  include  the  line 
of  resistance  within  the  limits. 

694.  Criterion.  If  the  line  of  resistance,  when  constnicted  by 
any  of  the  preceding  methods,  does  not  lie  within  the  middle  third 
of  the  arch  ring,  the  following  process  may  be  employed  to  deter- 
mine whether  it  is  possible,  or  not,  to  draw  a  line  of  resistance  in 
the  middle  third. 

Assume,  for  example,  that  the  line  of  resistance  of  Fig.  139  lies. 


ovGoQi^lc 


ABCHBS.  [chap.  Xrill. 

'lird  at  a  aod  b.  TCezt  dntv  a  line  of  resist- 
ance through  e  and  d,  the  points  where 
Bonnale  from  a  and  b  intersect  the  outer 
and  inner  boundary  of  the  middle  third 
respectively.  To  paae  a  line  of  resistance 
through  c  and  d,  it  is  necessary  to  deter- 
mine the  value  and  point  of  application  of 
the  corresponding  crown  thrust.  The 
condition  which  makes  the  line  of  resist- 
ance pass  through  c  is :  the  thrust  mjLTi- 
FLIED  BT  the  vertical  distance  of  its  point 
I  EQUAL  TO  the  load  on  the  joint  at  c  mitlti- 
dietance  from  c.  The  condition  that  makes 
pass  through  d  is:  the  thrust  multiplied 
mce  its  point  of  application  is  above  c  and 
I  between  c  and  rf  I3  equal  to  the  load  on 
!D  BY  its  horizontal  distance  from  (/.  These 
lations  which  contain  two  unknown  qnanti- 
I  distance  its  point  of  application  is  above  c. 
nations,  the  line  of  resistance  can  be  drawn 
U ready  explained. 

resistance  lies  entirely  within  the  prescribed 
it  is  possible  to  draw  a  line  of  resistance 
and  line  does  not  lie  within  the  prescribed 
obable  that  a  line  of  resistance  can  be  drawn 
y  of  finding,  by  a  third  or  subsequent  trial, 
in  the  limits  can  not,  in  general,  be  answered 
possibility  depends  upon  the  form  of  the 

ice  drawn  through  IT  and  Fgoes  ontaide  of 

ae  extrados  only,  as  at  a,  the  second  line  of 
iwn  through  c  and  F;  and  if,  on  the  other 
lelow  the  intrados  only,  as  at  b,  the  second 
Lrough  V  and  d. 

EEOBT.*  This  theory  is  the  one  most  fre- 
is  based  upon  the  hypothesis  of  least  crown 
assumes  that  the  external  forces  are  verticaL 

ee  the  Eecund  footrnote  page  466. 


ovGoQi^lc 


SBJ.  1.]  soheffleb's  teeobt,  175 

This  theory  ia  frequently  referred  to  as  assninitig  that  the  arch 
stoQes  are  incompreeBible;  bat,  fairly  coDaidered,  such  is  not  the 
case.  Dr.  Scheffler  duvelops  the  theory  of  the  positioo  of  the  line 
of  pressures  for  incompreBsible  TonBsoirsj  but  subsequently  states 
that  the  compressibility  of  the  arch  stones  canses  the  line  of  resist- 
ance to  retreat  within  the  arch  ring  at  points  where  it  would  other- 
wise reach  the  edge.  He  also  says  that,  if  a  line  of  resistance  can 
be  drawn  within  the  arch  ring,  that  nowhere  approaches  nearer  the 
«dges  of  the  joint  than  one  fourth  of  its  depth,  the  stability  of  the 
arch  is.  assured. 

This  theory  will  be  illustrated  by  two  examples. 

696.  First  Example.  Assnine  that  it  ia  required  to  determine, 
in  accordance  with  this  theory,  the  line  of  resiatance  for  the  circular 
segmental  arch  shown  in  Fig.  130.     The  span  is  50  feet,  and  tb^ 


77 

/ 

/    y 

y 

J/ 

// 

'  '^V^ 

'-^  . 

k...J 

h 

rise  ia  10  feet  The  Touaeoirs  are  3  feet  6  inchee  deep,  and  the 
spandrel  wall  rises  2  feet  10  inches  above  the  summit  of  the  arch 
ring.  In  this  example  we  will  follow  the  explanation  used  bj 
SchefBer.* 

The  first  step  is  to  find  the  amount  and  the  point  of  application 

of  the  resultant  of  the  exterbal  forces  acting  on  the  portion  of  the 

arch  above  the  auccessiye  joints.     Divide  the  aemi-arch  and  the 

spandrel  wall  into  any  coUTcnient  number  of  parts  by  Tertical  lines 

*  Cain's  "  FraoUcBl  Tbeorf  of  the  Arch,"  pp.  38-44. 


ovGoQi^lc 


476  AMCHEB.  [CHAF.  XTHL 

thiDDgh  F,  G,  H,  I,  J,  and  K,  u  Ehown.  The  poatioiu  of  tbe  act- 
nal  joints  are  asgnmed  to  be  not  yet  fixed ;  bat,  for  temporarj  pnr- 
poaes,  aasDme  ndiil  joints  to  be  dnwn  through  F,  G,  H,  I,  J, 
Mid  K.  Then  the  kod  on  any  part  of  the  axvh  is  aasomed  to  be 
proportional  to  the  area  aboye  it, — for  example,  the  load  on  CHGR 
is  asamed  to  be  proportioDsl  to  the  area  CSPD* 

Having  determiued  the  ares  representiDg  the  toads,  it  is  then 
neceraary  to  determine  (1)  the  nnmerical  Tulaes  of  the  &eveia1  toads 
and  the  dJetances  of  their  centers  of  gravity  from  a  vertical  throogh 
the  crown,  and  (2f  the  amoant  and  the  position  of  the  center  of 
gravity  of  the  loads  above  any  joint  The  steps  necesary  for  this 
are  given  in  Table  60. 

The  quantities  in  column  3  of  Table  60  are  the  lengths  of  the 
medial  lines  of  the  several  trapezoids.     Colomn  6  contains  the 

■  Nottoe  that  TtaOy  the  load  on  the  joiiit  8H,  tor  example,  ts  SHXPOS,  and  doC 
CNPB  aa  aboTe.  The  error  la  kast  near  the  crowD  at  llal  Eeginenlal  •icbea,  umI 
icTfaUst  near  the  aprtngliig  of  aeml-ciidilar  onea.  The  enor  could  be  -'' "'""'"*  (1> 
Dy  finding  the  weights  o(  OJVH  and  BOHS  gepaiatelj  and  oHmblnliut  them  Into 
a  tititde  reanlUuil  for  the  weight  oa  the  johil  h'H.  as  waa  d<»ie  in  f  fiSI:  or  (^  bj- 
4ra«iDg  tlK  arub  to  a  large  scale  OD  thick  paiier  and  cutting  oat  the  aeTeral  Eii-mded 
a^tm  which  icpieacpt  the  loads,  wfaeti  the  amonnis  of  the  Bemal  loads  can  be- 
delencined  readUf  from  the  wel^ta  of  corresponding  sections  of  the  paper,  and  the 
center  of  giavltf  of  each  secdon  can  be  fonnd  by  balancing  It  on  a  knife  edge. 

SchelBer  gives  tbe  foDowlng  emi^cal  and  avP")ziniate  method  of  altering  tha 
position  of  the  joints  to  correct  this  eiror.  Let  J>CG.  Rg.  131,  be  the  tide  of  tli» 
trapezoid,  nod   CB  the  nncotrected  Joint    From  b,  the  middle  point  of  tlU,  diaw 


Fia.  ISl. 


0/>:ai»ddTaw  6c  parallel  to  6£,  and  eft  parallel  to  CS.  ThenwUleAbetbeoonected 
Joint.  Conrersetr.  haTlog  given  tbe  jobit  CH,  Fig.  133,  to  find  tbe  side  of  tbe  trape- 
T^id  which  limllB  tbe  portion  of  tbe  load  upon  il,  throogh  Cdraw  i>8Tertlcal,  and 
draw  C^  parallel  to  Dbl/>  being  tbe  middle  polot  ol  OH) ;  tfaen,  from  g,  draw  dg  ver- 
tical, and  we  have  tbe  desired  side  of  tbe  trapezoid. 


jvGooi^le 


3BT.  1.] 


schbppi-eb's  THBOBT. 


TABLE  60. 

APFLicATioir  or  Soheftlbb's  Tbeobt  to  t&x  Abcr  Riko  bhowk  di 

Fib.  180,  pacib  47S. 


. 

.  1  . 1  . 

1 

1     • 

7 

• 

' 

1 

i 

The  Abodct.  and  Poamon 
Ckiteii  or  QttArm.  or 
aiv>BALLo*ra 

THB 

1                          TH«  BCT* 

E-'H 

Cdtie 

iBotm 

il 

1 1-^ 

1  sl 
■   =5 

IS 

ill 

III 

lii 
K 

it 

|lsi 

Height. 

width. 

Arofc 

s 

?;1 

1.7(1 

11 

il 

ei..w 

,11 

MS 

ill 

slTTlisi 

1 
.;J 

!i 

prodncts  of  tho  Dnmbere  in  columtiB  4  and  5.  Oolnmn  7  contains 
the  continned  sums  of  the  quantities  in  column  4.  Column  8  con- 
tains the  continned  sums  of  the  quantities  in  column  6.  Column  9 
is  found  by  the  principle  of  analytical  mechanics  :  the  distance 
of  the  center  of  parallel  forces  from  any  point  is  equal  to  the  sum 
ot  the  momenta  of  the  several  forces  about  that  point  divided  by 
the  sum  of  the  several  forces;  and  hence  the  numbers  in  column 
9  are  found  by  dividing  the  quantities  in  column  8  by  the  corre- 
sponding quantity  in  column  7. 

697.  The  second  step  is  to  find  the  minimum  thrust  which 
applied  at  U  ( UF  =  J  FE)  is  enfficient  to  prevent  the  semi-arch 
from  rotating.  The  origin  of  moments  is  considered  as  being  in 
the  successive  joints  at  one  third  of  the  depth  of  each  from  the 
intradoa. 

If  T=  the  thrust  and  y  —  ite  arms,  and  W=:  the  load  above 
any  joint  and  a;  =  its  ariU)  then  for  equilibrium  about  any  joint 


Wx 


as) 


rt  is  required  to  find  the  maximum  value  of  T. 


ovGoQi^lc 


[chap,  iviil 


The  W— in  terms  of  the  weieht  of  a  cubic  foot  of  the  masonrv — 


ovGoQi^lc 

J 


4RT.  l.j  bohepfleb's  thsobt.  47& 

nets.  Lay  off,  vertically,  a  diatance  a6  equai  to  the  first  quantity 
in  colamn  2of  Table  61;  this  tine  represents  the  weight  of  the  first 
Tooesoir  and  the  load  resting  upon  it.  From  b  lay  oS,  horizontally 
to  the  right,  a  distant''  //v  i^qual  to  tJie  last  quantity  in  column  7  of 
Table  61.  This  line  represents  the  horizontal  pressure  at  the  crown. 
Then,  by  the  principle  of  the  triangle  of  forces,  a  line  ca  repre- 
sents the  resultant  pressure  on  the  joint  BG;  and  this  line  pro- 
longed intersects  the  joint  RO  at  d,  which  is,  therefore,  the  center 
of  pressure  on  that  joint. 

To  find  the  center  of  presanre  on  the  second  joint,  lay  oft  from 
U,  horizontally  to  the  left,  a  distance  equal  to  the  second  quantity 
in  column  4  of  Table  61;  erect  a  vertical  equal  to  the  second  quan- 
tity in  column  3;  and  from  the  point  thus  found  lay  off,  horizon- 
tally to  the  right,  a  quantity  equal  to  the  last  quantity  in  column  7. 
Then  draw  the  third  side  of  the  triangle  of  forces,  and  prolong  it 
until  it  intersects  the  joint  at  e. 

By  a  similar  constmction,  the  centers  of  pressure  for  the  several 
joints  are  determined  to  be  f,  d,  e,f,  g,  h,  and  6,  as  shown  in  Fig. 
130.  A  line  joining  these  points  is  the  line  of  resistance  (not  shown 
in  the  figure). 

699.  The  preceding  method  of  drawing  the  line  of  resistance 
has  two  advantages :  (1)  The  center  of  pressure  dn  any  joint  may 
be  found  at  once;  and  (2)  any  small  error  in  draughting  is  confined 
to  the  joint  where  it  first  occurs.  Notice,  however,  that  the  method 
is  applicable  onlr  wJieu  the  horizontal  component  of  the  pressure  on 
the  several  joints  is  constant;  that  is,  this  method  is  applicable  only 
when  the  external  forces  are  assumed  to  be  vertical. 

Having  determined  the  line  of  resistance  by  the  above  method, 
the  stability  of  the  arch  can  be  discussed  as  described  in  g  690. 

700.  Second  Example.  Let  ns  construct,  according  to  this 
theory,  the  line  of  resistance  for  the  semi-arch  shown  in  Fig.  133, 
page  480,  which  is  the  same  one  discussed  in  §  681,  where  it  was 
shown  that  joint  4  is  the  joint  of  rupture,  and  that,  if  the  horizon- 
tal forces  be  disregarded,  the  maximum  crown  thrust  is  8,748 
pounds  (see  Table  59,  page  459). 

The  crown  thrust  is  laid  off,  to  any  convenient  scale,  from  S 
to  0 ;  and  the  loads  as  given  in  Table  59  are  laid  off,  to  the  same 
scale,   enccessively  from  0  downwards.     The    remainder    of    the 


ovGoQi^lc 


480  ABCHBS.  [chap.  XTIII. 

coustruction — ehown    b;  dash    lines — is  exactly  similar  to  that 
described  in  §  689  in  connectloD  with  Pig.  135,  page  467.- 


' 

V 

!«. 

Al. 

i^     i- 


701.  Erroneou  Applioatiou.  Frequent];  the  principle  of  the 
joint  of  rnptore  is  entirely  and  improperly  neglected  in  applying 
this  theory;  that  is  to  say,  the  crown  throst  employed  in  detemun- 


D.qitizeabvG00l^lc 


AET.  1.]  aCHBFFLBE'a  THEORY.  431 

ing  the  line  of  resistance  is  that  which  wonld  prodnce  equilibrium 
of  rotation  about  the  tpringhig  line,  instead  of  that  which  would 
produce  equilibrium  about  the  Joint  of  rupture.    5'or  example, 

instead  of  employing  the  maximum  Talue  in  the column  of 

Table  59,  page  459,  the  last  quantity  in  that  column  is  used. 

The  line  of  resistance  obtained  by  this  method  is  shown  in  Fig. 
133  (page  480)  by  the  dotted  line,  the  crown  thrust  (6,990,  as  com- 
puted in  Table  59,  page  459)  being  laid  off  from  CtoO,to  the  scale 
employed  in  laying  off  the  load  line. 

702.  The  error  of  this  method  is  shown,  incidentally,  in  §g  678^ 
82  and  §g  €88-701,  and  needs  no  further  explanation. 

The  amount  of  the  error  is  illustrated  in  Fig.  133.  According 
to  this  analysis,  the  line  of  resistance  is  tangent  to  the  intrados, 
which  seems  to  show  that  the  arch  can  not  stand  for  a  moment. 
However,  many  such  arches  do  stand,  and  carry  a  heavy  railroad 
traffic  without  any  signs  of  weakness  ;  and  further,  any  reasonable 
method  of  analysis  shows  that  the  arch  is  not  only  safe,  but  even 
extravagantly  so  (g  690). 

This  method  of  analysis  certainly  accounts  for  some,  and  per- 
haps many,  of  the  excessively  heavy  arches  built  in  the  past.  For 
example,  compare  8  and  9,  1?  and  18,  33  and  34,  53  and  54,  etc., 
of  Table  63  (page  602). 

703.  BeUahility  of  8cheffler's  Theory.  For  the  sake  of  com- 
parisons,  the  line  of  resistance  according  to  the  Rational  Theory 
{§§  688-94),  as  determined  in  Fig.  136  (page  467),  is  shown  in  Fig. 
133  by  the  solid  lines.  (Notice  that  Fig.  133  gives  the  lines  of  re- 
sistance, and  not  the  oquilibrium  polygons  as  in  Fig.  135.)  In  this 
particular  case,  the  difference  between  the  two  lines  above  the  joint 
of  rupture  is  not  material  ;  but  the  difference  below  that  joint  has 
a  very  important  effect  upon  the  thickness  of  the  arch  at  the  spring- 
ing, and  also  upon. the  thickness  of  the  abutment  (g  712). 

If  the  maximum  ratio  of  the  horizontal  to  the  vertical  compo- 
nent of  the  Qxterual  forces  (see  Qrst  paragraph  on  page  460)  had 
been  employed  in  determining  the  crown  thrust  and  the  line  of 
resistance,  there  would  have  been  a  material  diflerenoe  in  the  posi- 
tion of  both  the  joint  of  rupture  and  the  line  of  resistance  above 
that  joint.  Although  the  horizontal  components  of  the  external 
forces  can  not  be  accurately  determined,  any  theory  that  disregards 


ovGoQi^lc 


483  ABCHE8.  [CUAF.  ZTIII. 

the  existence  of  these  forces  can  not  be  considered  more  than  & 
loose  approximation. 

704.  Saskihe'b  Teeobt.  Althongh  this  theory  has  long  been 
before  the  public  and  is  ia  some  respects  much  superior  to  the  one 
in  common  use,  it  is  comparatively  but  little  employed  in  practice. 
This  is  probably  due,  in  part  at  least,  to  the  fact  that  Bankine's 
discussion  of  the  theory  of  the  masonry  arch  is  not  very  simple  nor 
very  clearly  stated,  besides  being  distributed  througbont  various 
parts  of  his  works.* 

Kankino  determines  the  thrust  at  the  crown  by  ffavier's  princi- 
ple (§  685) ;  but  he  makes  no  special  assumption  as  to  the  point  of 
application  of  this  thrust,  further  than  to  aesame  that  if  a  line  of 
resistance  can  be  drawn  anywhere  within  the  middle  third  of  the 
arch  ring,  the  arch  is  stable- 
In  that  part  of  his  books  which  precedes  the  discnssion  of  arches, 
Baokine  investigates  the  various  curves  which  a  cord  will  assume 
under  different  distributions  of  the  load  ;  and  subsequently  adopts 
these  curves  as  the  form  which  the  line  of  resistance  of  an  arch 
similarly  loaded  should  have.  The  discussion  of  these  curves  con- 
stitutes the  most  valuable  part  of  his  investigations  concerning  the 
stability  of  the  masonry  arch. 

705.  Cnrvatnre  of  the  Linear  Aroh.  The  curves  assumed  by 
a  cord  under  the  varions  conditions  of  loading,  can  be  applied  to 
linear  arches  (the  line  of  resistance  of  actual  arches)  by  imagining- 
that  the  burve  of  the  cord  is  reversed,  and  that  the  cord  itself  is 
replaced  by  a  thin  metal  strip,  which,  like  the  cord,  shall  be  prac- 
tically without  transverse  strength,  bnt  which,  unlike  the  cord, 
shall  be  able  at  every  point  to  resist  a  compressive  force  in  the  di- 
rection of  its  length.  The  amount  and  distribution  of  the  external 
forces  are  the  same  in  both  cases  ;  but  with  the  cord  they  act  out- 
ward, while  with  the  linear  arch  they  act  inward.  The  formulas 
and  diagrams  are  essentiaUy  the  same  in  both  cases.  The  curves 
assumed  by  a  suspended  cord  under  various  distributions  of  the 
load  will  now  he  briefly  considered.  In  each  case  it  will  be  assumed 
that  the  ends  of  the  suspended  cord  and  also  of  the  corresponding 
linear  arch  are  in  the  same  horizontal  line. 

1.  If  the  cord  is  acted  upon  by  vertical  loads  distributed  aiii- 

■  "ClTilEDgli>eeriiig,"aiid  "Applied  Meobuilcs." 


ovGoQi^lc 


ART.   l.J  BANKINE'B  theory.  4tiS 

formij  along  tbe  horizontal,  it  will  aasQme  the  form  of  a  parabola. 
This  case  does  not  occur  with  masonry  arches. 

2.  It  the  load  is  vertical  and  dietribnted  uniformly  along  the 
curve,  the  reealting  carye  ia  the  common  catenary,  of  which  the 
equation  is 

y=  !(£-+«--) (13) 

in  which  y  is  the  ordinate  to  any  point,  m  the  ordinate  to  the  apex, 
E  the  blue  of  the  Naperian  logarithms,  and  x  the  abscissa  corre- 
sponding to  y.  Approximately,  this  case  may  occur  with  masonry 
arches,  since  the  above  law  of  loading  is  nearly  that  of  an  arch 
whose  iutrados  is  the  common  catenary  and  which  supports  a  span- 
drel wall  of  masonry  having  a  horizontal  upper  surface  (see  2,  page 
445). 

3.  Three  points  fix  the  common  catenary  ;  and  hence,  if  the  posi- 
tion of  the  springing  lines  and  the  crown  are  assumed,  the  depth  of 
the  load  at  the  crown  is  fixed  by  the  equation  of  the  curve.  This 
limitation  would  often  interfere  with  the  use  of  the  common  cate- 
nary in  building  arches.  To  meet  this  difficulty,  Rankine  trans- 
forms the  common  catenary  by  the  principle  of  what  he  calls  paral- 

.  lei  projections,  i,  «.,  by  increasing  or  decreasing  one  set  of  the 
rectangular  co-ordinates  to  the  curve  without  changing  the  other, 
and  obtains  the  transformed  catenary.  The  equation  of  the 
curve  ia 

y  =  f  |.B--H^^-|,     ...    .    .     (14) 

in  which  y,  ia  the  ordinate  to  tbe  apex,  and  m  is  the  modulus  of  the 
curve  and  ia  found  by  the  formula 

(16) 
byp.  log. 

The  determination  of  values  of  y  by  equation  (14)  is  not  easy  except 
with  either  a  table  of  Naperian  logarithms  or  a  table  of  results 
deduced  therefrom,  and  even  then  it  is  tedioua. 

With  this  curve  we  may  assume  the  springing  lines,  the  crown, 
and  the  depth  of  load  at  the  crown,  and  then  compute  the  curve  of 
equilibrium.  The  transformed  catenary  differs  from  a  circular  arc 
between  the  same  pointa  only  in  being  slightly  (and  frequently  only 


ovGoo^^lc 


484 


[chap.  svin. 


Tery  slightly)  sharper  in  the  haunches ;  and  hence  it  ia  not  necea- 
uary  to  discuss  it  further.* 

4.  If  the  load  is  uniform  and  normal  at  every  point,  the  curre 
of  equilibrium  ia  plainly  a  circle.  An  example  of  this  case  would  be 
an  empty  maeonry  shaft  standing  in  water. 

5.  The  ellipse  ia  the  form  assumed  by  a  cord  under  a  load  com- 
posed of  horizontal  and  vertical  components  which  are  constant 
ulong  the  horizontal  and  vertical  lines,  but  which  differ  from  each 
other  in  intensity.  There  is  no  case  in  ordinary  practice  where  the 
preeauree  upon  an  arch  are  strictly  identical  with  those  which  give 
an  elliptical  curve  of  equilibrium.  The  curve  of  equilibrium  of  a 
tunnel  arch  through  earth;  when  the  depth  below  the  surface  is 
great  compared  with  the  rise  of  the  arch  itself,  approximates  to  an 
ellipse.  The  load  is  nearly  uniform  along  the  horizontal,  whUe  the 
horizontal  force  at  any  point  is  some  frjictional  part  of  the  vertical 
one  at  the  same  point ;  and  therefore  the  horizontal  forces  are 
nearly  uniform.  It  is  readily  shown  that  the  intensity  (the  pressure 
per  unit  of  area  perpendicular  to  the  force)  of  the  vertical  com- 
ponent t,f  to  that  of  the  horizontal  component  as  the  square  of  tlie 
vertical  diameter  of  the  ellipse  is  to  the  square  of  its  horizontal 
diameter  ;f  that  is  to  say. 


the  horizontal  axis  _  ./intensity  of  horizontal  component  . 
the  vertical  axis  ~~  intensity  of  vertical  component  "  '  ' 
6.  If  the  forces  acting  on  the  linear  arch  are  normal  and 
increase  in  intensity  in  proportion  to  the  distance  of  the  points  of 
application  from  a  horizontal  line,  the  curve  is  a  hydroxfatic  arch. 
A  tunnel  under  water  is  an  example  of  this  method  of  loading. 
The  form  of  the  curve  is  shown  in  Fig.  134,  of  which  only  the  portion 

3 BJ  C  is  avHilable  in  the  construction  of 

arches.     The  equation  of  the  curve  is 

p  ft  =  w  p„  Pa  =  a  constant,    .  (17) 

^  in  which  p  is  the  normal  pressure  on  a 

unit  area  at  any  point,  p  the  radios  of 

*  For  two  nomericd  examples  of  the  method  of  employlag  tbe  transformed  cale- 

nuj  in  tbe  deeign  of   an  areb,  see  an  article  hj  W.  H.  Booth  In  Van  Nostrand'a 

Engin'R  Mag.,  vol.  zizl,  pp.  I-IO ;  and  for  oao^er.  8ee  an  editorial  li 

Keum,  vol.  ivlll,  p.  372. 

1  Rankine's  Civil  Engineering,  p.  20B. 


Fra.  131. 


ovGoQi^lc 


AKT.   I.J  BANKINE'S  THEOBY.  4tl3 

ciUT&tnre  at  the  same  point,  y  the  distance  from  the  line  0  (the 
snr&tce)  to  any  point,  p^  and  y^  the  viiiues  of  p  and  y  for  the  point 
A,  and  v>  the  veight  of  a  unit  of  volume  of  the  loading. 

"  The  true  semi-ellipse  of  a  given  span  and  rise  differs  from  the 
hydrostatic  arch  by  being  of  somewhat  shai-pcr  curvature  at  the 
crown  and  springing  and  of  Bomewhat  flatter  curvature  at  th« 
haunches,  and  by  enclosing  a  somewhat  less  area.  The  application 
of  the  hydrostatic  arch  to  practice  is  founded  on  the  fact  that  every 
arch,  after  having  been  built,  subsideB  at  the  crown,  and  spreads, 
or  tends  to  spread,  at  the  haunches,  which  therefore  press  horizon- 
tally against  the  filling  of  the  spandrels ;  from  which  it  is  inferred 
as  probable  that,  if  an  arch  be  built  of  a  figure  suited  to  equilibrium 
under  fluid  pressure — i.  e.,  pressure  of  equal  intensity  in  all  direc- 
tions,— it  wilt  spread  horizontally,  and  compress  the  masonry  of  the 
spandrels  until  the  horizontal  pressure  at  each  point  becomes  of 
equal  intensity  to  the  vertical  pressure,  and  is  therefore  suf&clent  to 
keep  the  arch  in  equilibrio."  • 

7.  If  the  vertical  and  the  horizontal  components  of  the  normal 
force  differ  from  each  other  but  both  vary  as  the  distance  of  the 
point  of  application  from  a  horizontal  line,  the  curve  of  equilbrium 
is  the  gtostatic  arch.  An  arch  in  clean  dry  sand  is  the  best  example 
of  this  form  of  loading.  The  geostafcic  arch  bears  the  same  relation 
to  the  hydrostatic  arch  that  the  ellipse  does  to  the  circle.  The 
geostatic  curve  can  be  produced  from  that  of  the  hydrostatic  curve 
by  increasing  or  decreasing  one  set  of  ordinates  without  altering  the 
other.  If  px  be  the  horizontal  intensity  of  the  forces  acting  on  the 
hydrostatic  arch  and  p'^  be  that  for  the  geostatic  arch,  then 
p^  =  cp\ ;  and  if  x  is  the  horizontal  diameter  at  any  point  of 
the  hydrostatic  curve  and  z'  the  same  for  the  geostatic,  then 
x'  =  c3:.t 

8.  Rankine  next  discusses  the  following  more  general  problem  : 
"  Given  the  curve  of  a  linear  arch  and  the  vertical  components  of  a 
symmetrical  load,  to  find  the  intensity  and  distribution  of  the 
horizontal  components  necessary  to  produce  equilibrium. 

■  RBDklne'B  Civil  Englueerlug,  pp.  419-30. 

t  For  a  oumericat  ezampte  of  tbe  method  of  emplorlng  th«  seoBtatlc  <nirv«  for  Ui« 
iDlrados  at  tunnel  orcbee,  see  an  Brttcle— ' '  The  Emptoyment  of  HBthamatlokt  CnrraB 
as  the  InUados  of  Arobf"— br  W.  H.  Booth  in  T&n  NoBtnnd's  Engln'g  Hag.,  itA. 
xzz,  pp.  SSti-OO. 


ovGoQi^lc 


ABCHI&  [chap.  xnu. 

"Let  V  =the  Tcrtical  load  on  »ay  arc  DC, — represented  in 

F%.  135by  theUneff?; 
F,  =  the  Tertical  load  on  the  semi-arch  AC; 
ff  =  the  horizontal  load  on  any  arc  DC, — represented  by 

the  line  OF,  Fig.  135 ; 
ff,  =  the  horizontal  load  on  the  semi-arch  A  C; 
H,  =  the  compreasion  at  the  crown  C, — represented  by  the 

line  EC,  Fig.  135; 
O  =  the  compresaion  on  the  rib  at  any  point  D, — repre- 
sented by  ED,  Fig.  135  ; 
p,  =  the  intensity  of  the  horizontal  force,  t.  e.,  the  force 

pcrnnitof  area  perpendicular  to  its  line  of  action : 
p,  =  the  intensity  of  the  Tertical  force; 
P,  =  the  valoe  of  ^,  at  the  crown  C; 
A  =  the  radins  of  cnrrature  at  the  crown  C; 
i    =  the  angle  that  the  tangent  of  the  linear  arch  at  any 

point  makes  with  the  horizontal, — that  is,  t  =  the 

angle  EDO,  Fig.  135. 


Fra.  Ut. 


"Then       V=  ["  p,dx; (18) 

C=  Fcoaeci; (19) 

H-  Fcott; .    (20) 

„_dff_      d(Fcott)_      "Vdyl 

-'  The  integration  constant  for  (21)  is  R, ;  and  is  fonnd  by  equa- 
tion (1I)»  pttge  465,  which,  in  the  above  nomenclature,  becomes 

ff,=P*P»-" (82) 


ovGoQi^lc 


ABT.  1.]  RANKINB'S  THEORY.  4S7 

However,  lueforo  conclading.  this  phase  of  the  discuEsion  ot 
arches,  it  is  well  to  state  that  the  only  arches  in  common  use  are 
the  circular — cither  semi-circnlar  or  segmental — and  the  elliptic. 

706.  Stability  of  any  FropoKd  Arch,  To  apply  the  preceding 
principles  in  designing  an  arch,  it  is  necessary  to  know  both  the 
vertical  and  the  horizontal  forces  acting  on  the  arch.  Rankine 
assumes'"  (1)  that  the  vertical  force  acting  on  any  part  is  the  weight 
of  the  masonry,  earth,  or  other  load  vertically  above  the  same;  and 
^2)  that  the  horizontal  pressure  of  earth  is  given  by  the  formula 

J'.  =  »i|~S^' (23) 

1  +  Sin  0  '  '     ' 

ill  which  px  is  the  horizontal  intensity  at  any  point,  to  the  weight  of 
a  unit  of  the  t^arth,  (/  the  depth  of  earth  over  the  point,  and  0  tho 
angle  of  re|>ose.  In  the  above  nomenclature,  the  vertical  inten- 
sity is 

P,=  ivd. (24) 

By  an  application  of  those  two  principles  are  to  be  determined  the 
amount  and  distribution  of  the  vertical  and  the  horizontal  forces 
acting  on  the  arch;  and  then  the  equilibrium  curve  corresponding 
to  this  form  of  loading  (see  g  703)  is  to  be  adopted  for  the  intrados 
■of  the  proposed  arch. 

For  an  example,  take  the  case  of  an  arch  under  a  high  bank  of 
«arth  whose  angle  of  repose  is  30°.  Strictly,  the  curve  of  equi- 
librium is  the  geostatic  arch  (see  paragraph  7,  §  705);  but  it  will 
be  more  simple  and  sufBciently  exact,  if  we  assume  it  to  be  an 
«1]ipBe,  which  is  equivalent  to  assuming  that  the  rise  of  the  arch  is 
inconsiderable  in  comparison  with  the  depth  of  earth  over  it.  The 
intrados  is  then  tn  be  an  ellip)^  in  which 

the  vertical  axis    =|/K  =  j/l  +  B'P  0  _  ^        ,^^^ 
(lie  horiwntal  axis  Pm  1  —  sin  0  •  ■     \     / 

"If  the  earth  is  firm,  and  little  liable  to  be  disturbed,  the  propor- 
tion of  the  half-span — or  horizontal  semi-axis — to  the  rise — or  ver- 

•  Civn  Eogtaeeriag,  p.  «4. 

t  Rankine  ataUa  <ClTfl  Bngtneeiing,  p.  330)  that  the  boliiontal  preasnra  can  not 
be  grMfar  than  w  ft  i-.wj' *"********  " '^I'lgln^-  NoUoe  that  the  valoo  employed 
atere  la  ae  l^lmtiB. 


ovGoQi^lc 


488  ABCHBS.  [chap.  XVHI. 

tical  Bemi-axis — may  be  made  greater  than  js  given,  by  the  preced- 
ing eqnation,  and  the  earth  will  still  resist  the  additional  horizontal 
thruBt ;  bat  that  proportion  shoold  never  be  made  less  than  the 
value  given  by  the  equation,  or  the  sides  of  the  archway  will  be  in 
danger  of  being  forced  iuwarda."  * 

"  There  are  numerone  cases  in  wMch  the  form  of  the  linear  rib 
Baited  to  sustain  a  given  load  may  at  once  be  adopted  for  the  in- 
trades  of  a  real  arch  for  sustaining  the  same  load,  with  sufficient 
a  exactness  forpractical  purposes.  The  follow- 
Ling  is  the  test  whether  this  method  is  appli- 
cable in  any  given  case.  Let  A  CB  in  "Fig. 
136  be  one  half  of  the  ideal  rib  which  it  is 
proposed  to  adopt  as  the  intrados  of  a  real 
arch.  Draw  Aa  normal  to  the  rib  at  the 
crown,  so  as  to  represent  a  length  not  ex- 
ceeding two  thirds  of  the  intended  depth  of 
Draw  a  normal .  Bb  at  the  springing  of  a  length. 


Bb  _  thrust  along  rib  at  A  „  ^ 
la' 


(26> 


The  thrust  at  .^  is  found  by  eqnation  (11),  page  465  ;  and  the  thrust 
at  any  other  point  is  given  by  equation  (19),  page  486.  Construct 
a  line  acb  such  that  its  perpendicular  distance  from  the  intrados  at 
any  point,  cC,  is  inversely  as  the  thrust  along  the  rib  at  that  point. 
Then  if  acb  lies  within  the  middle  third  of  the  proposed  arch  ring, 
the  ideal  rib  ACB  is  of  a  suitable  form  for  the  intrados. 

707.  Rankine's  general  method  of  determining  the  stability  of 
a  proposed  arch  is  as  follows :  t 

"The  first  step  towards  determining  whether  a  proposed  arch 
will  be  stable,  is  to  assume  a  linear  arch  parallel  to  the  intrados  or 
sofiBt  of  the  proposed  urcli,  and  loaded  vertically  with  the  same 
weight,  distributed  in  the  same  manner.  Then  by  equation  (21), 
page  486,  determine  either  a  general  expresaion,  or  a  series  of  vul- 
ues,  of  the  intensity  p^  of  the  conjugate  pressure,  horizontal  or 
oblique  as  the  case  may  be,  required  to  keep  the  arch  in  equilibrio 

•  Rankine's  Civil  Engineering,  p.  484. 

t  Jbid.,  p.  417, 

X  IIAI.,  pp.  431-33. 


ovGoQi^lc 


AKT.   1.]  RANEINB'S  THEORY.  489 

nnder  the  giyen  vertical  load.  If  that  presanre  is  nowhere  nega- 
tive, a  carve,  nmllar  to  the  aeEomed  arch,  drawQ  throagh  the  middle 
of  the  arch  ring  will  be,  either  exactly  or  very  nearly,  the  line  of 
preBBore  of  the  proposed  arch;  p,  will  repreBent,  either  exactly  or 
very  nearly,  the  tntenaity  of  the  lateral  pressure  which  the  real 
arch,  tending  to  spread  oatwards  under  its  load,  will  exert  at  each 
point  against  its  spandrel  and  abutments;  and  the  thrust  along  the 
linear  arch  at  each  point  will  be  the  thrust  of  the  real  arch  at  the 
corresponding  joint. 

"  On  the  other  hand,  if  p^  has  some  negative  values  for  th& 
assumed  linear  arch,  there  must  be  a  pair  of  points  in  that  arch 
where  that  quantity  changes  from  positive  to  negative,  and  is  equal 
to  nothing.  The  angle  of  inclination  i  at  thiit  point,  called  the- 
aitgle  of  rupture,  ia  to  be  determined  by  placing  the  second  member 
of  equation  (21),  page  486,  equal  to  zero  and  solving  for  cot  i.  The 
corresponding  joints  in  the  real  arch  are  called  the  joints  of  rup- 
ture ;  and  it  is  below  those  joints  that  conjugate  pressure*  from 
without  is  required  to  sustain  the  arch  and  that  consequently  th? 
backing  must  be  built  with  squared  side- joints. 

"In  Fig.  137,  let  SCA  represent  one  half  of  a  aymmetrica.' 
arch,  KLDB  an  abutment,  and  C 
the  joint  of  rupture — found  by  the 
method  already  described.  The  point 
of  rupture,  which  is  the  center  of  re- 
sistance of  the  joint  of  rupture,  is 
somewhere  within  the  middle  third 
of  the  depth  of  that  joint;  and  from 
that  point  down  to  the  springing  joint 
B,  the  line  of  pressure  is  a  curve  sim- 
ilar to  the  assumed  linear  arch,  and  C— 
paralltl  to  the  intrados,  being  kept  in  fm.  m, 

equilibi'io  by  the  lateral  pressui-e  between  the  arch,  and  its  spandrel 
and  abutment. 

"  From  the  joint  of  rupture  C  to  the  crown  A,  the  figure  of  the 
true  line  of  presanre  is  determined  by  the  condition  that  it  shall  be 


ovGoQi^lc 


490  ARCHES.  [CHAP.    XVIII, 

i  linear  arch  balanced  nnder  vertical  forces  only ;  *  that  is  to  say, 
the  horizontal  component  of  the  thmst  along  it  at  each  point  ie  a 
constant  quantity,  and  equal  to  the  horizontal  component  of  the 
thrust  along  the  arch  at  the  joint  of  rupture. 

"The  only  point  in  the  line  of  pressure  above  the  joint  of 
rupture  which  it  is  important  to  determine  ie  that  of  the  crown  of 
the  arch.  A;  and  it  is  foilud  in  the  following  manner  :  Find  the 
center  of  gravity  of  the  load  between  the  joint  of  rupture  C  and  the 
crown  J I  and  draw  tlirough  that  center  of  gi-avity  a  vertical  line. 
Then  if  it  be  possible,  from  any  point,  such  as  M,  in  that  vertical 
line,  to  draw  a  pair  of  lines,  one  parallel  to  a  tangent  to  the  sof&t  at 
the  joint  of  rupture  and  the  otlier  parallel  to  a  tangent  to  the  soffit 
at  the  crown,  so  that  the  former  of  those  lines  shall  cut  the  joint  of 
rupture  and  the  latter  the  keystone,  in  a  pair  of  points  which  are 
both  within  the  middle  third  of  the  depth  of  the  arch  ring,  the 
stability  of  the  arch  will  be  secure ;  and  if  the  first  point  be  the 
point  of  rapture,  the  second  will  be  the  center  of  resistance  at 
the  crown  of  the  arch  and  the  crown  of  the  true  line  of  preasnres. 

"  When  the  pair  of  points,  related  to  each  other  as  above,  do  not 
fall  at  opposite  limits  of  the  middle  third  of  the  arch  ring,  their 
«iac't  positions  arc  to  a  small  extent  uncertain  ;  but  that  uncertainty 
is  of  no  consequence  in  practice.  Their  most  probable  positions  are 
equidistant  from  the  middle  lino  of  the  arch  ring, 

"Should  the  pair  of  points  fall  beyond  the  middle  third  of  the 
arch  ring,  the  depth  of  the  arch  stones  mast  be  increased." 

708.  Beliabllity  of  Bankine's  Theory.  1.  This  tbeoiy  is  ap- 
proximate since  it  makes  no  attempt  to  determine  the  trne  line  of 
resistance,  but  finds  only  a  line  of  resistance  which  lies  within  the 
middle  third  of  the  arch  ring. 

2.  The  value  of  the  radius  of  curvature  to  be  used  in  finding 
the  crown  thmst  is  indeterminate.  It  is  frequently,  but  erroneously, 
taken  as  the  radios  of  the  intrados  at  the  crown. 

3.  The  method  of  finding  the  center  of  preasnre  at  the  crown 
and  also  at  the  joint  of  rupture  assumes  that  the  portion  CMA, 
Fig.  137,  is  acted  upon  by  only  three  forces ;  viz.,  the  vertical  load, 
the  thmst  at  the  crown,  and  the  pressure  on  the  joint  of  mptare. 

*  Tram  this  It  appears  that  Ranldne  h1m«elf  dlBregards,  for  that  part  of  the  apch 
«boTe  the  Joint  of  ruptnre,  the  principal  characteristio  of  his  theory,  tIz.  :  the  reoog> 
nltlon  ot  the  horizontal  componecta  of  the  estwnal  fotoea ;  ud  benoe  tilts  Umkuj 
Is,  In  fMt,  the  nine  as  Bcbefllw<»  IM  a»-7W. 


ovGoQi^lc 


A.BT.   1.]  BAJTSIKe's  TBBOKT.  491 

This  is  erroueoaa  (a)  beoanse  it  neglects  the  horizontal  components 
of  the  external  forces,  and  hence  the  actual  center  of  pressure  at 
the  joint  of  rupture  is  nearer  the  intrados  than  the  position  of  0 
as  found  in  Fig.  137  ;  and  {h)  because  it  finds  a  new  value  for  the 
thrust  at  the  crown  which,  in  general,  will  differ  from  that  employed 
in  finding  the  position  of  the  joint  of  rupture. 

4.  Bankine  himself  says  that  the  method  of  §  707  is  inapplicable 
to  a  circular  arch  greater  than  90°,  and  gives  a  complicated  formula 
for  that  case. 

Kankine's  theory  is  more  complicated  and  less  accurate  than 
either  Scheffler's  (g  695)  or  the  rational  theory  (g  688). 

709.  Othik  Thxobieb  OF  THE  AXCH.  There  are  several  methods, 
in  more  or  less  common  use,  of  determiniug  the  stability  of  the  vons- 
fioir  arch,  many  of  which  are  but  different  combinations  of  the  pre- 
ceding principles,  while  some  have  a  much  less  satisfactory  basis. 
It  is  not  necees..ry  to  discuss  any  of  these  at  length ;  but  there  is 
one  which,  owing  to  the  frequency  with  which  it  ia  employed, 
requires  a  few  words.  It  is  the  same  as  Scheffler's  (§§  695-703),  ex- 
cept in  assuming  that  the  line  of  resistance  passes  through  the 
middle  of  the  crown  joint  and  also  through  the  middle  of  the  spring- 
ing joint.  The  line  of  resistance  is  then  determined  in  any  one  of 
a  number  of  ways ;  and  the  arch  is  said  to  be  stable,  if  the  line  of 
resistance  lies  in  the  middle  third  of  the  section  of  the  arch  ring. 
This  theory  Is  much  less  satisfactory  than  Scheffler'a  and  possesses 
no  advantage  over  it. 

710:  Tezoxt  OF  THs  Elastic  AsoH.  It  has  long  been  recognized 
that  all  theories  for  the  voussoir  arch  are  very  unsatisfactory  ;  and 
hence  it  has  been  proposed  to  consider  the  masonry  arch  as  an 
«lastic  curved  beam  fixed  at  its  ends,  and  examine  its  stability  by 
the  principles  employed  in  computing  the  strains  in  arches  of  iron 
or  wood.  There  is  no  essential  difference,  as  far  as  the  theory  is 
concerned,  between  the  iron  and  the  stone  arch ;  but  there  ia  great 
difficulty  in  applying  the  mathematical  theory  of  elasticity  to  the 
masonry  arch.  The  theory  of  elasticity  when  applied  to  the 
masonry  arch  has  the  following  sources  of  error,  in  addition  to  those 
of  the  ordinary  theory  of  the  elastic  arch  :  1.  There  is  great  un- 
certainty as  to  the  external  forces  {§  666).  %  We  have  no  definite 
knowledge  concerning  either  the  modulus  of  olseticity  {g§  16  and 
146)  or  the  ultimate  strength  of  masonry  {§§  221-23,  and  g|  246- 


ovGoQi^lc 


492  XBCHE3.  [CHAP.  ZTIH, 

49).  3.  The  stone  arch  is  Dot  homogeneous  ;  t.  e,,  the  modnlns  of 
elasticity  is  not  constant,  bnt  varies  betveen  that  of  the  gtone  and 
the  mortar.  4.  Slight  imperfectioue  in  the  worknutDship — as,  for 
example,  a  projection  on  the  bearing  surface  of  an  arch  stone  or  a 
pebble  in  the  mortar — would  break  the  continoity  of  the  arch,  and 
render  the  theory  inapplicable.  5.  The  stability  of  the  arch  would 
be  greatly  influenced  by  the  action  of  the  center, — its  rigidity,  the 
method  of  loading  it  to  prevent  deformation,  and  the  method  and 
rapidity  of  striking  it. 

The  application  of  the  theory  of  elasticity  to  stone  arches  has 
been  considerably  discussed  iu  lat«  years ;  but  it  is  generally  con- 
ceded that  the  results  are,  for  the  most  part,  illusory,  since  the 
much  simpler  methods  give  results  equally  reliable.  The  explana- 
tion of  the  theory  of  the  elastic  masonry  arch  as  given  by  Professor 
Greene  in  Part  III — Arches — of  his  "Trusses and  Arches"  is  all 
that  can  be  desired;  and  hence  this  theory  will  not  be  discussed 
here. 

711.  Stabhitt  of  Abutiixhtb  ahb  Fms.  The  stability  of  the 
abutment  is  in  a  measure  indeterminate,  since  it  depends  upon  the 
position  of  the  line  of  resistance  of  the  arch.  .The  stability  of 
the  abutment  may  be  determined  most  easily  by  treating  it  as  a 
part  of  the  arch,  i,  e.,  by  extending  the 
load  line  so  aa  to  include  the  forces  acting 
.upon  it  and  drawing  the  reactions  in  the 
usual  way ;  or  its  stability  may  be  deter- 
mined as  follows :  Assume  that  it  is  re- 
quired to  test  the  stability  of  the  abutment 
shown  in  Fig,  138.  Let  qc  represent  the 
direction  of  the  resultant  pressure  on  the 
joint  AB.  g  is  the  center  of  gravity  of  the 
section  ABC  of  the  abutment,  and  j,  that 
for  the  section  ABED*  At  a — the  point 
where  a  vertical  through  g  intersects  qc^ 
prolonged — lay  off,  to  scale,  a  line  ad  fequal  to  the  weight  of  ABC, 
and  also  a  line  ab  equal  to  the  pressure  qei ;  then  Ct  — the  point 
where  the  diagonal  ea  pierces  A  C — is  the  center  of  pressure  on  A  C. 


ovGooi^lc 


iKT,   1.]  STABILITY   OF  THE  ABUTMENT.  493 

In  a  similar  manner,  c,  is  found  to  be  the  center  ot  preeeure  on 

The  amount  of  the  pressure  on  ACie  given  by  the  length  of  the 
line  ae ;  and  the  stability  of  the  joint  against  crushing  can  be  de- 
termined as  deacribed  in-  §g  670-72  and  panigraph  2  of  §  690. 
The  stability  against  rotation  may  be  determined  as  described  in 
§  669  and  paragraph  1  of  g  690.  A  line — not  shown — connecting 
Ci,  c,,  C],  is  the  line  of  resistance  ot  the  abutment,  to  which  the 
joints  ahonld  be  nearly  perpendicular  (see  g  674  and  diTision  3  of 
§  690). 

712.  Tq  Fig.  133  (page  480)  is  shown  the  line  of  resistance  for 
the  abutment  according  to  the  rational  theory  of  the  arch  (gg  68&~ 
94),  and  also  tliat  according  to  Schemer's  theory  {§g  695-703),— 
the  former  by  the  solid  line  and  the  latter  by  the  broken  one. 
.iSince  to  oTerestimate  the  horizontal  components  of  the  external 
forces  would  be  to  err  on  the  side  of  danger,  in  applying  the  former 
theory  in  Fig.  133,  the  horizontal  component  acting  against  the 
abotment  was  disregarded  on  the  assumption  that  the  abutment 
might  be  set  in  a  pit  without  greatly  disturbing  the  surrounding 
earth.  If  the  horizontal  component  had  been  considered,  the  dif- 
ference between  the  lines  of  resistaoce  according  to  the  two  theories 
would  hare  been  still  greater.  Notice  that  the  analysis  which 
recognizes  the  existence  of  the  horizontal  forces,  t.  e.,  the  rational 
theory,  permits  a  lighter  abutment  than  the  theory  which  assumes 
the  external  forces  to  be  entirely  vertical. 

The  omission  of  the  horizontal  components  assumes  that  the 
only  object  of  the  abntment  is  to  resist  the  thrust  of  the  arch  ;  and 
that  consequently  the  flatter  the  arch  the  greater  the  thrust  and  the 
heavier  the  abutment.  Ordinarily  the  abntment  mnst  resist  the 
thrust  of  the  arch  tending  to  overtlirow  it  and  to  slide  it  outward, 
and  must  act  also  as  a  retaining  wall  to  resist  the  lateral  pressure  of 
the  earth  tending  to  overthrow  it  and  to  slide  it  inward.  For 
large  arches  the  former  is  the  more  important ;  but  for  small 
arches,  particularly  under  high  embankments,  the  latter  is  the  more  • 
important.  Hence,  for  large  arches  or  for  an  arch  having  a  light 
surcharge,  the  abntment  should  be  proportioned  to  resist  the  thrust 
of  the  arch;  but  for  small  arches  under  a  heavy  surcharge  of 
■earth,  the  abntment  shonld  be  proportioned  as  a  retaining  wall 
.(Chap.  XIV). 


ovGoQi^lc 


i^-i  ABCHB8.  .  [chap.  XTHL 

Although  the  horizontal  pressnre  of  the  earth  can  not  be  com- 
puted accurately,  there  are  many  conditions  under  which  the 
horizontal  compoaentB  should  not  be  omitted.  For  example,  if  the 
abutment  is  high,  or  if  the  earth  is  deposited  artificially  behind  it, 
ordinarily  it  would  he  safe  to  count  upon  the  pressure  of  the  earth 
to  assist  in  preventing  the  abutment  from  being  overturned  out- 
wards. Finally,  although  it  may  not  always  be  wise  to  consider  th& 
earth  pressure  as  an  active  force,  there  is  always  a  passive  resistance- 
which  will  add  greatly  to  the  stability  of  the  abutment,  and  whose- 
intensity  will  increase  rapidly  with  any  outward  movenieot  of  the- 
abutment  (see  hist  paragraph  of  g  66ti). 

For  empirical  rules  for  the   dimensions  of  abutments,  see  g^ 


Abt.  3.  Rules  Disiyed  frou  Poacticb. 

713.  In  the  preceding  article  it  was  shown  that  every  theory  of 
the  arch  requires  certain  fundamental  assumptions,  and  that  hence 
the  beet  theory  is  only  an  approximation.  Further,  since  it  is  prac- 
tically impossible,  by  any  theory  (§  BUS),  to  include  the  effect  of 
passing  loads,  theoretical  results  are  inapplicable  when  the  moving 
load  is  heavy  compared  with  the  stationary  load.  It  was  shown 
also  that  the  stability  of  a  masonry  arch  does  not  admit  of  exact 
mathematical  solution,  but  is  to  some  extent  an  indeterminate 
problem.  At  best  the  strains  in  a  masonry  arch  can  never  be  com- 
puted anything  like  as  accurately  as  those  in  metallic  structures. 
However,  this  is  no  serious  matter,  since  the  material  employed  in 
the  former  is  comparatively  cheap. 

Considered  practically,  the  designing  of  a  masonry  arch  ia 
greatly  simplified  by  the  many  examples  furnished  by  existing 
structures  which  afford  incontrovertible  evidence  of  their  stability 
by  safely  fulfilling  their  intended  duties,  to  say  nothing  of  the 
history  of  those  stmctnree  which  have  failed  and  thus  supplied 
negative  evidence  of  great  valoe.  In  designing  arches,  theory 
should  be  interpreted  by  experience ;  but  experience  should  be 
studied  by  the  light  of  the  best  theory  available. 

This  article  will  be  devoted  to  the  presentation  of  current  prac- 
tice as  shown  by  approved  empirical  formulas  and  practical  rules, 
(md  by  examples. 


ovGoQi^lc 


AET.  2.]  BULBS   DEBIVED   FBOU   PBACTICB.  49& 

714.  Ekpieical  FOKXTLAl.  XumerouB  formulas  derived  from 
existing  etruotiires  have  been  proposed  for  use  in  designing  masonry 
arches.  Such  formnlas  are  nseful  aa  guides  in  assuming  propor- 
tions to  be  tested  by  theory,  and  also  as  indicatiDg  what  actual 
practice  is  and  thns  affording  data  by  which  Co  check  the  results 
obtained  by  theory. 

As  proof  of  the  reliability  of  such  formulas,  they  are  frequently 
accompanied  by  tables  showing  their  agreement  with  actnal  struct- 
ures. Concerning  this  method  of  proof,  it  is  necessary  to  notice 
that  (1)  if  the  structures  were  selected  because  their  dimensions 
agreed  with  tfao  formula,  nothing  is  proven ;  and  (3)  if  the  stnict- 
nres  were  designed  according  to  the  formula  to  be  tested,  nothing 
is  proven  except  that  the  formula  represents  practice  which  is 
probably  safe. 

At  best,  a  formula  derived  from  existing  strnctures  can  only 
indicate  safe  constmction,  but  gives  no  information  as  to  the  degree 
of  safety.  These  formulas  usually  state  the  relation  between  the 
principal  dimensions ;  but  the  stability  of  an  arch  can  not  be  de- 
termined from  the  dimensions  alone,  for  it  depends  upon  varions 
attendant  circumstances, — as  the  condition  of  the  loading  (if  earth, 
upon  whether  loose  or  compact ;  and  if  masonry,  upon  the  bonding, 
the  mortar,  etc.),  the  quality  of  the  materials  and  of  the  workman- 
ship, the  manner  of  constracting  and  striking  the  centers,  the 
spreading  of  the  abutments,  the  settlement  of  the  foundations,  etc. 
The  failure  of  an  arch  is  a  very  instructive  object  lesson,  and  should 
be  most  carefully  studied,  since  it  indicates  the  least  degree  of 
stability  consistent  with  safety.  Many  masonry  arches  are  excessively 
strong ;  and  hence  there  are  empirical  formulas  which  agree  with 
existing  structures,  hut  which  differ  from  each  other  300  or  400  per 
cent.  All  factors  of  the  problem  must  be  steadily  borne  in  mind  in 
comparing  empirical  formulas  either  with  each  other  or  with  theo- 
retical results. 

A  number  of  the  more  important  empirical  formulas  vrill  now  be 
given,  but  without  any  attempt  at  comparisons,  owing  to  the  lack 
of  apace  and  of  the  necessary  data. 

716.  ThickneH  of  the  Arch  at  the  Crown.  ludesigninganarch, 
the  first  step  is  to  determine  the  thickness  at  the  crown,  t.  e.,  the- 
depth  of  the  keystone. 


ovGoQi^lc 


496  AECHE8.  [chap.  XVIIT. 

Let  d  =  the  depth  at  the  crown,  in  feet ; 

p  =  the  radins  of  cnrratDra  of  the  mtradoe,  in  feet ; 
r  =  the  rise,  in  feet  j 
t  =  the  span,  in  feet. 

716.  American  Practice.  Trantwine'e  fonnnla  for  the  depth 
ot  the  keystone  for  a  first-clots  eut-stone  arch,  whether  circular  or 
elliptical,  is 

d  =  _*^>±iii  +  o.a (27) 

"For  second^laaa  vsork,  this  depth  ma;  he  increased  abont  one 
eighth  part ;  and  for  brick  work  or  fair  rubble,  about  one  third." 

717.  English  Practice.  Bankiae's  fonnnla  tor  the  depth  of 
keystone  for  a  single  arch  is 

d  =  VOA^p ; (38) 

for  an  arch  of  a  series, 

rf=  V0.17p;. (29) 

And  for  tuimel  arches,  vhere  the  gronnd  is  of  the  firmest  and  safest, 

d=yO.U~, (30) 

«nd  for  soft  and  slipping  materials, 

d  =  i/'oM— (31) 

The  segmental  arches  of  the  Pennies  and  the  Slephensons,  which 
are  generally  regarded  as  models,  "hare  a  thickness  at  the  crown 
of  from  ^  ^0  -^  ot  the  span,  or  of  from  fyto-^ot  the  radins  of 
the  intradoB." 

718.  French  Practice,*  Perronnet,  a  celebrated  French  engi- 
neer, is  frequently  credited  with  the  formula, 

d  =  l^  +  i,s, (32) 

*  From  "  Proportions  of  Arches  from  Freacb  Praetlee,"  b7  E.  SbwmHi  Qonld 
in  Van  Nootrand's  Englii'g  Uag.,  vol.  zzji,  p.  450. 


ovGoQi^lc 


ABT.  2.]  BULSB  DEBITED   FROH   PKA.CTICE.  497 

H  being  applicable  to  archee  of  all  forme — setni-circalar,  segmental, 
elliptical,  or  basket-handled, — and  to  railroad  bridges  or  arches 
sustaining  heav;  surcharges  of  earth.  "  Perronnet  does  not  seem, 
however,  to  have  paid  much  attention  to  the  rule  ;  but  has  made 
his  bridges  much  lighter  than  the  rule  would  require."  Other 
formulas  of  the  above  fomij  but  having  different  constants,  are  also 
frequently  credited  to  the  same  authority.  Evidently  Perronnet 
varied  the  proportions  of  his  arches  accoiding  to  the  strength  and 
weight  of  the  material,  the  closeuess  of  the  joints,  the  quality  of 
mortar,  etc. ;  and  hence  diflerent  examples  of  his  work  give  differ- 
ent formulas. 

Dejardin's  formulas,  which  are  frequently  employed  by  French 
engineers,  are  as  follows  : 

For  circular  arches, 

if  -=   J,      d=l  +  (i.lp; (33) 

if  -=   f,     d  =  l+0.0&p;     ....  (34) 

if  -=    i,     d  =  H-0.035p;    ....  (:15) 

if  -  =  tV,     d  =  l  +  O.OZpi      ....  (36) 

F6r  elliptical  and  basket-handled  arches, 

if  ^=  J,  'rf=l  +  0.07A (3r) 

Groizette-Desndyers,  a  French  authority,  recommend*  the  fol- 
lowing formulas  : 

if  ->    i,    d  =  O.50  +  0.ZeVZ^;      .    .    .     (38) 

it-=i.     d  =  0.50  +  0.2GVTp;     .     .     .     (39) 

if-=^,    rf  =  0.60  + 0.80  VT^;    .    .     .     I40i 


ovGoQi^lc 


498  ABCHEB.  [chap.  xtih. 

719.  Notice  that  in  none  of  the  above  formulas  doea  the  char- 
acter of  the  material  enter  as  a  factor.  Notice  aim  that  none  ot 
them  has  a  factor  depending  npon  the  amount  of  the  load. 

Table  62  is  given  to  facilitato  the  compariaonB  of  the  preceding 
formulae  with  each  other  and  with  actual  stntctures.  Valnee  not 
given  in  the  table  can  be  interpolated  with  safQcient  accuracy.  It  is 
remarkable  that  according  to  all  formnlaa  credited  to  Ferronnet  the 
thickness  at  the  crown  is  independent  of  the  rise,  and  varies  onlj 
with  the  span.  Notice  that  by  Dejardin's  fomjnlaa  the  thlcknesB 
decreases  as  the  rise  increases, — as  it  shoald. 

TABLE  6S. 
OoKFABlsoH  or  libfFiBiCAL  FoBMUiiAa  FOB  Depth  <n-  Ektbtqhb. 


,  .™. 

Beml-drclft 

m-' 

e-* 

SPiii. 

Optn. 

Btak. 

10 

X 

VKt 

W 

m 

m 

» 

10 

100 

TiwitwtDe'a,  tor  llrat«lin  woA 

M 

I'.SI 

i.ae 

i.te 

1.70 
S.CM 

!:S 

b.a 

il 

l.M 

>7 

ril 

S'-K 

! 

i 

a'as 

8.48 
I'.U 

sio 

J.Ol 

_ 



720.  ThioknoM  of  the  Aroh  at  the  Springing.  Generally  the 
thickness  of  the  arch  at  the  springing  is  fonnd  by  an  application  of 
theory ;  and  hence  but  few  empirical  formnlas  are  given  for  this 
parpoee. 

Trauimine  gives  a  formula  for  the  thickness  of  the  abutment, 
which  determines  also  the  thickness  of  the  arch  at  the  springing 
(see  §  723). 

"The  angmentation  of  thickness  at  the  springing  line  is  made, 
by  the  Stephensons,  from  30  to  30  per  cent. ;  and  by  the  Bennies, 
^ibout  100  per  cent" 

721.  If  the  loads  are  vertical,  the  horizontal  component  of  the 
tximpression  on  the  arch  ring  is  constant ;  and  hence,  to  have  ths 
mean  pressnre  on  the  joints  uniform,  the  vertical  projection  of  the 


ovGoQi^lc 


ART.  a.]  BCLBS  DEKIVBD  PBOM   PRACTICE.  499 

joints  should  be  constant.  This  principle  leads  to  the  following 
fonnuU,  which  is  frequently  employed  :  Ths  length,  measured  radi- 
ally, of  each  joint  between  the  joint  of  rupture  and  the  crown 
should  he  such  that  its  vertical  projection  i»  equal  to  the  depth  of 
the  keystone.     In  algebraic  language,  this  rule  is 

1=  dasa  a, (41) 

in  which  I  is  the  length  of  the  joint,  d  the  depth  at  the  crown,  and 
a  the  angle  the  joint  makes  with  the  vertical. 

The  length  of  the  joint  of  rupture,*  i.  e.,  the  thicknesss  of  the 
arch  at  the  practical  springing  line,  can  be  computed  by  the  above 
formnla.  The  following  arc  the  valaes  for  circular  and  s^mentaL 
arches: 

If  ->    i:     i=2.00di («; 

"1=.    I,     l~\A<Ad; (43) 

"1=   \,     l-.=  l.%id; (44) 

"j  =  -h>     l  =  \.\^d; (45> 

"7=V».     i  =  1.10rf (46) 

722.  Thiokneu  of  the  Abatmentf     Trautwine's  formula  is 

i  =  0.a/)  +  O.lr  +  3.O, (47) 

in  which  t  is  the  thickness  of  the  abutment  at  the  springing,  p  the 
radius,  and  r  the  rise, — all  in  feet  "  The  above  formula  applies 
equally  to  the  smallest  culvert  or  the  largest  bridge — whether  cir* 
cuJar  or  elliptical,  and  whatever  the  proportions  of  rise  and  span — 
and  to  any  height  of  abutment.  It  applies  also  to  all  the  usual 
methods  of  filling  above  the  arch,  whether  with  solid  masonry  tO' 
the  level  of  the  top  of  the  crown,  or  entirely  with  earth.  It  giree- 
a  thickness  of  abutment  which  is  safe  in  itself  without  any  back' 
ing  of  earth  behind  it,  and  also  safe  against  the  pressure  of  the- 


ovGoQi^lc 


600  AACHI8.  [CBAP.  STUI. 

earth  when  the  bridge  is  tmloaded.  It  givee  abatmente  vhich 
alone  are  aafe  wheD  the  bridge  is  loaded ;  but  for  email  arcbeSr  tfae 
lormala  enpposee  that  earth  vill  be  deposited  behind  the  abut- 
mente  to  the  height  of  the  roadway.  In  small  bridges  and  large 
culverts  on  flrBt-clasa  railroads,  Bubject  to  the  jarring  of  heavy 
trains  at  high  qteeds,  the  comparative  cheapness  with  which  an 
excess  of  strength  can  be  thus  given  to  important  structnres  has  led, 
in  many  cases,  to  the  nee  of  abutments  from  one  fourth  to  one  half 
thicker  than  those  given  by  the  preceding  rule.  If  the  abutment  is 
of  rough  rubble,  add  6  inches  to  the  thickness  by  the  above  formula, 
to  insure  full  thickness  in  every  part."* 

To  find  the  thickness  of  the  abutment  at'the  bottom,  lay  off,  in 
Fig.  139,  on  =  ^  as  computed  by  the  above  equation  ;  vertically  above 


» lay  off  an  =  half  the  rise ;  and  horizontally  from  n  lay  off  aJ  =  one 
forty>eighth  of  the  span.  Then  the  line  An  prolonged  gives  the 
back  of  the  abntment,  provided  the  width  at  the  bottom,  tp,  is  not 
less  than  two  thirds  of  the  height,  ns.  "  In  practice,  os  will  rarely 
exceed  this  limit,  and  only  in  arches  of  considerable  rise.  In  very 
high  abutments,  the  abutment  as  above  will  be  too  slight  to  sustain 
the  earth  pressure  safely."  * 

To  find  the  thickness  of  the  arch,  compote  the  thickness  ce  by 
equation  (27),  page  496,  draw  a  curve  through  e  parallel  to  the 
intradoa,  and  from  b  draw  a  tangent  to  the  extrades;  and  then  will 
h/e  be  the  top  of  the  masoDiy  filling  above  the  arch.  Or,  instead  of 
drawing  the  extrados  ad  above,  find,  by  trial,  a  circle  which  will 
pass  throagh  b,  e,  and  b',  the  latter  being  a  point  on  the  left  abut- 
ment corresponding  to  ,i  on  the  right. 

*  Tnatwine'*  Englneer'a  Pockot-book. 


ovGoQi^lc 


ABT.  2.]  BDLB8  DBBITBD  FBOK  PBAOncB.  601 

Trautwine's  rale,  or  a  aimilar  one,  for  proportioning  the  abnl^ 
meat  and  the  backing  is  freqnently  employed.  For  euunplee,  see 
PUtee  IV  and  V. 

723.  Sankine  b&jb  that  in  some  of  the  beet  examples  of  bridges 
the  thickness  of  the  sbntment  ranges  from  (me  third  to  one  fifth  of 
the  ntdine  of  cnrratnre  of  the  arch  at  its  crown. 

The  following  formula  is  said  to  represent  German  and  Ruxsian 
practice, 

/  =  l  +  0.04(5s  +  4A), (48) 

in  which  A  is  the  distance  between  the  springing  line  and  the  top  of 
the  fonndstion. 

724.  DnDUmom  or  AontU  ABCBXB.  Table  63  {pages  502-3) 
gives  the  dimensions  of  a  nnmber  of  actual  structures,  which,  from 
their  vide  distribntion  and  the  frequency  with  which  most  of  them 
are  cited  as  examples,  may  be  taken  to  represent  average  practice. 
Unfortunately  the  details  concerning  most  of  them  are  very 
meager,  the  following  and  those  in  the  table  being  all  that  can  be 
obtained. 

No.  1  is  the  longest  span  ever  bnilt. 

No.  2  is  the  longest  span  in  existence.*  The  arch  is  a  circnlar 
arc  of  110°.  It  carries  a  conduit  (clear  diameter  9  feet)  and  a  car- 
riage-way (width  20  feet).  The  top  of  the  roadway  is  101  feet  above 
the  bottom  of  the  ravine.  Thevouaaoirs  areQuincy  (Mhsb.)  granite, 
and  are  2  feet  thick,  4  feet  deep  at  the  crown,  and  6  feet  nt  the 
springing.  The  spandrel  filling  is  composed  of  Seneca  aatidatone, 
which,  for  a  distance  above  the  arch  of  4  feet  at  the  crown  and  15 
feet  at  the  springing,  is  laid  in  regular  courses  with  joints  radial  to 
the  intradoB ;  and  hence  the  eSective  tliickness  of  the  arch  is  about 
8  feet  at  the  crown  and  about  21  feet  at  the  springing  (see  Fig.  159, 
page  525).  The  abutments  are  prevented  from  spreading  by  the 
bed-rock  in  the  side-hillB. 

No.  9  is  a  remarkable  bridge.  It  was  built  by  an  "nneducated" 
mason  in  1750;  and  although  a  very  rude  conetrnction,  is  still  in 
perfect. condition.  A  former  bridge  of  the  same  general  design  at 
the  same  place  fell,  on  striking  the  centers,  by  the  weight  of  the 
haunches  forcing  up  the  crown  ;  and  hence  in  building  the  present 
structure  the  load  on  the  haunches  of  the  arch  was  lightened  bt 

*  CoDoernlDg  Kvbed  danw,  n*  (oot  of  page  880  ftiid  top  of  881. 


ovGoQi^lc 


[chap.  xvni. 

TABLE 
Data  ConCBRKiRa 


S°^ 


ufTM.  P.B01)... 


CBlKMl... 


Bi  PnncB'.  cut  j;r*nll«  <se«  paivSM) 

W  itluid ;  smilu 

T.  te ..^^^. 

»Uii(«i,o»er  Seine.  France.     ' 

EtherowriTer.Etigluiil;  nQroad;  louratMDi 

Binhop  AuoklBnd.^ngluid:  turnptke;  builtlnlW);  T 

Welliiwtixi  bridge,  Leeds,  EdkIuiiI     

LoutaXlX 

Dfui  bridge,  iiaar  EdlnbiuKb,  Sooiuud;  turnpike.... 
UcklnR  Aqueduct,  CliempMkB  ft  Ohio  caiwl 


lucl.  EdkIuii 

-jrnnuir:  bric_  _ 

Orlnuu.  FnDoe:  TBllrou 

HutcbawiD  brUBe,  QlaHOW,  Scotlud 

Mb  bridfa.  PtallwlelpblB  ft  Re^idK  B.  B... . 
St.  Kkxenoe,  over  th«  Oiee,  Fninoe 


udstane  In  Ume  (no  aaod). . . , 


Allentown. KnKUuid;  tuniplke. 

BLaloe*.  Eiutlaiid;  turnpike.. 

BlAck  Rock  Tunnel  bridge,  Phlladelpiila  ft  RMdlns  B.  B. .. 


Swktan.  Phllsdelphl&  ft  Ri 
Brent  R.  R.  vlsdueu  Kngln 
WellcKlBT  brldm  at  Llmerii_.  ... 

Bour  bridKe.  K.nglftnd;  turnplka. 

Houehton  riTer.  Englimd;  railroad 

Bewdly.  EoKland;  turnpike 

Chemnul  Street  hridee.  FbllAdelplila;  brick  In  cemo) 
Orrollton  viaduct,  near  BalUmore;  ntllroad:  jtnnlte 
Uanwut.  In  DenblEhiihlre,  Wales;  built  in  l6Hj  tun 

Uonacacrrladuct,  Cbenpeake  ft  Ohio  cauaL 

OTertheTorth,  AtBtirting; 


>*er  the  Doubs,  Fnnce 

uThterrr.  France 

'laducl.  England:  brick  In  oement 

-     -      .j„rt fl*«ilaE.R..PhIlAdelphiA;  brloktaUniem 


June*  River  aqueduct.  Vi^ini 

Des  Baaan^i^wes,  Orltons  A  Toura, 


e<n»e,  orer 
hllAdeli^la 


Br  Cheeapeake  ft  Ohio  canali  rubbla  In  ea 


•.■lnni]Ar;E  =  el1lptlcal; 


ovGoQi^lc 


ABT.  3.] 


EDLES  DBBIVED  FBOV  PBi.(TnCB. 


Actual  Attcmts. 


Baf. 

AwtoMT. 

OCT,. 

^iu. 

SinL 

BxUni 

™o™-. 

"" 

c™. 

^■KS'- 

. 

B 

i 

E 

§ 
1 

1 

no 

s 

148 

140 
1«8 

Its 

11 

1D0 

S 

M 
l» 

to 

u 

ai 

1 

TS 

n 

u 
n 

70 

™ 

M 

1 

i 

H 

to 

M 
*S 

a 

T 

W.B 

L 

s' 

It 

■!., 

M 

?, 

as.t 

s 

1.40 

If 

m' 

Is 

11. TO 

w' 

IB 

L 

B.TB 

!?r 

IS 

i.. 

an 

I.8S 

:.. 

IB 

1W 

'S 

I<H 

1 
1 

1» 
4t 

% 
S 

a 

« 

44 

S 

N 

45 

M.S 

£ 

M 

/Ml. 

iV 

4.U 

i 

f.BI 

li 

4.00 
K.M 
S.00 

1 
IS 

4  M 

«:» 

4!bo 

11 

il 
1 

■.so 

!:!! 
11 

t.n 

I.TB 

il 

I.BO 

/Ml. 

? 

S;:;;;;;;;::^: 

IX 

!S 

J! 

is 

,^::z:z:: 

?-ffi 

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a.BO 

* 

W^kw 

ft 

■.M 

48 

<0 

t  Bm  I TH;  and  >1k>  FIs.  IBS.  pifa  BK. 


ovGoQi^lc 


5M  ABCHB8.  [chap.  XTUL 

leaving  horizoiitaL  cylindrical  openingB  (see  thrrd  paragraph  of 
6  730)  throngh  the  ^paodrel  filling.  The  outer,  or  showing,  arch 
stones  are  only  3.5  feet  deep,  and  that  depth  is  made  ap  of  two 
stones;  and  the  inner  arch  stones  are  only  1.5  feet  deep,  and  but 
from  6  to  fi  inches  thick.  I'he  stone  quarried  with  tolerably  fair 
□atnral  beds,  and  received  little  or  no  dresaing.  It  is  »  wagon-road 
bridge,  and  has  almost  no  spandrel  filling,  the  roadway  being  dan- 
geroualy  ateep.  A  strain  sheet  of  the  arch  shows  that  the  line  of 
resistance  remains  very  near  the  center  of  the  arch  ring  (see  §  730). 
The  mean  pressure  at  the  crown  is  about  344  pounds  per  square 
Inch.     On  the  whole  it  is  an  example  of  creditable  engineering. 

No.  11,  as  designed,  had  a  radius  at  the  crown  of  160  feet ;  but 
the  arch  settled  Z  feet  on  removing  the  center,  and  increased  the 
radius  to  abont  250  feet. 

Ko.  13  Is  noted  for  its  boldness.  This  design  was  tested  by 
building  an  eiperimental  arch — at  Sonpes,  France— of  the  propor- 
tions given  in  the  table,  and  13  feet  wide.  The  center  of  the  ex- 
perimental arch  was  struck  after  four  months,  when  the  total  set- 
tlement was  1.35  inches,  due  mostly  to  the  mortar  joints,  which 
were  about  one  quarter  inch ;  and  it  was  not  injured  by  a  dis- 
tributed load  of  500  pounds  per  square  foot,  nor  by  a  weight  of  5 
tone  falling  1.5  feet  on  the  key. 

No.  46  IB  said  to  have  "  approached  a  horizontal  line  in  conse- 
quence of  the  enbatitution  of  vehicles  for  pack-horses." 

726.  Table  63  affords  some  striking  comparisons.  For  exam- 
ple, Nos.  8  and  9  have  practically  the  same  span  ;  and  as  the  rise 
of  the  former  is  four  fifths  that  of  the  latter,  the  thickness  at  the 
crown  of  the  former  should  be  only  about  one  and  a  quarter  times 
that  of  the  latter,  while  in  fact  it  is  3.3  times  as  thick.  How- 
ever, the  former  carries  a  railroad,  and  the  latter  a  turnpike  ;  but, 
on  the  other  hand,  the  former  is  laid  in  cement,  and  the  latter  in 
lime. 

Nos.  11  and  13  have  nearly  the  same'span,  but  the  rise  of  the 
former  is  4.7  times  the  latter  ;  and  if  the  thickness  at  the  crown 
were  in  like  proportion — as  it  should  be, — that  of  the  former 
would  he  only  0.6  feet.  Also  compare  No.  33  with  No.  33  ;  and 
No.  33  with  Nos.  9  and  18. 

726.  Dimeniioni  of  Abutments.  For  examples  of  the  abutments 
of  raUway  culverts,  see  Tables  49-53  (pages  435-31).     Table  64, 


ovGoQi^lc 


AAT.  2.]  BULIS  DSBITBO  FBOU   PKACTICB.  505 

below,  giTfls  the  dimeosioaf  of  a  aumbw  of  abutmanto  tvfnaen- 
tative  of  French  railroad  preotioe. 

TABLE  04. 

DiMXBUOFB  ow  Abctukts  tkok  Fbemos  Railboad  PaAcncB." 


:^ 

■s 

1 

1 

1*^ 

t 

i>«r 

l.«6 

s.w 

1  HI 

s.n 

s.so 

IB.M 

IBH 

rm 

l^S 

B.W 

Ml 


eroehet,  ohamlii  da  for  de  Ttrim  &  ■ 

D«  LoDK-eiuiW,  ohemlD  <to  (w  da  Parte  i  CbBrlna, 

D'Enttal*ii,cki«mlD<lBt«rdaMonl 

D«PmiUb,cuu>I  at-HwUn 

Ds  la  BuUlle.  cuul  BL  Hutla 

De  HiiM  nunffni.  Ortcani  fc  Tom* 

SaoMnrru.  AaOM. 

Dm  FrulUen.  obemlD  da  ttrdn  Kord 

DaPaMa 

De  M«r7.  olwmin  da  fer  du  Mord 

Oe  OouluretM,  at  ArboU 

OiertbeSalat 

~   UriMdstAbaUoln,atP*rt«,aliemIiidef«rde 

StnaboUTK    

Orsr  UMFort)i,MBtlrllDB. 

Ht.  Nuenoa,  OTsr  (he  CUM 

OrertbeOlM.ohemin deter duNord  

De  DorUaliHi 

Elliftiox 

DaCbapoIlM  

DuCuialSt  Denli 

Da  Chateau-TMerTT 

De  DAle,  o*er  ehe  Doqba  . . 
We]l«1e7.  ■(  Limerick  .  ■  ■ 
D'Orleana,  chemla  de  Car  d 

DeTrilport  

De  NanUe,  OTer  the  Seine 
Da  NantllT.  o<er  the  Seine. 


n 


727.  lunTKAnon  or  Actual  Aboev.— For  illnstrationa  of 
stone  arahe«  for  railroad  cal verts,  see  Plates  II-V.  Fig.  143  (page  509) 
shows  a  50-foot  stone  arch  on  the  Fennsylrania  Railroad.  For 
brick  arches  for  sewers,  see  Figs.  148  and  149  (pages  AI3  and  514). 
For  an  example  of  a  brick  tnnnel-arch,  see  Fig.  147  (page  613). 
Cabin  John  arch,  the  longest  span  in  the  world  (see  No.  2  of  Table 
63,  page  502),  is  shown  incidentally  in  Fig.  159  (page  525), 

728.  MDtOE  Details.  Baeking.  The  backing  is  masonry  of 
inferior  quality  laid  outside  and  above  the  arch  etones  proper,  to 
give  additional  security.  Tlie  backing  is  ordinarily  coursed  or  ran- 
dom rabble,  but  sometimes  concrete.     Sometimes  the  npper  ends 

•  E.  Bhermaii  Oonld,  In  TaD  Noatrand'i  Engl^'g  Hag.,  toL  ntz,  ^  400. 


ovGoQi^lc 


606  ARCHES.  [chap.  XVIIL 

ot  tbe  arch  stones  are  cut  with  horizontal  snrfaces,  in  which  esse 
the  backing  is  built  Iq  courses  of  the  same  depths  as  these  steps 
and  bonded  with  them.  The  backing  is  occasionally  built  in  ra- 
diating couTEes,  whose  beds  are  prolongations  of  the  bed-joints  of 
the  arch  stones  ;  but  it  nsnally  consists  of  rubble,  laid  in  liorizontal 
courses  abutting  against  the  arch  ring,  with  occasional  arch  stones 
extending  into  the  former  to  bond  both  together.  The  radial 
joints  possess  some  advantages  in  stability  and  strength,  particu- 
larly above  the  joint  of  rupture  ;  but  below  that  joint  the  horizon- 
tal and  vertical  joints  are  best,  since  this  form  of  construction  the 
better  resists  the  overturning  of  the  arch  outward  abont  the 
springing  line.  Ordinarily,  the  backing  has  a  zero  thickness  at  or 
near  the  crown,  and  gradually  iucreases  to  the  springing  line  ;  but 
sometimes  it  has  a  considerable  thickness  at  the  crown,  and  is  pro- 
portionally  thicker  at  the  springing. 

It  ia  impossible  to  compute  the  degree  of  stability  obtained  by 
the  use  of  backing  ;  but  it  is  certain  that  tbe  amount  ordinarily 
employed  adds  very  greatly  to  the  stabUity  of  the  arch  ring.  In 
fact,  many  arches  are  little  more  than  abutting  cantilevers  ;  and  it 
is  probable  that  often  the  backing  alone  would  support  the  struct- 
ure, if  the  arch  ring  were  entirely  removed. 

729.  Spandrel  Filling.  Since  the  roadway  must  not  deviate 
greatly  from  a  horizontal  line,  a  considerable  quantity  of  material  is 
required  above  the  backing  to  bring  the 
roadway  level.  Ordinarily  this  space  is 
filled  with  earth,  gravel,  broken  stone, 
cinders,  etc.  Sometimes,  tc  save  filling, 
small  arches  are  bnilt  over  tbe  haunches 
of  the  main  arch,  as  shown  in  Fig.  140. 
The  interior  longitudinal  walls  may  be 
strengthened  by  transverse  walls  between 
them.  To  distribute  the  pressure  uni- 
formly, the  feet  of  these  vralls  should 
be  expanded  by  footings  where  they  rest 
upon  the  back  of  the  arch. 

730.  When  the  load  is  entirely  sta- 
tionary—as  in  an    aqnednct  or  canal 
]«.  bridge — or  nearly  so — as  in  a  long  span 

I  high  railroad  embankment, — the  materials  of  the 


arch  under  i 


ovGoQi^lc 


ABT.  3.]  BULBS  DEBITED  FBOU  P&iCTICB.  607 

Spandrel  fiUmg  ftnd  the  size  and  pOBition  of  Uie  empty  spaoea  may 
be  BQch  as  to  cause  the  line  of  reeistanoe  to  coincide,  at  least  very 
nearly,  with  the  center  of  the  arch  ring. 

For  example,  ABCD,  Fig.  141,  represetita  a  semi-arch  for  which 
it  is  required  to  find  a  disposition  of  the  load  that  will  cause  the 
line  of  resietance  to  coincide  with  the  center  line  of  the  arch  ring. 


Fib.  hi. 
Divide  the  arch  and  the  load  into  any  convenient  number  of  diT> 
sions,  by  vertical  lines  as  shown.  From  P  draw  radiating  lines  par- 
allel to  the  tangents  of  ibe  center  line  of  the  iu%h  ring  at  a,  h,  c, 
etc. ;  and  then  at  snch  a  distance  from  P  that  01  shall  represent, 
to  any  convenient  scale,  the  load  on  the  first  section  of  the  aroh  ring 
(including  its  own  weight),  draw  a  vertical  line  throngb  0.  The 
intercepts  0-1,  1-2,  2-3,  etc.,  represent,  to  scale,  the  loads  whidi  the 
several  diTisions  must  have  to  cause  the  line  of  resistance  to  coincide 
with  the  center  of  the  arch  ring.  I^y  off  the  distances  0-1,  1-2, 
etc.,  at  the  centers  of  the  respective  sections  vertically  upwards  from 
the  center  line  of  the  srcb  ring,  and  trace  a  carve  throagh  their 
upper  ends.  The  line  thus  formed — EF,  Fig.  141 — shows  the  re- 
quired amount  of  homogeneous  load ;  t.  e. ,  EF  is  the  contour  of  the 
homogeneous  load  that  will  cause  the  line  of  resistance  to  pass  ap- 
proximately through  the  center  of  each  joint. 

Hence,  by  choosing  the  material  of  the  spandrel  filling  and 


ovGoQi^lc 


W)8  ABCHB8.  [chap.  ZTm. 

urntoging  the  empty  spacee  so  that  the  actual  load  aball  be  eqnir- 
alent  in  intfltudty  and  dlBtribntion  to  the  reduced  load  obtuned  aa 
sboTe,  the  TonssoirB  can  be  made  of  moderate  depth.  The  yacaat 
spaoee  may  be  obtaioed  by  the  method  shown  in  Fig.  140  (page 
506)  ;  or  by  that  shown  in  Fig.  142,  in  which  /(  is  a  small  empty 
cylindrical  arch  extending  from  the  face  of  one  end  wall  to  that  of 
the  other.     (See  the  description  of  arch  N'o.'S,  g  734,  p.  501.) 

Notice  that  the  lines  radiating  sDCcessiTely  from  P,  Fig.  141 
(page  507),  will  intercept  increasing  lengths  on  the  load-line  ;  and 
that,  therefore,  the  load  which  will  keep  a  circular  arch  in  eqnilib- 
riam  most  increase  in  intensity  per  horizontal  foot,  from  the  crown 
towards  the  springing,  and  must  become  infinite  at  the  springing  of 
a  semi-circniar  arch.  Hence 
it  followB  that  it  is  not  practi- 
cable to  load  a  circnlar  arch, 
beyond  a  certain  distance  from 
the  crown,  so  that  the  line  ol 
resistance  shall  coincide  with 
the  center  line  of  the  arch 
ring. 

731.  Drainage.  The  drain- 
age of  arch   bridges  of  more 
than  one  span  is  generally  ef- 
fected by  giving  the  top  anr- 
^^- 1*-  face  of  the  backing  a  slight 

inclination  from  each  side  toward  the  center  of  the  width  of  the 
bridge  and  also  from  the  center  toward  the  end  of  the  span.  The 
water  is  thus  collected  over  the  piers,  from  whence  it  is  discharged 
through  pipes  laid  in  the  masonry. 

To  prevent  leakage  through  the  backing  and  through  the  arch 
sheeting,  the  top  of.  the  former  should  be  covered  with  a  layer  of 
paddle,  or  plastered  with  a  coat  of  best  cement  mortar  (see  §  141), 
or  painted  with  coal  tar  or  asphaltnm  (see  %  264). 

732.  For  an  illustration  of  the  method  of  draining  a  series  of 
arches,  and  also  of  several  minor  details  not  mentioned  above,  see 
Fig.  143,  which  represents  "Little  Jnniata  bridge  No.  12  "on  the 
Pennsylvania  Bailroad.* 


•Published  by  permlsBlon  of  Wm,  H.  Brown,  chief  en^neer. 


ovGoQi^lc 


AM.  8.] 


fiCLIS  DEBITED  FBOV  PBACTICE. 


jvGooi^le 


610  XBCHSS.  [chap.  XTIU. 

733.  Skioi  ABCzn.  Th«  onl]r  matter  requiring  Bpecial  mention 
in  connection  vitb  brick  arches  is  the  bond  to  be  employed.  When 
the  thickness  of  the  arch  exceeds  a  brick  and  a  ha\t,  the  bond  from 
the  soffit  outward  is  a  very  important  matter.  There  are  three 
principal  methods  employed  in  bonding  brick  arches.  (1)  The  arch 
may  be  bnilt  in  concentric  rings  ;  i.  e.,  all  the  brick  may  be  laid  as 
stretchers,  with  only  the  tenacity  of  the  mortar  to.nnite  tho  several 
rings  (see  Fig.  144).  ThiH  form  of  conBtractioii  is  frequently  called 
rowlock  bond,  (^i)  Part  of  the  brick  may  be  laid  as  stretchers  and 
part  as  headers,  as  in  ordinary  walls,  by  thickening  the  outer  ends 
of  the  joints — either  by  using  more  mortar  or  by  driving  in  thin 
pieces  of  slate, — so  that  there  shall  be  the  same  number  of  bricks  in 


each  ring  (see  Fig.  145).  This  form  of  construction  is  known  as  header 
and  slreicktr  bond,  or  is  described  as  being  laid  with  continuoux 
radial  joints,  (3)  Block  in  course  bond  ie  formed  by  dividing  the 
arch  into  sections  similar  in  shape  to  the  voussoirs  of  stone  arches, 
and  laying  the  brick  in  each  section  with  any  desired  bond,  bnt 
making  the  radial  joints  between  the  sections  continuous  from 
intradoB  toeitrados.  With  this  form  of  construction,  it  is  custom- 
ary to  lay  one  section  in  rowlock  bond  and  the  other  with  radial 
joints  continuous  from  intrados  to  extrados,  the  latter  section  being 
much  narrower  than  the  former  (see  Fig.  146). 

1.  The  objection  to  laying  the  arch  in  concentric  rings  is  that, 
since  the  rings  act  nearly  or  quite  independent  of  each  other,  the 
proportion  of  the  load  carried  by  each  can  not  be  determined,  A 
ring  may  be  called  upon  to  support  considerably  more  than  its  proper 
share  of  the  load.  This  is  by  far  the  most  common  form  of  bonding 
in  brick  arches,  and  that  this  difficulty  does  not  more  often  mani- 


ovGoQi^lc 


AX£.  Z.}  BULBS   DBBIVED   fBOK   FBACIIOI.  511 

fest  itaelf  is  doubtless  dae  to  the  very  low  onit  vorking  pressDre 
employed.  The  msan  preaenre  on  brick  musonry  arches  ordinarily 
varies  from  30  to  40  ponnds  per  square  inch,  ander  vbich  condition 
a  single  ring  might  carry  the  entire  pressure  (see  Tables  19  and  20, 
]>ages  164  and  166).  The  objection  to  thia  form  of  bond  can  be 
partially  removed  by  using  the  very  best  cement  mortar  between 
the  rings. 

The  advantages  of  the  ring  bond,  particularly  for  tunnel 
and  eewer  arches,  are  as  follows :  It  gives  4-iQCh  toothings  for  con* 
necting  with  the  succeeding  section,  while  the  others  give  only 
2-inch  toothings  along  much  of  the  outline.  It  requires  leas 
cement,  is  more  rapidly  laid,  and  is  less  liable  to  be  poorly  executed. 
It  possesses  certain  advantages  in  focilities  for  drainage,  when  laid 
in  the  presence  of  water. 

2.  The  obiection  to  laying  the  arch  with  continuous  radial  joints 
is  that  the  outer  ends  of  the  joints,  being  thicker  than  the  inner, 
will  yield  more  than  the  latter  as  the  centers  are  removed,  and 
hence  concentrate  the  pressure  on  the  intrados.  This  objection 
is  not  serious  when  this  bond  is  employed  in  a  narrow  section 
between  two  lai^r  sections  laid  in  rowlock  conraes  (see  Fig.  146). 

3.  When  the  brickwork  is  to  be  subject  to  a  heavy  pressure, 
some  form  of  the  block  in  course  bond  should  be  employed.  For 
economy  of  labor,  the  "blocks"  of  headers  should  be  placed  at  such 
a  distance  apart  that  between  each  pair  of  them  there  shall  be  one 
more  course  of  stretchers  in  the  outer  than  in  the  inner  ring  ;  but  a 
moment's  consideration  will  show  that  this  would  make  each  section 
shout  half  as  long  as  the  radins  of  the  arch, — which,  of  conrse, 
is  too  long  to  be  of  any  material  benefit.  Hence,  thia  method 
necessitates  the  use  of  thin  bricks  at  the  ends  of  the  rings. 

734.  Ezanplei  of  Brick  Arches.  The  method  of  bonding  shown 
in  Fig.  146  (page  510)  is  frequently  employed — as,  for  example,  in 
the  70-foot  brick  arch  of  the  Swatara  bridge  (Philadelphia  and 
Reading  B.  H.).  The  bonding  employed  in  arching  the  Yosburg 
tunnel  (Lehigh  Valley  R.  R.)  is  shown  in  Fig.  147  (page  512).* 

735.  Fig.  148  (page  fil3)  shows  the  standard  forms  of  large 
brick  sewers  employed  in  the  city  of  Philadelphia,  f     "  They  are 

•Prom  Rownberg's  "The  VoabnrBTnnnel,"  by  penntsslon. 
tR.  Bering,  In  Trans.  Am.  Soc  of  C.  R.,  vol.  Til,  pp.  WH-SJ.     Tbe  fllnBtraUona 
■n  t^>rDdnoed  from  ttioM  In  the  orlgjiul,  the  force  diagruns  being  omltied  bere. 


ovGoQi^lc 


Sl'2  ABOHia  [OHAP.  ZTIII. 

designed  for  a  masiniam  pressure  on  the  brick-work  of  80  ponnds 
per  square  inch,"  which,  considering  the  nsnal  HpeciflcatioDS  for 
such  work  (see  §  360,  p;  176),  seems  nnneceasarily  small  (see  Tables 
19  and  30,  pages  164  and  166). 

Fig.  149  (page  fil4)  shows  the  standard  forma  of  sewers  ia 
Washington,  D.  C*  "The  invert  as  shown  ie  the  theoretical  form, 
although  the  concrete  is  rammed  into  the  trench  and  nearly  always 
extends  beyond  the  limits  shown."  The  largest  sewers  have  a  trap- 
rock  bottom ;  the  intermediate  sizes  hare  a  semi-circular  vitrified 


Fio,  14?.— Boqd  aod  CeDtsr  of  Toiburi  Tunnel. 

pipe  in  the  bottom  ;  and  the  smallest  sizes  oonBist  of  sewer  pipes 
bedded  in  concrete. 

736.  Owing  to  their  great  number  of  jointa,  brick  arches  are 
liable  to  settle  much  more  than  atone  ones,  when  the  centers  are  re- 
moved ;  and  hence  are  less  saitable  than  the  former  for  large  or  flat 
arches.  Nevertheless  a  number  of  brick  arches  of  large  span  have 
been  built  (see  Table  63,  page  502),  Trautwine  gives  the  following 
description  of  some  bold  examples.  "  On  the  Filbert  Street  exten- 
sion of  the  Pennsylvania  R,  R.,  in  Philadelphia,  are  four  brick  arches 
of  50  feet  span,  and  with  the  very  low  rise  of  7  feet.  The  arch  rings 
are  ii  feet  thick,  except  on  their  showing  faces,  where  they  are  bat  2 
feet.     The  joints  are  in  common  lime  mortar,  and  are  about  ^  inch 

*  Report  of  the  Ck>nimlKlonen  of  the  DUtrtct  of  Colnmbta,  tor  Uie  rear  endtng 
JoBB  80, 18M,  p.  I'm.  For  delalli  of  qiuatltle*  of  nuterlal  raqnirad,  and  for  estl- 
■natei  of  cost,  m«  report  for  precedlnc  rear,  pp.  877-70. 


ovGoQi^lc 


ART.  2.]  BDLSS  DEBITED  VROK  FBA.CTICB. 


ovGoQi^lc 


ABcaXS.  [CHAf .  XVIU. 


OQQOO 


jvGooi^le 


ABT.  3.]  CSlfTEBS.  615 

thick.  These  four  arches,  about  200  yards  apart,  with  a  large  num- 
her  of  others  of  26  feet  span,  form  a  viadact.  The  piers  between 
the  short  spans  are  H  feet  thick,  and  those  at  the  ends  of  the  50-foot 
spaoa  are  18(  feet.  The  road-bed  is  about  100  feet  wide,  giviug  room 
for  9  or  10  tracks.  The  springing  lines  of  all  the  arches  are  about 
6  to  8  feet  above  the  ground.  One  of  the  50-foot  arches  settled  3 
inches  upon  permanently  striking  the  center ;  but  no  further  settle- 
ment baa  been  observed,  although  the  viaduct  has,  since  built  (1880), 
had  a  very  heavy  freight  and  passenger  traCBc  at  from  10  to  30  miles 
per  hour." 

737.  SFBClFlOATlon  FOX  Stosz  Axoess.  The  specifications  for 
arch  masonry  employed  on  the  Atchison,  Topeka  and  Santa  F6 
Bailroad  are  as  follows  :  * 

7SB.  Tlnt-ClMi  Areh  Xuonry  sb&ll  be  built  in  accordHnce  with  ibe  speci- 
flcatioDS  f  or  flrat-clasB  masoniy  [see  §  207],  with  tbe  exception  of  the  arch  sheet- 
ing and  ring  stones.  The  ring  stoiiea  shall  be  dressed  to  such  shape  as  the 
eaglaeer  shall  determioe.  The  ring  stonee  and  the  arch  sheeting  shall  b«  not 
less  than  ten  Inches  (10")  thick  on  Uie  Intrados,  and  shall  have  a  depth  equal 
tn  the  specUed  thickness  of  the  arch.  The  Jolnia  shall  be  at  right  angles  to 
tbe  Intrados,  and  tbetr  thickness  shall  not  exceed  three  eighths  of  an  inch  (|''). 
The  face  of  the  sheeting  stones  shall  be  dressed  so  as  to  make  a  cloee  center- 
ing joint.  The  ring  stones  and  sheeting  shall  break  joints  not  less  than  one 
foot  (I'). 

The  wings  shall  be  neatl;  stepped  with  selec^M  stones  of  the  full  width  of 
the  wing,  and  of  not  less  than  ten  Inches  (10")  in  thickness,  overlapping  by 
not  less  than  one  and  one  half  feet  (1^');  or  they  shall  be  finished  with  a  neatly 
capped  newel  at  the  end  of  each  wing,  and  a  coping  course  on  the  wing.  The 
parapets  shall  bo  finished  with  a  coping  coiirae  of  not  less  than  ten  inches 
<10")  in  thickness,  having  a  projection  of  six  inches  (0"). 

739.  SMond-ClaM  Andi  Xawnry  shall  be  the  same  as  first-class  Diasonry  (see 
§  20T>.  Thestooesof  tbe  arch  sbeeling  shall  be  at  least  four  Inche8(4")  in  thick- 
ness on  the  Intrados ;  shall  have  a  depth  equal  to  tbe  thickness  of  the  arch  ; 
shall  have  good  bearings  Ihrougbout ;  and  shall  be  well  bonded  to  each  other 
and  to  tbe  ring  Stones. 

740.  SFBOincAnoHB  FOB  Brick  Aechxs.  See  §g  260-61  (pages 
176-77). 

Art.  3.  Asch  Centerb. 

741.  A  center  is  a  temporary  structure  for  supporting  an  arch 
while  in  process  of  construction.  It  asually  consists  of  a  number  of 
frames  (commonly  called  ribs)  placed  a  few  feet  apart  in  planes 

*  For  general  spedQcatlona  for  railroad  nuMODrr,  sea  Appendix  L 


ovGoQi^lc 


516  ARCHES.  [chap.  XTIII. 

perpeodicalar  to  the  axis  of  the  arch,  aod  covered  with  narrow 
plauka  (called  laggings)  mnniDg  parallel  to  the  axis  of  the  arch, 
upon  which  the  arch  stones  rest.  The  center  is  asoaily  wood — 
either  a  solid  rib  or  a  truss, — but  is  sometimes  a  carved  rolled-iron 
beam.  In  a  trussed  center,  the  pieces  upon  which  the  ladings  rest 
are  called  back-piecef.  The  ends  of  the  ribs  may  be  supported 
by  timber  struts  which  abut  against  large  timbers  laid  upon  the 
ground,  or  they  may  rest  upon  a  ahoalder  on  the  abutment. 

The  framing,  setting  up,  and  striking  of  the  centers  {§§  752-55) 
is  a  very  important  paii  of  the  construction  of  any  arch,  particularly 
one  of  long  span.  A  change  in  the  shape  of  the  center,  due  to 
insufficient  strength  or  improper  bracing,  will  be  followed  by  a 
change  in  the  curve  of  the  intradoa  and  cousequently  of  the  line  of 
resiBtance,  which  may  endanger  the  safety  of  the  arch  itself. 

742.  Load  to  BI  Sufpobied.  If  there  were  no  friction,  the  load 
to  be  supported  by  the  center  could  be  computed  exactly  ;  but  fric- 
tion between  the  several  arch  stones  and  between  these  and  the 
center  rendera  all  (ormnlae  for  that  purpose  very  uncertain. 
Fortunately,  the  exact  load  upon  the  center  is  not  required ;  for  the 
center  is  only  a  temporary  structure,  and  the  material  employed  in 
its  construction  is  not  entirely  lost.  Hence  it  is  wise  to  assume 
the  loads  to  be  greater  than  they  really  will  be.  Some  allowance 
must  also  be  made  for  the  accumulation  of  the  material  on  the 
center  and  for  the  effect  of  jarring  during  erection.  The  following 
analysis  of  the  problem  will  show  roughly  what  the  forces  are  and 
why  great  accuracy  is  not  possible. 

To  determine  the  pressure  on  the  center,  consider  the  voassoir 
DEFQ,  Fig.  150,  and  let 

=  the  angle  which  the  joint  DE  make4 

with  the  horizontal ; 

I  fi  =  the  co-efiicient  of  friction  (see  Table  .36. 

.J  P^ge  315),  t.  6.,  I*  is  the  tangent  of 

the  angle  of  repose ; 

0  =  the  augnlar  distance  of  any  point  Crom 

the  crown ; 
W=  the  weight  of  the  voussoir  DEFO ; 
JV=  the  radial  pressure  on  the  center  dae  to 

the  weight  of  LEFG. 

If  there  were  no  friotion,  the  stone  DEFQ  would  be  supported 


ovGoQi^lc 


ABT.  3.]  CENTEB8.  517 

by  the  normal  reeistance  of  the  surface  DE  and  the  radial  reac- 
tion of  the  center.  The  pressure  on  the  enrface  DE  would  then 
be  W  GOB  a,  and  the  pressure  in  the  direction  of  the  radius  W  sin  a. 
Friction  causes  a  slight  iudetermiuation,  since  part  of  the  weight 
of  the  voussoirs  may  pass  to  the  abutment  either  through  the  arcb 
ring  or  through  the  back-pieces  (perimeter)  of  the  center.  Owing 
to  friction,  both  of  these  surfaces  will  offer,  in  addition  to  the 
above,  a  resistance  equal  to  the  product  of  the  perpendicular  pres- 
sure and  the  co-efflcient  of  friction  (foot-note,  page  276).  If  the 
normal  pressure  on  the  joint  DE  is  W  cos  a,  then  the  frictional 
resistance  is  n  Tt'cos  a.  Any  frictional  resistance  in  the  joint  DE 
will  decrease  the  pressure  on  the  center  by  that  amonnt ;  and  conse- 
qnently,  with  friction  on  the  joint  DE,  the  radial  pressure  on  tba 
center  is 

N—W  (sin  a  —  /I  COB  a) (49J 

On  the  other  hand,  if  there  is  friction  between  the  arch  stone  and 
the  center,  the  frictional  resistance  between  these  surfaces  will 
decrease  the  pressnre  upon  the  joints  DE,  as  computed  above ;  and 
consequently  the  value  of  JV  will  not  be  as  in  equation  (49). 

Notice  that  in  paasing  from  the  springing  toward  the  crown  the 
pressure  of  one  arch  stone  on  the  other  decreases.  Near  the  crown 
this  decrease  is  rapid,  and  consequently  the  friction  between  the 
voussoirs  may  be  neglected.  Under  this  condition,  the  radial  pres- 
sure on  the  center  is 

N=WcM0. (50) 

As  a  rough  approximation,  equation  (50)  may  be  applied  for 
the  first  30°  from  the  crown,  although  it  gives  results  slightly^ 
greater  than  the  real  pressures ;  and  for  the  second  30°,  equation. 
(49)  may  be  employed,  although  it  gives  results  less  than  the  actna}> 
pressure ;  and  for  the  third  30°,  the  arch  atones  may  be  considered 
self-supporting. 

743.  The  value  of  the  co-efl9cient  to  be  employed  in  equation 
(49)  is  somewhat  nncertain.  Disregarding  the  adhesion  of  the 
mortar,  the  co-efficient  varies  from  about  0.4  to  0.8  (see  Table  36^ 


ovGoQi^lc 


SIS  ABOBBB.  [OHAP.  ZTin. 

page  316) ;  and,  including  the  adhesion  of  good  cement  mortar,  it 
may  be  nearly,  or  even  more  than,  1.  (It  is  1  if  an  arch  stone 
remains  at  rest,  withont  other  rapport,  when  placed  upon  another 
one  in  snch  a  position  that  the  joint  between  them  makes  an  angle 
of  iS"  with  the  horizontal.)  If  the  arch  is  small,  and  consequently 
laid  up  before  the  mortar  has  time  to  harden,  probably  the  smaller 
value  of  the  co-efficient  should  be  used ;  but  it  the  arch  is  laid  up 
80  slowly  that  the  mortar  has  time  to  harden,  a  larger  value  could, 
with  equal  safety,  be  employed.  As  a  general  average,  we  will 
assume  that  the  co-efficient  is  .68,  t.  e.,  that  the  angle  of  repose 
is  30°. 

Notice  that  by  equation  (49)  JV  =  0,  if  tan  a  =  ft;  that  is  to 
say,  JV  =  0,  if  tx  =  30°.  This  shows  that  as  the  arch  stones  are 
placed  upon  one  another  they  would  not  begin  to  press  upon  the 
center  rib  until  the  plane  of  the  lower  face  of  the  top  one  reaches 
an  angle  of  30°  with  the  horizon. 

Table  65  gives  the  value  of  the  radial  pressure  of  the  several  por- 
tions of  the  arch  upon  the  center ;  and  also  shows  the  difference 
between  applyiug  equation  (49)  and  equation  (50).  Undoubtedly 
the  former  should  be  applied  when  the  angle  of  the  lower  face  cf 
any  arch  stone  with  the  horizontal  does  not  differ  greatly  from  30°; 
and  when  this  angle  ia  nearly  ftO",  then  equation  (50)  should  be  ap- 
plied. It  is  impossible  to  determine  the  point  at  which  one  equation 
becomes  inapplicable  and  the  other  applicable ;  but  it  is  probably 
safe  to  apply  eqnation  (49)  np  to  60°  from  the  horizontal. 

744.  Example.  To  illustrate  the  method  of  using  Table  65, 
assume  that  it  ie  required  to  find  the  pressure  on  a  back-piece  of  a 
20-foot  semi-circular  arch  which  extends  from  30°  to  60°  from  the 
horizontal,  the  ribs  being  6  feet  apart,  and  the  arch  stones  being  2 
feet  deep  and  weighing  150  pounds  per  cubic  foot.  Take  the  sum 
of  the  decimals  in  the  middle  column  of  Table  C5,  which  is  3.19. 
Thismuatbemultiplied  by  the  weight  of  the  arch  resting  on  S°  of  the 
center.  (In  this  connection  it  is  convenient  to  remember  that  an 
arc  of  1°  is  equal  to  0.0175  times  the  radius.)  The  radius  to  the 
middle  of  the  voussoir  is  11  feet,  and  the  length  of  3°  of  arc  is  0.38 
feet.  The  volume  of  2°  is  0. 38  X  5  X  2  =  3.8  cubic  feet ;  and  the 
weight  of  %"  is  3.8x150  =  570  pounds.  Therefore  the  pressure 
on  the  back-piece  is  570x3.19  =  1,818  pounds. 


o;Gooi^lc 


AET.  3.] 


The  Raslu.  Pbbwdrs  of  thb  Abch  Bn 
or  A  SBia-AHca,  oh  ths  Cknteb. 


!iudull  Paosnu 

n  Tsum  OF  ma 

Amle  of  n 

(  I^IWUI       WciOHT  or  THB  Aboh  aroHB.      1 

Faotwit 

BOBItO 

ITAI, 

Br  Kq<u"ii>n  iW) 

By  Equation  (»). 

80 

O.OO 

sa 

0.04 

84 

0.U8 

88 

0.13 

88 

018 

40 

0.30 

43 

0.24 

0.«7 

44 

0.38 

0.60 

40 

0.83 

0.78 

46 

086 

0.74 

00 

«.40 

0.78 

K 

0.45 

0.83 

eo 

0.64 

0.8B 

OS 

0.91 

70 

0.04 

80 

0.98 

M 

1.00 

745.  Owam  POun  or  Chitksi.  Solid  Woodfln  Bib.  For 
flat  arches  of  10-foot  span  or  noder,  the  rib  may  consist  of  a  pUnk, 
a,  a,  Fig.  ISl,  10  or  13  inches  wide  and  1^  or  2  iuchea  thick,  set 


edgewise,  and  another,  i,  of  the  same  thickness,  trimmed  to  the 
curve  of  the  intrados  and  placed  above  the  first.  The  two  should 
ne  fastened  together  by  nailing  on  two  cleats  of  narrow  boards  as 
snown.     These  centers  may  be  placed  2  or  3  feet  apart 


ovGoQi^lc 


520  ARCHES.  [CHA.P.  XVIlt. 

746.  Bailt  Wooden  Bib.  For  flat  arches  of  10  to  30  feet  span, 
the  rib  may  coneiBt  of  two  or 
three  tbicknesees  of  short 
boards,  fitted  and  nailed  (or 
bolted)  together  as  shown  la 
Fig.  152.  An  iron  plate  is 
often  bolted  OD  over  the  joints 
(see  Fig,  147,  page  512),  which 
adds  materially  to  the  rigidity 
^'^  '"  of  the  rib.      Centers  of  this 

form  have  an  astonishing  strength.     Traatwine  gives  the  two  fol- 
lowing examples  which  strikingly  illnstrate  this. 

In  the  first  of  these  examples,  this  form  of  center  was  employed 
for  a  semi-circnlar  arch  of  35  feet  span,  having  aroh  stones  2  feet 
deep.  "  Each  rib  consisted  of  two  thicknesses  of  2-inch  plank,  in 
lengths  of  abont  6.5  feet,  treenailed  together  so  as  to  break  joint. 
Each  piece  of  plank  was  12  inches  deep  at  the  middle,  and  S  inches 
at  each  end,  the  top  edge  being  cut  to  suit  the  cnrve  of  the  arch.  The 
treenails  were  1.25  inches  in  diameter,  and  12  of  them  were  used  to 
each  length.  These  ribs  were  placed  17  inches  apart  from  center  to 
center,  and  were  steadied  together  by  a  bridging  piece  of  1-inch 
board,  13  incbes  long,  at  each  joint  of  the  planks,  or  about  3.25  feet 
apart.  Headway  for  traMc  being  necessary  under  the  arch,  there 
were  no  chords  to  unite  the  opposite  feet  of  the  ribs.  The  ribs  were 
covered  vrith  close  board-lagging,  which  also  assisted  in  steadying 
them  together  transversely.  As  the  arch  approached  about  two 
thirds  of  its  height  on  each  side,  the  ribs  began  to  sink  at  the 
haunches  and  rise  at  the  crown.  This  was  rectified  by  loading  the 
crown  with  atone  to  be  used  in  completing  the  arch,  which  was  then 
finished  without  further  trouble." 

The  other  example  was  an  elliptic  arch  of  60  feet  span  and  15 
feet  rise,  the  arch  stones  being  3  feet  deep  at  the  crown  and  4  feet 
at  the  springing.  "Each  frame  of  the  centre  was  a  simple  rib  6 
inches  thick,  composed  of  three  thicknesses  of  2-inch  oak  plank. 
In  lengths  (abont  7  to  15  feet)  to  suit  the  curve  and  at  the  same 
time  to  preserve  a  width  of  about  16  inches  at  the  middle  of  each 
length  and  12  inches  at  each  of  its  ends.  The  segments  broke 
joiDts,  and  were  well  treenailed  together  with  from  ten  to  sixteen 


ovGoQi^lc 


JLBX.  3.]  GESTEBS.  531 

treenailB  to  each  length.  There  were  do  chorda.  These  liba  were ' 
placed  18  inches  from  center  to  center,  and  were  steadied  against 
one  another  by  a  board  bridging-piece,  1  foot  long,  at  every  5  feet. 
When  the  arch  atones  had  approached  to  within  about  12  leet  of 
each  other,  near  the  middle  of  the  span,  the  sinking  at  the  crown 
and  the  rising  at  the  haunches  had  become  so  alarming  that  pieces 
of  13-  X  13-inch  oak  were  hastily  inserted  at  intervals  and  well 
wedged  against  the  arch  stones  at  their  ends.  The  arch  was  then 
finished  in  sections  between  these  timbers,  which  were  removed  one 
by  one  as  the  arch  was  completed." 

Although  the  above  examples  cian  not  be  commended  as  good 
construction — the  flexibility  of  the  ribs  being  so  great  aa  to  endanger 
the  stability  of  the  arch  daring  erection  and  to  break  the  adhesion 
of  the  mortar,  thus  decreasing  the  strength  of  the  finished  arch, — 
they  are  very  instructive  as  showing  the  strength  attainable  by  this 
method. 

747.  The  above  form  of  center  is  frequently  employed,  partic- 
ularly m  tunnels,  for  spans  of  20  to  30  feet,  preoautiona  being  taken 
to  have  the  pieces  break  jointa,  to  secure  good  bearings  at  the 
joints,  and  to  nail  or  bolt  the  several  segments  firmly  together. 
The  centers  for  the  35-foot  arch  of  the  Musconetcong  (N.  J.)  tun- 
nel (Lehign  Valley  R.  R.)  consisted  of  segments  of  3-inch  plank, 
5  feet  8  inches  long,  14  inches  wide  at  the  center,  and  8  inches  at 
the  ends,  bolted  together  with  four  ^-^nch  and  four  f-inch  bolts 
each,  and  14-  X  6-inch  pieces  of  plate-iron  over  the  joints.  Where 
the  center  was  required  to  support  the  earth  alao,  a  three-ply  rib 
was  employed;  hut  in  other  positions  two-ply  ribs,  spaced  4  to  5 
feet  apart,  were  used.  Centers  of  this  form  have  ancceesfully  stood 
very  bad  ground  in  the  Mnscouetcong  and  other  tunnels;*  and 
hence  we  may  infer  that  they  are  at  least  sufficiently  strong  for  any 
ordinary  arch  of  30  feet  span. 

Althongb  not  neceasary  for  stability,  it  ia  wise  to  connect  the 
feet  of  the  rib  by  nailing  a  narrow  board  on  each  side,  to  prevent 
the  end  of  the  rib  from  spreading  outwards  and  presdng  against  the 
masonry — thus  interfering  with  tiie  striking  of  the  center, — and  also 
to  prevent  deformatton  in  handling  it. 

*  Drinker'!  TnimelfD;,  p.  648. 


ovGoQi^lc 


032 


[chap.  zthz. 


748.  Braeed  Wooden  Bib.  For  semi-circolar  arches  of  15  to  30 
feet  span,  a  coDstnictioD  Bimilar  to  that  shown  in  Fig.  147  (page  512) 
may  be  employed.  The  segmeDts  ahonld  consiBt  of  two  thiclcnesBes 
of  1-  or  2-iiich  plank,  according  to  span,  from  8  to  12  inchea  wide 
at  the  middle,  according  to  the  length  of  the  segments.  The  hori- 
zontal chord  and  the  vertical  tie  may  each  be  made  of  two  thick- 
neseeB  of  the  plank  from  which  the  segments  are  made. 

For  greater  rigidity,  the  rib  may  be  further  braced  by  any  of 
the  methode  shown  in  ontline  in  Figs.  153,  154,  155,  or  by  obTions 


modifications  of  them.  The  form  to  be  adopted  often  depends  npon 
the  paasage-way  required  ander  the  arch.  Fig.  153  is  supported  by 
a  poet  under  each  end;  in  extreme  cases.  Fig.  154  maybe  supported 
at  the  middle  point  also;  and  Fig.  155  may  be  supported  at  both 
middle  points  as  well  as  at  the  ends. 

Since  the  arch  masonry  near  the  springing  does  not  press  upon 
the  center,  it  may  be  laid  with  a  template  before  the  center  is  set 
up;  and  hence  frequently  the  center  of  a  eemi-circular  arch  does 
not  extend  down  to  the  springing  line.  For  examples,  see  Figs. 
147  and  15t)  (page  512  and  524). 

Center  frames  are  put  together  on  a  temporary  platform  or  the 
floor  of  a  large  room,  on  which  a  full-size  drawing  of  the  rib  is  first 
drawn. 

749.  TnuMd  Center.  When  the  span  is  too  great  to  employ 
any  of  the  centers  described  abore,  it  becomes  necessary  to  construct 
trussed  centers.     It  is  not  oeceBsary  here  to  discuss  the  principles 


of  truosing,  or  of  finding  the  strains  in  the  several  pieces,  or  of 
determining  the  sections,  or  of  joining  the  several  pieces, — all  of 


ovGoQi^lc 


ABT.  3.]  CBNTEBS.  SSS 

which  are  fally  described  in  treatises  on  roof  and  bridge  constrao- 
tion.  There  is  a  very  great  variety  of  methods  of  constructing  such 
centers.  Figs.  156  and  157  show  two  common,  simple,  and  efficient 
general  forms. 

760.  Cakbes.  Strictly,  the  center  should  be  constrncted  vith 
a  camber  jast  oqnal  to  the  amount  it  will  yield  when  loaded  with 
the  arch ;  but,  Bince  the  load  is  indeterminate,  it  is  impossible  to 
compute  what  this  will  be.  Of  course,  the  camber  depends  upon 
the  unit  strain  in  the  material  of  thecenter.  The  rule  id  frequently 
given  that  the  camber  should  be  one  fowr-hundrtdth  of  the  radius; 
but  this  is  too  great  for  the  excessirely  heavy  centers  ordinarily 
used.  It  is  prol^bly  better  to  build  the  centers  true,  and  guard 
against  undue  settling  by  giving  the  frames  great  etiffnras;  and 
then  if  unexpected  settling  does  take  place,  tighten  the  striking 
wedges  slightly. 

The  two  sides  of  the  arch  should  be  carried  up  equally  fast,  to 
prevent  distortion  of  the  center. 

761.  BTtmnw  or  AOTITAL  ClHTZU.  For  an  example  of  a 
center  employed  in  a  tunnel,  see  Fig.  147  (page  512). 

Fig.  158  (p^  534)  shows  the  center  designed  for  the  60<foot 
granite  arches  of  the  recently  completed  Washington  bridge  over 
the  Harlem  River,  New  York  City.*  The  bridge  is  80  fuet  wide, 
and  fifteen  ribs  were  employed.  Notice  that  the  center  does  not 
extend  to  the  springing  line  of  the  arch  ;  the  first  fifteen  feet  of 
the  arch  vure  laid  by  a  template. 

Fig.  159  t  (page  625)  shows  the  center  employed  in  constructing 
the  Cabin  John  arch,  which  carries  the  Washington  (D.  C.)  aque- 
duct over  a  creek,  and  which  is  the  largest  masonry  arch  in  the 
world  (see  No.  3,  Table  63,  page  502).  The  arch  is  20  feet  wide- 
and  five  ribs  were  employed. 

762.  BTUKDiG  THZ  CehteS-  The  Hethod.  The  ends  of  the  ribs 
or  center-frames  usually  rest  upon  a  timber  lying  parallel  to.  and 
near,  the  springing  line  of  the  arch.  This  timber  is  supported  by 
wedges,  preferably  of  hard  wood,  resting  upon  a  second  stick,  which 
isiu  turn  supported  by  wooden  posts — usnallyone  under  each  end  of 
each  rib.     The  wedges  between  the  two  timbers,  as  above,  are  used 

•  Published  by  permission  of  Wm.  R.  IlntloD,  chief  englijeer. 

*  Compiled  from  pbotogr&phs  taken  during  the  progren  of  the  work  (18B6-40),  bj 
iMurteiiir  of  Gen.  M.  C.  Kelgi,  chief  engineer. 


ovGoQi^lc 


[CHAP,  xvin. 


ovGoQi^lc 


AST.  3.] 


ovGoQi^lc 


S26  ARCHBS.  [chap.  ZTIO. 

in  remoTing  the  center  after  the  arch  U  completed,  and  are  known 
u  ttriking  wedges.  They  consist  of  a  pair  of  folding  wedges — 1  to 
%  feet  long,  6  inches  wide,  and  having  a  slope  of  from  1  to  fi  to  1  to 
10 — ^placed  nnder  each  end  of  each  rib.  It  is  necessary  to  remoTe 
the  centen  slowly,  particnlarly  for  large  arches ;  and  hence  the 
striking  wedges  should  haTe  a  very  slight  taper, — the  larger  the  epao 
the  smaller  the  taper. 

The  center  is  lowered  by  driving  back  the  wedges.    To  lower 

-  the  center  uniformly,  the  wedges  mnst  be  driven  back  equally. 

This  is  most  easily  accomplished  by  making  a  mark  on  the  side  of 

each  pair  of  wedges  before  commencing  to  drive,  and  then  moving 

each  the  same  amount. 

763.  Instead  of  separate  pairs  of  folding  wedges,  as  above,  a 
compound  wedge,  Fig.  160,  is  sometimes  employed.     The  pieces 


A  and  B  are  termed  striking  plates.  The  ribs  rest  upon  the  former, 
and  the  latter  is  supported  by  the  wooden  posts  before  referred  to. 
The  wedge  C is  held  in- place  during  the  construction  of  the  arch 
by  the  keys,  K,  K,  etc.,  each  of  which  is  a  pair  of  folding  wedges. 
To  lower  the  center,  the  keys  are  knocked  out  and  the  wedge  Cis 
driven  back. 

The  piece  C  is  usually  as  long  as  the  arch,  and  supports  one  end 
of  all  the  ribs ;  but  with  large  arches,  say  80  to  100  feet  span,  it  is 
customary  to  sapport  each  rib  on  a  compound  wedge  running 
parallel  to  the  chord  of  the  center  (perpendicular  to  the  axis  of  the 
aroh).  Instead  of  cutting  the  striking  plates  A  and  B  as  shown  in 
Fig.  160,  the  compound  wedge  may  play  between  tapered  blocks 
gained  into  A  and  B.  The  piece  C  is  usually  made  of  an  oak 
stick  10  or  1%  inches  square.  The  individual  wedges  are  from  4  to 
6  feet  long. 

For  the  larger  arches,  the  compound  wedge  is  driven  back 
with  a  heavy  log  battering-ram  suspended  by  ropes  and  swung 
back  and  forth  by  hand.     The  inclined  surfaces  of  the  wedges 


ovGoQi^lc 


ABT.  3.]  CEKTEBS.  537 

should  be  lubricated  when  the  center  is  set  op,  so  ae  to  facilitate 
the  striking. 

754  An  ingenioQg  device,  first  employed  at  the  Font  d'Alma 
arch — 141  feet  span  and  28  feet  rise, — coosiated  in  supporting  the 
center-frames  by  vooden  pistons  or  plungers,  the  feet  of  which 
rested  on  sand  confined  in  plate-iron  cylinders  1  foot  in  diameter 
and  about  1  foot  high.  Near  the  bottom  of  each  cylinder  there  was 
a  ping  which  could  be  withdrawn  and  replaced  at  pleasure,  by  means 
of  which  the  outflow  of  the  sand  was  regulated,  and  consequently 
also  the  descent  of  the  center.  This  method  is  particularly  use- 
ful for  large  arches,  owing  to  the  greater  facility  with  which  the 
center  can  be  lowered.     See  Fig.  158,  page  S24. 

765.  The  Time.  There  ia  a  great  difference  of  opinion  as  to  the 
proper  time  for  striking  centers.  Some  hold  that  the  center  should 
be  struck  as  soon  as  the  arch  is  completed  and  the  spandrel  filling 
is  in  place;  while  others  contend  that  the  mortar  should  be 
given  time  to  harden.  It  is  probably  best  to  slacken  the  centers  as 
soon  as  the  keystone  is  in  place,  so  as  to  bring  aU  the  joints  under 
pressure.  The  length  of  time  which  should  elapse  before  the  centers 
are  finally  removed  should  vary  with  the  kind  of  mortar  employed 
(see  Fig.  5;  page  89)  and  also  with  its  amount.  In  brick  and  rubble 
arches  a  large  proportion  of  the  arch  ring  consists  of  mortar  ;  and 
if  the  center  ia  removed  too  soon,  the  compression  of  this  mortar 
might  cause  a  serious  or  even  dangerous  deformation  of  the  arch. 
Hence  the  centers  of  such  arches  ehould  remain  until  the  mortar 
has  not  only  sot,  but  has  attained  a  considerable  part  of  its  ultimate 
strength  (see  Fig.  5,  page  89), — this  depending  somewhat  upon  the 
maximum  compression  in  the  arch.  It  is  probable  that  a  knowledge 
of  the  elasticity  and  of  the  "  set"  of  mortar  would  give  some  light 
as  to  the  best  time  to  strike  centers ;  but  nnfortunately  our  infor- 
mation on  those  topics  is  very  limited  (see  §  146). 

Frequently  the  centers  of  bridge  arches  are  not  removed  for 
three  or  fonr  months  after  the  arch  is  completed  ;  but  usually  the 
centers  for  the  arches  of  tunnels,  sewers,  and  culverts  are  removed 
as  soon  as  the  arch  is  turned  and,  say,  half  of  the  spandrel  filling  is 
in  placa. 


ovGoQi^lc 


jvGooi^le 


APPENDIX   I. 


SPECIFICATIONS  FOR  MASONRY* 


OoiavlBKUnMd 

Masoorf  lor  BaSr 

Arcbltectural  MaaoDij 

LajdDfi  Miuonr;  in  Freealiv  WeotbBT '■    Ml 

Ratlkoad  Masonry,  t 

General  Provlglons.  All  stone  used  for  the  dlBereD t  ckssea  of  nmaoary 
must  be  fuTDiabed  from  the  best  quarries  in  the  vicinity,  subject  to  the  ftp- 
proTttl  of  tlie  engineer.  Brick  masonrj  shall  st  all  times  be  substituted  for 
stone,  when  so  desired  by^  the  engineer. 

Inipaotloa.  Ali  materials  will  he  subject  to  rigid  inspection,  and  any  thftt 
have  t>eeD  condemned  must  be  Immediately  removed  from  the  site  of  the  work. 
The  work  wiii  be  done  under  the  supervision  of  an  inspector,  whose  duties 
tviil  be  to  see  that  the  requirements  of  these  specificatiODS  are  carried  out;  but 
hh  presence  is  in  no  way  to  t>e  presumed  to  release  in  any  degree  the  responsi- 
bility or  obligation  uf  the  contracior. 

Laying  Xasanry.     Ali  classes  of   masonry  laid  in  cement  must  be  neatly 

Elnted  with  cement  morlar,  finely  tempereci.  No  masonry  of  any  kind  must 
covered  until  it  has  been  inspected  and  accepted  by  the  engineer.  No  ma- 
sonry will  be  allowed  to  be  laid  in  freezing  weather.  [Many  specifications 
omit  this  condition.  See  "  Spec ili cations  ftr  Laying  Masonry  m  Freezing 
Weather,"  page  MS.} 

lleainrsmeDt  of  Hasonry.  Ail  masonry  and  brick-work  will  tie  built  ac- 
cording to  the  plans  and  instructions  furnished  by  the  engineer,  and  will  t>e 
eslimated  and  paid  for  by  the  cubic  yard,  computing  only  the  actual  solidity 
thereof.  No  constructive  or  conventional  measurement  will  be  allowed,  any 
rule  or  custom  in  the  section  of  the  country  through  which  the  road  passes  to 
the  contrary  notwithstanding.  The  price  per  cubic  yard  paid  for  masonry 
«nd  brick-work  will  Include  the  furnishing  of  ali  material,  scaffolding,  cen- 
tering, and  all  other  expenses  necessary  to  the  construction  and  completion  of 
the  mafionry  or  brick-work.  Ail  "  dressed  "  or  "  cut-stone"  work— such  as 
copings,  bridge-seats,  cornices,  belt-courses,  water-tables,  brackets,  corbels, 
etc.  —furnished  under  the  plans  of  the  engineer  will  be  paid  for  by  the  culilc 
yard,  under  the  claasiQcation  of  the  masonry  in  which  they  occur,  with  an 
nddiliouai  price  per  square  foot  of  the  entire  superflciai  surface  of  the  stones 
■'  dressed,    or  "  cut,"  or  "bush-hammered," 

Altowanoe  for  Extras.  No  allowance  will  be  made  for  timber,  or  work  on 
snme,  used  in  scaffolding,  shoring,  or  centering  for  arches, — excepting  only 
timber,  sheet-piling,  or  foundation  plank,  necessarily,  and  t^  order  of  tne  en- 
gineer, left  in  the  ground.     No  allowance  will  be  made  U     '  ■       -      • 


■  Bee  also  the  qwdflcatlons  In  the  bod;  <rf  tl>e  bo  k.    Sm  "  SpecUcsticau  '  In  Index. 

-t  Tboe  speoUcaCioDs  ore  tbe  Mine,  except  Id  form,  as  (hoM  emploTed  Id  the  oonsCroctlon 
'  the  "Wen  Shore"  Railroad,  butdo  not  dUter  maMrlall;  from  (twee  used  In  other  road% 
id  have  traqueattr  heeo  iiccepted  as  (he  standard. 


ovGoQi^lc 


530  SPECIFICATIONS  FOB  KABOITBT.  [aPP.  I. 

taj  damage  he  may  sustain  bj  reason  of  floods  or  other  causes;  but  aucb 
dnkluing,  baillUjP,  or  pumpiag  from  fouodattoDB  aa  the  engineer  may  decide  to- 
be  necesHBry  will  be  paid  for  at  H  price  to  be  flzed  by  Ibe  eneiueer. 

Fintt-tilaetB  Maaonrywill  consist  of  quarry- faced  ash lar  [sue  g§200-07] 
laid  in  horizontal  courees  bavlug  parallel  beds  and  vertical  joints,  oi  not  less. 
Uian  len  inches  |10"|  nor  more  than  thirty  inches  (80 ")  in  tbfclEQeBS, — decreas- 
ing la  thickness  regularly  from  the  bottom  to  the  top  of  the  wall,— laid  flush 
in  oement  mortal-  of  the  quality  hereinafter  specined.  Each  course  must  be 
thoroughly  grouted  before  the  succeeding  one  is  laid. 

BUaafStonei.  Strelefi^i  must  be  not  less  than  two  and  one  tialf  feet  (3j') 
Dor  more  than  six  feet  (3}  In  leng-th,  and  not  less  than  one  and  one  half  feet 
(Xi'}  in  width,  nor  less  in  width  than  one  and  one  half  (1|)  limes  their  depth, 
HgadBT»  must  not  be  leas  than  three  and  one  half  feet  (Sj')  nor  more  than  four 
and  one  half  feet  (4^')  la  length — where  the  thickness  of  the  wall  will  admit 
of  the  same.^and  not  less  than  one  and  one  half  feet  (If )  in  width,  aor  less 
in  width  thaa  they  are  in  depth  of  course. 

Ootting.  Every  stone  must  be  laid  on  its  natural  bed.  All  stones  must, 
have  their  beds  well  dressed,  parallel  and  true  to  the  proper  line,  and  made  al- 
ways as  large  as  '.he  stone  will  admit  of.  The  beds  aiid  sides  of  the  stone  must 
be  cut,  before  being  placed  on  the  work,  bo  as  to  form  julats  not  exceeding  one 
half  inch  (i")  In  width.  No  hammering  on  a  stone  will  be  allowed  after  it  js- 
seti  but  if  any  inequalities  occur,  they  must  be  pointed  off.  The  vertical 
joints  of  the  luce  must  he  not  leas  tlian  eight  inches  (8")  in  from  the  face,  and 
as  much  more  as  the  stone  will  admit  of.  All  corners  and  batter  lines  must  be 
run  with  a  neat  chisel  draft  one  and  one  half  inches  {\\")  on  each  face.  The 
projections  of  the  quarry  facebeyund  the  draft  lines  must  not  exceed  four  inches 
(4")i  and  in  the  wde-walls  of  tunnels  this  projection  m>ist  not  exceed  cwa 
inches  (2"). 

Bond.  The  masonry  shall  consist  of  headers  tnd  stretchers  alternating.  At 
least  ooe  fourth  of  it  shall  consist  of  headers  extending  entirely  through  the 
wall,  and  every  header  shall  be  immediately  over  a  stretcher  of  tue  underlying- 
course.  The  stones  rtt  each  course  shall  be  so  arranged  as  lo  form  a  proper 
bond— in  no  case  less  thtn  one  foot  d')— with  the  stones  of  the  underlying  course. 

Backing  The  backing  shall  be  of  good-sized,  welt-shapcd  stones,  laid  so 
as  to  break  joints  and  thoroughly  bond  the  work  in  hU  dlreclions,  and  leave  no 
(^aces  between  them  over  six  inches  (8")  in  width,  which  spaces  shall  l>e  filled 
with  small  stones  and  Eipalls  well  grouted. 

Coping.     All  bridge-seats  and  lops  of  w 
course  of  such  dimensions  and  projections  ;  , 

dres.ied  and  cut  to  a  true  surface  on  lop  and  front  edges,  in  conformity  with, 
diagrams  for  same  which  will  be  furnished  by  the  engineer. 

Foondatioa  CoiuiM.  All  foundation  courses  must  be  Inid  with  selected 
flat  sfoiius,  not  less  than  Iwetve  inches  (13")  thick,  nor  of  less  superficial 
:e  than  fifteen  (in>3qMarc  feet. 

Secoud-class  Masonry  [^S  208-13]  will  consist  of  broken  range  rubble 
of  superior  quality,  laid  with  horizontal  beds  and  vcrilcal  joints  on  the  face, 
with  no  stone  less  than  eight  inches  i8 '}  in  thickness — unless  otherwise  directed 
by  the  engineer, — well  bonded,  and  leveled  as  well  as  can  be  without  hammer- 
dressing  No  mortar  joint  shall  exceed  three  quarters  of  an  inch  (t"|  in  thick- 
ness. All  comers  and  quoins  shall  have  hammer-dressed  beds  and  joints;  and 
all  corners  and  baiter  lines  shall  be  run  with  an  inch-and-one-balf  II  j")  chisel 
draft.  At  least  one  fourih  {V)  of  the  stones  in  the  face  must  he  headers  evenly 
distributed  through  the  wall, 

Bridge.seatsaudtopsof  walls  shall  be  coped  in  the  some  manner asspeclfled 
for  first-class  masonry.  Stones  in  foundation  courses  shall  be  not  leas  than 
twelve  inches  (r,i")  ttuck,  and  shall  contain  not  less  than  twelve  (13)  squar» 
feet  of  surface. 


large  fl 


ovGoQi^lc 


SAILROAD  HASONBT.  531 

Third-class  Masonry  will  coosistor  good  subebutial  rubble  [ggSlB-lTf 
Iftld  In  cement  mortar.  All  stones  shall  be  perfectly  Bound,  and  sufflciently 
large  to  make  good,  well-bonded,  strong  work;  and  sball  be  laid  on  tbeir 
natural  beds,  in  tlie  most  subataiiilBl  manner,  and  witb  as  much  neatness  at  ■ 
this  description  of  work  admits  of.  The  stones  In  the  foua<latlons  must  be  not 
lens  than  ten  inches  (10")  thick,  and  shall  contain  not  less  than  tea  (10)  square 
feet  of  Eiirfuce;  and  euch  shall  he  Qrmly,  solidly,  and  carefully  laid. 

First-class  Arch-culvert  Masonry  shall  be  huilt  in  accordance  - 
with  the  specifications  for  first  class  masonry,  with  the  exception  of  the  arch 
sheeting  an<l  the  ring-stones.  The  ring!<  shall  be  dressed  to  such  size  and 
shape  as  the  engineer  shall  direct.  The  ring-stones  and  sheeting-stones  aball 
not  be  of  less  thickness  than  tch  inches  (10")  on  the  inimdos,  and  shall  be 
dressed  with  three  eighths  inch  ({")joiDtB,  and  shall  be  of  the  full  depth  speci- 
fied (by  drawings  or  otherwise)  for  ine  thickness  of  the  arch.  The  jomtB  must 
be  made  on  truly  radial  linea,  and  the  face  of  the  slieeting-atones  must  be- 
dressed  to  make  close  ]oints  with  the  center.  The  ring-stone  aad  sheeting- 
stones  shall  break  jolols  by  not  less  than  one  foot  (!')- 

The  wing  walls  shall  be  neatly  stepped,  in  accordance  with  the  drawings' 
furuished,  with  selected  stones  of  the  full  width  of  the  wing  and  of  not  leas 
than  ten  inches  (10")  in  thickness,  no  stone  bcia^  covered  less  than  eighteen 
inches  (16")  by  the  one  next  above  it;  or  the  wmg  shall  he  finished  with  a 
neatly  capped  newel  at  the  end,  and  n  coping  course, — as  may  be  selected  by 
the  engineer.  The  parapet  shall  be  finished  with  a  coping  course  of  full  width 
of  parapet,  with  such  proiecliou  as  may  be  directed  by  the  engineer,  the  stone 
to  be  not  less  than  ten  inches  (10")  thick. 

Second-clajus  Arch-ciilvert  masonry  shall  be  of  the  same  general 
character  and  description  as  second-class  masonry,  with  the  excepilon  of  tl 


ing-stODes  and  the  arch  sheeting.  The  former  shall  be  dressed  as  specified, 
or  first-class  arch-cnlverl  masonry.  The  latter  shall  consist  of  selected  stones; 
of  the  full  depth  of  the  arch,  and  shall  have  a  good  bearing  throughout  the- 


thickness  of  the  arch,  and  shall  be  well  bonded.     Sa  stone  shall  be  leas  tl 
six  Inches  (S")  in  thickness  on  the  inlrados. 

Box-culvert  Masonry  willbe  good  rubble  [see  g§  218-17],  neatly  laid 
up  with  square-shaped  stones  of  a  size  and  quality  satisfactory  to  the  engineer. 
The  end  piirapet  walls  and  also  the  side  walls  for  three  feet  (8)  from  the  ends 
shall  be  laid  in  good  cement  mortar.  When  box  culverts  are  ordered  to  be 
laid  up  entirely  in  cement  mortar  [see  §  214J,  they  will  be  classified  as  third- 
class  masonry,  and  must  conform  to  the  specifications  for  the  same. 

The  covering- stone  for  all  box  culverts  shall  be  not  U-^s  than  ten  Jnchea 
(10")  in  thickni'Hs,  and  must  have  a  good,  solid,  well-leveled  hearing  uu  the 
side  walls  of  not  less  than  fifteen  inches  (13' ). 

Vitrified  Pipe.  In  localities  where  but  a  small  quantity  of  water  passesr 
vitrified  pipe  will  be  substituted  for  ciilveria  when  so  ordered  by  the  engineer. 
Sizes  of  twelve  112"),  fifteen  (15"),  or  eighteen  (18")  inches  in  diameter  may  be- 
used,  and  must  be  of  the  best  quality  double  strengtli,  vitrified  culvert  pipe, 
subject  to  the  approval  of  the  engineer.  Vitrifi(-d  pipes  must  be  well  and  care- 
fully bedded  and  laid  [see  Figs.  97-99,  pages  409-10],  lu  accordance  with  the 
Instructions  of  the  engineer, 

IlctniiilnE  Wnlls  will  be  classified  as  second-  or  third-class  maaonrjr 
laid  dry,  as  may  be  ordered  in  each  particular  case. 

Slope  Walls  will  be  of  auch  thickness  and  slope  as  directed  by  Ihe  en- 

S'neer.  The  stones  must  reach  entirely  through  Ihe  wall,  and  be  not  less  than 
ur  inches  (4")  thick  and  twelve  inches  (12 ')  long,  laid  with  close  joints,  and 
as  free  as  possible  from  spalls.  The  foundations  must  be  prepared  and  laid  as 
directed  by  the  engineer. 

Stone  Paving  shall  be  made  by  setting  on  edge  stone  from  eight  (8")  to 


ovGoQi^lc 


632  SPECIFICATIONS  FOK  HASONBT.  [APP.  I. 

flftMQ  incbea  (IS")  in  depth,  laid  either  diy  or  grouted  with  Btrong  ccmcDt 
moiUr,  w  Duty  be  dhiectea  by  the  engiaeer. 

Riprapi  When  required  by  the  engineer,  the  face  of  embuikiiieDts  and 
the  foot  of  slopes  shall  be  prutecied  from  the  action  of  water  by  a  faciug  ot 
riprap  Bloue,  or  of  brush  and  stones,  or  by  n  relalning  wall,  aa  may  be  directed. 
Tne  riprap,  when  used,  shall  be  laid  by  hand  by  competent  workmen,  and 
ihall  be  of  such  thlckaesa  and  slope  and  of  Buch  undiened  atone  aa  the  en- 
gineer may  direct 

Brick  Mason 
well  tempered,  har 
'crooked,  or  salmon  bricks  will  under  any  circumEtAncee  be  allowed  in  the 
work.  The  brick  shall  be  well  soaked  in  water  before  being  laid,  and  shall 
be  laid  in  hydraulic  cement  mortar  of  the  quslily  hereafter  specitted,  with 
such  thickness  ot  joint  and  styleof  bond  [§342  and  §73S]  aa  shall  bn  prescribed 
by  the  engineer.  Orout  will  be  aubetituted  for  mortar  when  ordered  by  ifae 
engineer. 

Brick  arching  must  be  covered  on  the  back  with  a  coat  of  strong  cement 
.mortar  one  Inch  (1")  thiclc.  In  tunnel  arching  wherever  a  seam  of  water  is 
met.  the  arcti  must  be  covered  with  rooflogfelt;  or  with  a  course  of  asphalium 
'(applied  hot)  of  such  thickness  as  may  be  directed  by  Ilie  engineer,  and  Ihia 
covered  with  a,  plastering  of  cement  mortitr  so  as  lo  make  the  arch  impervious 
to  water.  A  properly  formed  drainage  channel  shall  be  left  iittbe  backing  of 
the  arch  and  side  walls,  with  suitable  openlugs  for  Ihe  escape  of  the  water,  at 
such  points  and  of  such  size  as  may  be  directud  by  Ihe  engineer.  The  keying 
of  all  arches  shall  be  most  carefully  done,  and  in  such  manner  as  may  from 
time  to  lime  be  directed  by  the  ongiueer.  The  packing  between  the  arch  and 
timnel  roof  shall  never  be  put  in  until  al  least  lorty'eight  (4tj)  hours  after  the 
^section  has  been  keyed. 

Cement.  The  cement  must  be  of  the  best  quality  of  freshly  ground  hy- 
draulic cement  [of  tljeRusendalelype — see  g  72],  and  be  equal  in  quslily  to  the 

best  brands  of cement.     It  will  be  subject  to  test  by  the  engineer  or  his 

appointed  inspector,  and  must  stand  a  tensile  stress  of  fifty  (GUj  pounds  per 
square  inch  of  sectional  area  on  specimens  allowed  aset  of  thirty  (GO)  minutes 
in  air  and  twcnty'four  &i)  hours  under  water  [see  g  60,  and  art.  S  of  Chapter 
IIU 

Itfortar.  The  morlar  shall  in  all  cases  be  composed  of  one  (1)  part  in  bulk 
of  the  above  apecitied  hydraulic  cement  to  two  <'J)  parts  in  bulk  of  clean, 
sharp  sand,  well  aud  thoroughly  mixed  together  in  a  clean  box  of  boards,  be- 
fore the  addiliou  of  the  water.  It  must  be  used  immediotely  after  being 
mixed:  and  no  mortar  left  over  night  will,  under  anv  pretext,  W  allowed  to 
be  used.  The  sand  and  cement  used  will  at  all  times  be  subject  to  inspection, 
lest,  and  acceptance  or  rejection  by  the  engineer. 

Concrete.  The  concrete  shall  be  composed  of  two  (21  parts  In  bulk  of 
hard,  sound,  and  acceptable  stone — broken  to  a  size  that  will  pass  in  any  direc- 
tion through  a  two-inch  {2")  ring,  thoroughly  clean  and  free  from  mud.  dust, 
dirt,  or  auy  earthy  admixture  whatever, — and  one  (1)  [>art  of  freshly-made 


cement  mortar  of  the  quality  above  described.  The  concrete  sboU  be  quicklv 
laid  in  sections,  in  layers  not  exceeding  nine  (B)  inches  in  thickness,  and  aball 
be  thoroughly  mmmcd  until  the  water  flushes  to  the  surface.  It  shall  be  al- 
lowed al  least  Iwtlve  (12i  hours  to  set  before  any  work  is  laid  on  it 

Foundations.  Ezoavatlooi.  Foundations  for  masonry  shall  be  excavated 
to  such  depths  as  may  be  uecesearv  W  secure  a  solid  bearing  for  the  masonry. 
— of  which  the  engineer  shall  be  tne  judge.    The  materials  excavated  wUI  be 


10  tpetM  sigiilflcaDce  (ne  |  K,  page  tfj. 


ovGoQi^lc 


BAILBOAD    HA80MRT. 


stiall  be  deposited  in  the  contiguous  embankment:  and  aoy  matedal  UDllt  for 
8uch  purpose  Bball  be  deposited  outside  the  roadway,  or  m  such  place  an  the 
engineer  shall  direct,  and  bo  that  it  shall  not  Interfere  with  any  dTain  or  water 
course.  Id  case  of  foundations  in  rock,  Ibe  rock  must  be  excavaled  u>  such 
depth  and  in  such  form  as  may  be  required  by  the  engioeer,  and  must  be 
dressed  level  lo  receive  the  foundation  course. 

Artifloial  Foondatlant.  When  a  eate  and  solid  foundation  for  the  masonry 
can  not  be  found  at  a  reasonable  depth  (of  which  Ihe  engineer  is  lo  be  the 
Judge).  Ihe  contractor  shall  prepare  such  artlflciai  foundations  as  the  engineer 
may  direct. 

FaTlng.  Box  culverla  and  small  bridge  abalments  may  have  a  paved  foun- 
dation, if  so  directed  by  the  engineer,  by  setting  stones  on  edge,  breaking 
joints,  and  extending  across  the  entire  nidth  of  the  foundation. 

Timber.  Timber  foun  dations  shall  besuchaa  the  engineer  may  by  drawing* 
or  otherwise  prescribe,  and  will  be  paid  for  by  the  thousand  feet,  board  mea» 
lire. — the  price  to  include  the  cost  of  material,  framing,  and  putting  in  place. 
All  timber  must  be  sound,  straight- trained,  and  free  from  sap,  loose  or  rotten 
knots,  wind  shakes,  or  any  other  defect  that  would  impair  its  strength  or 
durability.  It  must  be  sawed  (or  hewed)  perfectly  straight  and  to  exact 
dimensions,  with  full  corners  and  square  edges.  All  framing  most  be  done 
in  a  thorough,  workgianlike  manner.  Both  material  and  workmanship  will 
be  subjeia  to  (he  inspection  and  acceptance  of  the  engineer. 

Flllag.  All  piles  shall  be  of  youug,  sound,  and  tnrifty  white  oak,  yellow 
pine  or  other  timber  equally  good  for  the  purpose,  acceptable  to  the  engineer. 
They  must  bo  at  least  eight  inches  (8")  in  diameter  at  the  small  end  and  twelve 
Inches  (13")  in  diameter  at  the  butt  when  sawn  ofl;  and  must  be  perfectly 
straight  and  he  trimmed  close,  and  have  the  bark  stripped  oS  before  they  are 
driven.  The  piles  must  be  driven  Into  hard  bottom  until  they  do  not  move 
more  than  one  half  inch  d")  under. Ihe  blow  of  a  hammer  wclgbinglwo  thou- 
sand (2,000)  pounds,  falling  twenty-five  feet  (25')  at  the  last  blow.  They  must 
be  driven  vertically  and  at  the  distances  apart,  transversely  and  longitudinally, 
required  by  the  plans  or  directious  of  llie  engineer.  They  must  be  cut  oil 
square  at  the  butt  and  be  well  sharpened  to  a  point;  and  when  necessary,  in 
the  opinion  of  the  engineer,  shall  be  shod  with  Iroti  and  the  heads  boiind  with 
iron  hoops  of  such  dimensions  as  he  may  direct, — which  will  he  paid  for  the 
same  as  other  iron-work  used  in  found  at  Ion  x. 

The  necessary  length  of  piles  shall  he  ascertained  by  driving  test  piles  In 
different  parts  of  the  localities  in  which  they  are  lo  be  used.  In  case  a  single 
pile  shall  not  prove  long  enough  to  reach  hard  bottom,  two  shall  be  spliced 
together  as  follows:  The  head  shall  be  sawed  off  square,  and  a  hole  two  Inches 
(3  )  in  diameter  and  twelve  Inches  (13")  deep  shall  be  bored  into  it;  and  into 
ibis  hole  a  circular  white  oak  treenail  twenty-three  Inches  (28")In  length  shall 
be  well  driven.  Then  another  pile  similarly  squared  and  bored,  and  of  as 
large  a  diameter  at  the  small  end  as  can  be  procured,  shall  be  placed  upon  the 
lower  pile,  brought  to  its  proper  position,  and  driven  as  before  directed.    All 

files,  when  driven  lo  the  required  depth,  are  to  be  cut  off  truly  square  and 
□rizontal  at  the  height  given  by  the  engineer;  and  only  the  actual  number  of 
lineal  feet  of  the  piles  left  for  use  in  Uie  foundations  after  being  sawed  off, 
will  be  paid  for. 

Iron.  All  wrought  and  cast-Iron  work  ordered  by  the  engineer  will  be 
paid  for  by  the  pound,— Ibc  price  to  include  the  cost  of  materia],  manufac- 
ture, and  placing  in  the  work. 

Caffar-daiDi,  Where  coffer-dams  are,  In  the  opinion  of  the  endneer.  re- 
quired for  foundations,  the  prices  provided  in  the  contract  for  timber,  piles, 
and  iron  in  foundations,  will  be  allowed  for  the  material  and  work  on  same, 


ovGoQi^lc 


Tools.  All  tools  ueceBsary  for  the  execution  of  the  coDtract.  iacludiug 
jDOrtar  boxes,  will  be  furuistiea  by  tlie  contractor  nt  his  owd  expeoBe. 

StajiriQK.  All  Btft^ng  required  for  tlit  execution  of  tbe  work  done  under 
coairaci  shall  be  (uruisheil  by  ilie  contractor  at  Lis  own  expense.  The  rail- 
way company  will,  however,  upou  tbe  completiou  oF  atiy  structure,  purcbuae 
■of  ibe  foutructor  such  Blagiug  muterial  as  it  can  aUvanlngeouslj'  use,  aud  pay 
(he  contractor  for  such  muterial  au  amount  wblcb,  in  tbe  opinion  of  Ibe  rail- 
waTCompany's  engineer,  bIuiU  Eeein  reasonublc  and  JuBt. 

ExcuvtttioiiH.  Dry  excavations,  or  excavationa  above  water,  will  be 
made  by  tbe  coumclor  wheu  so  ordered  by  tliu  railway  company.  Wet  exca- 
Talious,  or  excavutiouB  below  water,  will  ne  made  by  the  railway  company, 
excepting  wlieu  a  apccial  arrangement  Is  made  with  the  contractor.  All  exca- 
Tatious  will  be  claBsilied  as  tiiber  earth,  loose  rock,  or  solid  rock. 

When  the  excavaiiou  fur  any  hlruclure  is  made  entirely  by  the  contractor. 


634  SPECIFICATIONS  FOR  MASOKRY.  [apP.   L 

which  1b  underslood  aa  covering  all  risks  from  high  water  or  otherwise,  drain- 
ing, baiting,  pumping,  and  all  mutcriuls  connected  \rilh  the  coSer-dama. 
Sheet -pi  line  will  Ire  classed  us  plank  in  foundations;  and  if  left  in  the  ground 
will  be  paid  for  by  the  thousand  feet  (1,000),  board  a 

Bailboad  Buildinoi 


apecitied  in  the  contract.  »lien  an  excavation  is  made  io  part  by  tbe  railway 
company's  force  aud  is  duished  by  the  couti-actar's  force,  or  when  coniractor'a 
force  assists  railway  company's  force  in  making  any  excavation,  contractor  will 
be  paid  for  tbe  actual  time  Ihst  bis  force  ia  employed,  at  laborer's  current  rale 
per  day  pluE  ten  per  cent.  In  case  contractor  furniabes  a  foreman  for  such 
work,  time  charged  for  foreman  must  not  exceed  one  day  for  foreman  for 
each  ten  days  of  labor,  and  contractor  will  be  paid  for  the  services  of  such 
foreman  at  a  rate  per  day  not  to  exceed  the  current  wages  paid  foremen  of 
labu:  ers  plus  ten  per  cent.  In  case  contractor  uses  masons,  foremen  of  mnsons, 
or  other  skilled  labor  for  the  execution  of  tbe  above  "extra"  or  "time"  work, 
tbe  wages  and  time  allowed  will  be  the  same  aa  it  would  be  if  tbe  work  bad 
been  performed  and  supervised  by  laborers  and  foremen  of  laborers.  When 
"extra"  or  "  time"  work  is  performed  by  con Iraclor'B  force,  and  is  supervised 
by  contractor's  foreman,  who  at  the  same  time  and  place  baa  charge  of  and 
is  supervising  "contract"  work,  no  pay  will  be  allowed  contractor  for  such 
supervision,  except  when.  In  tbe  opmion  of  the  railway  company's  engineer, 
It  may  seem  reasonable  and  jusl. 

All  excavations  shall  be  made  strictly  fn  accordance  with  tbe  plans  fur- 
nished by  the  railway  company  and  tbe  slakes  set  by  the  railway  comfiany's 
engineer,  aud  shall  be  executed  in  a  neat  and  workmiinlike  manner.  Where 
excavations  are  made  under  the  supervision  of  tbe  contractor,  his  agent  or 
foreman,  any  erroneous  or  unnecessary  excavation,  and  any  masonry  conse- 
quent to  such  erroneous  or  unnecessary  excavation,  shall  be  entirely  at  the 
-contractor's  expense,  unleas  the  contractor  can  show  thai  auch  unneceaasry 
■work  was  caused  by  errora  in  the  plans  furnished  by  the  railway  company,  or 
by  errors  in  the  railway  company's  engineer's  stakes  or  inslruclions. 

When  excavation  is  made  for  concrete,  great  cure  mnsl  be  taken  to  make 
tbe  pitsor  trenches,  as  tbe  case  may  be,  of  tbe  exact  width  and  depth  required 
for  the  concrete,  aud  any  uniiecessiiry  excavation  made  or  soncrete  used  on 
account  of  lack  of  such  care  oi'  tbe  part  of  Ibe  contractor  will  be  at  hia  ei- 
peiue.     ExcBoa'^B  for  stone  footing  courses  will  be  tnade,  when  not  other- 


TopAa  and  Banta  Ft  BaOrowL 


ovGoQi^lc 


RAILROAD  BUILDIKOS.  535 

wise  ordered,  eigbl  inches  (8")  (four  inches  (4")  oa  eacL  side)  wider  tliaii  the 
fooling  course.  Kxcavatiooa  for  walls  not  h&viiig  footinc  courses  will  be 
made,  when  nol  oiherwiae  ordered,  Iwelve  inches  (Vi")  (3x  inches  (6' )  on 
each  side)  wider  thao  the  wall  is  thick. 

Before  masonry  is  built,  excavations  must  be  cleared  of  all  loose  earth, 
mud,  or  other  ohjectiooable  material. 

Stone.  Btone  will  be  furnished  by  Ibe  contractor  at  his  own  expense,  and 
be  of  a  quality  suitable  for  the  diSerenl  classes  of  masonry  hereinafter  speci- 
fied, and  be  subject  to  the  iaspectiou  and  acceptance  uf  the  railway  company's 
eiigineer.  Stone  will  be  loaded  on  cars  and  unloaded  by  the  coalractor  al  hla 
own  expense.  Stone  will  be  delivered  by  the  railway  company  on  the  nearest 
available  side  track  to  the  work,  aud  no  charges  whalsoever  will  tie  allowed 
contractor  for  hauling  stone  from  cars  to  the  work,  except  in  extreme  cases, 
where,  in  the  opinion  of  the  railway  company's  en^aeer,  such  charges  may 
appear  reasonable  and  Just, 

Saud.  All  sand  for  mortar  or  concrete  will  be  furnished  by  the  conlractor 
at  hia  own  espense.  When,  in  the  opinioo  of  the  railway  company's  engineer, 
sand  can  not  be  secured  by  contractor  within  reasonable  distance  by  wagon 
haul  and  at  a  reasonable  price,  transportation  by  rail  will  be  furnished  by  the 
railway  company,  it  being  optional  with  the  railway  company  at  what  point 
sand  shall  be  procured.  Whcu  railway  company  furnishes  transportation  for 
sand,  cara  shall  be  loaded  and  unloadea  by  contractor  at  his  own  expense. 

All  sand  furnished  by  contractor  shall  be  clean  aud  sharp,  and  sublect  to 
the  inspection  of,  and  reiectiou  by,  the  railway  company's  engineer.  When, 
in  the  opinion  of  the  railway  company's  engineer,  sand  requires  screening,  it 
shall  be  screened  by  the  contractor  at  his  own  expense. 

Cement  and  Lime.  All  cement  and  lime  will  be  furnished  by  the 
railway  company  at  its  own  expense;  and  will  be  delivered  on  cars  on  the 
nearest  available  aide  track  to  the  work.  It  shall  be  unloaded  by  the  con- 
tractor at  his  own  expense,  and  shall  be  piled  up  in  such  manner  by  him  as  the 
railway  company's  engineer  may  direct.  Cement  and  lime  shall  be  covered 
and  protected  from  the  weather  by  the  contractor  at  hie  own  expense,  in  such 
manner  as  seems  suitable  to  the  railway  company's  engineer;  and  the  con- 
tractor will  be  held  responsible  for  the  value  of  any  cement  damaged  on  ac- 
count of  unsuitable  protection. 

Water.  Water  reiiuired  for  all  work  done  under  contract  shall  be  fur- 
nished by  the  contractor  at  his  own  expense.  No  charges  made  by  contractor 
ior  hauling  water  will  be  allowed.  Wlien,  in  the  opinion  of  the  railway  com- 
pany's engineer,  water  can  not  be  procured  by  the  contractor  wilhin  reason- 
able wagon  haul,  or  at  a  reasonable  expense,  it  will  be  furnished  by  the  rail- 
way company. 

Mortar.  Except  when  otherwise  ordered,  all  mortar  shall  be  thoroughly 
mixed  in  a  box,  in  the  following  proportions:  One  (1)  part  cement,  two  (3) 
pans  sand,  witii  sufficient  water  to  render  the  mixture  of  the  proper  consist- 
ency. Care  must  be  taken  to  thoroughly  mix  the  sand  and  cement  dry,  in  Ihe 
proportions  specified,  before  the  introductiou  of  water  into  the  mixture.  Mor- 
tar shall  not  be  mixed  except  as  it  is  used,  and  no  mortar  must  tie  allowed  to 
stand  over  night  in  mortar  boxes  or  elsewhere. 

Coucretc.  All  concrete  shall  consist  of  one  (11  part  cement,  two  (3)  parts 
sand,  and  six  (8)  parts  broken  stone,  together  with  suftlcicnt  water  to  mix  the 
sand  and  cement  to  the  consistency  of  good  mortar  for  masonry.  The  pro- 
portion of  sand,  cement,  broken  stone,  and  the  iguanllty  of  water  used  In  the 
mixture,  moy  be  varied  at  the  optiou  of  the  railway  company's  engineer. 

Stone  shall  be  of  a  quality  acceptable  to  the  railway  company's  engineer, 
and  be  broken  so  that  seventy -Ave  (TS)  per  cent,  will  pass  through  a  iwo-incb 
<2")  riiie  and  so  that  all  will  pass  through  a  two  and  one  half  inch  (24") 
Ting.    Broken  stone  shall  be  free  from  mud,  dirt,  and  other  objectionabla 


ovGoQi^lc 


8PB0IFICATIOHS  FOB  VASONBT.  [APP.  I. 

o  the  iuapectlon  of,  and  rejedioii  bj,  the  lafl- 

The  lADtTstid  "cement  muBt  be  tboroughl;  mixed  dry,  in  a  clemn,  tl^t 
mortar  boi,  before  the  introduction  of  wftt«r;  aoA  &rter  water  ie  app)j«d  to  lh« 
mixture,  the  whole  muRl  be  norked  over  with  hoes  until  a  good  mortar  of 
proper  consisteocy  U  secured.  After  the  mottar  is  made,  the  broken  stone 
mml  be  tboroughlj  drenched  |wl)h  clean  water,  and  then  shall  be  added  U> 
the  mixture  in  [he  proporlion  slated  above— or  in  any  other  proportion  which 
the  railway  company's  engineer  may  specify.  The  concrete  must  then  be 
worked  over  and  mixed  until  each  atone  is  completely  covered  with  mortar 
and  all  spaces  between  the  stones  entirely  tilled  with  same. 

The  concrete  shall  be  deposited  in  horiEoalal  layera  not  eiceedlDK  twelve 
inches  (13')  in  depth,  and  shall  be  thoroughly  tamped  when  BO  requirra  by  tbe 
railway  company's  engineer. 

Rubble  3£asoury.  Knbble  masonry  will  be  classifled  aa  either  henvy 
rubble,  foundation  rubble,  pier  rubble,  or  uncoursed  hammer-sqiured  rubble. 
The  latter  will  be  called  for  convenience  squared  rubble  [see  g§  208-12]. 

r^v;  Bnbbla.  When  not  otherwise  specidud  or  shown  ou  tbe  plans,  foot> 
In^  course!!  will  be  built  of  rubble  masonry.  When  footing  courses  exceed 
tlii'ity  inches  00 ')  in  width,  (he  masonry  will  be  classided  as  heavy  rubble; 
and  when  thirty  inches  (iiO")  or  less  in  width,  the  masonry  will  be  classified  aa 
fonndaiion  rubble. 

Heavy  rubble  footing  courses  shall  be  built  of  well-Beiecied  stone,  which 
shall  have  a  tbickneas  not  l|:s9  than  [he  beigbt  of  tbe  fooling  course.  Bach 
stone  sbnil  have  a  bottom  bed  of  good  surface  over  its  entire  area,  which  shall 
be  horizontal  when  the  stone  Is  in  position.  As  much  of  the  upper  surface  of 
eacb  stone  as  will  be  directly  under  the  masonry  to  be  put  above  the  footing 
course  shall  be  uniform  and  parallel  to  the  bottom  bed.  At  leiLst  one  third  '}> 
of  the  length  of  the  Footing  course  shall  be  built  of  througb-Rione,  and  a 
larger  proportion  shall  be  furnished  by  the  contractor  when,  in  the  opiuioa 
of  the  railw^  company's  engineer,  more  through-stone  are  re<iuired  to  >iccure 
stability.  No  stone  shall  be  used  which  will  not  bond  or  extend  under  the 
masonry  to  be  built  above  the  footing  course  a  distance  equal  to  at  least  one 
third  lj|)  the  thickness  or  width  of  the  masonry;  and  not  more  tban  two  s!one» 
shall  be  used  at  any  section  to  make  up  tbe  total  width  of  tbe  fooling  course, 
and  tlie  exposed  face  oF  each  stone  shall  be  at  least  twelve  inches  (i'i  )  in  length. 

Alt  stones  must  be  roughly  Jointed  with  a  hammer  for  a  distance  back 
from  their  faces  equal  to  tbe  projection  or  oEEset  of  the  footing  course.  No- 
spaces  to  exceed  forty  (40)  square  inches  in  area  shall  be  filled  with  spalls  or 
chips,  and  the  total  area  of  all  spaces  must  not  exceed  Jive  (5)  per  cent,  of  the 
area  of  tbe  footing  course. 

All  stone  when  placed  in  position  must  be  thoroughly  rammed  imtil  firmly 
embedded  in  a  bed  of  mortar,  which  shall  first  be  placed  id  bottom  of  excava- 
tion or  trench,  and  after  stone  are  placed  in  position,  all  joints  must  be  well 
grouted  with  mortar.  When  so  required  by  the  railway  company's  cnffincer, 
fuutiuir  cour.ses  shall  be  built  exactly  to  the  dimensions  shown  on  drawings  or 
spceihcutions,  or  with  their  edges  built  to  a  line. 

Fooadatlon  Bubblt.  In  general,  and  when  not  otherwise  speciSed,  all  masonry 
below  the  bottom  of  water  table  or  below  tbe  top  of  rail  for  stone  buildings, 
and  all  masonry  below  the  sill  of  wooden  buildings,  will  be  classiHed  as  foun- 
dation rubble,  except  footing  courses  more  tban  thirty  inches  (30 ')  in  width, 
which  will  bo  classified  aa  heavy  rubble.  Foundation  rabble  may  be  required, 
however,  for  any  portion  or  for  all  the  maaonry  in  any  structure,  in  which 
case  DO  additional  price  shall  be  allowed,  except  when,  id  tbe  opinion  of  tbe 
railway  company's  engineer,  it  sball  seem  reasonable  and  just. 

In  this  class  of  masonry  no  stone  having  an  exposed  face  shall  be  less 
than  one  twrniy-fourth  i^.^)  of  a  foot  in  cubical  contents  nor  less  than  two 
Inches  (i")  thick.     Any  stunc  smaller  tban  this  will  be  conddered  a  si»]l; 


ovGoQi^lc 


BAILROA.D  BriLDINGS.  637 

and  sptUli  Are  not  to  be  used  to  exceed  seven  (7)  per  ecDt.  of  the  entire  mass. 
The  contractor  will  not  be  required  to  furnish  Btone  (except  for  through- 
■tooe)  Isreer  than  odc  and  one  balf  feet  {1^')  la  cubical  contents,  but  the  stone 
used  shall  not  average  less  than  one  half  ({)  of  a  cubical  foot  in  contents.  Ho-' 
stone  nhall  be  u«ed  which  doea  not  bond,  or  extend  Into  the  nail,  at  least  six 
Inches  (6").  One  through -alone,  whose  face  area  shall  not  be  less  than  one 
half  (1)  of  a  fiuperdcial  foot,  will  be  required  for  each  sixteen  (16)  auperflclal 
feet  01  face  measurement  of  wall,  and  more  than  this  may  be  required  by  the- 
railway  company  when,  in  the  opinion  of  its  engineer,  a  larger  pioporlion  of 
through-Elone  U  required  to  secure  stability;  prrrvided,  however,  Ihat  the  con- 
tractor shall  in  no  case  be  required  lo  furnish  tbrough-stone  to  exceed  ten  (10) 
per  cent,  of  the  entire  mass.  At  least  twenty  (20)  per  cent,  of  the  entire  ma- 
sonry shall  consist  of  beadera,  or  bond  stones.  In  walls  twenty-four  inches 
(S4'')  thick  or  less,  these  headers  shall  be  at  least  two  thirds(|)  the  thickness  of 
the  wall  in  length;  and  in  walla  more  than  twenty-four  Inches  (34")  thick,  they 
shall  bo  of  sufficient  length  and  be  so  placed  as,  in  the  opinion  of  the  railway 
cooipany'a  engineer,  seems  necessary  to  secure  well-bonded  and  stable  work. 

Each  stone  shall  be  laid  in  its  quarry  bed,  and  any  stone  set  on  edge,  or 
with  the  planes  of  its  strati ti cation  vertical,  will  be  rejected  nud  ordered  re- 
moved at  the  expense  of  the  contraclor.  Stones  shall  be  hrmly  bedded  in 
mortar,  and  all  spaces  and  joints  thoroughly  grouted  with  same. 

Piar  Enbhle.  Piers  or  pedestals  whose  horizontal  sectional  area  Is  nine  (0)- 
square  feet  or  less  will  be  classlbed  as  pier  rubble.  When  this  areaexcceds 
nine  (9)  square  feet,  the  maaoury  will  be  classed  as  foundation  rubble.  Foot- 
ing courses  for  such  piers,  when  not  exceeding  sixteen  (16)  square  feet  in  arra, 
will  t)e  classed  as  pier  rubble;  and  when  exceeding  this  area,  they  will  be 
classified  as  heavy  rubble. 

Footing  courses  must  be  built,  so  far  as  practicable,  in  accordance  with  the. 
preceding  speciUcatioos  for  heavy  rubble  masonry.  Masonry  In  piers  above 
footing  courses  must  be  carefully  built  of  well-selected  sioae,  having  horizon- 
tal beds  and  vertical  joints,  ana  be  thoroughly  bonded;  corners  and  faces 
must  be  built  true  and  plumb.  The  specillcalions  for  foundation  rubble,  so 
far  as  practicable,  shall  apply  to  this  class  of  masonry. 

Each  pier  or  pedestal  shall  be  furnished  with  a  hammer- dressed  cap  stone 
not  less  than  six  inches  (6")  thick,  of  same  area  aa  pier,  which  loust  be  accu- 
rately set  at  the  requited  level.  The  price  of  this  cap-stone  must  be  Included 
in  the  contract  price  wir  cubic  yard  for  this  ctass  of  masonry. 

■qoarad  Bubble.  When  not  otherwise  specified,  the  walls  of  all  stone  build- 
ings above  the  bottom  of  the  water-table  will  be  built  of  uucourscd  squared 
rubble. 

Iq  general  the  speciSoationa  for  foundation  rubble  will  apply  to  this  class 
of  masonry,  the  diClcrencc  between  the  two  claases  being  in  the  construction 
and  linish  ot  the  outside  face.  The  outside  face  of  the  wall  will  he  built  of 
well-selected  stones,  aa  nearly  uniform  in  color  as  possible,  which  shall  be- 
neatly  squared  to  rectangular  faces,  and  which  in  all  cases  shall  be  laid  on 
thefr  natural  or  quarry  beds.  The  beds  of  the  stones  shall  be  horizontal  and 
the  side  joints  vertical,  and  no  joints  lo  exceed  three  fourths  (J)  of  an  inch  will 
be  allowed.  No  stone  having  a  face  area  of  less  than  eighteen  (18)  square 
inches  or  a  thickness  leis  than  three  inches  (S")  shall  be  used ;  and  the  average 
face  of  all  the  stones  ^11  not  be  less  than  seventy-two  (73)  square  inches. 

The  inside  face  shall  be  built  and  finished  in  accordance  with  the  specifica- 
tions for  foundation  rubble. 

Corners  of  all  building  shall  be  built  up  with  quoin  stones,  uniform  in  size 
and  arrangement,  for  which  no  extra  pay  will  be  allowed  contractor.  Drafts 
will  be  cut  on  the  comers  when  so  Jpecified  or  shown  on  plans.  All  joint* 
shall  be  cleaned  or  raked  out  for  a  ulstance  of  three  quarters  of  an  Inch  ({"), 
and  neatly  pointed  with  a  raised  joint.  The  mortar  used  for  pointing  shall  be 
composed  of  auch  material  as  the  railway  company's  engineer  may  select. 


ovGoQi^lc 


038  SPSCIflCATIONS  FOB  HASOKBT.  [APP.  I. 

OpeoiD,^  foi  windows,  rtoura,  or  for  other  purpoaea,  will  be  made  ia  walls 
wbet.  specified  or  sUowd  od  pltias.  The  jaiobe  of  sucb  openiogs  sball  be 
neatly  cut  to  a  true  aod  smooth  surface,  aod  be  droTe  tooled,  ci'aDdfllled,  or 
tooth-tuced  [see  pages  125-34,  particularly  138  sud  133],  as  may  be  requirtd 
by  ibe  railway  company's  engloeer.  Bed-joints  of  jamb-stones  must  be  care' 
fully  cut,  so  that  uo  joint  lo  exceed  one  half  an  inch  (i  ")  will  appear  on  the 
exposed  face  of  the  jumbe.  Jatnb-stones  shall  be  uniform  in  height,  and  one 
half  shall  be  I h rough-stones,  lu  general  the  anangement  of  jamb-stones  will 
be  hIiowu  on  drawiugs. 

The  contract  price  for  noy  opening  shall  include  the  coat  of  cut-stoae  sills. 
lintels,  arches,  jamb-stoues,  or  any  other  cut-stone  work  required  for  that 
opening.  In  case  no  contract  price  is  made  for  any  opening,  the  contractor 
will  be  paid  such  price  sa,  in  the  opinion  uf  the  railway  company's  engineer, 
seems  reasonable  and  just. 

Cut  st«ne  shall  be  furnlEbed  and  put  In  place  b^  the  contractor  when  bo  re- 
quired by  the  railway  company.  The  stone  furnished  shall  be  of  the  quality 
nquired  for  the  work,  aud  acceptable  to  the  railway  company's  engineer;  and 
must  be  cut  strictly  in  accordance  with  the  plans  and  speciti cations  in  each 
case,  and  must  be  bo  cut  as  to  lie,  when  in  position,  on  natural  or  quarry  beds. 
Cut  stone  will  bo  paid  for  at  the  price  apecllled  In  contract,  and  In  case  cut 
stone  is  furnished  by  the  contractor  for  which  there  is  no  contract  price,  a 
price  will  be  paid  which,  in  the  opinion  of  the  railway  company's  engineer, 
aeems  reasonable  and  just. 

Cut  stone,  or  dimension  atone  for  cu^8tone  work,  may  be  fumiahed  by  the 
railway  company  at  its  own  expense,  and  the  contractor  required  to  set  the  ctit 
atone  In  position,  or  lo  cut  and  set  the  rough  dimension  alone,  Inwbich  case  the 
contractor  will  be  paid  for  the  work  either  as  "extra"  or  "time"  work,  or  at 
a  price  which,  in  the  opinion  of  the  railway  company's  engineer,  may  seem 
reasouable  and  just. 

Wall  Masonry.  All  walls  shall  be  built  to  a  line  both  Inside  and  out- 
aide,  and  both  faces  shall  be  finished  with  a  smooth  anil  uniform  surface, 
which  shall  be  fial-pointed  with  a  trowel,  in  a  neat  and  workmanlike  manner. 

The  upper  courses  of  all  walls,  when  leveled  or  finished  for  the  reception  of 
superstructure,  shall  be  tirovided  with  a  Ihrougb-slone  at  each  end,  and  also 
one  through-slone  for  at  least  each  five  (6)  lineal  feet  of  wall.  These  Ihrouj^h- 
stone  shall  be  dressed  on  their  top  beds  and  accurately  set  to  a  level  one  half 
inch  (i")  below  the  level  of  the  bottom  of  the  superstructure.  Between  these 
through-stone  the  walls  must  be  carefully  laid,  with  tbe  upper  beds  of  Ibe 
4toues  brought  up  flush  with  the  lop  of  the  above-described  through-stones  so 
as  to  secure  a  perfectly  level  aurface  for  the  top  of  the  wall.  In  uo  case  shall 
spalls  or  chips  be  used,  except  in  vertical  joints. 

The  contractor  will  make  such  openinaa  In  walls  as  are  required  for 
windows,  doors,  or  other  purposes.  No  additional  pay  will  be  allowed  fi^ 
such  openings,  except  where  Jamba  are  to  be  cut,  and  cut-stone  sills  or  linlela 
are  retjuired,  in  which  case  such  price  per  opening  will  be  allowed  as,  in  the 
opinion  of  the  railway  company's  engineer,  may  seem  reasonable  and  just.  Cut 
or  drenaed  dime  us  ion- stone  will  be  furuiahed  and  set  In  position  when  ao  re- 
quired by  plans  or  spec Iti cations,  and  will  be  paid  for  by  the  railway  company 
at  Kiich  price  as  may,  in  the  opinion  of  its  engineer,  seem  reasonable  and  just. 
Wood,  iron,  or  other  material  which  may  be  required  lo  be  built  into  the  ma- 
sonry shall  be  properly  put  iulo  position  by  the  contractor,  and  no  extra  pay 
'  shall  be  allowed  for  such  work.  I'he  cubical  cotitents  of  auch  material,  how- 
ever, will  not  be  deducted  from  tbe  measurement  of  the  masonry. 

When  ao  required,  the  contractor  shall  plaster  the  outside  surface  of  base- 
ment or  oiher  walls  with  hydraulic  morlar,  composed  of  sUch  materials  as  tha 
railway  company  may  aelecl.and  lor  such  work  the  railway  company  will  pay 
the  contractor  a  price  per  square  yard  In  addition  lo  the  contract  price  of  the 
jnasonry. 


ovGoQi^lc 


ARCHITECTUEAL  MASOJtKY,  CHS 

Foundations  for  Trestles.  Faun dni Ions  for  tresile  bents,  such  aa  are 
built  for  coal  climw,  will  l>e  clas^itied  as  foundation  nibble,  and  must  be  built 
with  grtsal  uare.  Tbe  lower  footlDg  coureu,  vbeu  excecdiug  tbirtf  incbea  (SO") 
Id  wialli.  will  be  cluBscd  us  heiivy  rubble.  The  upper  couree  sball  Lave  one 
hamraer-drfsst-d  llirough-stoue  at  eacU  end  of  wall,  and  at  least  Ibiee  such 
through -atonea  between  the  end  Ibrough-Hloues;  otherwise  the  top  course  will 
be  finished  in  acpordance  with  the  second  paragraph  under  "  wall  masonry  " 
above.  Thia  does  not  apply  to  bent  foundations  inside  of  cual-chiite  biiild- 
iog,  which  will  be  built  in  the  same  manner  aa  foundation  walls  in  general. 

W'ell-wall  Masonry.  Wull-waiUwillbeclasaiUedasfouudatfonmbble. 
Welt  masonry  will  be  built  under  the  supervision  of  the  well  foreman  who  has 
'Charge  of  the  well  excavation,  and  coniractor'a  foreman  shall  execute  the  work 
^strictly  in  accordance  with  instructions  giveu  by  him.  When  well-walls  are 
■sunk,  or  settled,  an  the  excavation  Is  mane  p^al  care  must  be  taken  to  make 
the  outside  surface  perfectly  smooth  and  uniform;  and  as  manj  headers,  not 
to  exceed  the  maximum  heretofore  specified,  may  be  required  as,  in  the  opin- 
ion of  the  railway  company's  engineer  or  well  foreman,  are  necessary  to 
secure  slability. 

Measurement  of  Masonry.  In  measuring  masonry  paid  for  by  the 
'Cubic  yard,  all  openings  will  be  oeducted,  and  the  number  of  cubic  yards 
Tvlll  be  the  actual  cubical  cooleuts  of  the  miisonry  built.  The  cubical  contents 
-of  cut  stone,  iron  work,  timber  or  other  material,  Dullt  into  the  masonrv  by  the 
'Contractor,  will  not  be  deducted  from  the  cubical  coolants  of  the  whole  mass. 

Architectckal  Masonby.* 

'  Permit.  The  contractor  for  the  masonry  shall  take  out  a  building  per- 
zolt,  including  water  for  himself  and  plasterer  and  all  other  contractors  that 
may  require  water  about  the  building  during  the  progren  of  the  work.  This 
■contractor  shall  also  take  out  street  and  ohatruction  permit,  and  permit  for 
building  curb  and  retaining  walls.  The  cost  of  the  above  permits  la  to  be  in- 
-cluded  in  the  estimate. 

Grade.  The  inside  grade  at  the  building  shall  be  such  as  the  superlntend- 
•ent  aliall  direct.  At  the  time  of  starting  any  pier,  this  contractor  shall  ascer- 
tain from  the  superintendent  the  height  the  inside  grade  shall  be  set  atxivelbe 
«atabiisbed  outside  grade,  taking  Into  consideration  the  settlement  that  may 
«ccur  during  the  progress  of  the  work. 

Kxcavation.  It  is  the  intention  that  Ibis  contractor  shall  call  at  the 
building  and  examlce  for  himself  the  exact  situation  of  the  building  site.  He 
■tliall  remove  from  the  premiacsall  eartb  or  debris,  except  that  which  the  super- 
intendent may  consider  good  for  use  in  the  grading  required  about  the  build- 
ing. Thia  contractor  shall  complete  such  grading  about  the  building  as  may 
be  found  necessary.  All  sidewalk  stone  that  may  be  found  In  coDDection  nitn 
the  excavation  shall  be  removed  by  the  mason,  the  said  stone  becoming  his 
properly.  The  same  shall  apply  lo  any  foundation  stone  or  other  material 
that  may  be  found  In  excavating,  although  none  of  said  material  sball  be  used 
in  connection  with  the  new  work  about  the  building. 

This  contractor  shall  excavate,  according  to  drawings,  for  all  walla,  piers, 
areas,  etc.,  the  intention  being  that  the  general  level  shall  be  excavated  simply 
to  the  level  of  the  finished  basement  floor.  All  trenches  shall  be  excavated  to 
the  neat  siie  aa  near  aa  practicable;  and  eachshall  be  leveled  loa  line  on  llie  bot- 
tom, ready  to  receive  the  foundation.    At  suchtime  as  the  superintendent  shall 

•  Except  In  torm.  tbfse  speclflcstlona  ar«  tbnae  emplored  by  Buraluiii  &  Knot,  archi- 
tects. OhlcaiFO.  for  the  Socle^  ot  Bavlntcs  Buildtns,  deTdaiid,  Ohio,  and  oootorm  cloKlj  to 
abe  Rcneral  form  empiorad  b;  these  architects. 


jvGooi^le 


UO  SP8C1PICATI0H8  FOB  MASOWKT.  [APP.  I. 

direct.  Ihfs  contractor  aball  level  aO  tbe  bssement  surfiuxs  aod  floors  of  areas 
to  a  line  UnishiDg  three  inches  (8")  below  the  top  of  tbe  level  of  the  flniAed 
bsMment  Hooib,  and  leave  itae  surface  ready  to  receive  the  work  of  other  coa- 
tractors.  When  considered  oecesssr;  in  the  Judgment  of  the  saperiDtendent, 
sli  earth  shall  be  tamped  lolidly  and  then  be  wet. 

If  any  pockets  of  quicksand  are  found,  this  contractor  shall  excavate  tli» 
same,  and  till  in  uotidly  with  concrete  composed  of  clean  broken  stone  of  a  size 
that  will  pnss  through  a  two-inch  (2")  ring  and  English  Poriland  cement,  pro- 
pordoited  t  to  3,  rammed  solidly  into  place  iu  the  pockets,  iu  layers,  as  the 
superintendent  may  direct.  None  of  the  sand  that  may  be  found  while  ex- 
cavating shall  be  used  in  connection  with  any  of  the  work  about  tbe  building. 

After  all  foundations  or  retaining  walls  are  in  and  fixed,  this  contractor 
shall  tump  tlie  eartli  solidly  around  Ihem,  leaving  it  level  to  s  line  within 
eighteen  inches  (IS")  of  the  finished  grade,  and  ready  to  receive  the  work  of 

Balllug.  This  contractor  shall  do  all  bailing  and  draining  of  trenches  or 
basemeut  surfaces  that  may  be  found  necessary  during  the  progress  of  the  work. 

Slioriuu:.  Thiscouliactor3li:ill  protectall  walla  of  the  bdjoiniag  buildings, 
underpin  allwalls  that  may  be  considered  necessary— in  tbe  Judgment  uf  the 
anperinlendent — to  place  ibe  new  work  or  to  prevent  injury  of  the  old  work, 
make  good  all  repairs,  provide  aucb  cuttiuL'  as  may  be  found  necessatr  to 
place  the  work,  and  leave  the  adjoining  buildings  as  good  as  at  the  start.  The 
cost  of  this  work  is  to  be  included  in  bis  estimate.  This  contractor  shall 
furnish  and  put  in  place  any  sheet  piling  that  may  be  required  to  retain  the 
earth  white  the  footings  are  being  put  in.  and  include  all  costs  of  the  same  hi 
hls-estimaies. 

Pt^tevtion,  This  contractor  shiill  use  proper  care  and  diligence  in  bisc- 
ing  nnd  securing  all  paru  of  the  work  against  storm,  wind,  and  the  action  of 
frost.  Every  night  during  freezing  weather,  each  pier  or  wall  shall  be  covered 
on  top  with  sail-cloth,  and  the  covering  shall  extend  down  over  the  face  of  all 
green  work 

Con«Tete  Footiiig^a.  This  conirsclor  shall  provide  a  frameof  tbe  area 
oC  the  pier,  composed  of  two-inch  (2")  plank,  so  arranged  that  the  parts  can  be 
withdrawn  and  the  pier  left  isolated  after  tbe  concrcle  is  set  [see  g  SO'l].  All 
footiciga  not  otherwise  indicated  shall  be  constructed  of  concrete  furnished  by 
this  contractor.  The  cement  shall  be  flrsl-qualily,  fresh  Utlcn,  or  any  other 
equally  good  quality  approved  by  the  architects.  The  contractor  at  the  time 
of  BitlimUtiug  his  proposal  shall  state  the  kind  of  cement  be  intends  using. 
The  sand  shall  be  clean  and  sharp.  Tbe  stone  shall  be  clean  limestone,  crushed 
to  a  size  that  will  pass  through  a  two-inch  <3")  ring,  and  screened.  The  con- 
crete shall  be  composed  of  these  ingredients  in  the  following  proportions:  one 
(1)  part  of  hydraulic  cement,  one  (1)  part  of  sand,  and  two  (31  parts  of  crushed 
limestone.  The  cement  and  sand  sliati  be  mixed  dry,  and  the  mixture  wet 
with  a  quantity  of  water  sutHcient  to  reduce  it  to  the  consistency  of  mortar. 
The  stone  and  mortar  shnll  be  thoroughly  mixed  and  hitd  in  trencues  as  soon 
as  possible,  in  layers  of  not  more  than  six  inches  \li'')  in  thickness., and  be 
rammed  until  the  water  rises  freely  to  the  top. 

All  concrete  footings  shall  be  carefully  leveled  or  pitched  with  concrete, 
and  be  left  ready  to  receive  the  piers,  walls,  or  columns,  in  each  case  as  par- 
ticularly indicated  on  the  dniwiiigN, 

Railroild-Rall  Footings.  All  railroad  mils  that  may  be  required  In 
connection  with  tbe  foundations  shall  be  of  Bessemer  steel,  weighing  not  less 
than  siily-dve  (85j  pounds  per  yard,  straight  and  sound,  cullo  the  neat  lengths 
indicated  on  the  drawings.  Ait  railroad  rails  shall  be  furnished  by  this  con- 
tractor, and  by  him  set  In  place  to  centers  and  levels  as  indicated  on  the  dia- 
grams.    None  of  these  railroad  rails  are  to  be  painted. 

"-- -,e  used  in  connection  with  steel- rail  footings  shall  be  composed 


ovGoQi^lc 


ABCHITECTDtlAL  U&SONBT.  541 

of  one  (1)  pari  of  flrel-quiility  Englisli  Portland  cemcot— or  any  other  equally 
.good  quaUty  approved  by  tbc  arcUllecls, — one  (1)  part  of  clean  sharp  aana,  ana 
two  (3)  pariB  ot  clean  limestone  cruahed  to  cbeatQUt  size.  TbU  concrete  shall 
be  lulled  as  for  concrete  fooIiagB,  and  shall  be  rammed  in  solidly  between  Ihe 
rails;  and  each  tier  shall  be  neatly  squared  at  the  outer  edge. 

Rubble  Masonry.  All  piers  colored  blue  on  the  drawings  Bbnll  be 
classed  as  cut  stone,  and  shall  be  furnished  and  set  in  place  by  another  cod 
tractor;  but  all  walls  colored  blue  on  the  drawings— referring  particularlv  to 
foundation  walls  tor  boiler-bouse,  foundation  wall  for  staircase  way  in  alW, 
area  walls,  curb  walls,  and  curtain  walls  between  plera— shall  be  classed  as  nib- 
ble masonry,  and  shall  be  furuiahed  and  set  in  place  by  the  mason. 

All  stone  used  in  connection  with  nibble  masonry  aball  be  of  selected,  large 
size,  lirst-quality  stone,  laid  to  the  lines  on  both  sides,  well  filled  toother  md 
thorougblv  pointed,  frequent  headers  that  extend  through  the  wall  being  pro- 
vided. All  stone  shall  be  not  less  than  two  feet  sli  Inches  (3'  6")  long,  one  foot 
six  inches  (1'  <1"|  wide,  and  eight  Inches  (8")  thick,  eKcept  such  aa  may  be  found 
necessary  lo  level  up  a  course  to  the  required  height.  The  Intention  is  that  all 
walls  shall  be  laid  in  courses  about  one  foot  six  inches  (1' e")  in  height, 
leveled  off  at  each  course.  Each  stone  shall  have  hammer  dressed  beds  and 
joints,  and  shall  be  firmly  bedded  and  be  well  cushioned  into  place.  All 
joints  shuU  be  filled  with  mortar.  The  facing  of  all  walls  shall  be  laid  ran- 
dom range,  and  the  face  of  the  stone  shall  be  coarse  bush-hammered. 

At  the  time  of  compietingthe  retaining  walls,  this  contractor  shall  excavate 
at  least  one  fool  iV)  on  the  outside  of  the  wall,  and  point  up  all  Joints  on  the 
ouUide;  and  then  provide  and  apply  a  coal  of  firsl-qualily  English  Portland 
ccmenl,  not  less  than  a  half  inch  (i")  thick,  lo  the  outside  of  the  wall  from  top 
to  bottom.  No  cement  covering  will  be  required  on  the  curb  walls.  All  Joints 
showing  inside  the  building  shall  be  raked  out  and  neatly  pointed  up  with 
cement;  and.  In  addition,  the  face  of  w&Us  coming  in  connection  with  the  area 
«ha11  be  squared  up.  the  Joints  finishing  not  to  exceed  one  half  inch  (i")  thick. 

Ail  curb  walls  that  may  bo  required  to  receive  the  side-walks  shall  be 
brought  to  such  levels  us  the  superintendent  shall  direct,  and  shall  be  cemented 
■on  lop  and  left  ready  to  receive  the  side-walks — which  shall  be  furnished  and 
set  by  another  contractor,  None  of  the  screen  walls  shall  be  sol  in  place  until 
such  time  as  the  superintendent  shall  direct.  The  foundation  for  the  slaircase 
bay  in  the  alley  shall  be  set  in  place,  after  the  building  Is  partly  completeit,  at 
Huch  time  as  Ihe  superintendent  may  direct.  This  contractor,  at  the  time  of 
starting  this  work,  shall  fiirnUh  such  anchors  as  may  be  considered  neces- 
sary. In  the  Judgment  of  the  superintendent,  to  attach  his  work  to  (hat 
already  In  place,  and  shall  do  all  cutting  and  fitting  that  may  be  found  neces- 
sary to  properly  place  his  work. 

Hortar  tor  Bobble  Kasonry,  All  rubble  masonry  above  referred  to  shall 
be  laid  in  mortar  composed  of  perfectly  freah  Utica  cement— or  other  eijually 
as  good  approved  by  the  architects, — mixed  In  the  proportion  of  one  ( I )  part 
of  cement  to  two  (3)  parts  of  clean  sharp  coarse  sand.  The  sand  and  cement 
Ahall  be  mixed  In  a  box  dry;  then  wet,  tempered,  and  immediately  used. 

Common  Bricb-work.  All  walls  orsections  colored  red  on  Ibe  draw- 
ings or  otherwise  indicated  to  be  of  brick,  shall  be  of  selected,  flrvt-qualily, 
hard-burned  Chicago  sewer  brick — or  other  equally  good  quality  approved  by 
the  architects.  The  above  quality  of  brick  shall  be  used  throughout  the  entire 
work,  except  that  hollow  fire-clay  brick  shall  be  used  in  connection  with  all 
'  IB  between  windows  on  elevations  above  the  first  story,  and  for  the  back- 
all  stone-work  above  "-'  ' '  -■-'  -'-'-•'- a... ,. »t_  •._._ 

shall  be  used.     No  pressed  o 
this  work. 

All  brick  shall  be  well  wet.  except  in  freezing  weather,  before  being  laid. 
JIach  brick  shall  be  laid  with  a  shove  Joint,  in  a  full  bed  of  mortar,  all  inter- 


ovGoQi^lc 


543  SPECIFICATIONS  FOR   MASONKT.  [APP.  L. 

Btices  being  thoroughly  filled;  and  where  the  brick  come«  tn  connection  with 
ancbors,  each  one  shall  be  "brought  borne"  to  do  all  the  work  poodble.  Up 
to  aud  [Deluding  the  flflh  story,  cTerv  fourth  course  shall  coDsist  of  a  beading 
coiine  of  whuTe  brick  extending  through  the  entire  tbichuess  of  the  walls; 
above  Che  fifth  story,  eveiy  sixth  couiw:  shall  be  a  heading  course.  All  mor- 
tar joints  shall  be  neatly  struck,  as  is  customary  for  "  first-class  trowel  work." 
All  coui^ca  of  brick-work  shall  bo  kept  level,  and  the  bonds  shall  be  accurately 
preserved.  When  necessatr  to  bring  auy  course  to  the  required  height,  clip- 
ped courses  shall  be  turmed,  as  iu  no  case  shell  any  moi-iar  joints  finisb  more 
than  one  half  inch  (i")  thick.  All  brick-work  shHil  be  laid  to  the  lines,  and 
each  tier  kept  plumb,  the  inteution  being  that  none  of  the  wicdow.f  ranies  shall 
be  set  in  place  until  the  roof  is  on. 

All  lintels  over  openings  indicated  in  conned  ion  with  brick  parlilion  walls 
In  basement  shall  be  of  steel  railroad  rails,  aud  shall  be  furnished  and  set  in 
place  by  the  mason.  These  rails  sbail  be  painted  one  coat  of  mineral  paint  be- 
fore being  brought  to  the  building. 

All  cm  stone  shall  be  hacked  as  fast  as  the  superintendent  miiy  consider 
proper,  and  the  mason  shall  build  Id  all  anchors  thut  may  be  furnished  by  the 
contractor  for  the  cut  stone.  When  openings  or  slots  are  indicated  in  connec- 
tion with  walls,  the  size  and  position  of  the  same  shall  be  such  as  the  superin- 
tendent shall  direct,  unkEts  otberwife  shown.  This  contractor  shall  leave 
openings  to  receive  all  registers  that  m^iy  be  required  in  connection  with  Ibe 
heating  or  ventihiiiQg  system,  aud  shall  also  leave  openings  In  conucction  with 
the  comer  vaults  at  such  places  In  the  floor  and  ceiling  as  the  superinteudeut 
shall  direct. 

All. masonry  that  may  be  required  at  the  time  of  setting  the  boilers  shall  be 
furnished  and  set  in  place  by  the  conlmctor  for  steam-beating  apparatus. 

"■■-■■         ■      All  n      - 


Mortar  far  Srlok-wark.  All  morlur  used  in  connection  wiih  sewer  brick, 
together  with  the  mortar  in  the  brick  parapet  walls  and  the  chimney  above 
the  roof  line,  shall  beconiposcd  ot  two  (3)  parts  of  lime  mortar -made  up  very 
poor,— and  one  (1)  part  of  first-quality  Utica  cement — or  other  equally  good 
approved  by  the  architects.  Said  morlar  shall  be  used  immediately  after  being 
mixed,  aud  in  do  case  shall  any  be  used  that  has  stood  over  nighl. 

The  remaining  brick-work,  including  the  fire-brick  hereinafter  referred  lo, 
shall  be  laid  in  mortar  composed  of  best  slaked  lime  and  coarse  sharp  clean 
sand  of  approved  qiiality. 

Brick  ArclieH.  Where  arches  are  indicated  in  connection  with  the  first- 
story  banking  vault  or  in  connection  with  roadway  in  the  court  on  the  north 
front  of  building,  said  arches  shall  be  formed  with  common  brick  laid  in  row- 
lock courses,  regularly  bonded  [see  8'?831  The  mortar  for  this  work  shall  con- 
sist of  one  <I)  part  Fori  land  cement  and  three  (8)  parts  clean  sharp  sand.  Eac-h 
brick  shall  be  laid  with  a  ohove  joint:  and  each  rowlock  course  shall  be 
cemented  ou  top  at  the  time  of  laying  the  next  course'.  The  last  course  shall 
be  cemented  on  top,  and  be  left  ready  lo  ri'ceive  the  concrete  floor  or  roadway 
— which  shall  be  provided  by  another  coniraclor. 

All  centers  that  may  be  required  in  connection  with  (his  work  shall  be 
furnished  and  set  iu  |>tace  by  the  carpenter;  and  none  of  said  centers  shall  bo 
removed  until  such  lime  as  the  superintendent  shall  direct.  After  the  same 
have  been  removed,  this  contractor  shall  thoroughly  clean  down  all  face-work. 

All  iron  indicated  in  connection  with  Ibis  work  shall  be  furnitihtd  and  set 
ill  place  by  the  contractor  for  conslnictional  iron  work,— except  the  bearing 
plates,  which  shall  be  bedded  by  the  mason. 

Smoke  Britchinjr.  The  smoke  briichin^  indicated  in  connection  with 
the  main  bnltcr-stack  will  be  furnished  and  set  in  place  by  the  contractor  for 
constructional  iron,  although  the  mason  shall  back  up  the  same  at  such  time 
as  the  superintendent  shall  direct. 

Fire-brick.    The  lining  shown  to  stand  alone  In  connection  with  the 


ovGoQi^lc 


A,BOHITECrCRAL   3CAS0NRT. 


All  fire-clav  brick  ahafl  be  laid  in  flnt-class  fire-clay  mortar,  eocb  brick 
beiog  laid  with  a  solid  Joint  neatly  struck  ou  each  side  with  a  trowel. 

Hollow  Fire-clay  Brivk.  All  brick  used  in  conncctioD  wiib  the 
spandrels  above  the  flrst  story  od  all' elevHtiona,  tL>getber  with  alt  backiae  re- 
quired in  iionnection  wttli  the  stone  work  above  the  lop  of  the  eizlith-3tory  floor- 
beams,  shoJl  consist  of  flrBl-quality,  hard-buroed,  fire-clay,  bolTow  brick,  equal 
in  quality  to  sample  lo  be  seen  at  the  office  of  the  architecU.  £acti  brick  shall 
be  laid  with  a  shove  Joint,  This  contractor  shall  point  up  Ihis  work,  aod 
leave  the  surfaces  of  the  walls  amootli  aud  ready  lo  receive  plastering. 

Cllttlog  ami  Fitting'.  This  contractor  shall  do,  promptly  and  at  the 
time  the  superintcudeul  so  directs,  all  cutting  and  tilling  that  may  he  required 
in  connection  with  the  mason-work  by  other  contractors  to  make  their  work 
come  right,  and  shall  make  good  after  them. 

Settiu^  Irou-work.  It  is  tbt;  intention  that  all  coast  ruction  al  iron- 
work shall  oe  furnished  and  net  in  place  by  another  contractor,  nnd  that  all  Iron 
aball  t>e  hoisted  from  the  outside  of  the  building  by  means  of  a  derrick.  In 
setting  the  beams  and  columns  in  place,  the  mason  shell  keep  pace  with  the 
contractor  for  constructional  iron  work,  and  at  no  time  shnll  the  mason  be  left 
one  story  behind  the  constructional  iron-work.  Each  beam,  girder,  orcolumn 
shown  10  rest  on  the  masonry  shall  be  provided  with  iron  plates  by  the  COQ- 
Irnctor  for  constructional  iron,  said  plates  being  furnished  to  the  mason  at  the 
sidewalk;  and  themasoti  shall  set  the  same  in  place,  firmly  bedded  in  mortar, 
at  such  position  or  height  as  the  superintendent  shall  direct. 

All  ITOD  wall-platea  that  may  be  required  to  receive  the  flre-clay  arches 
will  be  tumlahed  at  the  sidewalk  by  the  constructional- iron  contractor;  and 
this  contractor  shall  set  each  in  sucn  position  and  at  such  height  as  die  super- 
intendent shall  direct. 

Cut  StoDe.  All  parts  colored  blue  on  the  drawings,  or  otherwise  Indi- 
cated to  be  of  stone,  or  usually  classed  as  cut  slone,  shall  be  furnished  and  set 
la  place  by  the  contmclor  for  ciil  stone.  The  same  shall  apply  for  the  terra- 
cotta roof  copings  indicated.  All  mortar,  staging,  or  hoisting  appaiatus  that 
may  he  required  in  connection  with  this  work  slisll  bf  fomisbed  try  the  con- 
tractor for  cut  stone.  All  cut  stone  will  be-  set  from  the  outside;  but  tne 
mason  sb^l  back  up  all  cut-stone  work  iti  a  iiianDcr  approved  by  the 
auperintendent. 

Latino  Hasohbt  in  Pkrezino  Weiathbb. 

Masonry  shall  be  laid  in  freeElng  weather  only  la  case  of  absolnte  neces- 
sity, and  tuen  only  by  permission  of  the  engineer.  When  neceisary,  masonry 
iiiny  be  laid  in  freezing  weather,  provided  (1)  that  the  stone  or  brick  nhile  ■ 
twiug  laid  are  dry  and  perfectly  free  from  snow  or  ice;  (2)  that  there  is  added 
to  the  water  used  in  roiling  the  mortar  1  per  cent,  of  salt  for  each  Fahrenheit 
<tegree  below  freezing  ;  and  (8)  that  the  mortar  ii  mixed  rather  dry.  Any 
masonry  laid  In  freezing  weather  shall  not  he  pointed  until  warm  weather 
in  the  spring.* 

•  For  ■ddlclonal  precautions  that  ma;  be  preacrlbed,  tea  H  111-148,  pagw  lcS-4. 


ovGoQi^le 


APPENDIX  n. 


SUPPLEMENTAEY  NOTES. 


Note  1>  Labor  Bt^nlrtd  In  Qounlnf 
bibor  required  In  quturying  the  Hlone  [gn< 
the  Croton  River  nearNr  -  ""--■-  "'•-  "^ 
plugs  aod  feaibers. 

Labob  SsquiRKD  nr  Quabbtiiio  Ohkibb. 


„.      The  foUowlDx  table  ihows  the 

gnelm]  for  the  Boyd's  Comer  dam  on 
Tork  City.  Tbestoue  to  becut  wasqilU outirilh 


Km>or  LuoR. 

DATS  PSB  CcBtO  TABD. 

Bough  <tc«e. 

Stone  to  be  cut. 

IFn«»..., 

if 

Labor  louUngie* 

several  kinds  of  masonry  for  the  New  York  Department  of  Docks,  In  1874-5. 
Between  December  1B73  and  May  187S  with  an  average  force  of  40  stone- 
cutters,  2,065  yards  of  granite  of  the  following  kinds  were  cut  iu  tbe  Depart- 

"  1.524  yards  of  dimensloD  stone  were  cut  into  headers  and  stretchers 
TbU  stone  was  cut  to  lay  ^-Inch  beds  and  joints,  tbe  faces  being  pointed  work, 
with  a  cbUel  draft  U-incbes  n id e.  The  headers  averaged  3  feet  on  tbe  face  by 
8  feet  in  depth;  and  the  slrelcbtrs  averaged  6  feet  long  by  2  feet  deep,  the  rise 
being  30,  28,  and  38  inches  for  tbe  different  courses.  The  average  time  of 
stone-cutter  cutting  one  cubic  yard  waa  4.58  d^s  of  8  hours;  and  lue  average 
cost  of  cutting  was  $37.64  per  cubic  yard  (tL.03  per  cubic  foot}. 

"  310  yariA  of  coping  were  cut  to  lav  i-iach  beds  and  joints,  pointed  on 
tbe  face  with  chisel  drait  same  as  headers  and  stretchers,  and  8-cut  patent- 
bammered  on  top.  with  a  round  of  Si  Inches  radius,  the  dimensions  being  3 
feet  long,  4  feet  wide,  and  2i  feet  rise.  The  average  time  of  stone-cutter 
cutting  ona  cubic  yard  was  6.38  days,  and  tbe  average  cost  of  cutting  $88.07 
per  cubic  yard  ($1.41  per  cubic  fool). 

"  281  yards  of  springers,  keystones,  etc..  for  arched  pier  at  the  Battery, 
were  cut.  These  stones  were  of  various  dimensions,  part  being  pointed  work 
and  part  S-ctll  patent -hammered.  Tbe  average  time  of  slone-cutt«r  cutting 
one  cubic  ynrd  was  6.88  days,  and  the  average  cost  of  cutting  was  $41.85  per 
cubicyard  ($1.56  per  cubic  foot). 

"  The  abovecoat  of  cutting  includes,  besides  stone-cutter's  wages,  lalrar  of 
moving  stone,  nil  material  uscd^uch  as  timber  for  rolling  stone,  new  tools, 
etc.. — sharpening  tools,  soperinlendence,  and  interest  on  stone-cutter's  shed^ 
blacksmith  shop,  derrick,  sud  railroad.  These  expenses,  in  per  cents,  of  the 
total  cost  of  cutting,  are  as  follows:  superintendence  6:  sharpening  tools  IS; 
labor  roiling    stones    80;    interest  on  sheds,   derrick,  and  railroad    1;   new 

*  J.  James  R  Croeii,  In  Trani.  A^,  Soc.  of  C.  E.,  Vol.  m,  pwa  SU 

t  Aum  an  attlole  b;  Wm.  V.  KmciMj,  la  Ikaaa.  Am.  Stn.  or  O.  S.,  ToL  IT.,  pp.  SlO-11. 


ovGoQi^lc 


ftUPPLBMBNTABY  NOTBa. 


g  Btone  1;  total  G2  per  cent.,  which,  added  ti 
.  ^YSB  the  tot&l  cost.    During  the  last  year  s 

_ e  required  to  do  at  leaai  13  superficial  feet  per  day  of  beds  and 

Jcdc'^,  or  iti  equivalent  In  pointed  or  fine  cut  work.  The  BTerage  day 'a  work 
of  each  stone-cutter,  during  one  year  and  a  half  in  which  118,w8  superflcial 
feet*of  beda  and  Joiuta  were  cut,  was  IS.S  square  feet  per  day,  for  which  he 
received  14.00. 

"  The  following  table  ahows  the  amount  of  granite  that  a  stooe-cutler  can 
cut  in  a  day  of  8  houia. 


Labok  Rs4tcuiXD 

IB  CtlTTDIO  GbAHITB. 

bMDOvVoaa. 

"SIX-:.- 

Hew  York. 

f^^^^^iii.aM>«i,i,^^gi^-mi, 

19 

10 

T.JT 

u 

?.B 
B.U 

i:S 

is.a 

P«D-h»roiBmjd..          

SS 

Note  3.  Oett  of  CattiB;  Oianlto.*  The  average  day's  work  of  a  tnati 
in  cutting  Uie  face  of  granite  pitch-faced,  range,  squared-sUine  masonry 
<§  107,  page  187)  of  the  Boyd's  Comsr  dam,  aa  deduced  from  three  and  ahalf 

J  ears'  work  In  which  5,300  cubic  yards  were  cut,  was  6,878  square  feet,  the 
imenslous  of  the  ataaes  being  1.6  feet  rise,  S.6  feet  long,  and  3.7  feet  deep; 
and  the  averure  day's  work  In  cutClog  the  beds  to  lay  t-liich  Jolnta  waa  18.7 
square  feet.  The  granite  coping,  composed  of  two  courses — one  of  12-iDch 
riac,  80-inch  bed,  and  Sf-feet  average  length,  and  one  of  24rlnch  rise.  48-Inch 
bed,  and  84-feet  average  length. — the  top  being  pean.hammered,  the  face 
being  rough  with  chisel  draft  around  it,  and  the  beds  and  Joints  cut  to  lay 
i-incli  joints,  required  0.1  days'  work  of  the  cutter  per  cubic  yard. 

"  In  cutting  thegranit^for  the  nite-houses  of  the  Crotou  Reservoir  at  Eighty- 
sixth  Street,  New  York  Citv,  In  1861-3,  the  minimum  day's  work  for  a  cutter 
waa  fixed  at  15  superficial  feet  of  Joint.  This  included  also  the  cutting  of  a 
-chisel  draft  around  the  face  of  the  stone,  which  costs  per  linear  foot  about  ono 
fourth  aa  much  as  a  square  foot  of  joint,  making  the  actual  limit  equivalent 
to  about  17.7  square  feet  of  joint.  On  this  work,  the  proportion  to  be  added 
to  the  cost  of  the  cultera  to  ^ve  the  total  cost  waa  aa  follows,  the  average  for 
19  monUia'  work:  for  superintendence  8  per  cent. ;  sheds  and  tools  7;  sharpen- 
ing l4>ols  11;  labor  moving  stone  in  yard  10;  drillers  plugging  off  rough  tacea 
4:  maktega  total  of  40  per  cent,  to  M  added." 

Note  4.  Ooit  of  Laying  Out  ttMs.f  Host  of  the  cut  atone  was  laid  by 
one  mason,  nore  than  two  not  being  employed  at  any  time.  The  mason's 
'  gang  also  shifted  derricks.  The  coat  of  hauling  stone  to  the  work  varied 
with  the  poattion  of  the  blocks  In  the  yard  and  whether  they  were  assorted 
there  into  courses  or  lay  promlscuoualy.  The  amount  of  labor  required  in 
laying  the  msaonry  waa  as  follows: 

■  ProiD  an  atcouDt  at  tbe  conntnictloa  of  ttae  Bord'a  Conuir  dun  on  ttw  Crolon  River 
aaar  Hew  York  ClQ'.lbr  J.  Janes  B.  Croaa,  la  Trans.  Am.  Soo.  atCX.,  Vol.  HL,  pp.  a«-«4. 
tIbid..p.WI. 


ovGoQi^lc 


fiCPPLEMEKTABT  NOTES. 


[app.  n. 


Labor  RaqunisD  m  Latik«  Cur-aroira  Hasohbt. 


Amount  pnt  Cmo  Yabo. 

Eon)  or  LiBO>. 

Hoiited  br  BmhJ. 

HotaedbyttteuL 

6K. 

lOtoWft 

WWlOft 

»to»(»^ 

o.wo 

0.1B4 
0.100 
0,W7 

6:i«i 

1.OT0 

,      O.IIB 

O^BS 
O.Hl 

oow 

( 

DTD 

ow 

m 

S.S80 

Note  K.  Coat  of  BraaUnr  9tm»  for  Cannreta  ■  "  The  BtODe  [enetss]  for 
the  concrete  wm  broken  to  be  not  more  than  3  inches  In  Ita  l&rgestdtmeiisioD. 
A  BlSike  Btone- breaker  of  IGinch  jaw.  driven  by  a  IS  horse -power  enetne.  waa 
used.  The  stone,  which  was  obtained  from  the  surface  and  frum  old  fence 
walla  in  the  vicinity  of  the  work,  whs  tough,  and  used  up  the  laws  very  faet. 
A  movable  jaw  ordinarily  lasted  30  days.  The  Blone  was  delivered  to  the 
breaker  by  carts.  havioK  been  Qret  sledged  to  the  proper  size — about  13  Inches 
square  by  6  inchea  thick.  The  machine,  when  monlng  at  full  speed,  with 
one  man  feeding,  two  men  supplying  him  with  stone,  one  keeping  Ibe  screen 
clear  and  helping  to  fill  barrows,  Iwn  wheeling  away  the  stone,  and  one  on 
the  dump,  could  oreak  144 cubic  feet  In  an  hour,  oral  the  rate  of  54.4  cubic 


of  breaking  for  the  last  year  was  8.8  cubic  yards  per  hour,  which  maybe 
assumed  as  the  economical  rale  for  the  1 5-inr,h  machine.  The  largest  machine 
<20-iQch)  will  break  8  cubic  yards  per  hour,  if  fed  to  that  capacity;  but  6  cubic 
yards  per  hour  is  more  economical.  The  following  table  gives  the  cost  In 
time  of  breaking  the  stone: 

IiAsoH  Rbqotrbd  IK  Bkeakiko  Btohb  tor  Comcbvtb. 


■ 

DlTB  PI>  Cdmo  Tabd. 

1B>7 

ISM 

1888            18M 

IS 

o.sso 

0,'on 

!;S 

si 

Laboran  l<Ad?ns  cartot 

Carts  hail linK       -  ■■     

il 

Total  number  ot  cubic  rartB  broken 

ATerBRe  uumberor  cubic  fsnlg  broken  p«rdar.-. 

w 

■  From  an  account  ol  the  construction  ot  Che  Bord's  Comer  dam  on  tbe  Ci 
DearNewTorhCitr,  byj,  JamoaRC™w.  loTrann.  Am.Soc.  ot  C.  K..  Vol.  IIL. 

t  ■■  The  difference  In  sli-dKinE  ta  occounted  for  thuH:  In  1687  mAn.t  fence-wall 
MonoB  were  niied,  which  newled  no  Bledgine,  but  were  hard  to  cru-b     t"  IMS  : 
the  quarry,  which  required  uleifKlne,  was  almost  BiclustTcly  ueed, 
ouanr  spaUa  were  used.    In  imnhftfltonewoBquarriedtort'- >— 
nearly  ill  "f  it  was  eledged.    The  carttiiR  aad  tending  varied 

Ipers,  fuel  and  repalra  ot 


stone-yard  and 


jvGooi^le 


APP.  il]  bdpflementaby  notes,  547 

Note  41.  Cdft  «f  ImMidiag  Lun  BtMiM  in  Coaanti.*  "Tbe  Ifiree  ud- 
wrougbt  stone  kill  in  the  concrete,  from  tbe  fouDdations  to  within  4S  ^et  of 
tbe  top  ot  the  dum,  were  set  In  lull  mortar  beds  aod  the  surfaces  plastered 

Just  before  concrete  nns  laid  around  tbem.  The  letting  was  done  uiosily  by 
aborers,  ooe  mason  superintending.  The  cost  Id  day's  work  per  cubic  yard 
was  u  follara : 

Labob  RoquiKED  TO  Ihbkd  Labqb  Stones  m  ConcsxTX. 


Cdbic  YAao. 


KlRD  a>  lUBOR. 


Laboren  setlug  r 

"         plaiurf DK 

"         loMfiw  LBBrm 

Tmdu  transfDrUDg:  stone 

Total  quattl[vt&t<l.Gublc  yards.. 


"  Tbe  cttat  of  the  mass  of  concrete  and  large  stone,  as  laid  In  1667,  was 
69^  per  ced.  of  tbe  cost  of  the  concrete  alone;  and  in  1868  it  was  84J  per 
cent,  of  suiii  cost.  If  tbe  large  stones  do  not  exceed  'iH  per  cent,  of  tbe  mass. 
the  cost  of  the  maw  is  reduced  about  10  per  cent,  below  concrete  cost,  wbile 
Its  speciflc  |nkvlty  is  Increased  about  8  per  cent." 

Note  T.  CnuhlnK  flttsngth  of  Sswtr  Pipe.  Experiments  made  at 
Chicago  iu  1879  by  W.  D.  iloiehkiss,  and  reported  to  the  author  by  Black- 
mer  and  Pwt,  of  Bt.  Louis,  gave  the  strength  of  ordinary  sewer-pipe  as  fol- 
lows, when  tested  as  described  on  page  408:  one  12-incb  and  bve  15-inch 
pipes  falledftt  an  average  pressure  of  S,504  lbs.  per  sq.  ft.  of  horizontal  sec- 
tion; aud  tTo  IS-inch  and  two  IS-lnch  were  not  crushed  by  an  average  pres- 
sure ot  9, (KB  lbs.  per  sq.  ft. 

Note  8.  Holding  Fowsr  «f  Drift  Bolts.  According  to  experiments 
'  made  nndeltbe  autbor'a  d1recilon,§  tbe  average  holding  power  oi  a  1-incb 
round  rod  4Hven  into  a  Jg-iucb  hole  In  pine,  perpendicular  to  the  grain,  is 
601  pounds ber  linear  inch  (8  Ions  per  linear  foot);  and  under  the  eame  con- 
ditions tbe  holding  power  of  oak  is  1,300  pounds  per  linear  inch  [7.8  Ions  per 
linear  footl  The  holdinr  power  of  a  bolt  driven  parallel  to  the  grain  Is 
almost  exactly  lialf  as  mucli  as  when  driven  perpendicular  to  tbe  grain.  If 
tbe  bolding:  power  of  a  1-Inch  rod  In  a  ^|-Iucb  bole  be  designateil  ss  1 ,  the 
holding  po«er  in  a  ))-incb  bole  is  1.S9.  in  a^finch  bole  3. 13,  and  in  a  )]  Inch 
hole  l.OB.     the  holding  power  decreases  very  rapidly  ss  the  bolt  is  withdrawn, 

r;rt-lH.1U  ill  the 


t.  both   b  ultimate  holding  power  and   in  holding  |i 


r  wjiiar 


*  J.  JauiHi  R.  Ctdm  In  Trar 


lectBd  up^ra  or  the  civil  Enrii 
DC  ThtncKnogiaph,  pp.  SS-Sq. 
t  TrckiUvTaph,  Unlverslt]'  oC  1 


wrs'  Club  nr  Ibu  {jalrenlly  i 


itllilDoU,No,4,'pr«l» 


I  Tht  TrckiUvTa^.  Unlversit]'  oC  iuinota,  Mo.  B,  pp.  S9-41. 


ovGoQi^lc 


D.qitizeabvG00glc  I 


PLATE    I. 

CAISSON,  CRIB  AND  COFFER-DAM, 

Havbb  de  Oracr  Bbidqb. 

FOR  TBZT,  na  PAOB  SSfl. 


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PLATE    II. 

6-FOOT  ARCH  CULVERT. 

Illinois  Centkal  Standard, 
fob  tbzt,  ibb  faob  «m. 


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PLAi'e  111. 
8-FOOT  AUOH  GULYEBT. 

0.     K.     A2TD    a.    StANDABD. 

FOB  TBXi;  ftBB  PAam  m 


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jjGooi^le 


10-FOOT  ARCH   CULVEBT. 

SSKI  CIIWUL4B. 

4,    i'.   ano  S.    K.  StahdasO. 

•■Of    VEXI    iH*    ?AUF  l». 


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PLATE  V. 

10-FOOT  ARCH  OVI.VEBT. 

axaKXKTAL. 

A.  T.  AiTD  S.  F.  t^Ajnuuta 

roa  TIXX.  KBB  F&OB  «■> 


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jvGooi^le 


PLATB  VU 

18-FOOT  STANDARD  AHOH  OITIiTEB? 

fin  TBIT,  us  f ASS  iA  \ 


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INDEX. 


form,  as* 

Jiy  of  moKDry,  SO,  18S 


icpOtttl 
potrition,  no 
Irob,  alMKDMtitot,  itabflJtr,  tfB,  «W 
I  bwsktnfft  isOS 


deflnltlons,  SIB 

ezamiila.  cUitD  JohD  *rdi,  BK 
,  ■tooebHdnia, 

tunnel  arch,  BK 
_  Wutamgtoo  bridn,  SU 
kMd  Bupported,  siT 
nutHne  fonnrlTg,  BTO,  fOS 
etrllcliur.  mecbod.  SSS 

time,  to? 

oulvert,  4IB 

eo8i.4Si 

«XBmplps.4U 

AtcEliMt,  T.  A 


>,  T.  A  S.  T.,  BBKineiital,  4» 


aifc»«o,  K,  A 

eon,  in 
nUnoIa  CoDtnU,  ■entdronkr,  «M 

■taodArd  ««tiiental,4tt 
JODoUon  ot  wlnra  to  body,  «0 
mMOni?.  ™«t  or,  1B7.  IBt,  ISO 

quality  ot,  ISK 
Vectflcatknia,  fomiiUtEotu,  «>,  Ua 

pCTtnc,  148 
•WDeuliil  w.  Hical-clrcular,  4^ 
roUj  of  *liiB«,  «B 
•Irtlnitlon,  of  kfodi  of  arebeg,  Ml 
c^put.oCuisrob.  440 


Arehea.  dlmeoaioni  of  abutnMoto,  HI 

ralea  deriTod  from  pracUcti,  4M 

tbJcl(iienofabiilment,4M 
tUckimskt  crovn,  American  B 
Uce,4W 
Eii^h  pncrlcn.  4W 
French  praettoe,  4M 
thlelnuaBU  BprJngiliK.  4llt 
dntnaKoGOS 

Uieory  of.  4(1 


elaMlc,  Uieory  o 
engrailun.  MB 

InTerWd,  for  fot_ 

JplDt  Of  nipKire,  4BJ 
limof  resfitance.  de 


bypothcdis  of  Icaac  preeom.  H 
bTPoUmb  of  l«u  crnwn  thru 

Wnl  of  niptupe.  4B7 
l^Tler  B  principle.  4CS 
WlDkler'i  hypotfiesta,  4ffi 


method  of  fallun. 


criterion,  479 

■rmmetrieal  load.  4M 
Renenl  aolutlOD.  4Ba 
■pedal  solution,  4e» 

inuymmelrleal  load.  471 
Scbemfr-stbeoiT,4T4 

alfKbraic  aorution.  4:11 


>  tbewT.  «8> 


Tariotu  tbeoria  nfsnvd  Ic 


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&BT— BBI 

Artiflcdid  none,  lU 
BilOD-Ooigiiet,  lit 


bmcking.  140 

deSnilionB,  IBS 

dreuine,  IgB 

mortar  required  per  jari,  U 


ralajftbrioit ,__ 

■on.TopekaASaoMF^  bndceabnt- 
onlfsrt.  Inm  ^pe,  41 


-^ a.4tl.4aB 

■emi-drcul&r  Mch.  489,  410. 4ST 
Ax,  sad  Taotb«x.  IM 

Barter,  deflnitlan,  lU 

Bxarlug  pllaa.  Hfl 

BearlDR  powar,  pile*,  q.  t.,  Sa 


iBtalr  biidce,  pier,  Sffl 
pneainuta  louDduloo,  calnon, 
<iaat,SD3 

Irictronal  realsUnoe,  X7 
rale  ol  Blublnit.  UG 
BlMtfng  In  compraasBd  olr.  WIS 
erlok.  •bftorptive  power,  tl,  t»,  41 
srcbca.  bond.  SIO 

eiBinplee.SII,  EIS,M4 
'bumEDE-.  84 
oZualflcaUon.  SS 
^rs-briclE,  how  made.  K 
elaaUdC}',  co-efllolent  ot,  14 


data  tor  MCI  inaMs,  brick 
labor  requfred.  174 
monuT  required.  174 


•pedfljslioiia^arobes,  ITT m,  Ut 


reqiilRlWB  for  good,  87 


data.  18,  40 
Bridge  abuinwDt,  • 


BBI— C] 
Were 


Bridie  piers. 

Bond,  biiek  arches,  ft 
briok  masoiirr.  101 


deuuipHoD,  196 

Buah-hammer,  IX 
BulldineBConec,  cbuatflcaUen,  M 

requldid*  for  good.  8 

leete,  t ;  tee  af»  Btone. 
Bulldliiga,  data  tor  compatlnc  wel^t  of, 

specifloBEloiK  tor  biick-wOrfc  far,  Ml 


pier,  ouUfne  of,  STB 
presHire  on  touadatiou,  ITT 
Btablllt;  of,  871 
Monea  Id  a  courae  of,  US 

diseiWH,  SOO 
pDeiunaKc.  384.  SM 

Blolr  bridge,  284 

fint  use  or,  380 

eaidlnK,  sse 

Havre  de  Qnee  bridn,  M 
Canadian  box  colrert,  JA 


natunLOa 
deflnitlon,  U 

BpHclAcatloni.  TBo 

weli^t.  per  ban«J,  54 
Portland,  congUUKf  of  ntame,  TBd 

deacHptiun.  Gl 

apedllcatlons,  78*,  78/^785,  Wt 
(treuKth,  B7,  ftio,  TSd,  TBa,  fVi  !M 
tealH.  aee  teaEa  betoxr, 
welsht  per  barrel,  84 
Boaendale,  dellaltloa,  SS 
alag,M 

ipecl  Deal  Inns.  qnalltT,  American,  Ttig 
Englleb,  TSa 
FrcDch,  TSe 
German,  TSd 
detliery  sod  alorace,  78rk 


IrsTa,  S),  T 


flneuiw.  «,  88.  784  ;«<,  TV,  n 
•el.  lime  of,  SO 
•oundneas.  to.  TBii,  TSa,  TSe 

aevele^-Hied.  WaU  of,  ES 
■pedfic  grsTlty,  U 


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rapidUj'  ot  ■pplylDft  I 

eight.  t*,eS 
lUifunl  pomp 
ler  at  luunda 

Center  of  ffTBTlt;  or  trapevilil,  t"  fliitl,  BIB 
Center  of  prengure  an  (ouiidutUHi.  ahi 
Chaooelini  *ad  vcdglug,  qiwtrrjIdK  by,  IIS 
CblMl.  piUiblns,  U7 

■plIitlnK.  IsS 

fioth.  j% 
Chlcuo.  K.  *  H.  tnh  eulTert.  *K.  4M 
Co  cfflctent  of  McUon,  (uuiidkUoiia.  ir,t 

manoorj.  115 
«oSBr-dam.  definition.  KB 

coiiBtruotiOD.  US,  SW 

double,  ttl 

"     redsOncobridKe.M) 


Iron.  Ml 


>lr,  phjilolot;lcAl'effeat,an 
-air   procnw   tar    rouudaUoDa, 


'^''^fcT' 


Bconomlciof,  Ilia  _ 

InindlrDW  tor  •  7"^  11>9.  lUfc 
UrltiK.  ;l:))i 

proportlonii.  theory  At,  lOt 
•trenitb,  1»p 
o<imprBMl*e,  ll%> 


Cotiiimc-  and  pilea  for  roundatlona,  9M 

Colt,  we  tbe  srUcle  in  question. 
Coulomb's  theory  at  retuiotDK  wall,  Ml 
<Jonr  aCoDM  tor  box  ciilTi^ne,  396 
Uwory  tor  IblcknsB.  «W 

tonnulaa,  BW 

pTBctLoal  data,  401 


dlmeniiona  of  the  pipe,  tifl 
end  trail*,  content!  of,  <14 
eiunplee,  41*.  410 
lance.  41S 
welf^t  ot  the  pipe,  tlS 


contenta,  401,  «M,  4(» 
oau.«B 

dimenilant,  «B,  4M,  Ml 
dMiUe.40G 
cod  walla,  MB 
examjdea, «».  4IM,  M 
fouDdstloD.  W! 
08110017.  QuUI'r  of.  401 
■psolAcatluna,  401,  tU 


001.— EFT 
le  hoi.  Standard  form,  40 
ore  K.  K.,  401,  4M 


coat  of  the  pipe,  410 
end  walls. «« 

maCerial  required.  411 
urenirtli  at  the  pipe.  408 
vaier-way  miulnHl,  SSI 
(ormulu.  m 
for  quanilty  of  floir.  SH 
Uryer-e  tor  the  area.  tM 
TafbM'a  for  tbe  an-a.  BM 

Bractical  methoil  of  finding.  > 
IDE  plleroundatlon.  »6 
t-yllndA^  mrtace,  method  ot  R 

Dam.  arched  tu.  rraTity.  ItD 
blblioKniph;.  £4 
currod  BniTlty.  B>1 
eartb.  SB 
grarlty,  B" 


CQrred  KraTlty.  Wl 

■traifiht  •jreei  oi.  ttraliht  toe,  aW 


Cain'*,  sa 
Kranta'*.an 
method  of  flDdlDK.  XT 
Quaker  Brldce,  US 
■lldlnR.  SIS 
qualliy  of  maaonry.  tSS 
when  employed,  as 
wUtb  on  top,  BSS 
nok-fill.  384 
COM.  BST 

irben  employed.  BBS 
elone-lllled  timber  crib,  MB 


Dorcbester  BaiidvtoDe.  SO 
DowpI,  IBB 
DrHl|tBB.Bn 

Htlroy.  !71 

Horrl*  ft  Cumi 

mild  pump,  S~ 
Dredrinpthr-' 
DHttlioru,  d 

hoMlnit  power,  KB 
Drills  iiKd  in  quarrylnc,  HB 


\g  pile*  w 


m  brickwork.  iH 


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BogrkTlDgi.  tor  list  A  •«  Table  of  Ooa- 

BMInuh*  data  for,  brtok.  46.  IT.  178,  IH 

t^eiuent,  W,  88 

lime,  St 

mortu',  88,88 

umd,  TOMB 
ExciTator,  oomDrMaed-4lr,  IR;  *««  alto 

Dredmaiia  Pumiia. 
Bn>kMl*es,  118 

dywunlM,  UI 


■MMiDK  power  oi  rocE,  job 
beulDB  power  ol  MDd,  ISt 
beeiInK  power  of  Kinl-liqald  soil,  IM 

■UIII1IIU7,  IM 
bed  ot,  defined,  tSS 
brldce  plen.  IM,  SH;  *«  oiM  tetow. 
bulldlncs,  188 


bearins  power  ot  hIIb.  □.  t.  abon,  IBS 
eoDBOlIdMlDe  tbe  eoll.  IW 
depth  required,  IK 


tooUnBH,  MtKootinra. 
frDlase.  q.  t., «^at 
load  u>  be  aappoited,  IN 
pnea,  «ee  Piles, 
piles  aod  ffriJIase,  SOS 
pllee  and  concrete,  at 
preparing  (be^bed,  91) 


IdPn 


,1fi~ 


prooBaa,>14,  Se 
lion  ot  ibe  dam. 

puddle  wall,  W) 
HUtBKe.  Kfi! 

repari^  tile  'bed.  X64 


M.  IDS.  SIG,  «6 

t  vartouB  procesaee  compared,  SIO 
Dd  erect  calnson  proceHs,  S68 
iimMiaa  ot  (he  caisson,  SB! 
m  ot  the  crib,  UN 

cxckvatinB  (he  slw.  STD 

prioolple  ot  (be  method,  EST 


drainage.  IBS 

dredging  tbrougb  wells,  371 
dredges,  q.  T..S71 


(ubes^STS 


hiiok  orllndets.  IT 


Bawkeabury  bridge,  S7t 
Pougbkeepale  bridge,  tn 
trictlonai  retlelanee  m  ilDklBC,  I7B 


maaonrj.KT 
freeiioa  proceed  W 
adTautanOW 

oost,aor 

deiatla,B07 
hiMorr.MT 

prino^lle,  807 
tootlDgt,  (M  Foottnsi  al 
frlcdODal  reslBtance.  Ot 
Iron  crllndoTe,  SVfl 
masoDrf  crlinden.  87 

wood  piles,  S17,  M8 

HawkesbatT  brfdn,  ITS 
iDdependent.  IMTmI) 
loverted  areb.  818 
lateral  yielding,  808 

pile,  we  Piles. 
piles  and  gritlagit,  m 
piles  and  ooocnite.  HH 
pn-pariug  the  bed.  SIS,  tM 
Point  PleasaiiL  brtdee.  eot 


adTanlages.  808 

alr-cbunber.  S84.  887, 896 

alr.lack  construction.  181,  8M,  MO, « 

posltlOD,  880 
ceInoD.18t 

Blair  brMge,  «4 

Havre  de  Qrace  brtdge,  q^  T.,  188 
oompre*sed-ulr  process,  Wl9 
cott,  Blair,  888 

Brooklyn,  SOS 

European  examples,  8M.  HO 

""iSdToraoeraM 


Pbllsd^phla,  808, 8M 
deBoldons.  S7S 
examples.  Brooklyn,  B8S 


Bt««l-tall  footings,  lU 

limber  In,  888 

timber  tootlngB,  Ul,  US 


ovGoQi^lc 


viiuuuiuunHMBa.«H 
wind.  cIT^  of,  Wt 
Preciipe  at  mortar.  I(U 

nuwonrj' tn,  MS 


i   at.  for  Coundatlona, 


,  OniDd  Forka  pivot  pMr,  tSO 
^IrlllBge.  SIS 
<lroiiL,l« 
-Quaponrder,  110 


Imperrlous  morur,  101 


\&pmAta\  i4on  ^or  iomxiMoaa,  3M 


erof.  «8. 

frtcttona]  nslataiiiM  Ib  sink  Ids.  3TS 
method  of  aloklnK,  »«,  361 
Iraq  pllts.  SIS 


Eranti'i  proSle  for  nwaoDtr  dama,  M 


LIH— KOS 

tealliiK.  M 

weight  per  barrel,  N 


HacUoeB.  pne-dKrins.  tSX 
Haaonrr,  aahUr,  mi  Ashlar, 
briok,  •«  Brink. 


It.  aetuaLV 
iridsepler.  1 

allrmdmBK 


aaUen.  IH,  180 
IBO 

r,  1ST,  100 


of  DusoniT,  briob,  in,  SW 

, as.  DM 

Kedina  aandatono.  81 
Hortar.  absorpclTfl  power.  II 
amouni  requ[red  per  j-ard  of  maaonir,  M 
cemsDt.  chann  of  Tolnme  In  MtUng.N, 
earned  i-lttno,  ioo  pBi  lit,  16o 

co-efflcleal  of  elactldty  of.  14 
compreHloD  oL  IM 
coat.  S3 

aUMIclty,  M.  ]U, 
enlmalea,  data  for.  «t 
(nHclns.  effect  of,  10* 
«rrout.» 

DTdnuilfc  oomant,  83 
hydraulic  lime,  ta 
Ingredlenta  for  a  yard.  88 
Imperrioui  to  walor,  101 
lime.  81 

Ijins-cemont,  IOO  i 

natural  «*.  Portland.  ■>,»  ' 

Fgrtland  tu.  natural,  M,  St 
proportioning,  method  of,  Bi 
re-t«mporgg,  9S 
BtreDKOi.  8T 

adbeelTe.  M 

comproMfte.  K 

i.iL'reaBeH-lihagcM 

teiiBile,  9i 


.u 


jvGooi^le 


KOE— FIL 
Kortar.  alrenBlb,  IrmuTene,  II 

Hud-pump,  Sn 

Nippur  pUe-drlnr,  W 
Mlcn>«lrc«rfDe.  110,  IH 

Open  JdIbH  In  m  triA,  fSl 

pBMDt  liunmer,  UT 
PSTlnr,  t«B,  KM 

doM.  IBT,  ISO 

for  totmdUloiu,  WT.  Mt.  US 
PblUdelptala,  pueamMIc  pllo*,  eoU  M 

■tudard  brtek  lewfln.  511 
Ft)Tsl<i|oEkal  affect  ot  oomprasBd  >It 


OtoM  ■entlon,  STB 

•xamplca,  in,  SM  381, 1 
Cudilturl  pUB,  »B 
dlniendiMH.  bottom,  >78 

exampleg.  ITS,  no.  »8-a 

lop,tin,38t 
rouadMIOD*.  K/l;  M<  al«> 


.  Ki&MioaK,  3B1,  oar 

pnot.  S7> 
W^iiUt7  of,  »7 

onwblBK,  tbaoi7  of,  STl 
uuTDAnovl  ozample,  ** 

-  *    — Elof.WT 


tcie,  eBretat. 
0  umerlau'ezunple, 


ixampie,  ff 

if,a<rf 


tutor  of  ufetF.  MS 
tonniilu.  emplrioU.  Ml 

Beautoy'i,  MS 
Enitliietrtiur  News',  Mft 
Huvrell'srSl^ 
Ktuwn-BSU 

TnuCKloe'*,  SU 
ntlmiaL  IM 
uitbor'a,  M) 
iUDklDe'i,  BU 
W«lrt)Mh't,  MI 
frlcUonal  rMliMiice  i^,  MT,  M 
load,  nfe,MB 
ultimate.  MT 
butt  H  lop  dovn,  SSI 


Id  piles.  In  fDundatloni,  SH 


irrillapi.SM 
potftloB  of  dUm,  ao 
aairlDK  off  Ihe^lea,  K 


pneumatic,    tSI ;   an  (il»  FoondMions^ 

sand! 107 

"rewfsil" 

baarlne  power,  MB 
abMt.«g 
slia«.ttO 

BpeoiSeatiooi,  BU.  SBt 
■pIMni.XII 
top  m.  butt  dowD,  KI 
used  to  conioUdale  soil,  IPT 

bearlos  power  JM  beartnc  pcnnr.abava- 
apeclBcatioas,  no,  US 
FlWriTer.m 
drop  hammer.  39 
Mctloo  clutoh.  Its 

alvam  n.  drop  haomgr,  Ht 
dynamic^,  327 
rricCloa  clutch.  «S 
euti  powder,  ax 
hammer  a.  Jet,  S» 


bami 


9r-]et.  an 


•  Jet*: 


E^le^driTJOK.  coat  of,  »> 

bridge  constniclioo,  SSI 

foundations,  UK 

harbor  woA.  BS 

railroad  coaatmcUou.  90 

railroad  repairs,  SSI 

tiTsr  protectloo,  SSS 
PlIchinK  chisel.  1ST 
Pivot  pPer,  STB 
Plane  surfaces,  method  of  fnnlnc  In  Mooe^ 


si  of  pDeumatic  fouadatlooB.  SO 


Pneiimallc  louudatlons.  see  Foondatjoin, 

pneumaElc. 
Point.  IBT 

PotntlnB.Ul  IBU 

Polni  Pleasant  bridRe.  eost  of  foundation, 
Pounhkeepsle  bridge,  foundation  deeori bed. 


■H  on  masixuT,  bilcJc,  IM,  IGt 


jvGooi^le 


for  vKXr-ji-t  plledriver,  OS 
mudpump,  sSi 
pHlnoinoter.  Xi 

■tMUD  ■JphOO,  m 

QuarrrlDK,  ITS 

by  ohaQMlliu  ■nd  wedoiiw.  UH 

by  eiploelvBMi?  ^ 

bj>  hand  tools,  us 
Qiwlu,  deflmd.  lae 

Railroad  masouiy,  olaMAcUlou,  lOt 

tpecjOoallons,  SIS.  BU 
BrnklDe-B  tbMiT  of  the  arch,  4W 
BolUirlBs  arobaa  for  retoinliie  walla,  SS 

dincultlsa  Id  (fasorlH  tK 
dlmensJoua^  empMcS  nilwfor, 

BbdI.  Bakcr'a,  M  ' 

^Rllgh.  US 


laiiit-Uini.  3St 
Kankine'*  UiHir;,  MS 
■**>>[lity.  theory  of,  S3»,  a» 
applicabf llty  of,  ii6 
aBKumptlonB  n«««nn,  Stt 
Coulomb!  thoorr, 84| 
stirchaived  wall,  S43 
rBllnbilily,  84! 
&II.1.1M  a  theory.  S48 
weyi»uch'«  theory.  MS 
fen  era!  for::iura,  3M 
aureh™"^  aarlb-surtaoe,  S<D 
rellabllHy '  »48 
Riprap.  HS.m      "^^  *'■•»• 

Rubble  DianoDry,  US 
COM,  IK.  180 
oouiwd,  1ST 

mortar  required  par  yard.  BB,  IM 
■pw'flo^on*.  H^  Ml,  688,  Ml 

data  for  eellmaiei,  gg 

rsqulrftee  fori[ood,  TSd    '' 
durability.  TU, 
flneneBB.  7M.  ?W 
■harptiegi.  TOft 

welcbt,  TJ,*^  :m 

SMid-iirt.  an 

Sand-pump,  !W 

isar-xi~  ■FSf^r*  "-■■ " 


BET— STE 

Bewer-plpa.  co«t.  iw 
»*r»liltth.  (OS.  M7 

aibley  bridge,  suldliur  the  catano 
plera.  speclnGMiona  tor  Wi^ 

Skew  arch,  deflued.  Mil 

Blope-wall  maaonry.  H7 
coet,  IBT,  ISO 
apedflcaUous,  MT,  Ul 

SS  ^"'e'lT,!^"''  '"■  brtok-wo 

Bonlt.  deflued,  440 

BoU.  bearing  power  of,  188 

cUy,  lis 

rook.  188 

Bemi-llqiiid  aoli,  m 

teiUng,  method  of,  im 
eramining.  method  of,  181 
injprovlDjt,  method  ot  iss 
BmDdrel.  deflned,  440 
I     lUIInK,  archea  In.  COB 
'  „     dnUnajfe  of,  SOS 
SpedflcatlODa, 
•rehoulrart  masonry.  4SE,  681 
aruijiievtiical  maaonrT  U4  am 
•ahlar.  148.  M)  ''  ™-  *" 

box  cuIveriB,  401,  SSI 
"'il'''!."^''''-  "Phaa,  m,  sn 
buildlngilTS,  Sfl 

bridge  pW,ni 

cement,  TBrf,  ««,  78/,  78o,  78* 

concrete,  B3*.  M5,  M(i 

foundaliona,  4*8,  US 

maaonry, 

aahian'ila    ' 
brickwork,  irs,  m 
buildings  arvhltecturaL  Sn 

railroaa.6S4  ^ 

paring.  148 
pedeatal,  S8S 

rubble.  147,  BSI,  U8,  541 
alope-wall.  147 

piers.  3S1,  Me 

piles  -HO.  MS 

rubble  masonry.  147,  OSI,  BSt  Ml 

alopa-wall  mavinry,  147,  Mr 


sqoared-sIoDe  masonry 
8plfcli.«  piles,  ai 


14S 


nortar  required  per  yard,  144 
ipecillcatlons.  I44ri«l,  BW 


Standard  stoiia-boi  culTort,  409 


EJeie  nandatone 
bridge  fokindal 


jvGooi^le 


8TE— BTO 
Bteel-nll  tooUagi.  UK.  t40 
SioDe.  abaarbiDK  power,  11 
9>cii«,  uvflLacroua.  90 
«rlinoi^.  I1S6 

oninhlng  >Irengtfa,  8 


BUba.'ll 


flne-uoliitfd,  in 
roufFb- pointed,  181 
rubW;  184 
loath  aird.  Ittt 
jncrtptlDii.  artmcUl,  lit 

■ftodBtoDe,  S9 

itinhiaif.  1,  IE 
d«Uruclive  mfnaU,  IS 
pTMtrfJDg,  mechodsot.n 
TWiaLlne  BKeola,  IT 
BeuoiiiUK.  effBCtof,  13 
teatinr.  mbtbod  Dt,  SO 
vUBcUl,  SD 

ftbaoTptlTe  powsr,  11 

add.  effeot  oF.  n 

fttmOflohere,  ettriA  Of,  IS 

Bnrd<a  mcUiod,  13 

—  ■ili.gBtrenKth.a 

jDlDMlDa,  n 


Kiqulalua  for  , 
Muiditoiwa,  deacriUlan 
■llleei>iM,lS 


■TO— TAZ 

teone,  equarBd,  piu-'li-fiued.Ul 
quarrr-fBcad!  11a 
■trengih,  cruthing.  q.  v^  fl 

^  blbliosrspIlT  oT,  IS 


in.  brick 


etone-culDng  MOM,  dcacrtbad,  lit 
Blone  Rriiider,  199 
Stone  pUnar,  ID) 
Stone  pollahEr,  191 
Stone  MWB,  lis 

Sutfacea,  method  of  fonntoKi  U( 
melhod  o(  flDlihlnc,  ISI 


Vitrified  pipe,  aatt,  t 

BCrengtFi,  ink,  MT 
welslit.  410 

Wall,  deflnlttODiof  putaof^  11B 
""-— xdiurfiioo,  nW— -'  -** '■ 

iloftoa  brick  ee 


Water  requlnd  for  oi 
,  lllj 


Meier'B,  tU 

Wareriy  sandetone,  SI 

Woep  iiol™,  Ml 


of  t^ftliilnir  walk,  M 


'elt^t.  bricK.  4 
build  lusa.  an 

cement,  barret,  Si 
cubic  toot,  as 


Tltrlfled'pipe,  410 
Taaoo  BiTer  bridsB,  cvhUDK  tbs  aatoMa.lN 


ovGoQi^lc 


jvGooi^le 


jvGooi^le 


jvGooi^le 


jvGooi^le