REESE LIBRARY
UNIVERSITY OF CALIFORNIA.
, 189 &>
NOTES ON CYLINDER BEIDGE PIEES
AND THE
WELL SYSTEM OF FOUNDATIONS.
NOTES ON CYLINDER BRIDGE PIERS
AND THE
WELL SYSTEM OF FOUNDATIONS.
Especially written to assist those engaged in the
construction of
, Bocfes, IRiver^ldalls, Weirs, etc,
BY
JOHN NEWMAN,
Assoc.M.Inst. C.E., F.Impl.InsL,
AUTHOR OF
"Notes on Concrete and Works in Concrete" ;
11 Earthwork Slips and Subsidences upon Public Works" ;
"Scamping Tricks and Odd Knowledge occasionally Practised upon
Public Works"; etc., etc., etc.
LONDON :
E. & F. N. SPON, 125, STRAND.
NEW YORK :
SPON & CHAMBERLAIN, 12, CORTLANDT STREET.
1893.
X. OF J
PREFACE.
THIS book has been especially written to assist those
engaged in designing or erecting Cylinder Bridge Piers
and Abutments, and Concrete, Brick, f or Masonry Wells,
as applied to Bridges, Quay-, Dock-, and River- Walls, etc.
Many of the chapters have recently appeared as serial
articles in THE ENGINEERING REVIEW.
It will be seen, by reference to the Table of Contents
and the Index, that most of the chief points requiring
attention in the design, sinking, or erection of Cylinder
Piers or Wells, either by compressed air, dredging, or open-
air excavation, from the first sketch and calculation to
the completion of the work, are examined. The strains
caused by wind-pressure on bridge piers, or the lateral
thrust of earth on abutments and walls, are only very
cursorily referred to, as there are many excellent treatises
and papers on those subjects, whereas information on the
matters herein mentioned is only to be' fragmentarily
obtained, and after considerable research in the various
engineering journals, books, and reports of this and other
countries, and especially in the engineering press.
In 1873 a Miller prize was awarded to the author by
the Council of the Institution of Civil Engineers, for a
VI PREFACE.
short paper upon the calculations necessary in designing
Iron Cylinder Bridge Piers, it being afterwards published
by permission. The pamphlet having been many years
out of print, and several engineers and bridge-builders,
here and abroad, having unsolicitedly testified to their
having received "much help" from it, the whole subject
has been considered de novo ; and although this is by no
means an exhaustive treatise, it being a kind of miniature
cyclopaedia on " Cylinder Bridge Piers and the Well
System of Foundations," and as the application of
cylinder and well foundations has since been much
extended, the hope is cherished that the book may be
equally useful to the Engineer, Bridge-Builder, Contractor,
and Student.
J. N.
LONDON, 1893.
CONTENTS.
CHAPTER I.
GENERAL DESIGN 1—10
CHAPTER II.
To DETERMINE THE REQUIRED DIAMETER OF A CYLINDER
BRIDGE PIER 10—24
CHAPTER III.
LOAD ON THE BASE 24—33
CHAPTER IV.
SURFACE FRICTION 33—39
CHAPTER V.
SINKING CYLINDERS ; GENERAL NOTES 40 — 49
CHAPTER VI.
SINKING CYLINDERS ; STAGING; FLOATING OUT 50 — 53
CHAPTER VII.
REMOVING OBSTRUCTIONS IN SINKING, AND " RIGHTING "
CYLINDERS 53 — 57
CHAPTER VIII.
KENTLEDGE ... ., 58—65
CHAPTER IX.
HEARTING 65 — 69
Vlll CONTENTS.
PAGES
CHAPTER X.
THE COMPRESSED-AIR METHOD OF SINKING CYLINDERS ... 70—72
CHAPTER XI.
LIMITING DEPTH ; AIR SUPPLY AND LEAKAGE 73 — 80
CHAPTER XII.
EFFECTS OF COMPRESSED AIR ON MEN 80—83
CHAPTER XIII.
AIR LOOKS 83—87
CHAPTER XIV.
WORKING-CHAMBER, AND METHOD OF LIGHTING IT 87—90
CHAPTER XV.
EXCAVATING AND DREDGING APPARATUS FOR REMOVING THE
EARTH FROM THE INTERIOR OF A CYLINDER OR WELL 90—103
CHAPTER XVI.
NOTES ON SOME DREDGING APPARATUS USED IN SINKING
BRIDGE CYLINDERS AND WELLS 103 — 111
CHAPTER XVII.
SAND-PUMPS, SUCTION, COMPRESSED-AIR, AND WATER-JET
DREDGERS 111—118
CHAPTER XVIII.
THE WELL SYSTEM OF FOUNDATJONS FOR BRIDGE PIERS,
ABUTMENTS, QUAYS, AND DOCK WALLS, ETC 118—129
CYLINDER BRIDGE PIERS.
CHAPTER I.
GENERAL DESIGN.
IN this book purely theoretical questions will not be specially exam-
ined, the object being to practically explain the chief points requiring
consideration in the correct design of cylinder bridge piers and the
well system of foundations, and in the prosecution of the sinking opera-
tions connected therewith. Reference will also be made to the load
upon the base, surface friction, methods of sinking, and the general
operations necessary in the design and erection of bridge piers or wells
constructed according to the methods herein mentioned.
First, it may be stated as an axiom that no system of bridge piers or
foundations can be universally recommended, because of the varying
nature and condition of the ground and the different general circum-
stances. The cylinder pier system is usually employed where great
lateral stability is not required ; it is especially adapted for an insistent
weight, and where a heavy load has to be supported without materially
obstructing a river or waterway. It is obviously safer and cheaper to
give too much waterway than too little ; but economy of space in
navigable rivers and rapid tideways is generally absolutely imperative
in piers, both during erection and when erected ; therefore, apart from
other questions, the advantage of the cylinder method of foundations is
apparent.
In deciding whether to use well foundations instead of iron cylinders
filled with concrete, brickwork, or masonry, several questions must be
taken into consideration, and among others may be named the following :
The character of the soil, which should be sand or loose strata not
firmer than sand ; the probability of debris, and boulders, and other-
obstructions such as a hard stratum being encountered, in which case it
may be advisable to adopt iron cylinders or the caisson system ; the rela-
tive cost of the various types of bridge pier, as it may so happen that
iron is cheap when bricks or Portland cement are dear ; the length of
the season during which operations can be carried on ; and the assured
2 CYLINDER BRIDGE PIERS.
ease and rapidity of erection. If the pier has to be made in a swift
current, iron cylinders are to be preferred to wells, as there may be
difficulty with the joints. In compact soil the difficulty of sinking a
comparatively blunt-ended cylinder, such as brick or concrete, on a
curb, gives a decided preference for an iron cylinder with a fine-cutting
Provided the shoe, or curb, in non-metallic cylinders be made of the
necessary strength, and the cutting edge of sufficient sharpness to be able
to penetrate the soil without bending, and provided the ground should not
be of an unequal degree of hardness, and the steining be well bolted and
bonded, there is no reason why, with due care, partly non-metallic
cylinders should not succeed in all ordinary loose soil. The thin cutting
edge and complete union of the several parts are the chief advantages
of metallic cylinders over non-metallic ; but, on the other hand, the
non-metallic possess greater weight, and therefore do not require so
much loading during sinking operations. A consideration of the merits
and demerits of each system naturally suggests a combination of the
two methods of construction, by a union of the thin cutting edge of
the metallic cylinder with the weight of the non-metallic, the cutting
edge being at the outside diameter of the well, and the steining supported
on a plate stiffened and strutted to the iron ring, and the whole of the
steining bolted to the iron curb, iand bonded throughout ; but it is well
to remember that with the ordinary curb and usual construction of the
steining, the well system is very likely to be unsuccessful in any soils
except loose sand and strata of that nature, unless special dredging
plant is employed and more than ordinary care taken in sinking the wells.
In the preceding remarks on the well system and non-metallic cylinders,
they are not assumed to be sunk by the pneumatic method.
In situations where there is great packing of ice in the rivers, as in
North Russia, Canada, and North America, bridges are not built on
simple iron-cylinder piero, ahliough these have been used in combination
with the crib and other systems, because they do not afford sufficient
lateral stability and weight to resist the packing of ice against them,
and the severe blows which they would receive from large masses of
fi oating ice ; but they have been found most economical for river bridges
in the tropics.
A system adopted by Mr. T. W. Kennard, at the Buffalo Bridge, on
the Great Western Railway of Canada — where, owing to the immense
force of the ice, very massive piers were required — was as follows : —
Their lower portions were composed partly of broken stone in timber
cribwork, and partly of masonry placed within wrought-iron cylinders,
these latter being inside the timber cells ; above the water line the pier
consisted of ashlar masonry. By these means a cheap and effective pier
was obtained, the great expense of set masonry was obviated, there was
GENERAL DESIGN.
sufficient mass to resist the force of the ice, and the piers were erected
much quicker than if constructed of ashlar. The top ring of the
cylinder was enlarged, so as to meet the next adjacent ring. The
cylinders were 12 ft. in diameter. The width of the cribwork was 20 ft.
The cylinders were placed 15 ft. apart, from centre to centre, and formed
a single row. The almost constant depth of water was 40 ft. Where
timber is cheap and stone at hand, this system is economical, quick, and
effective for rivers subject to ice-floes, and where great stability and
weight are essential.
The difficulty of binding cylinders together when sunk in a loose
soil, so that they may act in accordance, is a reason against the use of
this system for the whole of a pier of an arched bridge, unless it is
combined with other methods ; but in a firm stratum, with ordinary
precautions, there is no reason why they should not be built upon with
security against both scour and movement from thrust. Formerly
cylinders from about 6 to 10 ft. in diameter were considered the han-
diest sizes for sinking ; but now they are used with economy and
success up to a diameter of about 21 ft. Cylinder foundations can be
sunk to great depths and in deep water ; they are, in such situations,
generally to be preferred to brick, masonry, or concrete piers, having no
casing or requiring the erection of temporary cofferdams. The iron
casing only wants ordinary staging, and protects and stiffens a cylinder
bridge-pier, and prevents lateral movement in the hearting.
With cylinders of Portland cement, one of the chief precautions to be
taken is to keep the interior dry by making thoroughly sound and reliable
joints between the blocks. The effects of any leakage of water through
the casing must be considered, in order that the hearting may be pre-
served in good i condition, and protected from the action of air and
water.
In the case of cylinders of considerable height above the ground, the
diameter of the column should be sufficiently large to give lateral
stability ; but as the higher the column the larger the base, it is gene-
rally sufficient to calculate the area of the base ; however, the reducing
ring should not be too abrupt, because the strain on the hearting in that
portion of the cylinder above the reducing ring should not much exceed
that below it. The load upon the hearting at the top of the cylinder, at
the point of enlargement, and at the base, should be calculated. The
enlarged base afforded by the use of a conical ring is of general utility
where the strata have no great bearing power ; but when the base of
the cylinder rests on rock there is no reason why the column should not
be of one diameter throughout, as the rock is able to bear as much
compressive strain as the hearting.
The best position for the commencement of the enlargement, or
tapering, is just above the ground or the bed of the river, as there
E2
4 CYLINDER BRIDGE PIERS.
is then the least possible obstruction to the river, and increased area of
the base and surface are obtained. When the lengths of the rings are
from 6 to 9 ft., the diameter of the lower edge of the reducing-ring is
ordinarily from about 1*4 to 1*5 times the upper diameter, and the slope
from about ^ to £ to 1. The conical reducing-piece sometimes has a
vertical bearing on the hearting, which may be obtained by having on
the base of the reducing-ring an internal disc with an opening equal in
diameter to that of the top rings of the cylinder, the disc being stayed
and strengthened by vertical ribs. If there is no special reason to the
contrary, the cylinders should be placed immediately under the main
girders, and they should be braced together either at or about their tops ;
but care must be taken that the bracing is sufficiently high in a navigable
or tidal river, so that a barge or vessel cannot be sunk by being held
under it. Cast-iron arches are sometimes turned between the cylinders,
the level of the crown of the arch nearly corresponding with that of
the top of the column. When the cylinders are connected at their
summits by a girder, and the main beams of the bridge are firmly
attached by an adjusting expansion • arrangement to the tops, and the
height of the cylinder above the ground is not more than four times the
diameter, only light bracing, if any, in ordinary situations is usually
requisite ; but when the main beams rest on rollers bracing is required.
Should the height of the cylinder above the ground be from five to
eight times the diameter, strong bracing is necessary, and it should
increase as the difference between the height and the diameter of the
column becomes greater. The tops of the cylinders should be connected
by horizontal beams.
The iron cylinder system of bridge foundations is not economical if
many cylinders have to be sunk close together ; the most efficient em-
ployment of that method is where one cylinder is sufficient for one main
beam of a bridge, and only two to four cylinders are required for one
pier. It is generally adopted for foundations in deep water, and of
considerable depth in the ground. The well system is economical in
sand or silt, and where the water is of moderate depth, and when the
depth is too great for the employment of compressed air, provided special
plant and excavating apparatus is used. In a tidal river the iron cylinder
casing might be omitted at about low-water or flood-level, as the
masonry or brickwork can then be built up in the open, but it should
only rest upon the hearting and not upon the iron rings. Where rock
crops out on the surface, or nearly so, cylindrical foundations are
suitable, but the surface of the rock must be levelled by divers or by other
means, so that the cylinder may have a level bed ; and the system is
good if a hard substratum is soon reached after penetrating the upper
strata.
In an opening bridge care must be taken that sufficient transverse
GENERAL DESIGN. 0
stability is given to the piers, so as to resist the motion of opening and
closing ; therefore, should the pier be composed of cylinders, they must
be arranged and braced accordingly. On the Boston and Providence
Railroad, U.S.A., cylinders 6 ft. in diameter were sunk 10 ft. into the
mud, and twelve piles were driven in the interior of the column 40 ft.
into the mud, or 30 ft. below the cylinders ; the interior was then filled
with cement concrete, and increased bearing was thereby gained.
The cylinder system has been used in the following manner in order
to shorten the span of a bridge. The diameter of a cylinder has a set off
of about 1 ft. 6 in., or 2 ft. on each side, upon which are firmly fixed two
inclined struts which support the girders, in addition to the cylinder
which is carried up to the underside of the superstructure. The base of
these inclined struts should be out of the reach of blows from barges or
shipping, etc., therefore this method appears better adapted for un-
navigable rivers or land piers, than for rivers with any traffic.
With regard to the best form for a pier with an iron casing, experience
shows that the circular is to be preferred, unless there are special reasons
to the contrary, not only because a better casting can be thereby obtained,
but also on account of sinking operations, as it has been found that if
the columns are of an oblong, square, or flat elliptical section, and the
soil is not homogeneous, they assume in sinking an oblique direction,
and are difficult to get down in an exactly vertical position. The cylin-
drical is also the best form for resisting internal pressure and collapse.
One of the objections to all forms excepting the circular or elliptical, is
that they only have long straight side walls to resist the pressure of the
earth, and the various strains during sinking. In all soils likely to swell
such as some of the clays, the circular form is the best ; and it is the
strongest form for the amount of metal used.
In deciding upon the relative position of the cylinders on plan, it
should be remembered that in sand and moist soils much difficulty has
been experienced in sinking cylinders when they have been placed veiy
close together, as they have a tendency to draw one towards the other.
About 3 ft. should be the minimum distance between the surfaces of the
cylinders ; and for considerable depths practice shows that in sand they
should not be nearer together than from one-fourth to one-fifth of their
diameter, the minimum distance being as before stated.
If the question arises whether one or two large cylinders should be
used, instead of many smaller columns, experience seems decidedly to
point to the former being preferable, as they can be sunk with much
greater certainty and at a less proportionate cost than the smaller
cylinders, and are not so liable to get out of the vertical in sinking.
In order to lessen the frictional adhesion in sinking, the cutting edge
is sometimes swelled out a little larger than the other cylinder rings, by
making the top of the commencement of the V-shaped cutting edge
fi CYLINDER BRIDGE PIERS.
with an external projection o± about £ in. beyond the outside diameter
of its upper part. The cutting ring is usually thicker than the other
lengths of the cylinder, and is brought to a taper to facilitate the sink-
ing. It is generally about \ in. to £ in. thicker than the ring above ;
there is no use, however, in having a thicker casing, if strength alone is
required, than 2£ in., as the strength of the metal per squar^ inch
decreases very considerably beyond a certain thickness, if the rings are
cast by the ordinary method. The thickness of the cutting ring and
edge should . be regulated by the nature of the soil through which the
cylinder is to be sunk, and by the character of the obstructions likely to
be encountered. If boulders are probable, and the cutting edge has to
be thrust through them, it should be proportionally strong. It is usually
made from one-third to one-half the height of the other rings, being
but seldom above 4 ft. 6 in. in height.
If cylinders have to be sunk by the compressed ah* system at
great depths, as from 80 to 100 feet below water, there will be con-
siderable difficulty in keeping the column air tight, and a strain of some
moment will be brought upon the casing from the pressure of the air
requisite for the expulsion of water at such a depth. The thickness of
the ring must be sufficient to sustain the weight necessary for sinking,
and the strains brought upon it during that operation, in addition to the
internal pressure arising from the use of the compressed air system. The
rings are always made thicker than theory demands to provide for possible
defects and the natural porosity of the metal. The thicknesses of metal
generally used range from 1 in. to If in. A very small thickness would
suffice to keep the hearting in position until it is set, but during sinking
operations the cylinder has to resist various strains, and before it is
filled it has frequently to withstand the pressure of the water. If the
compressed air system is adopted the cylinder is also subject to internal
strain. The flange joints should therefore be broad, and be planed if the
pneumatic method of sinking is used at a considerable depth, or be care-
fully packed so as to distribute the strain, and give a uniform bearing
and a fit over the entire surface.
Cast iron cylinders 6 ft. 6 in. in diameter, 1£ in. and 1£ in. in thick-
ness, have been cast in 9 ft. lengths in one piece. They have also been
cast of greater diameter, such as 10 ft. to 15 ft., in 6 ft. lengths. In
cylinders of ordinary diameter, it is advisable to lessen the length of
each ring and make them in one piece, thus obviating the necessity of
vertical joint flanges, the weight of which and the horizontal flanges
amounts to a considerable percentage of the total weight of the cylinder
Before deciding upon the lengths of the cylinder rings, it is advisable
to inquire the sizes that manufacturers will undertake to cast soundly
without extra cost ; the saving in weight by lessening the number of
joints, and the augmented lateral strength and air and water tightness
GENERAL DESIGN. 7
thereby gained, may also compensate for the increased cost of the
rings.
In having the rings cast in one piece for large diameters, although the
vertical joints are not required, yet owing to the increased number of
horizontal joints, consequent upon the diminished lengths, it is obvious
there is a point when the greater number of horizontal joints will require
the same amount of metal as if vertical joints had been adopted. Each
particular case must determine whether it is advisable or cheaper to
have the rings with or without vertical joints ; at the same time it
should not be forgotten that very large homogeneous castings are more
difficult to obtain than moderately sized pieces. The rings are usually
cast in 9 ft. lengths. Care should be taken that any ornamental caps
placed on the top of the upper ring of the cylinder are from 2 in. to
3 in. at the least below the bearing plates of the girder to prevent them
being crushed. It is almost always impossible to sink several cylinders
so that their tops are all level, as the subsidence under a load is hardly
ever uniform, or the strata exactly horizontal. The capital, or top
making up ring, should therefore not be cast until the test load has been
removed from the columns.
Delay in attaching the top making-up ring is, however^ frequently
inconvenient, for when the castings have to be shipped, months may
elapse before they are delivered. To obviate this, the next ring to the
making-up piece is now sometimes made of a height of from 2 to 5 ft.,
and an adjustable top or making-up ring, from 2 to 3 ft. in height, is
provided of larger diameter than the outside diameter of the cylinder,
so that it can be bolted to the lower ring in any position required, the
bolt holes in the lower ring being made on the site.
The object of the cutting ring being to cause easy and vertical
penetration, it is clear that its form should be suited to the earth it has
to penetrate. A chisel-pointed cutting edge is perhaps the best. With
the view of preventing cracking of the cutting ring consequent upon its
encountering an obstruction in sinking, such as boulders, tree stumps,
seams of rock, and to resist the various strains caused by unequal load-
ing of the cylinder or resistance of the ground, it has been made of
wrought iron because of its less liability to fracture from blows and its
more uniform strength, but care should be taken that it is well strutted
and stayed so that no deformation can take place. Cast iron rings,
however, are to be preferred for all the other rings, as these are more
easily and quickly bolted together and are cheaper.
As an example of the unequal strain a cutting ring may have to
sustain, let us assume a cylinder to be 11 ft. in diameter, and 1£ in. in
thickness. The area of the cutting edge would be (132 + 1£) x
3*1416 X 1£ = 629 square inches. Taking the weight of the iron only
in the cylinder at, say, 50 tons, and the kentledge at the high figure of
8 CYLINDER BRIDGE PIERS.
350 tons, or a total weight of 400 tons, if the load and resistance were
equable over the surface in contact, the pressure would be ffg = 0'64
ton per square inch, a very light load on good cast iron. But, as the
strain may be unequal, and the cutting edge only rest, for example, for
4 ft. of its entire length upon a boulder, strains of various kinds may
be caused ; and if the whole weight be concentrated upon the boulder
the cutting edge would be subject to a strain of
400 tons c K , . ,
— — - = 5'5 tons per square inch.
4o X Ij
Although it is improbable the ground upon which the boulder rested
would sustain such a weight, even if jammed between rock, still the
strains on the cutting edge may be very irregular and severe, and wLile
one part is not even in contact with the ground, another may be heavily
strained, and this without considering the effect of the direction of the
load, but merely taking it as vertical and direct-acting and the cutting
edge as flat. Hence, although there may be no apparent fault in the
metal, .the cracking of the cutting ring in boulder ground or soil of
unequal character is not unlikely under such circumstances. As
boulders frequently occur in shoals in the bed of a river, it is well to
determine, in deciding upon the site of a bridge, whether a slight
change in its position may not considerably increase or decrease the
cost.
It is advisable to remember in fixing upon the diameter of a cylinder
or well, that by increasing the diameter the length of the perimeter of
the cylinder or the cutting edge is reduced as compared with the area,
and also the frictional resistance in the same proportion, thus lessening
relatively to the area of the cylinder the liability of the cutting edge
meeting with an obstruction. If the cylinders have to be sunk to
considerable depths it is more by chance that they can be sunk in their
exact position, and therefore the diameter should be sufficiently large to
admit of unavoidable deviation from the true position, and not less than
1 ft. to 2 ft. should be allowed for possible divergence.
It can be claimed that where the ground is of varying hardness, and
boulders or inclined thin strata of rock have to be penetrated, cylinders
of small diameter are to be preferred, because sinking operations must
be suspended until the obstruction is removed, and also in uneven soil a
cylinder may partly rest upon a firm foundation on one side and on soft
yielding ground on the other ; whereas, in using two or more small
cylinders instead of one large one, each can be sunk to different depths
until a firm foundation is reached ; and where a rock bed has a con-
siderable inclination, or in perhaps the worst case that may occur,
namely, when the cutting ring reaches a dipping stratum and the ground
on the lower side of the cylinder is softer than the upper, then the
cylinder is being pressed towards the soft lower side and may soon
GENERAL DESIGN. 9
become slanting unless prompt measures are taken to counteract the
pressure and produce equilibrium, and this is easier to accomplish in
small cylinders. However, obstructions can be better removed in
cylinders of large diameter, as methods of treatment can be adopted
that cannot be used in a confined space. On the whole, the balance of
advantage rests with large cylinders, but each system is likely to have
advocates except in ground of a homogeneous nature, when undoubtedly
large cylinders are to be preferred for the reasons previously named,
and particularly for railway bridges, because they are more massive, and
therefore better able to withstand not only a sudden and unequal rolling
load, but also the horizontal thrust caused by the application of quick-
acting continuous brakes in retarding or stopping a train upon a
structure.
The joints of cylinders can be caulked with iron rust cement for half
of the outer thickness of the rings ; and the space upon the inner half
can be filled either with neat Portland cement, or one of fine sharp sand
to one of Portland cement, so as to make it practically air-tight should
it be expected that the pneumatic process of sinking may have to be
used. In order to allow for concrete in the hearting swelling during the
process of setting, or for unequal contraction or expansion of iron and
the material in the cylinder, or freezing of water, the cylinders can be
lined with tarred felt.
Cylinders with vertical sides are to be preferred to those with a
splayed or trumpet-shaped end, as they are more likely to sink evenly
and vertically, because they do not offer so much surface and resistance
to any obstruction, nor do they disturb so much ground or impair any
guidance that may Ife received from the earth, although, even if parallel
sides are adopted, it by no means follows that cylinders will sink ver-
tically.
In designing any temporary works, such as staging, care should be
taken, especially in a soft river bed of mud or silt, that they are not
unequally weighted, or the ground may be forced in one direction,
causing undue pressure upon, or a run of soil into the cylinder.
The sinking operations connected with it should be duly considered in
determining the general form of a cylinder and the manner of the
weighting, which will be hereafter referred to under a separate head.
Particularly in loose soil, experience shows that a fully weighted cylinder
sinks quicker with fewer "blows" of soil into the interior and less
trouble than one in which the loading is intermittent or comparatively
light. With the view of utilising the permanent hearting of the cylin-
der for weighting the rings, an annular plate, made to support an inter-
nal ring of concrete, masonry or brickwork, is occasionally used, thus
lessening the temporary load required for sinking operations, and keep-
ing the centre of gravity of the cylinder lower than when its top is
. OPTHE
UNIVERSITY
10 CYLINDER BRIDGE PIERS.
temporarily loaded. In deciding upon the thickness of this annular ring
of the hearting, sufficient working space must be left, so that excavating
operations can be carried on with ease ; perhaps the best material for
such casing is Portland cement concrete, as it can be so made that it
will fill the spaces between the flanges, ribs, feathers, lugs, and bolts,
so as to leave no voids.
CHAPTER II.
To DETERMINE THE REQUIRED DIAMETER OF A CYLINDER
BRIDGE PIER.
The following formulas* will give the required internal diameter of a
cylinder bridge-pier, when the resistance from the frictional surface and
the flotation power of the cylinder are disregarded : —
Let D = the required diameter of the cylinder in feet.
s = the safe load in tons per square foot upon the foundation.
W = the weight in tons of the superstructure on the cylinder,
including the rolling load.
w = the weight in tons of the cylinder, including the hearting.
A = the required area of the foundation in square feet.
Then A = ^±J?
and as the diameter of a circle = 1*128 \ area of circle,
D = M28V/(W + ").
The value of w may be readily obtained by using the diagram Fig.
1, and that of W is known at the time of designing the pier.
Should any support from surface friction be taken into calculation,
for ordinary depths in the ground, heights, and other conditions,
D x 0-75 to D x 0-85
will approximately give the required diameter of the cylinder.
There are cogent practical reasons which prevent the frictional resist-
ance being relied upont and they will be hereafter named, unless it is
certain thai such surface friction cannot be disturbed or impaired.
The flotation power of the cylinder is not considered as a means of
permanent support, because of its small value and mutability.
The diameters of the cylinder in the diagram of weights are given
immediately below the horizontal base line, together with the mean
REQUIRED DIAMETER,
It
VERTICAL
'Ns 109 fa 9 100 iay 3<to +00 too
01 A M ETE RS
THICKNESS OP
C4ST IRON RIN«S I
IN. INCHES.
167
FEET
Note. — The weights in the diagram are calculated on the assumption
that the hearting of the cylinder is Portland cement concrete. If brick-
work, the weights will be about 16 per cent, less for picked stock bricks
set in Portland cement mortar.
12 CYLINDER BRIDGE PIERS.
thicknesses of the cast iron cylinder rings. An addition of 20 per cent.
is made to the weight of the iron rings to allow for joint-flanges, bolts,
lugs, bosses, etc.
Should the weight of a 10 ft. 6 in. cylinder be required, 45 ft.
in height, the vertical line upon which the scale must be placed is mid-
way between the 10 ft. and 11 ft. vertical lines. The required height
is half-way between the 40 ft. and 50 ft. in height curved line, and
in like manner any other dimensions or heights may be scaled. The
diagram, which in other respects is self-explanatory, was made with the
particular object of quickly and easily obtaining the value of w for the
preliminary calculation of the required diameter of a cylinder bridge-
pier, and for this purpose the weight of a wrought-iron cutting ring may
be considered to be that of a cast-iron one.
Some formulae are appended that may be found useful in calculating
the required diameter of an iron cylinder bridge-pier : —
Let D = the internal diameter of the cylinder in feet.
\V = the weight in tons of Portland cement concrete in the
cylinder per lineal foot of the height of the cylinder, if the
weight of Portland cement concrete is taken at 136 Ibs. per
cubic foot.
W = D* x 0-048.
Let B = the weight of brickwork in Portland cement mortar, calcu-
lated at 112 Ibs. per cubic foot, per lineal foot of the
height of the cylinder.
B = D2 x 0-040.
Let I = the approximate weight of cast iron in tons per lineal foot
of the height of the cylinder, including an allowance of 20
per cent, for joint flanges, ribs, bosses, lugs or strengthen-
ing brackets, bolts, etc.
Thickness of cast iron
in the cylinder rings.
Inches.
f
If
The following is an empirical rule, deduced from many examples, for
ascertaining the preliminary value of D in the case of cylinders of
moderate total height, with the reducing ring at about the ground line ;
and for spans between 60 ft. and 200 ft., when two cylinders are used
I
—
D
V
•048
I
D
V
•064
I
_
D
V
•080
I
_
D
V
•096
I
_
D
Y
•m
I
_
D
V
•197
I
_
D
V
•143
I
D
X
•158
REQUIRED DIAMETER. 13
for a single line of railway, and a weight of 5 tons per square foot is
taken as the safe load on the foundation, and the support from surface
friction is disregarded : —
Let D = the internal diameter of the subterranean portion of a
cylinder bridge-pier.
d = the internal diameter of the cylinder above the ground, or
reducing ring.
s = span.
Then D = j~8.
In the above rule d =— — . — .
1-4 to 1-5
If the safe load on the base is taken at, say, 6 tons per square foot
instead of 5 tons, v/(D2 x |) must be taken, and so in proportion
for any other coefficient of the safe load on the foundation per square
foot.
If support from surface friction is to be taken into calculation, then
D, approximately = 0'8^/s.
As in girders there is a limiting span, so in cylinder bridge-piers there
is a limiting height for every diameter, beyond which the weight of the
cylinder without any load will exceed the safe strain that the base or
foundation will bear.
Let s = the safe load, in tons, on the foundation per square foot.
A = the area of the base in square feet.
W = the weight, in tons, on the cylinder from the superstructure,
and the rolling load.
w = the weight of the cylinder per foot of height.
D = the diameter of the cylinder below the reducing ring, in
feet.
d = the diameter, in feet, of the cylinder above the reducing
ring.
H = the limiting height of the cylinder, in feet, measured from
the base.
Then H = <s * A>~W.
W
EXAMPLE —
Let s =5 tons per square foot.
D = 12 feet .-. A = 113'10 square feet.
d — 8 feet.
W = 80 tons.
Respecting the value of w, it would not be economical, or in accord-
ance with the principles of correct design, for the cylinder to be of the
same diameter throughout, excepting on rock foundations, when the
14 CYLINDER BRIDGE PIERS.
load on the base approaches that which the hearting will safely
bear. It is impossible to give any rule as to the exact position of the
reducing ring ; but in the case of ordinary foundations and conditions!
by assuming that the portion of the cylinder sunk into the ground is
one-third of the total height of the column, and that D = 1-5 c?, 10, in
this example, will equal 4 in. in height of a 12 ft. cylinder, + 8 in. in
height of an 8 ft. cylinder ; w .'. = 5'15 tons, the hearting being Port-
land cement concrete.
H = (5 * 113-10)-80 = M.27 ft_
5*15
If the diameter had been taken as the same throughout,
H = (5 X 113-10)-80 = 6Q.70 ft
8
A comparison of the two limiting heights will at once show the great
advantage and economy of a reduction of the diameter of the cylinder
above the ground-line.
The following is a calculation by aid of the diagram and the
formulae for the required diameter of the cylinders for a railway
bridge : —
DATA. — Span 120 ft. Single line of railway of 4 ft. 8£ in. gauge.
Two cylinders, each supporting one main beam. Cylinder to be
sunk 30 ft. into the ground. Height of cylinder above the bed
of river, 40 ft. Total height of cylinder, 70 ft. Reducing ring
to commence at the bed of the river. Thickness of cylinder ring,
1£ in. Column to be rilled with Portland cement concrete
throughout. Safe load upon the foundation per square foot =
5 tons. Frictional resistance and flotation power not taken into
account. Load on concrete per square foot not to exceed 7 tons.
Rolling load to be calculated at 1£ ton per lineal foot.
APPROXIMATE WEIGHT OF SUPERSTRUCTURE.
Tons per
lineal luot.
Girders, cross-girders, etc., 120 ft. span, weigh, say,
75 tons = 0-625
Roadway planking or floor = 0'161
Permanent way and ballast : —
2 lineal ft. of rails at 72 Ibs. per yard = 0*022
Fastenings = 0*002
Two longitudinal sleepers at 25 Ibs. per foot ... = 0*022
Ballast. 16 ft. x 1 ft. X 3 in. thick = 4 cubic ) _ Q.™
ft. x 150 Ibs. = 600 Ibs f ~
Total weight of superstructure per lineal foot ... 1-100
REQUIRED DIAMETER. 15
Rolling load .................. 1-250
Total weight of superstructure and live load, in tons,
per lineal foot ................. 2'350
Weight of superstructure on one cylinder, rolling load included,
_ 120 X 2-35
Assume D = ^span = ^/I'20 = say, 11 ft.
The cylinder is, therefore, 11 ft. in diameter for the 30 ft. in the
ground.
Let d = diameter of the cylinder above the ground,
d = ii = say, 7 ft. 6 in.
I'D
The cylinder is therefore 7 ft. 6 in. in diameter for the 40 ft. above
the ground.
By diagram, the weights of the cylinder scale respectively : —
Tons.
For the 11 ft. diameter, 30 ft. in height ... — 204
For the 7ft. 6 in. diameter, 40 ft. in height ... = 132
336
Tons.
Superimposed load on one cylinder as before ... = 141
Weight of cylinder complete as above ...... = 336
Total load on base 477
By formula : —
D = 1-128
W = 141 tons, w = 336 tons, s = 5 tons.
Therefore D = M28\/(141 + 336) = 11 ft.
The portion of the cylinder in the ground is 11 ft. in diameter, there-
fore the area of the base = 95-04 sq. ft. , and the load on the base
477
per square foot = — —- = 5 '02 tons.
The normal load on the soil, which is assumed to be sand and to weigh
•055 ton a cubic foot, at a depth of 30 ft. = 0'055 ton X 30 = 1*65 ton
per square foot.
16 CYLINDER BRIDGE PIERS.
Tons.
Total pressure on the base from the cylinder, super-
structure, and rolling load, per square foot ... = 5"02
Normal pressure of the soil on the base, as above... = 1*65
Excess of pressure on the foundations in tons per
square foot above the normal pressure ... = 3 '37
The load on the concrete hearting per square foot at the commence-
ment of the enlargement ring is as follows : —
The weight of concrete in a 7 ft. 6 in. cylinder is 8'05 tons per lineal
yard.
Tons.
Concrete 8'05 tons x 13* yards ......... = 107-33
Superstructure and rolling load ......... = 141*00
248-33
The internal area of a 7 ft. 6 in. cylinder = 44-18 sq. ft.
f)A Q.Q9
The load on the concrete hearting per square foot - = 5'62 tons.
44-18
The load from the concrete would be slightly less than this because the
commencement of the reducing ring would probably be about 9 ft.
above the ground, but this value is sufficiently near for all practical
purposes. Should the 7 ft. 6 in. in diameter iron rings for this 40 ft.
length be taken as bearing upon the concrete by means of the horizontal
flanges, which should be the case, the strain on the concrete would be
increased by 0'72 ton x 40 ft. = 28*80 tons, or an additional strain of
= 0-65 ton per square foot,
making a total load ©f 5'62 + 0-65 = 6-27 tons per square foot, which
strain is well within the safe limits of good Portland cement concrete
properly mixed in the ordinary proportions.
If support from surface friction was relied upon, the required value
of D would be about, D = 0*8 x 11 = say, 9 ft., and the diameter
above the reducing ring, say, 7 ft.
Tons.
Weight of a 9 ft. cylinder, 30 ft. in height ... = 137-40
Weight of a 7 ft. cylinder, 40 ft. in height ... = 115-92
253-32
Weight of supersti ueture and rolling load, as before = 141*00
Total = 394-32
SUPPORTING POWER.
Tons.
Area of a 9 ft. cylinder = 63-62 sq. ft. X 5 tons = 318-10
Surface friction 29*06 X 24 ft. x £ of a ton , = 87*18
Total 405-28
It will be noticed that support from surface friction is not taken into
account for the first 6 ft. in depth of the ground. The depth relied
upon for permanent support being 30 — 6 ft. = 24 ft.
The safe frictional resistance per square foot is calculated at
of a ton = = 280 Ibs.
The load on the concrete hearting per square foot at the commence-
ment of the reducing ring is as follows : —
The weight of the concrete, in tons, per lineal yard of the height of a
7 ft. cylinder is 7*02 tons.
Tons.
7-02 tons x 13i lineal yards 5= 93*60
Superstructure, etc., as before = 141-00
Total 234-60
Square feet,
Internal area of a 7 ft. cylinder ......... 3= 38'49
234-60
Load on concrete per square foot =
Add the strain per square foot from the iron
rings which equals ... ... ... ...... 0'70
Total load 6'79
The following tables will be found useful in the calculations required
in designing a cylinder bridge-pier or in adopting the well system of
foundations for bridges, dock-walls, quays, weirs, or other purposes : —
18
CYLINDER BRIDGE PIERS.
TABLE A.
No. 1.
No. 2.
No. 3.
No. 4.
No. 5.
Weight in tons
Weight in tons
Contents in
of concrete
of brickwork
Internal dia-
meter of cylinder.
Internal area
of cylinder in
square feet.
cubic yards per
lineal yard of
the height of
in Portland
cement per
lineal yard of
in Portland
cement per
lineal yard of
cylinder.
the height of
the height of
cylinder.
cylinder.
4ft. 0 in.
12-56
1-40
2-30
1-89
4 ft. 6 in.
15-90
1-77
2-90
2-39
5 ft. 0 in.
19-64
2-18
3-57
2-94
5 ft. 6 in.
23-76
2-64
4-33
3-56
6 ft. 0 in.
28-28
3-14
5-15
4-24
6 ft. 6 in.
33-19
3-69
6-05
4-98
7 ft. 0 in.
38-49
4-28
7-02
5-78
7 ft. 6 in.
44-18
4-91
8-05
6-63
8 ft. 0 in.
50-27
5-59
9-17
7-55
8 ft. 6 in.
56-75
6-31
10-35
8-52
9 ft. 0 in.
63-62
7-07
11-60
9-54
9 ft. 6 in.
70-89
7-88
12-93
10-64
10 ft. 0 in.
78-54
8-73
14-32
11-79
10 ft. 6 in.
86-59
9-62
15-78
12-99
lift. Oin.
95-04
10-56
17-32
14-26
lift. 6 in.
103-87
11-54
18-93
15-58
12 ft. 0 in.
113-10
12-57
20-62
16-97
12 ft. 6 in.
122-72
13-64
22-37
18-41
13 ft. 0 in.
132-74
14-75
24-19
19-91
13 ft. 6 in.
143-41
15-91
26-09
21-48
14 ft. 0 in.
153-94
17-11
28-06
23-10
14 ft. 6 in.
165-13
18-35
30-09
24-77
15 ft. 0 in.
176*72
19-64
32-21
26-51
15 ft. 6 in.
188-69
20-97
34-39
28-31
16 ft. 0 in.
201-06
22-34
36-64
30-16
16 ft. 6 in.
213-83
23-76
38-97
32-08
17 ft. 0 in.
226-98
25-22
41-36
34-05
17 ft. 6 in.
240-53
26-73
43-84
36-09
18 ft. 0 in.
254-47
28-27
46-36
38-16
18 ft. 6 in.
268-81
29-87
48-99
40-33
19 ft. 0 in.
283-53
31-51
51-68
42-54
19 ft. 6 in.
298-65
33-18
54-42
44-79
20 ft. 0 in.
314-16
34-91
57-26
47-13
2 i ft. 6 in.
330-07
36-68
60-16
49-52
21 ft. 0 in.
346-36
38-48
63-11
51-95
The weight of Portland cement concrete is taken at 136 Ibs. per cubic*
foot, or 1*64 tons per cubic yard.
The weight of brickwork in Portland cement mortar is taken at
112 Ibs. per cubic foot, or 1-35 tons per cubic yard.
Column 3, when multiplied by the height of cylinder, in lineal yards,
will give the contents in cubic yards.
REQUIRED DIAMETER.
19
Columns 4 and 5, when multiplied by the height, in lineal yards, foi
which the Portland cement concrete, or the brickwork in Portland
cement mortar, extends, will give respectively the weight in tons.
The internal areas of the cylinder only are given, as they alone are
required in calculating the sustaining power derived from the area of
the base of the cylinder, as the weight of the bridge rests upon the
hearting and not on the ironwork.
In the tables the internal diameters of the cylinder are commenced at
4 ft. and increase by increments of 6 inches to 21 ft. The former may
be considered as nearly the least practical diameter of a cylinder founda-
tion. The cylinder, if of less diameter, would partake more of the
nature of a pile or column, being of itself the support to the super-
structure of the bridge, and not, as is the case in an iron cylinder
bridge-pier, merely the skin, as it were, containing the hearting which
actually supports the weight of the superstructure of the bridge.
For ease of calculation the contents are given in cubic yards per
lineal yard of the height of cylinder, as brickwork and concrete are
usually measured by the cubic yard.
TABLE B.
No. 1.
No. 2.
No. 3.
No. 4.
No. 5.
Internal dia-
Thickness of
cast iron in
Weight of cast
iron in cylinder
in tons per
Surface area in
square feet, in
contact with
Loss of weight
from immersion
in water in tons
meter of cylinder.
cylinder ring
in inches.
lineal foot of
the height of
earth, per lineal
foot of height of
per lineal foot
of height of
cylinder.
cylinder.
cylinder.
4 ft. 0 in.
f
•160
12-96
•372
•215
13-09
•380
]1
•269
13-22
•387
H
•324
13-35
•395
4 ft. 6 in.
1
•180
14-53
•468
l
•241
14-66
•476
ii
•302
14-79
•485
]L
•364
14-92
•493
5ft.'oin.
1
•265
16-23
•584
n
U
•334
16-36
•594
y)
•403
16-49
•603
|
•472
16-62
•613
5 ft'.' 6 in.
•292
17-80
•703
i
•367
17-93
•713
M
•442
18-06
•723
3
•517
18-19
•734
6 ft. 0 in.
1
•318
19-37
•832
JJ.
•400
19-50
•843
lj
•481
19-63
•855
M
If
•563
19-76
•866
6 ft. 6 in.
1
•344
20-94
•972
c2
20
CYLINDER BRIDGE PIERS.
TABLE B (continued).
No. 1.
Internal dia-
meter of cylinder.
No. 2.
Thickness of
cast iron in
cylinder ring
in inches.
No. 3.
Weight of cast
iron in cylinder
in tons per
lineal foot of
the height of
cylinder.
No. 4.
Surface area in
square feet, in
contact with
earth, per lineal
foot of height of
cylinder.
No. 5.
Loss of weight
from immersion
in water in tons
per lineal foot
of height of
cylinder.
6ft. 6 in.
1*
•432
21-07
•985
55
•520
21-20
•997
55
If
•609
21-33
1-009
7 ft. 0 in.
1
•370
22-51
1-124
55
1*
•465
22-64
1-137
55
4
•560
22-77
1-150
55
if
•655
22-90
1-163
7 ft. 6 in.
•396
24-086
1-286
55
ij
•497
24-216
1-300
55
4
•599
24-347
1-314
55
if
•700
24-478
1-328
8 ft. 0 in.
i
•422
25-656
1-459
55
4
•530
25-787
1-474
55
4
•638
25-918
1-489
M
if
•746
26-049
1-504
8 ft. 6 in.
1}
•563
27-358
1-659
jj
4
•677
27-489
1-675
55
if
•792
27-620
1-691
55
2
•906
27-751
1-707
9 ft. 0 in.
11
•596
28-929
1-855
11
4
•716
29-059
1-872
55
1!
•837
29-190
1-889
55
2
•957
29-321
1-906
9 ft. 6 in.
4
•628
30-500
2-062
»
4
•756
30-631
2-080
j)
If
•884
30-762
2-098
55
2
1-012
30-890
2-116
10 ft. 0 in.
4
•662
32-071
2-280
55
4
•795
32-202
2-299
5J
if
•929
32-333
2-318
55
2
1-060
32-463
2-336
10 ft. 6 in.
4
•694
33-641
2-509
55
4
•834
33-772
2-529
5)
If
•975
33-903
2-548
2
1-116
34-034
2-568
11 f tO in.
4
•726
35-212
2-749
5)
i£
•873
35-343
2-769
55
if
1-021
35-474
2-790
55
2
1-167
35-605
2-810
lift 6 in.
H
•913
36-914
3-021
»5
if
1*067
37-045
3-042
»>
2
1-220
37-176
3-063
11
2i
1-376
37-307
3-085
12 ft. 0 in.
1|
•952
38-485
3-284
J5
If
1-113
38-615
3-306
REQUIRED DIAMETER.
TABLE B (continued).
21
No. 1.
Internal dia-
meter of cylinder.
No. 2.
Thickness of
cast iron in
cylinder ring
in inches.
No. 3.
Weight of cast
iron in cylinder
in tons per
lineal foot of
the height of
cylinder.
No. 4.
Surface area in
square feet, in
contact with
earth, per lineal
foot of height of
cylinder.
No. 5.
Loss of weight
from immersion
in water in tons
per lineal foot
of he>ght of
cylinder.
12 ft. 0 in.
2
1-273
38-746
3-328
u
2*
1-434
38-877
3-351
12 ft. 6 in.
U
•991
40-055
3-557
u
If
•158
40-186
3-580
u
2
•325
40-317
3-603
2*
•493
40-448
3-627
13 ft? 0 in.
ll
•031
41-626
3-841
99
If
•204
41-757
3-865
99
2
•377
41-888
3-889
99
2i
•550
42-019
3-914
13 ft. 6 in.
•070
43-197
4-137
99
if
•250
43-328
4-162
99
2
•430
43-459
4-187
95
2i
•612
43-590
4-212
14 ft. 0 in.
If
•109
44-768
4-443
99
If
•296
44-899
4-470
2
•488
45-030
4-497
2i
•672
45-161
4-523
14 ft.' 6 in.
ii
•148
46-339
4-760
If
•342
46-470
4-787
99
2
•535
46 • 600
4-814
99
2i
1-730
46-732
4-841
15ft. Oin.
4
1-188
47-909
5-088
99
if
1-388
48-040
5-116
2
1-588
48-171
5-144
99
2i
1-788
48-302
5-172
15 ft. 6 in.
lj
1-227
49-480
5-427
If
1-433
49-611
5-456
99
2
1-639
49-742
5-485
59
2i
1-846
49-873
5-514
16ft. Oin.
1£
1-266
51-051
5-778
99
If
1-479
51-182
5-808
99
2
1-692
51-313
5-837
2i
1-905
51-444
5-867
16 ft'.' 6 in.
1*
1-306
52-622
6-139
99
If
1-525
52-753
6-170
99
2
1-744
52-881
6-200
99
21
1-964
53-015
6-231
17 ft. 0 in.
1*
1-345
54-193
6-511
99
If
1-571
54-324
6-542
99
2
1-795
54-454
6-573
99
2i
2-022
54-585
6-605
59
2*
2-248
54-716
6-637
17 ft. 6 in.
H
1-384
55-763
6-894
H
If
1-616
55-894
6-926
22
CYLINDER BRIDGE PIERS.
TABLE B (continued).
No. 1.
Internal dia-
meter of cylinder.
No. 2.
Thickness of
cast iron in
cylinder ring
in inches.
No. 3.
Weight of cast
iron in cylinder
in tons per
lineal foot of
the height of
cylinder.
No. 4.
Surface area in
square feet, in
contact with
earth, per lineal
foot of height of
cylinder.
No. 5.
Loss of weight
from immersion
in water in tons
per lineal foot
of height of
cylinder.
17 ft. 6 in.
2
1-848
56-025
6-958
jj
2i
2-081
56-156
6-991
))
2£
2-313
56-287
7-023
18 ft. 0 in.
4
1-423
57-334
7-288
tj
if
1-662
57-465
7-321
M
2
1-901
57-596
7-353
j)
2i
2-141
57-727
7-387
5j
2£
2-380
57-858
7-421
18 ft. 6 in. H
1-463
58-905
7-693
»
If
1-708
59-036
7-727
if
2
1-953
59-167
7-761
j)
2i
2-200
59-298
7-795
M
2£
2-446
59-429
7-829
19 ft. 0 in.
1*
1-502
60-476
8-108
jj
If
1-754
60-607
8-143
j)
2
2-006
60-738
8-178
»
2*
2»259
60-869
8-214
i)
2^
2-512
60-999
8-249
19 ft. 6 in.
H
1-541
62-047
8-535
))
if
1-800
62-177
8-571
||
2
2-061
62-308
8-607
5)
2i
2-322
62-439
8-643
))
2£
2-578
62-570
8-679
20ft. 0 in.
1*
1-581
63-617
8-972
jj
If
1-846
63-748
9-009
jj
2
2-111
63-879
9-046
Jj
2±
2-376
64-010
9-083
M
2}
2-641
64-141
9-120
20 ft. 6 in.
H
1-620
65-188
9-421
||
if
1-891
65-319
9-459
jj
2
2-162
65-450
9-497
||
2±
2-433
65-581
9-535
J)
2j
2-704
65-712
9-573
21 ft. 0 in.
H
1-659
66-759
9-880
||
if
1-937
66-890
9-919
jj
2
2-215
67-021
9-958
||
2*
2-493
67-152
9-997
h
2§
2-771
67-283
10-036
The thicknesses of iron in the table are taken from general practice,
and are the least and the greatest thickness of cast iron in the cylinder
for the respective diameters ; many of the thicknesses of metal are those
adopted in existing examples.
REQUIRED DIAMETER. 23
The weights in Table B are the nett weights of the cast iron rings
only, and no allowance is made for ribs, lags, or strengthening brackets,
bosses, joint flanges, horizontal and vertical stiffeners, for which 20 to
25 per cent must be added to the weights given.
Column 3, when multiplied by the height of the cylinder in lineal feet,
will give the weight of cast iron rings only in cylinder in tons.
Column 4, when multiplied by the depth in lineal feet the cylinder is
sunk in the ground, and by the frictional resistanca of the ground per
square foot of the surface area of the cylinder in decimals of a ton, will
give the resistance due to surface friction in tons.
Column 5, when multiplied by the depth of water in feet at the lowest
tide or depth, gives the flotation power, or loss of weight from immer-
sion of the cylinder, in tons. NOTE. — In shallow rivers, and where the
cylinder is of small diameter, this may be disregarded for all practical
purposes.
The weight of cast iron per cubic foot is taken, for ease of calcula-
tion, at 448 Ibs., which = 0'20 = |th of a ton. The weight of a cubic
foot of fresh water is taken at 0*02786 of a ton.
The forces governing the stability of cylinder bridge foundations
may be thus summed up : —
The supporting power is derived from : —
1. The area of the base, which is as the square of the diameter.
2. The area of the surface in contact with the earth, which varies as
the diameter and the depth the cylinder is sunk in the ground.
3. The safe load per square foot on the base, or the bearing support
due to the internal sectional area of the cylinder.
4. The safe load on the frictional surface per square foot, or the
bearing support due to surface friction.
5. The flotation power, or loss of weight from immersion in water,
which varies as the square of the diameter and the depth of
water.
The non-supporting power is : —
1. The weight of iron in the cylinder.
2. The weight of the hearting in the cylinder.
3. The weight of the superstructure or load on the cylinder from
girder and the rolling load.
NOTE. — The first two items vary as the diameter and height of
cylinder.
From the preceding statements it will be gathered that the diameter
of the cylinder is regulated : —
1. By the weight superimposed, which varies as the span, width of
roadway, load, and number of cylinders of which the pier
consists.
24 CYLINDER BEIDGE PIERS.
2. By its own weight, which varies as its own height and diameter.
3. By the depth it is sunk into the ground.
4. By the resistance from friction of the ground on its surface.
5. By the safe load on the base.
6. By its flotation power, or loss of its weight from immersion in
water.
It is evident for the cylinder to be stable that the safe load on the
base, plus the resistance from friction of the ground on its exterior
surface, plus the flotation power, must equal the weight superimposed,
plus the weight of the cylinder complete ; and may thus be ex-
pressed : —
Let S = Safe load on the base of a cylinder.
R = Eesistance from friction of ground on the surface of a
cylinder.
F = Flotation power or loss of weight of the cylinder from
immersion in water.
W = Weight superimposed, including the rolling load.
C = Weight of cylinder complete.
Then for cylinder to be stable —
(S + R + F) must not be less than (W + C).
CHAPTER III.
LOAD ON THE BASE.
HAVING calculated in detail the required diameter of a cylinder pier
for a railway bridge, the load upon the base will be especially examined;
but here it is advisable to name a few points to be considered in deciding
upon the width of the openings and the form of the superstructure.
In designing most bridges, the chief object is to determine the
number of spans required in a certain length to give the necessary
stability and utility at a minimum cost ; but the nature of the ground
may govern the number of openings, as the safe load upon it may not
allow of the most economical spans being adopted, because they would
cause too great a weight upon the foundations, its even distribution
being considered expedient. Also, if the current of a river is swift, the
bed covered with boulders to an unknown depth, the safe-bearing soil
believed to be inclined, and the shore on each side firm rock, a single
span bridge may be the most economical.
LOAD ON BASE. 25
In yielding or alluvial soil any form of arch may be objectionable
because of the thrust, and also it probably will be well to consider a
continuous girder as prohibited. In Holland, because of the frequency
of soft, yielding, alluvial foundations, continuous girders are very rarely
used. The design may therefore be limited to some form of girder or
truss producing as vertical a strain as possible upon the piers or abut-
ments.
The superstructure can be estimated very closely, provided the
method of erection has been duly considered in the design, for in some
cases the problem of erection is almost the chief element, and overrules
many other considerations ; but the cost of the foundations cannot be
deduced from any formula, and even the nature of the strata may not
be known with certainty.
Consequent upon the increase of dead weight as compared with the
moving load, arches or girders of large span are not so affected by
rolling and sudden loads and vibration as those of small span. It may
so happen that for a large span an arch may be the most economical
form by which to bridge an opening, but owing to the difficulty of
obtaining immoveable abutments or piers to receive the thrust, it may
have to be abandoned, and there may also be objections to it from a
local difficulty of erection. If the piers are simply braced iron piles or
light columns, girders are used in order that any lateral thrust may be
reduced to a minimum. It is very seldom that an arch, whether metal,
brick, or stone, or a girder of a bridge fails, but weakness in the foun-
dations, being the cause of settlement, results in deformation and ulti-
mate destruction.
The weight of a pier has also to be considered, for if masonry, brick-
work, or concrete, whether encased or not, it may be too great for the
foundations to bear unless the base is spread out ; for taking the weight
of Portland cement brickwork at 112 Ibs. per cubic foot, and supposing
a pier to be 100 feet in height, the load upon the ground at the surface
from its own weight would be 5 tons per square foot, and if Portland
cement concrete, about 6 tons. In erecting a girder by rolling out, a
pier may be severely strained, and beyond a 'certain span calculations
may show that erection by that method may not be advisable for other
reasons, and the cantilever-built-out-from-shore-or-pier, or similar
system, may have to be adopted with a comparatively light central
girder.
For the piers and abutments of a bridge it may be an advantage to
employ material which acts as a monolithic mass, such as Portland
cement concrete, and not brickwork or masonry, for the joints are of
somewhat uncertain and unequal strength, and particularly for the
anchor blocks of suspension bridges.
Having very briefly indicated some matters that affect the founda-
i~LlES
OF THE
UNIVERSITY
CALIFORNIA-
26 CYLINDER BRIDGE PIERS.
tions, it is apparent that in designing a bridge the nature of the founda-
tions, system of piers or abutments, manner, ease, and rapidity of erec- .
tion, the strongest and cheapest form, character of the load, purpose of
bridge, and the best material to use have to be simultaneously con-
sidered in the light of the circumstances of each case, all of which may
and probably will, greatly vary.
The load upon the base will now be especially referred to.
First, the importance of ascertaining the nature of the earth, the posi
tion of the strata, and the depths at which they occur is evident.
Borings have frequently proved unreliable, particularly when they are
merely superficial, for then a film or crust may be mistaken for a solid
rock bed. In any case of importance they should only be trusted for
the place where they are made, and not as indicating the nature or con-
dition of the soil over a considerable area. When pits cannot be sunk,
it is desirable that the bore-holes should be frequent.
Excavating pits, using test bars, and driving piles are some of the
methods of determining the character of foundations, but care should
be taken to ascertain in boring that boulders, or thin strata of hard
gravel, are not considered to be solid rock. In sand, mud, or soft clay,
they can be made by means of an iron pipe and the water-jet system.
Experience has proved that boring with an auger is not so reliable as
with a tube, such as is used for artesian wells. In the case of augers
when boulders are encountered, further boring is usually arrested in that
place, and another bore-hole has to be commenced. Trial pits, where
practicable, should be preferred to boring, and they should, if possible,
be sunk to a depth below the lowest level of the intended foundations.
In testing ground by borings, several should be made, as one hole might
encounter a boulder or some hard soil, such as indurated clay, and the
latter may adhere to the auger and arrest its progress ; the specimen
then brought up, being crushed and pressed together, will appear to be
firmer than the actual condition of the ground, and will usually indicate
rock or hard ground at a higher level than it exists. If it should be
thought that the nature of the strata or their thicknesses may vary over
or near the site, the question has to be considered whether it is advisable
to lay dry the foundation in order that its characteristics may be known
and unequal subsidence prevented. Irregular ground should be avoided
in which to sink cylinders or wells, as it is then difficult to effect vertical
einking.
The area of the base is the principal source upon which the stability
of a cylinder foundation depends, as it is generally unalterable. A con-
siderable margin of stability should in all cases be allowed, as from
the nature of the calculations exact results cannot be attained. The con-
dition of the earth in each case should be considered, and in works of
magnitude it is advisable to make experiments extending as long as prac-
LOAD ON BASE. 27
ticable, and for at least a month ; for it is false economy not to carefully
ascertain the character, condition, and other circumstances of a founda-
tion destined to support any part of a structure, a failure of which may
result in serious consequences. A continuous surface possesses greater
sustaining power than the same area in detached portions, as the adhe-
sion of the sides is not destroyed ; similarly the load that a tenacious
earth will support upon a small area is somewhat greater than over a
large area, because the lateral surfaces are relatively larger in propor-
tion to the area, and, therefore, the effect of cohesion is proportionately
greater ; but in loose soils it is not so, for cohesion exists but in name,
and the ground around would be upheaved upon an excessive load being
superimposed. The weight upon the soil on which narrow walls rest, or
whenever it is subject to frequent changes in the direction and amount
of pressure, should be less than for foundations which are of consider-
able continuous extent and depth.
In testing the weight any earth will support, it is not so much the
first settlement, provided it is not excessive, that it is desirable to know,
but whether after the first settlement it ceases, or the earth, as it were,
reacts and rebounds, which it may do in firm ground to the extent of
one-eighth to half an inch. If so, the ground is not overloaded, and is
only being compressed to firmness, and not crushed.
After ascertaining by experiment the pressure any earth will bear over
a given area, the object should be to make the soil neither drier nor
wetter than that of its natural state when experimenting, and it should
be maintained in that condition. In testing the weight which a soft
earth will support, some days should be allowed for the sinking of the
test platform, and such subsidence should be known periodically by
means of careful levels. A month is not too long for a reliable and
complete test, as many soft soils continue to yield. In soft clay soils
considerable depression often proceeds for weeks after a load has been
applied, but, except in peculiar earths, such settlement will ultimately
be imperceptible, and will practically cease. Although it may not be
absolutely necessary to experiment when the nature of the ground is
well known, wherever stability is of great importance, the cost of a
practical experiment being so small, there is no sufficient reason why an
actual test of the sustaining power of the soil should not be made in
the majority of instances, for there are many earths whose friction
and cohesiveness can alone be depended upon for resistance to displace-
ment. In such cases the initial pressure upon the earth should not be
much exceeded. The character of the load should be considered,
whether it is fixed or moving, and allowance be made when the
live load is large as compared with the dead weight, especially in
sandy soils. The experiments of Professor Stokes, 1849 ; M. Phillips,
1855 ; M. Renaudot, 1861 ; M. Bresse, 1866 ; and recently of Dr.
28 CYLINDER BRIDGE PIERS.
Winkler, and others, show that the increase of the intensity of strain
consequent upon the dynamic effect of a suddenly-applied moving load
may be as much as 33 per cent, more than that of the computed
statical pressure.
The normal pressure upon a foundation should be considered in
determining the safe load upon the base. It is obvious that if the
material is excavated, the initial pressure on the soil is removed. In
loose, non-cohesive earths the load may be increased when the depth
is considerable, as the soil has been subject to a greater normal pressure
due to the we'ght of the soil upon it at any depth, but it is not ad-
visable to consider such increase of bearing power of the soil, unless
at any depth it is found that the normal pressure augments the bearing
power and makes the earth more dense, which may be approximately
ascertained by experiment. In such event the load upon the base can
be increased by the weight of the normal pressure removed. Supposing
5 tons per square foot was known to be the safe load upon the surface
of the ground, and at any depth it was found that the normal pressure
of the soil was 2 tons ; 5 + 2 = 7 tons placed at that depth would
equal 5 tons at the surface. In the worst case, when the loose earth
is of great depth, and it is certain that it cannot be tapped or disturbed
at the depth at which it is decided to place the foundations of a
structure, and provided the load is not more than the normal pressure,
it is not probable that it will subside or slip, as no additional weight is
ii
Let D = the depth in feet of a foundation from the surface of the
ground.
„ W = the weight of a cubic foot of soil in decimals of a ton.
„ P = the normal pressure on the foundation in tons per square
foot.
Then P = D X W.
EXAMPLE. —
Let the soil be damp sand ; then W =, say, 0-055 ton per cubic
foot. Let D = 50 feet ; then P = 50 X 0'055 = 2'75 tons. The
normal pressure which is removed is therefore 2'75 tons per square
foot. Should the safe load on the base be taken as 5 tons, the excess
of pressure above the normal pressure is 5 — 2'75 = 2'25 tons. It is
but necessary to examine the loads put upon screw piles, to see that
this weight is considerably less than chat which might be safely
imposed.
A weight of 5 tons per square foot is generally accepted as the safe
load on the blade of a screw pile in firm compact sand, the whole area
of the blade being usually considered as support. In this case the
normal pressure on the soil is not removed, and the 5 tons pressure is
LOAD ON BASE. 29
an additional load. Although the shaft of the pile displaces some
material, it makes the soil more dense, and therefore heavier, in its
immediate vicinity.
For the purpose of comparing the load on the base in a cylinder and
a screw pile bridge, let the depth of the foundation be 15 ft., the soil
damp, firm, compact sand. The excess of load above the normal
pressure on the base per square foot, cylinder pier
= 5 tons — P = 5 — (15 X 0-055) = 5 — 0-825 = 4-175 tons.
The excess of load, above the normal pressure, on the base per square
foot, screw-pile pier=5 tons, or 20 per cent, more pressure than that of
the cylinder pier. The same co-efficient of safe-load on the base for a
screw-pile foundation, in which the normal load on the soil is not
removed, should not he taken for that of a cylinder pier, because in the
former case the foundation is unseen, and it is not absolutely known
whether the blade of the screw has remained uninjured in the process
of screwing, apart from the question whether the whole area of the
blade of a screw-pile should be considered as support ; but on the
contrary, in a cylinder pier, the foundation is visible ; it is known that
the whole area of the base is utilised, and that the normal pressure of
the soil is removed. An examination, therefore, of past practice shows
that the load on the soil from a screw-pile pier is relatively considerably
greater than that of a cylinder pier, notwithstanding that in one case
everything is known, and in the other, in great measure, is a matter of
conjecture. There is no reason why the load on a cylinder pier base
should not be somewhat more than that upon a screw-pile foundation ;
but it is difficult to estimate the actual load that is imposed on the base
of a cylinder bridge pier, because of the surface friction, which acts in
supporting the load, and therefore reduces the weight on the foundation.
Unequal loading of the base may be caused by wind-pressure on a
pier, in addition to the normal or initial compressive strain from the
weight of the pier and the load; it should therefore be ascertained
whether the resultant of the weight of the pier and load on the
structure and the side wind-pressure cuts the base so as not to bring a
tensile strain on the windward side, and a compressive strain on the
leeward side, of any serious amount on the foundation, or the brickwork,
masonry, or concrete. If it can be done economically, the initial com-
pressive strain should balance any tensile strain that may arise on the
windward side of the pier from the wind-pressure. The effects of the
above strains will be transmitted to the foundation, if the latter is
placed nearly on the surface, and the load on the base on the leeward
side may be considerably increased above the initial strain from the
weight of the pier and the load. It is therefore obvious that in such
situations the load on the base should be less than if the pressure was
30 CYLINDER BRIDGE PIERS.
always stable, hence the importance, in order to ensure equal pressure on
the base, of the filling in a cylinder bridge pier, and the material of any
other similar structure, acting as one mass, and being of uniform
quality at any level, and of the pier being firmly supported around its
circumference or sides by the soil. In the case of foundations of con-
siderable depth, these variable forces will be distributed, provided the
pier acts as a monolith, so that their effects will not be materially felt
on the base.
In the case of soft strata of great depth, and where it is impracticable
to obtain firm, hard foundations, a good plan is to weight a few piles
every 4 or 5 ft. or so as they are driven, and to note on each occasion
the weight they will bear without sinking ; it can thus be ascertained
whether the bearing power increases with the depth sunk, and the best
depth to place the foundations is known. The experimental piles should
be driven in different places, and over the area of the foundation ; they
must not be drawn, but cut off.
Cylinder and pile foundations should be weighted with a load equal to
the greatest they are likely to be required to sustain, and the equally
distributed load on the hearting of the cylinder should be allowed to re-
main for some days, to see if there is any settlement, and the longer
this temporary weighting is continued the more reliable is the test.
Careful daily observation should be taken to ascertain if any subsidence
has taken place ; there will almost always be some subsidence under a
test load, and it will probably vary in different piers ; and although the
testing may delay the progress of the works, for the sake of safety it is
well that it should be done, unless other opportunities offer of obtaining
a true test during sinking operations, and after they are completed,
without incurring the expense and delay of temporary loading, which
may be a costly undertaking.
It has been proved by practical experience that materials uniform in
size and homogeneous in character form the most compact and impene-
trable masses. The great stability of breakwaters formed of materials
of uniform size, and the firmness of macadamised roads, are proofs of
this. The same rule applies to soils. It is the separation of the larger
bodies from the smaller that causes a want of cohesiveness and weight-
sustaining power.
Near the mouths of rivers, islands often consist of detritus liable to be
washed away by a stronger flood than that which deposited them, and
also to be eroded by the action of waves, therefore the actual site of a
river pier should invariably be examined before sinking a cylinder,
although the nature and position of the strata may have been thoroughly
ascertained, because stumps or logs of trees or wreckage may be
embedded in the soil, which should be removed before commencing
operations. Where a stratum of good bearing soil, such as gravel,
LOAD ON BASE. 31
overlies soft ground of great depth, by increasing the bearing area on
the firm earth it may be unnecessary to go to any great depth, but
provision must be made against scour.
In foundation and general work, rocks are usually not loaded with a
greater weight than from 8 to 18 tons per square foot, according to the
character of the rock. As the crushing strength has often been
ascertained from cubes, and not from prisms, rectangular blocks, or
irregularly-shaped pieces, and as the resistance of rocks to transverse
strain or breaking across is considerably less than the compressive
strength, and varies greatly, and not always according to the crushing
resistance of the material, from 8 to 20 tons per square foot is a prudent
limit for the safe load, and should not be exceeded, unless under
exceptional circumstances, as unequal bearing may greatly intensify
the strain, and irregularity in the texture may reduce the resisting
powers to that of the weakest part. Sandstone rock that can be
crumbled in the hand should not be loaded with more than 1£ to If
ton per square foot, but the strength and weight of sandstone varies
considerably. Reference to authorities on the resistance of stones to
crashing, tension, and transverse strain, will give ths approximate safe
load per square foot ; but in foundations, i.e., on the rock in its natural
location, it should not exceed one-tenth of the ultimate resistance, and
the compressive strength should not alone be taken as a guide to the
safe load, but the resistance of the rock to tensional and transverse
strain should always be considered in foundation work. The value
given for the particular sandstone rock named is for the softest earth
that can be called rock, and is merely stated to show that, although
some earths may be generally classed as rocks, their bearing power
may be limited. The safe load upon an artificial rubble or rock mound
foundation depends upon its character, firmness, and solidity when
deposited, and upon that of the ground on which it is placed. No
general value can be named, although it may be classed as clean or
compact gravel.
The following values of the safe direct compressive load per square
foot on soils have been carefully compiled from actual practical work,
but, of course, are only intended as a guide to the safe load on any
earth. The condition of the soil in each particular case must be taken
into consideration, and in works of any magnitude, experiments should
be made under the same conditions to which the permanent works will
be subject, and with the ground both wet and dry. For ordinary con-
ditions of soil, and for the usual depths of foundations, which are
assumed to be beyond weather influences, the values given will be found
to be approximately correct. The normal pressure or initial weight on
the base from the soil is not taken into consideration.
32 CYLINDER BRIDGE PIERS.
Approximate Safe
Description of Earth. Maximum Load in
Tons per Square Foot.
Bog, morass, quicksand, peat moss, marsh land, silt ... 0 to 0' 20
Slake and mud, hard peat turf 0 to 0*25
Soft, wet, pasty, or muddy clays, and marsh clay ... 0' 25 to 0*33
Alluvial deposits of moderate depths in river beds, etc... 0' 20 to 0*35
NOTE. — When the river bed is rocky, and the
deposit firm, they may safely support 0'75
ton.
Diluvial clay beds of rivers ... ... ... ... 0' 35 to 1*00
Alluvial earth, loams, and loamy soil (clay and 40 to 70
per cent, of sand), and clay loams (clay and about
30 per cent, of sand) 0'75tol'50
Damp clay I'50to2'00
Loose sand in shifting river bed, the safe load increasing
with depth 2'50to3'00
Upheaved and intermixed beds of different sound clays 3 • 00
Silty sand of uniform and firm character in a river bed
secure from scour, and at depths below 25 ft. ... 3 '50 to 4*00
Solid clay, mixed with very fine sand ... ... ... 4*00
NOTE. — Equal drainage and condition is espe-
cially necessary in the case of clays, as
moisture may reduce them from their
greatest to their least bearing capacity.
When found equally and thoroughly mixed
with sand and gravel, their supporting
power is usually increased. All the values
given are for foundations at depths beyond
weather influences.
Sound yellow clay, containing only the normal quantity
of water 4'00to6'00
Solid blue clay, marl and indurated marl, and firm
boulder gravel and sand 5'00to8'00
Soft chalk, impure and argillaceous ... ... ... 1* 00 to 1*50
Hard white chalk 2'50to4'00
Ordinary superficial sand beds ... ... ... ... 2*50 to 4*00
Firm sand in estuaries, bays, etc. 4* 50 to 5* 00
NOTE. — The Dutch engineers consider the safe
load upon firm, clean sand at 5£ tons per
square foot.
SURFACE FRICTION.
Very firm, compact sand, foundations at a considerable
depth, not less than 20 ft., and compact, sandy
gravel 6'00to7'00
NOTE. — The sustaining power of sand increases
as it approaches a homogeneous, gravelly
state.
Firm shale, protected from the weather, and clean gravel 6*00 to 8*00
Compact gravel 7'OOto9'OG
NOTE. — The relative bearing powers of gravel
may be thus described :—
1. Compact gravel.
2. Clean gravel.
3. Sandy gravel.
4. Clayey or loamy gravel.
Sound, clean, homogeneous Thames gravel has
been weighted with 14 tons per square foot
at a depth of only 3 to 5 feet below the
surface, and presented no indication of
failure. This gravel was similar to that of
ft clean pebbly beach.
CHAPTER IV.
SURFACE FRICTION.
THE lateral frictional resistance of the soil on a cylinder pier or well
is most frequently not considered as a means of reliable support. The
vibration to which most structures are subject tends to destroy surface
friction, and the latter is often of an irregular character. Boulders will
sometimes hold a cylinder, and if digging out round the base of the
column during sinking is adopted, the friction will be reduced. The
process of sinking cylinders and wells lessens the surface friction of
the soil, because of its loosening the external earth, much of which
often gets forced up into the interior of the cylinder, and its place will
be supplied by soil having but little cohesion with the firm ground
around the cylinder, although the loose earth will become consolidated
after a time, and may have of itself considerable frictional resistance.
When the earth has been so loosened, or previously dredged, until
D
34 CYLINDER BRIDGE PIERS.
consolidation has been effected by time and settlement, which usually
increases the friction of repose, the surface friction is too variable and
uncertain to be safely trusted. Thus, when cylinders or wells are sunk
close together in loose, granular soil, the coefficient of surface friction
is less than when they are placed at considerable intervals, although
ultimately it may be of the same value.
Percolation of water and air lessens the frictional resistance of all
soils, but in sinking through most clays, if water reaches them, they
will swell and grip a cylinder. This is especially the case when a thin
bed of clay occurs in sandy soil. The gripping action will not, how-
ever, give a true coefficient of the friction between damp clay and any
material, and as the quantity of water in clay in its natural condition
varies from about 5 to 13 per cent., the coefficient of surface friction
will also not be the same for each kind of clay.
The level of saturation of permeable soil often varies with the water
level in a river, and therefore the support from surface friction will
change, and may almost be destroyed to a certain depth, as some portion
of the earth in contact with the cylinder may be in a state approaching
saturation while other parts are nearly dry.
When a hole has to be dredged in the centre of a cylinder to a depth
considerably below the cutting edge, in order to cause a cylinder to sink
through a stratum of clay resting upon sand, the latter will rush in
when the clay bed is perforated, and this action may so disturb the soil
around the cylinder as to decrease the natural surface friction for some
time after a bridge is finished, for the disturbance of the soil will cause
local settlement which will proceed until the earth becomes consolidated.
If the surface of iron is neither greased nor lubricated, there is usually
very little variation of friction due to changes of temperature, moisture
and disturbance being the two chief agents of deterioration, and as the
ease with which earths can be disturbed, and their perviousness or
imperviousness greatly vary, the coefficients of friction will also be
different. Another cause of variability in the frictional resistance is
that sometimes a cylinder is not vertical, the friction increasing as it
loses its perpendicularity.
Whether the surface friction is uniform in value and immutable are
the chief questions to determine.
It is important to remember, should the support which a column
may receive from surface friction be suddenly removed by scour, or
any of the agencies previously and hereafter mentioned, that an
impactive force of serious amount will at once be brought upon the
base ; the sudden sinking of cylinders after being earthbound proves
that the surface friction may quickly cease, or become very small.
No doubt the frictional resistance of some soils is great, and the fact
that the stability of timber piles is principally dependent upon it for
SURFACE FRICTION. 35
support, and almost wholly so in soft sand and such soils, shows that
surface friction can be trusted in some cases.
If the soil through which a column or .pile is driven is of the same
character, and there is no probability of the frictional resistance being
disturbed, a certain amount of support may be calculated from this
source, and although it is impossible to give any absolute coefficient
for the friction on the surfaces of piles or columns, a close approximation
may be attained by a comparison of soils and circumstances. A crucial
test is obviously the most reliable way of ascertaining the frictional
resistance, as even the same strata, under different conditions, will give
various results, although the values may not deviate to any great extent.
Friction during motion is generally considered to be less than the force
necessary to overcome it when at rest, and undoubtedly this is the case
when the surfaces are similar, and are smooth and hard and not easily
impressed, as iron, granite, concrete, and metals generally ; but when
they are comparatively soft and incapable of resisting indentation
at any pressure that they may have to bear, the difference between
the coefficient of friction during motion and that at the commencement
of motion or of repose will not be so marked ; for other resistances
may come into action not due solely to surface friction of the
mass. A surface may become indented or roughened, thus offering
opposition to motion not existing at the commencement of movement,
and particularly so in any earth of a mixed character possessing hard
particles, such as boulders or sand in clay. On the other hand, in the
case of hard rock, solid clay, or other homogeneous earth, the
difference between friction during motion, and that of friction at rest
may be reliably determined. In soils of a granular or gritty nature,
small particles become detached during motion, and by pressure occupy
or become wedged into any cavities upon the surfaces, and therefore
offer resistance which is not alone due to friction of a mass upon a mass.
From this cause, friction during motion may seemingly even become
greater than during rest, but with material consisting of rounded particles
that will not wedge, the friction upon a sliding surface may be lessened
by reason of the grains revolving.
Friction is the chief cause of stability in granular soils and those
readily affected by moisture, which have for practical purposes no
immutable cohesion. In few earths are both cohesion and friction of
considerable and reliable value, one or the other quickly becoming
impaired or destroyed. Deterioration is caused by such various means
that each earth must be separately considered, and also the circum-
stances under which it is placed. The particles of the earth may be
dissolved by water and become in a muddy state, or they may be
considered insoluble as in clean sand and gravel, although in compact
sand or gravel the cementing material may crack and weather. Cohesion
D2
36 CYLINDER BRIDGE PIERS.
may be also more quickly impaired by certain action than friction, and
vice versa. It is advisable to ascertain that any earth is uniformly
affected throughout the mass, and to prevent or provide against
deteriorating influences, for it is useless to declare any' -earth possesses
considerable frictional resistance or cohesion when the power can be
quickly dissipated by ordinary atmospheric action, and to rely for
permanent stability upon such property. In ordinary earths, not rock,
it will generally be found that cohesion is small or insignificant in soil
having a coefficient of friction of some moment, and the reverse. In
most earths friction, although it is affected in a greater degree by
vibration, has to be relied upon, and not cohesion, as the latter is
variable and may exist almost unimpaired in a lump which, neverthe-
less, may become detached because of fissures. The coefficients of
friction of different earths are also better known than the cohesion ;
but how easily even friction is impaired may be gathered from the
sudden manner in which cylinders will sink after having hung for days
by surface friction, or been held by the transitory expansion of clay.
It has been noticed in sandy soils that the surface friction on a
cylinder, when sinking operations are not being carried on, and when
the material is being raised from the interior, is different ; the latter
resistance being from 20 to 25 per cent, less than the former, owing to
the disturbance resulting from the sand being forced up through the
bottom. The frictional resistance may be also lessened by the method
of sinking a cylinder, which subject will be examined in subsequent
chapters.
In the case of earths partaking of the nature of sand and gravel,
which allow of free percolation of water, the permanent friction
depends, within certain limits, on the force with which they are pressed
together, if not to such an extent as to make them compact and dense,
and they will have their frictional resistance increased with the head of
water, if the soil is thoroughly waterlogged ; but in impermeable soils
there will be no practical increase from this source.
As timber is liable to indentation, the friction will increase, to some
extent, with time ; but in the case of iron or hard surfaces, it will not
be augmented after the soil has assumed its normal condition. It is
usually found that when the earth is compact and dense there is less
lateral pressure, or surface friction, than in the case of loose and
incoherent soils. G-ritty soils and clay loams have considerably greater
frictional resistance than oily, soft clays. Moisture affects the latter
earth more than any other soil usually met with.
In sinking cylinders in mud, if desired, the surface friction can be
increased by depositing fine sand against the surface of the column, as
the particles of the sand will adhere to it to a considerable extent.
The surface friction of iron piles, or cylinders, per unit is considerably
SURFACE FRICTION. i>7
less than that of timber piles, on account of the hardness, smoothness,
and evenness of the surface of iron, as compared with the roughness
and compressibility of wood. Therefore a coefficient for the supporting
power from friction on the surface of a wooden pile will not be
applicable to that of an iron column. Excepting in the case of mud
and silt, the frictional resistance of unplaned cast iron has been
ascertained from practical experiments to be about 25 per cent, less than
the values for wood. As the outer cylindrical surface of brick wells is
generally smoothly plastered or rendered, or has a coating of Portland
cement, it may be considered the same as an unplaned .superficies of
cast iron.
It is obvious that the permanent safe load from frictional resistance
of fine soft drift sand should not be taken as equal to that of firm sand,
although the former may cause greater resistance to sinking. Friction
upon a dry surface is almost invariably greater than that upon a wetted
surface, and is so beyond all question upon any plane lubricated with
an unguent. The disturbing and enfeebling effect of water may be
judged from a careful analysis of many reliable experiments to ascer-
tain the frictional resistance in the case of the same material in a dry
and in a wet state on an unplaned surface of cast iron, and on timber
piles. It shows the following results : —
That the frictional resistance of an unplaned surface of cast iron on
wet sand is about 16 per cent, less than the resistance on the same
material when dry. With wooden piles it is about 12 per cent, less,
and about 40 per cent, less in sandy clay and gravelly clay soil.
In sandy gravel the resistances are practically the same, whether the
soil is wet or dry.
When both materials are in a wet state, sand gives about 20 per cent,
more friction than sandy gravel.
The surface friction of masonry and brickwork on dry clay is reduced
by from 25 to 30 per cent, when the clay is wet.
Mixed soils, such as clay loams, loams, sandy loams, usually give less
surface friction than either the clay or sand of which they are composed
when unmixed ; and it may be stated generally that the resistance from
surface friction of the ground increases with the smallness and angu-
larity of the particles composing soil of the nature of sand or gravel.
With regard to the question whether the frictional resistance increases
in the same soil according to the depth a cylinder is sunk into the
ground, it cannot with safety be assumed that it becomes greater, for
although many instances have occurred which proved that it does
increase, not a few have shown that it does not. What is the reason of
this discrepancy? Broadly, the different condition of the earth in
pervious ground, the depth of water, the manner of sinking a cylinder,
the state of the surface of the cylinder, whether sinking operations are
38 CYLINDER BRIDGE PIERS.
continuous or intermittent, and variation in the cohesive power of the
soil. Theoretically, the friction should vary with the depth and the
lateral pressure. The results of tests taken while sinking cylinders or
caissons are here alone considered, and they indicate, especially where
granular earth is in a state of saturation, that the frictional resistance
increases regularly with the depth, but that in dry earths the increase is
small. In granular earths the augmentation in the value of surface
friction is more marked than in non-granular soil, and in muddy clay
and sandy mud, at ordinary depths, such as 30 to 60 ft., the increase
is insignificant. In the case of clean sand, it increases ; but in gravelly
sand and gravel usually very little below a depth of from 10 to 15 ft.
In calculating permanent support from surface friction the total
depth a cylinder is sunk in the ground can scarcely be taken, even if
the river bed be secured from scour, for the surface friction for the
first few feet is small, and seldom in ordinary sand and clay and
gravelly sand beds exceeds 40 Ibs. per square foot at about 3 ft. in
depth, 80 Ibs. at 6 or 7 ft., and 120 Ibs. at about 10 ft.
It is advisable to allow a smaller coefficient for surface friction in
cylinders of small diameter than for those sunk in the same soil of large
diameters, because in a cylinder of large diameter the proportion of its
circumference to the area of the base is small. On the contrary, where
a cylinder is of small diameter, the circumference is nearly equal to the
area of the base. For instance, in a cylinder 4 ft. in diameter, the
areas of the cylinder and the circumference are equal ; whereas in one
of, say, 20 ft. in diameter, the area of the base is five times greater
than the circumference.
The safe frictional 'support in the case of a stable or fixed load, may
be taken as more than that with rolling loads, which may cause
vibration in the cylinders or piles.
The experiments of Mr. Longridge, M.Inst.C.E., in Morecambe Bay,
showed that by vibration the bearing power of driven timber piles was
reduced to one-fourth or one-fifth of that when subject to a steady
non-vibratory load.
The following values are not especially given for the purpose of
determining the safe frictional resistance which may be relied upon as
permanent support, but they have been carefully deduced, and may be
considered as closely approximate. It is well to make experiments with
the soil through which the cylinder is to be sunk, when in a loosened
condition, in its normal state, and when impregnated with water. The
values stated are for soils in the ordinary condition usually met with in
sinking cylinders. They are taken from many practical examples, but
it is well to repeat that in the same soil the frictional resistances often
greatly vary, owing to the amount of moisture in the earth ; the rough-
ness, evenness, and smoothness of the face in contact with the soil ; the
SURFACE FRICTION. 89
compactness, looseness, or degree of fineness of the strata ; and the
manner in which the load is applied, whether suddenly or gradually ;
and the mode of sinking the cylinder. As the girders in a cylinder
bridge-pier do not rest upon the iron rings, but upon the hearting of the
cylinder, the only direct connection between the casing and the hearting
is by means of the horizontal joint flanges of the cylinder. Should the
hearting and the rings be unconnected, of course there can be no
permanent support from surface friction. The values on unplaned cast
iron are for depths not less than 15 ft.
Approximate Surface
Description of Earth, and material in contact. Friction per square
ft. in Ibs.
Mud and silt, on dry timber sawn piles 100 to 150
„ „ on clean, unplaned cast iron 50 to 70
Sandy mud, on clean, unplaned cast iron ... ... 150 to 250
Muddy clay and viscous mud, on clean, unplaned cast
iron ... 250 to 400
NOTE. — The frictional resistance generally in-
creases with mud and silt some 25 per
cent, between depths of 6 ft. and 20 ft.,
but after the latter depth it frequently
augments but little.
Silty fine sand, liquid when disturbed by water, on
unplaned cast iron 250 to 300
Soft clay, on timber sawn piles 160 to 180
Ordinary sand, on unplaned cast iron ... ... ... 300 to 400
Clean river-bed sand and gravel, on unplaned cast iron 400 to 600
Hard compact clay, with a tenacious surface, on un-
planed cast iron 900 to 1,000
Ordinary clay beds, on unplaned cast iron ... ... 700 to 800
Sharp sand, on clean, timber sawn piles 1,100 to 1,500
Fine soft drift sand, on clean, timber sawn piles ... 1,500 to 1,700
NOTE. — In the case of clays, the gripping
action upon a cylinder consequent upon
then* expansion on exposure to moisture
or air may make the surface friction
appear to be much larger than that
caused by ordinary frictional resistance
only. The values are for clay containing
the normal quantity of water.
40 CYLINDER BRIDGE PIERS.
CHAPTER V.
SINKING CYLINDERS; GENERAL NOTES.
IN deciding upon the method to be employed in sinking a cylinder, or
the means by which the excavation in its interior shall be effected, no
prejudice should exist for the absolute use of one system over that of
others ; because each method may be useful under certain circumstances,
and the shortness of the season during which piers can be erected, may
cause the selection of the method of sinking to resolve itself into
almost a mere question of which is the speediest. Open air river-pier
foundations are to be preferred, but these can generally only be adopted
in shallow rivers of depths such as 10 ft. or so, and when the river is
free from heavy floods, but if a cylinder can be sunk to a firm and
sufficiently watertight stratum, they can be used to any reasonable
depth, as the bottom becomes water-sealed and the water can be pumped
out.
A reliable comparative table of the cost of sinking cylinders is difficult
to attain, on account of the different circumstances and conditions under
which they have to be sunk, for even the time required to sink any
column cannot be foretold exactly, as an accident, or difficulty with one
cylinder may cause considerable delay, and affect the progress of the
others. The rate and cost of sinking, depends upon so many things,
such as the nature of the soil, whether it is free from boulders or other
obstructions, the absence of "blows," the size of the cylinder, its
position as regards another column, the method adopted in sinking, the
excavating apparatus used, the depth below the water-level and bed of
the river, the number of men employed, and whether they are experienced
workmen, and upon other contingencies, that it is impossible to lay
down any fixed rate. The nature of the strata, the number of cylinders
to be erected, the plant at hand, etc., vary greatly, and in many instances
the cost of sinking columns of the same diameter in similar soil has
disagreed considerably, owing to local conditions. To obtain a firm
foundation for a bridge-pier in a soft river bed with a swiftly flowing
current is always a more or less arduous undertaking, and the difficulties
increase according to the depth below water.
It is most important that the ground should be of the same character
over the whole horizontal area of a cylinder, in order that there may be
uniformity in the rate of descent, which is to be preferred to irregular
and sudden motion, and that sinking may be vertical, as, if it be harder
on one side than another, tilting may be expected, and precautions should
be taken to support the side on which a tendency to incline occurs.
Some of the many different ways of sinking cylinders may thus be
enumerated.
SINKING CYLINDERS. 41
1. The plenum or compressed air method. The vacuum system being
considered obsolete.
2. Forcing down the cylinder by weights, and excavating the
material in the interior by means of dredgers and excavators.
3. Forcing down the cylinder by weights, and excavating the
material in the interior by means of divers.
4. Forcing down by weights, and by dredging the material in the
interior, until an impermeable stratum, such as clay, is reached,
then by pumping until the cylinder is dry, or water-sealing the
bottom of the cylinder by means of cement concrete.
5. The same method of forcing down the cylinder, and by dredging
the earth inside, until rock is reached, when the bed is levelled,
if necessary by divers, and sufficient cement concrete is deposited
to prevent the water issuing up, the remaining water in the column
is then pumped out, and the work proceeded with as on dry
land.
6. The same method of forcing down and excavating by dredgers,
etc., till the intended depth is reached, the bottom is then inspected,
and the work done by means of a diving-bell lowered inside the
cylinder. This method of sinking was suggested by Mr. E. A.
Cowper, M. Council Inst, C.E.
7. By a combination of the compressed air methods with systems
2 to 5.
It is frequently specified that the cylinders are to be sunk so as to
leave the bottom dry, and that the concrete is not to be passed through
water. Such a stipulation in permeable strata involves either the
adoption of the pneumatic method, or that described in No. 6 paragraph.
On the Continent, it is almost always specified that the bottom of the
foundations shall be examined, and that the concrete hearting shall not
be passed through water ; this clause necessitates the use in most cases
of compressed air to lay the base dry, but the extreme limit at which
it can be used is about 120 ft. below water, at a greater depth some
other method of sinking must be adopted ; and not only is the working
time very small at depths over 80 ft. or so below water, but injury
and even fatal results to the men follow, and have followed, its
adoption. In some situations there may be necessity for such a clause,
but to stereotype it is unadvisable, because of the expense of obtaining
a dry bottom, although, of course, an examination of unsubmerged
ground is always to be preferred to that of submerged earth. If the
compressed air system was used where simple dredgers or excavators
would suffice, it appears from a comparison of examples that from three
to five times more money would be spent than was necessary ;
but if excavators were used for soils for which they were not
designed, or if many large boulders or obstrju^Ofts- are. expected
E LJB
OF THE
UNIVERSITY
42 CYLINDER BBIDQE PIERS.
to be met with, the compressed air system would be required,
provided the depth is not too great, which question will be hereafter
referred to ; as the excavation can then be carried on as if on dry
land.
The size of a cylinder will, to some extent, govern the apparatus to
be used. The pneumatic system cannot be conveniently employed with
cylinders of less diameter than 5 ft. Care should be taken in devising
apparatus that the men are put in such a position that they can freely
work. If rapid sinking is of importance, the weight of the cylinder
with the kentledge should considerably exceed the friction on the
surface of the cylinder, and it may then become a question to determine
whether or not it would be advisable to adopt one large and heavy
caisson, although it may be more expensive, than several cylinders
which would be comparatively light, and would require a longer time to
sink them, the object being to cause the downward pressure to be
much in excess of any surface friction.
In a clay soil, cylinders can be sunk by being forced down by
weights, and by excavating the material inside after it has from time
to time been pumped sufficiently dry. The excavation for cylinders of
small and ordinary diameter is sometimes done by divers, but it is slow
work and of doubtful economy, except in small cylinders, when sand
and loose soil overlie an impermeable clay stratum which, on being
penetrated a few feet, will water-seal the cylinder, and enable it to be
pumped dry enough for excavation to be completed in the open air.
Where possible, sinking cylinders by means of weights and excava-
ting by hand, if the water can be removed by baling or easily by
pumping, should be adopted, as being the cheaper methods ; but if the
water is considerable, or fluctuating, dredgers may be preferable, not
only on the ground of economy, but also to prevent a run of soil and
diminish the quantity of excavation, as the water being in the cylinder
will not allow the earth to rush in. The disturbance caused by the
ingress of loose soil may be so great as to move the earth for some
distance around a cylinder, and militate against vertical sinking, there-
fore it may be inexpedient to pump out the water and leave the bottom
unbalanced by its pressure. It may be necessary to use compressed air
where obstacles such as large boulders are met with, or where the
ground is difficult or too hard to economically dredge. In deep
foundations a combination of the compressed air system and pumping
might be used under certain circumstances, for instance, if a water-
tight stratum was encountered during sinking by the compressed air
method ; as after it had been reached and been penetrated to a little
depth, any water could be pumped out ; but, as a rule, it is not
necessary to penetrate a watertight stratum very far, for it generally
affords a good foundation. Advantage and economy are gained by the
SINKING CYLINDERS.
disuse of the compressed air system in putting in the lower portion of
the hearting.
In a favourable situation, cylinders can be sunk by merely having a
hand-pump or two to keep out the water, a ladder placed down the side
of the cylinder, a double-purchase crab winch on a platform over the
cylinder, in addition to the ordinary staging. Of course, this method
can only be used if the pumps are able to keep down the water
sufficiently for the men to excavate in the open air, if not, dredging
machinery or divers in helmets, must be employed until a watertight
stratum is reached, when the water can be pumped out and the work
proceeded with. The river bed over the site of the piers should first be
levelled by bag and spoon, or other dredger, as it lessens the amount of
the excavation in the cylinder, and gives an even surface upon which to
pitch the cutting ring.
Where loose soil, such as mud, silt, sand and gravel, overlies an
impermeable stratum at a moderate depth, cylinders can be sunk as
follows : — By erecting a pile-staging around the site, and bolting
together and calking a sufficient height of rings on the platform to
reach, when sunk, a little above the water level ; or, if a tidal river,
above low water level ; they are then lowered by a travelling crane
working on the staging, the loose top soil is taken out by a dredger, and
as the cylinder sinks fresh rings are added until the impermeable soil is
reached, when the water is pumped out and the excavation continued.
If a river bed be dry for a certain season, sinking cylinders may thus
be conducted. The cutting ring can be conveyed to the site upon a
light temporary railway, and be placed in its correct position, the
excavation being done by simple digging, lengths of the cylinder being
added, and work so carried out until, upon the water-bearing level being
reached, it becomes necessary to use dredgers.
With respect to staging, it will be considered in a subsequent chapter.
Great care should be taken at the commencement of sinking opera-
tions that a cylinder is perfectly vertical, as both time and money are
thereby saved. A simple plan by which it may be known whether a
cylinder is sinking vertically, is by hanging several plumb-bobs outside
a column. In a rapid river there is especial difficulty in sinking it
truly vertical, and allowance should be made for unavoidable divergence
in sinking. It is easier to guide a vertical-sided' cylinder or caisson
than a truirpet or bell-shaped one, and the former will sink straighter
than the latter, and has the best chance of retaining perpendicularity.
In ordinary firm soil, when cylinders are carefully guided for the first
10 to 15 ft. of sinking, and to 20 to 30 ft. in loose soil, provided the
rings are tightly and truly bolted together, they generally go down
vertically. To make the sinking uniform, and to prevent tilting, the
excavation should be effected on every side as equally as possible.
44 CYLINDER BRIDGE PIERS.
Perhaps the hest way to proceed is first to excavate in the centre, and
then to work from there towards the circumference in all directions.
The levels of the excavation in the cylinder should be constantly ascer-
tained, so as to keep the bottom as nearly level as practicable.
It is desirable to know if there is a probability of the cylinder sinking
suddenly many feet. In that event it may destroy the staging, and
perhaps not sink vertically. A thorough knowledge of the strata will
generally enable this point to be decided, but in sinking the first cylinder
there should be special precautions against such an occurrence, and the
manner of its sinking should be noted as a guide to the probable pene-
tration of the other columns.
As both cylinders and wells have become inclined from having the
material scooped out under the cutting-ring to a considerable depth
when hanging from surface-friction only, and from this friction being
suddenly overcome, it is advisable not to allow the column to be sus-
pended from surface friction more than three to four feet, according to
the diameter, above the bottom of the excavation in the cylinder
During the commencement of sinking operations the column should be
most carefully watched, to see that it is sinking equally, and that there
is no tendency to incline in one direction.
If cylinders have to be sunk near buildings, and through sandy or
loose soil, precautions should be taken against the internal excavation in
the cylinder disturbing the foundations of structures in the vicinity, and
therefore as little material as possible should be removed. If any
buildings or wells near the site show signs of cracking, the excavations
should be at once stopped to see what further preventive measures are
necessary.
Experience in several cases has shown that when two cylinders have
to be sunk close together, or where the distance between them is not
greater than the diameter of the cylinder, they should be sunk alter-
nately, as there is a tendency, when they are being sunk simultaneously,
to draw towards each other. There is always considerable difficulty in
sinking cylinders close together in sand and loose soil, and as a rule it is
easier to sink one large cylinder than two smaller ones in making a pier.
In some instances the tendency to draw together has been counteracted
by having one cylinder sunk half a diameter in advance of the other.
Should two parallel rows have to be sunk very near to one another, say
2 or 3 feet apart, one row should be sunk before the other, or they can
be started at different ends, or from the centre towards the ends, the
object being to disturb as small an area as possible of the soil in the
locality of the cylinders at any one time. It is also advisable to sink
the columns that are in one line alternately in preference to sinking the
next adjacent. The reason of this tendency to draw is believed to be
that the sand or sail around the column is in an agitated state, owing to
SINKING CYLINDERS. 45
the sinking operations, and if two cylinders are sunk close together the
soil between them will be the softest and .most loose, and there will
therefore be a tendency to cant over at that point. Excavating in a
cylinder in sandy soil sometimes throws the neighbouring columns out
of the perpendicular when they are sunk in close proximity, and they
are also liable to become jammed. Particularly when cylinders have to
be sunk to considerable depths, the interval between them should be as
much as possible, in order to prevent contact caused by deviation from
perpendicularity in sinking.
In sinking a cylinder to a hard stratum which dips at a considerable
angle, it may fall over when being sunk. This tendency can be
provided against by supporting it by tackle at two or three places in its
height. A cylinder must also be secured where the soil is of a soft,
semi-fluid character, or of a rocky nature. In sinking them in a silty
bed where there is considerable range in the tides, special means should
be taken to prevent overturning, as when the tide rises the weight of
the column is reduced considerably if the water is excluded, and the
effects of the current are more severely felt. In such situations the
cylinder should be sunk as rapidly as possible, so as to obtain a good
hold in the ground to counteract the tilting force. In sinking cylinders
in tidal waters having a great rise of tide, the column must be prevented
from floating at high water, because, if it excluded the tide, particularly
at the commencement of sinking operations, it might be lifted, provided
the bottom was closed, after work was suspended, also before inflating
the air chamber, when using the compressed air system, it is necessary
to know that the cylinder at all times is sufficiently heavy to obviate
floating. If it should be necessary at any time to flood a cylinder or
caisson in using the same method of sinking, the object should be to
substitute the compressed air by the water, so as always to maintain the
same pressure ; for if the air be discharged before the water reaches the
roof there will most probably be a sudden sinking of the cylinder. The
escape of the air can be regulated by the pressure gauges, the air pumps
being worked or stopped according as pressure is or is not wanted.
A method of testing whether cylinders have reached firm ground
without the aid of divers, or requiring the bottom to be made dry, is by
having several borings made around them and near to them ; but this
system is not always reliable, and can only safely be adopted where there
is no doubt about the nature, thickness, and position of the different strata;
and it is but a makeshift, for divers should be sent down to clear away
any rubbish that may have accumulated at the bottom, and to level the
base for the hearting, which should always extend closely around the
cylinder, should it be decided that it is unnecessary to make the
foundation dry before depositing the concrete in a cylinder when sunk
to the intended depth.
46 CYLINDER BRIDGE PIERS.
It is important, particularly in sandy soils, to prevent the ingress of
the earth into a cylinder. To obviate or lessen such an occurrence,
the column should be sunk at a rate corresponding to that at which the
excavation is removed, but at first sinking should be slow, until the
cylinder has taken a fair bearing, when it should be gradually in-
creased.
Outside scour or subsidence of a river bed during sinking operations,
with the consequent rush of soil into the cylinder, is sometimes checked
by bags rilled with clay or impermeable earth being deposited round the
outside of the column. It is not advisable to use stone or a hard sub-
stance for this purpose during sinking, although a most excellent
material to prevent scour when the cylinder is sunk to the required
depth, because the stones may get under the cutting edge, and then will
impede easy and vertical sinking. Loose stones in any soil are generally
troublesome in cylinder sinking, and are to be regarded as obstructions.
A system sometimes adopted is to tip, before insertion of the cutting
ring and during sinking operations, clay on and around the site
where the cylinders are to be sunk, so as to lessen the ingress of
water while pumping. As sandy soil is the most frequent earth to
" blow " and rush in, it may be well to remember that perfectly clean
sand seldom becomes quicksand, but that a small admixture of clayey
matter is sufficient to enable it to be in a condition ready to be converted
into a quicksand.
As a rule, in tidal waters, the greatest downward motion of a cylinder
may be anticipated at low water. In driving or sinking hollow piles or
columns in quicksand, the sand will run in according to the depth of the
bed and outside head of water. Should the water be pumped out from
the interior, weighting will often stop this ingression. During sinking
operations, if the compressed-air system is not used, the cylinder should
be kept full of water in order to prevent a run of sand at the base.
When the water is lowered in the cylinder in sandy and loose soils, a
" blow " will frequently occur, that is, the soil will rush up from below,
and in very loose material may nearly fill the cylinder. " Blows " will
also occur in cylinder sinking from the compressed air rushing out under
the cutting edge. They may then be arrested by slightly lowering the
air pressure, which must be done very carefully, or the water may come
in and endanger the lives of the men. A " blow " may be permitted to
continue for a short time if it is found that a return wave, as it were,
of water takes place. " Blows " are mainly caused in loose porous soil
by changes in the water level of the river, whether owing to great range
of tide, or wave action. When a run of sand takes place in a cylinder,
and it has been stopped by letting in water, or by a layer of stone,
gravel, clay, or other means in the cylinder, before recommencing
sinking operations the sand should be allowed time to subside and get
SINKING CYLINDERS. 4?
into a state of rest. On the other hand, when no " blows " occur, in
mixed soils, or where bubbles of air appear through the water, sinking
should be carried on without intermission, so as to prevent the soil
settling and subsiding, and the smaller particles incorporating with the
larger and becoming consolidated.
To prevent a temporary rush of sand or loose soil from entering a
cylinder, to lessen the disturbance of material round it, and to give it
time to settle, a moveable diaphragm can be placed upon the bottom
ring of the cylinder, with a valve opening inwards, which if shut stops
the ingress of the material. It is important that the inside of a cylinder
should not become choked by the ingression of earth, as then not only is
there more soil to excavate, but the weight required to sink it will be
increased, for there will be the interior surface friction to overcome as
well as the exterior, and two simultaneous resistances to penetration
instead of one ; therefore the internal sides should be kept free from
contact with the earth in the cylinder. Again, the soil that is forced
into the cylinder frequently only comes from one side, and that the
softest and loosest, then sinking will probably not proceed vertically
and the column may be drawn towards the side where the soft or loose
earth occurs. In sinking cylinders through quicksand or very soft soil,
the bed of the river outside the column should be watched to see if its
surface subsides ; should this be the case, it shows that there is a run
of the soil. In most instances the quantity of material taken out of the
cylinders in loose soil is greater than the contents of the column. In
cohesive soils the increase may be but little, perhaps not more than 20
per cent.; but in deep beds of sandy and loose earth, it is seldom less than
from 40 to 100 per cent, in excess of the contents of the subterranean
portion cf the cylinder. As this excess of soil must come from the
outside of a cylinder and be drawn in, it disturbs and cracks the sur-
rounding earth and contributes to prevent vertical sinking. Should
"blows" occur in a quicksand, the cylinder may become filled with
sand and water to the water-level outside. The external and internal
pressures should be balanced, or but a slight preponderance of water
outside should be allowed to obviate any tendency of loose soil to
" blow," and the water inside should be lowered or raised as the outside
water ebbs or flows, for the excavating apparatus may take out of the
cylinder, with the earth, more water than percolates in the same time.
If it is possible to balance the waters during sinking, comparatively
little more material than the contents of the cylinder will require to be
removed, and " blows " will be prevented. Should the sinking be
suddenly arrested, it may often be resumed by lowering either the air-
pressure or the water inside the cylinder, the usual result being that the
water then infiltrates through the earth outside into the interior of the
cylinder, and consequently loosens the soil upon which the cutting ring
48 CYLINDER BRIDGE PIERS.
rests. It will generally occur that when it is low water, and a column
of water is in the cylinder considerably higher than the level of the
river outside, less earth will be brought up by dredgers than when the
water-levels nearly correspond. Where the dredging system of sinking
is adopted, the best plan is to make the depth of water inside identical,
or nearly so with that outside, and to rely upon deadweight to cause the
cylinder to penetrate ; but when the soil is open and allows of free per-
colation it is usually found if the water outside is sufficiently higher
than that inside as to cause disturbance of the f rictional surface, conse-
quent upon the unbalanced pressure, that cylinders sink easier. In soft
and muddy soils the water levels should nearly correspond, any difference
increasing as the earth becomes firmer, less pervious, and the particles
of which it is composed, harder. In impermeable soil, such as clay, it
is advantageous to have the water considerably lower inside than outside,
so as to facilitate sinking, as no " blows " are probable. However, if the
water outside be allowed to have too great a preponderance, an upheaval
of the earth inside will take place, which only increases the quantity to
be excavated and jams the cylinder. Therefore, when there is but little
earth inside, it is advisable not to draw off any more water as soon as
the column begins to sink. Should a river-bed be dry at low water, or
the water then be of little depth, excavating in the open may be possible
for a few hours each day, and in order to prevent a " blow," water can
be admitted into the cylinder as the tide rises outside, and the greatest
head of water can be ascertained which the earth can bear without its
percolating in such quantity as to stop excavation by hand. It is
essential that cylinders be sunk rapidly in sandy and loose soils. An
excess of weight for sinking is therefore an advantage, because any
little expense in temporarily loading the cylinder is soon compensated ;
as, by reason of the rapid sinking, the outside soil will generally be pre-
vented from entering the cylinder to any great extent. With the
compressed air system among some of the expedients used to lessen the
ingress of the soil into the cylinder, it has been found that by working
the air-pumps rapidly, and by sending in the maximum quantity of
compressed air some time before operations are commenced upon each
day or shift, and during work, and by enlarging the base of the cylinder
a little beyond the diameter of the bottom ring, the water is driven to
some extent out of the sand or loose soil which consequently possesses
more cohesion, and does not run so quickly into the cylinder. It may
also be advisable to excavate at opposite points, but in doing this the
column must not be tilted. It has been suggested that where the soil
is of an extremely moveable character, the material should be expelled
outwards and not taken through the cylinder.
In sinking cylinders through sand with a thin bed of clay intervening,
the columns will very probably become earth-bound, and although they
OFTHE ^\
UNIVERSITY)
IFORNiA^X
SINKING CYLINDERS. 49
may sink through the clay into the sand, if water percolates to some
clays they swell, and will grip the cylinder, but by excavating the sand
so as to cut away the stratum of clay touching the cylinder it will go
down at once. When cylinders hang or refuse to sink, notwithstanding
the earth being excavated from beneath, on the water being lowered in
the C3rlinder some 6 to 8 ft. below the outside water level, they will
often at once go down, the pressure on the bottom being reduced, and a
flow created at the base. With brick wells this is a somewhat risky
operation, and the better way is to keep the water at nearly the same
level, rather lower on the inside, in order to obtain pressure from the
outside, but the nature of the soil, an^ special circumstances must
decide this point. As in sand and similar soil, the more it is agitated on
the surface of the cylinder the less the frictional resistance becomes, small
perforated pipes can be put down round the outer circumference of the
cylinder, and on water being pumped or discharged into them under
considerable hydrostatic head, the surface becomes disturbed. This
system has been used with success and economy to sink wooden piles
in sand, into which they could only be driven with great difficulty.
It is possible, as large tarpaulins spread over the bottom of a river
have been used for passing a breach in tunnol-work, that they might be
useful to abate surface disturbance in loose soils in cylinder sinking.
They are also of assistance when laid on the bottom and round the sides
of a foundation, in preventing cement being washed out of concrete, and
in conducting water to a pumping sump, if a considerable flow is
encountered.
If the water which comes up from the bottom of the column brings
with it mud and sand, and the cylinder will not go down to the proper
depth on account of the strata, or some obstruction which cannot be
removed by dredging, divers must be employed, or the compressed-air
system. In countries, as in India, where at certain seasons river-works
cannot be executed, only those cylinders should be commenced that can
be completed in one season, or made secure before the floods, and work
during their continuance will have to be different from that at other limes.
In firm clay the cylinder need not penetrate more than from 7 ft. to 10
ft., if protected from scour and movement of every kind ; and similarly
4 ft. to 5 ft. in compact gravel, and 3 ft. in rock, where the strata are
all of considerable thickness, the depth becoming greater according as
the earth is more affected by moisture and other deleterious influences.
In clay, muddy, peaty, or vegetable soil, men often complain of the
fetid atmosphere of a cylinder, and instances have occurred in sinking,
in which fatal effects have arisen from the noxious gases generated in
decayed earth or soil saturated with impure water. It may therefore
be necessary to introduce fresh air into a cylinder, and to use
disinfectants in order to purify it.
£
CYLINDER BRIDGE PIERS.
CHAPTER VI.
SINKING CYLINDERS ; STAGING ; FLOATING OUT.
CYLINDERS are usually properly adjusted and guided in sinking by a
temporary timber framework ; but in an exposed situation, and where
the bed of the river is treacherous, and there is a great depth of water,
fixed staging for erecting cylinders may be economically impracticable
or objectionable, and the pontoon system of floating out and sinking
may be preferably adopted. High and low level staging is sometimes
used, the rings being placed upon the low level stage, and the crane or
lifting apparatus on the high level platform. A few guide-piles driven
by means of barges or suitable floats, so as to secure the cylinder in a
correct and vertical position, and aid its perpendicular subsidence are
most useful, or an adjustable frame fixed on the river bottom, the size
of the cylinder, is sometimes employed. If the depth is too great for
timber guide piles, iron piles can be used.
There is no doubt that a cylinder is far easier kept in a vertical
position during sinking than straightened after it is inclined, and a little
expense in staging will often save both time and money. In addition
to guiding a cylinder, the staging must act as a platform for lowering
the rings, the hearting, mixing concrete, and be of sufficient extent so
that dredging or excavating, raising and lowering, or compressed air
machinery can be placed and easily worked thereon, should it be
necessary. In order to lessen the height of the staging, triangular-
shaped pockets have been cast on the outside face at the base of the
reducing ring at intervals around it into the horizontal seats of which
guide poles fitted, and the segments above the reducing ring were fixed
from this temporarily fixed staging, no driven piles being required.
This system was adopted at the Albert Bridge, Chelsea, England.
As considerable time is occupied in fixing and removing staging, in
rivers subject to a prolonged flood season when operations on river piers
have to be discontinued, it is necessary that the work be so arranged
that there is no occasion to discharge men who may be difficult to re-
engage, and in order to economise time it is advisable to require as little
staging as possible, and so designed as to be quickly erected and re-
moved. A floating timber gangway, sufficiently wide for conveyance
of the materials for the piers, placed across a non-navigable river has
been found to much facilitate the work.
It may be well to name a few recent methods of erecting staging and
cofferdams for river piers under somewhat exceptional circumstances.
Where a streak of rocky soil unexpectedly occurred in erecting the
staging and a cofferdam for a bridge-pier, the following expedient was
adopted. Iron rods 2 to 2£ in. in diameter were fixed in the bottom of the
timber piles, the lower end of the rods were split in order to receive a fine
SINKING CYLINDERS. STAGING. FLOATING OUT. 51
wedge. Holes were bored in the rock, into which the split rods were
dropped, and on their being driven down the wedges caused the ends of
the rods to splay out and thus firmly hold in position the foot of the pile.
To accelerate the erection of bridge-pier cofferdams, corrugated iron sheets,
stayed with timber framing and weighted with rails, have been recently
employed in sandy and gravelly soil with success. Rails have also been
placed in holes in rock at intervals of from 6 to 10 feet, and walings
fastened to the rails, and sheet piles driven between them, puddle being
deposited at the base. Corrugated iron plates with overlapping edges
which fitted into guide plates that bound the two together, were also
used at the New Tay Bridge instead of a timber cofferdam, because of
the shallowness of the soft stratum, 6 in. in thickness, above the rock.
Old boats lashed together, and connected by timbers, have also been
filled with stone or clay, and sunk and surrounded with material until
they were firmly embedded in the river bed and a rigid base formed for
the piles of the staging or raking struts. Tlu's method of making a
foundation for piles and temporarily fixed stage for cylinders has been
used when the river bed was rock, and also when it was loose sand.
With regard to the pontoon system of floating out cylinders or
caissons for bridge piers, two pontoons or barges with a platform on
them are usually employed, with an opening a few feet larger than the
diameter of the cylinder in the covering between them, and both pon-
toons are planked over and firmly connected. In order to lessen the
expense of specially built pontoons they are sometimes designed so as
to be afterwards used as landing stages, or as river-service vessels.
In a rapidly flowing river of considerable depth it is necessary in
floating out to have command over the bottom of the cylinder or caisson
as well as the top, as neither can be sufficiently controlled from the top
only. Chain cables 1£ in. to If in. in diameter, about 45 to 60 fathoms
in length, attached to anchors weighing from 21 to 40 cwts., are fre-
quently used for ordinary cross moorings. Large pontoons require
in a soft bed anchors weighing about 3 tons each. To keep the pontoons
steady in a strong current the moorings must be strained tightly ; a
capstan is therefore generally fixed on the pontoon, and a chain housed
round a bollard on it. In some of the modern pontoons for floating out
cylinders, the chain cables pass in at the bottom of the pontoon, through
an inclined cable-trunk over a deck-roller at the top, and are held by a
link-stopper attached to an adjusting or straining screw, which works in
a gun-metal nut by means of gearing, the whole being secured to the
pontoon deck by plate-iron framework. The moorings being accurately
laid, the tightening of the chain-cables by the screw-gear adjusts the
pontoons exactly on the centre line of the bridge. In all loose soils,
experience has proved that it is the scope given to the moorings that
makes them secure ; therefore, they should never have a vertical hold,
• 2
52 CYLINDER BRIDGE PIERS.
although the more a cable is payed out, the more difficult it is to lift
the anchor. Should the anchors at first let down not give a good hold,
they should be weighed and cast afresh, with a greater length of cable.
In quicksand the moorings become faster by time ; but if they should
tend to approach the vertical, they should be lifted and recast. A scope
or length of cable found in loose soil to give stability to a pontoon, is
from twenty to twenty-five times that of the range of the tide ; and,
should there be no tide, from ten to fifteen times the depth of water.
The more cohesion the soil forming the bed of the river possesses,
the steeper can be the inclination of the moorings. Mushroom anchors
are found to be most effectual for mooring lightships in deep water. In
mooring on an exposed coast, the chains on the offshore side, and against
the set of the current, should be stronger than those on the inshore
side.
A great improvement on the pontoon system, moored by chain cables,
was that adopted for the pontoons at the New Tay Bridge, which were
fitted with four large hollow wrought iron cylindrical tegs. By means of
hydraulic apparatus, these legs could be raised or lowered when the
pontoons were floating, and when the legs were firmly bedded in the
sand of the river bed, the whole pontoon could be raised or lowered by
the hydraulic apparatus. The pontoon had two rectangular openings,
large enough to let the bases of the cylinders pass through. On the
pontoon there were steam engines for working the excavating apparatus,
and a concrete-mixing machine, besides steam cranes for lifting and
lowering, and various other apparatus. The caisson was kept perpendicu-
lar by the rigidity of the pontoon and without mooring chains.
A temporary bottom is sometimes attached to a cylinder against the
internal flanges, so that it floats until it is known that the ground is
sufficiently solid to bear its weight. In swift currents difficulty is
experienced in floating out cylinders of small diameter, such as from 5
to about 8 feet. If the weather should be stormy it will be economically
impossible to steady such cylinders sufficiently for sinking. If desired,
pontoons can be flooded so as to partly sink when the column is sus-
pended by them over the site.
The height of the cylinders to be floated out by barges or pontoons
depends upon the depth of the water at high tide, and also on the
contour and nature of the ground. It is prudent to ascertain whether
the level of the bed of the river varies much along the course of tow-
age, and care must be taken that the cylinder or caisson does not ground
at low tide. Built-up cylinders from 40 to 60 ft. in height have been
floated out and sunk into position before lengths were added to keep
them above high-water level. While the cylinder is being lowered from
the pontoon, and when floating over its site, two or three lengths can be
added. The column should not be left until it has a bearing in the
REMOVING OBSTRUCTIONS, AND "RIGHTING." 53
ground of not less than about ± of its total height, or in the case of
a caisson about •£ of its greatest horizontal length, or it may be over-
turned or floated. In all cases when the centre of gravity of the column
is high, precautions must be specially taken against overturning by
lashing its top and bottom to the pontoons, or otherwise supporting it.
If the compressed-air system is to be used in sinking, by having a
movable closed top on the cylinder, air can be pumped in, and the
column will float, it can then be carefully brought to the required
position, and the air being let out slowly the cylinder will sink. This
method is sometimes adopted with caissons built on shore, and launched
down an ordinary slipway. Two or three of the bottom rings of a
cylinder reaching above low-water mark have been built up on the fore-
shore of a river, and fixed to two girders resting on temporary wooden
supports. At low water barges or pontoons are introduced under the
girders, the whole being lifted bodily as the tide rises, with the excep-
tion of the supports, which may not always be needed. The connections
between the pontoon girders and the cylinder rings should be so made
that they can be readily unshipped. Rings of the cylinder or caisson
and part of the hearting can be added as the work proceeds, or in a large
caisson having buoyancy compartments, concrete can be deposited to help
the sinking operations.
CHAPTER VII.
REMOVING OBSTRUCTIONS IN SINKING AND "RIGHTING" CYLINDERS.
ALTHOUGH cylinders can penetrate obstacles, such as logs of timber,
sunken vessels, and quicksands, which are difficult to overcome with
other systems of construction, still boulders and stony and other debris
often give serious trouble, and cause considerable loss of time and
money. In some cases there may only be difficulty for the first fifteen
or twenty feet of sinking in loose soil, such as silt, mud, and sand, it
being then overcome by the weight of the cylinder ; on the other hand,
the difficulty of removing them may increase with the depth, and this
is more probable. Boulders, which often vary in size from that of large
stones to masses of rock weighing as much as from six to eight tons ;
lumps of hard clay and sunken trees are frequently encountered in the
noles and depressions in river beds, and often tilt cylinders during the
operation of sinking. If the compressed air system is not used, and
54 CYLINDER BRIDGE PIERS.
boulders, trunks of trees, and driftwood, etc., are expected to have to
be excavated, divers should be sent down the cylinder at intervals to
examine the interior, in order that necessary precautions may be taken.
Owing to variation in the size and hardness of boulders in some sandy
and gravelly soils, one cylinder may take much longer to sink than
another. It is difficult to remove boulders or debris and prevent delays,
or to level rock foundations without the employment of pneumatic
apparatus, or skilled, not ordinary, divers.
When large boulders are under a cutting edge, it is not an
easy matter to remove them safely, for if they are pulled into a
cylinder, a " blow " of soil frequently follows, and breaking them up
may be a very slow process. The simplest way of removing them, or
tree stems, is by pushing them out, by cutting out, which is a
somewhat slow operation, or by drawing them into the cylinder, but the
latter method cannot always be effected, and in loose soil will probably
cause " blows," nor can they always be thrust out. They can also be
displaced by splitting up with plugs, wedges, jumpers, by drilling,
or by undermining and drawing into the cylinder, and then by break-
ing them to convenient sizes for raising and discharging. Tree
stems and logs have also been cut through under water by means of
an axe blade attached to the monkey of a pile driver, and by divers
augering out and cutting them to pieces. In situations where, at the
commencement of sinking, large boulders have been drawn towards, or
have rolled against the cylinder, they have been removed by the column
being lifted, and by drawing them within the circumference of the
cylinder.
When the compressed air system is used, as the ground at the bottom
of the cylinder is not submerged, it is at once seen when boulders or
debris are in the soil, and many methods of removing obstructions can
be prosecuted with facility, which it would be impossible to employ
with effect if water were in the cylinder ; and in consequence of the
slow rate of progress by other means than visible excavation, the
pneumatic method of sinking may become indispensable.
When the boulders extend considerably under the cutting edge, say
from two to three feet, circumstances will show whether it is better to
pull them into the cylinder, or to chip them to pieces. The latter should
be done for a little distance beyond the cylinder, so as to prevent the
edges holding the column. To push them out will probably be im-
practicable. Where boulders are packed together closely with decom-
posed rock, steel-pointed picks may not excavate or break them up, but
heavy steel bars driven in with sledge hammers, or dropped inside a
pipe from a considerable height, or guided by other means, may shatter
them. If concreted gravel or clay is found between boulders, they
will generally not be so difficult to break up as when united with de-
REMOVING OBSTRUCTIONS, AND "RIGHTING." 55
composed rock. Jf it is decided to draw the boulders into a cylinder,
as much of the ground as possible in which they are embedded should
be first cut away, and in order to lessen any ingress of soil, and to give
it time to settle, it may be advisable to temporarily weight the earth at
the base of the cylinder during the operation of pulling in the boulders,
and for some time after, depending upon the degree of looseness of the
ground. The cutting edge of the bottom ring should be protected
against damage in attempting to thrust it through boulders, but it is
not easy to strengthen it, and the result may be that, if it is of cast
iron, it will be cracked and shattered ; if of wrought iron, it will be
bent, deformed, and crushed. In all cases it is far the better plan to
dislodge the boulders, than to attempt to thrust the cylinder through
them, which will usually be found ineffectual, and generally a dangerous
operation.
Cylinders are sometimes firmly held by a clay stratum, which is, as a
rule, an easier obstruction to overcome than boulders, loose stones, or tree
logs ; it may then be advisable to excavate or dredge a hole considerably
below the cutting edge in order to cause the cylinder to sink, but as
much provision as possible should be made against a run of loose soil
into the cylinder. The resistance to be destroyed in such a case is not
merely the surface friction, but the gripping action caused by the
swelling of the clay. In addition to that named, more weighting ; the
drilling of numerous holes in the cylinder through which compressed air
can be discharged ; driving hollow perforated iron tubes at intervals on
the outside of the cylinder, and ejecting water under considerable pres-
sure through them to soften the clay and reduce surface friction, holes
being first made in the clay by augers or boring tools can be tried.
The following expedients might be employed as a kind of last resource.
As the swelling of clay is chiefly caused by water, if, without injury,
the surface of the cylinder could be made sufficiently hot, the clay
would shrink and the surface friction would be reduced. The expansion
of the iron rings might also very slightly compress the soil, and on
the metal cooling the contraction would probably cause a void, howevei
small, between the outer surface of the cylinder and the earth, indepen-
dently of the shrinking of the clay should that appreciably occur. As
the action of an acid on clay tends to soften it, an acid fluid might be
discharged into the clay at intervals, through holes in the cylinder rings,
although its effect on the metal casing would be deleterious.
With regard to the employment of explosives for removing obstruc-
tions, they have been successfully used in large caissons, the reasonable
precautions in blasting in a confined space being observed, but in small
cylinders the result generally is that the cutting ring becomes cracked
and blown out when of cast iron, and deformed when of wrought iron,
but if the ring can be so strengthened as to continue to equally and
56 CYLINDER BRIDGE PIERS.
properly sink, cracks are not of much importance, provided surface
friction of the rings against the earth is not relied upon for permanent
support, as the weight of the superstructure will rest upon the hearting
only, but should the cutting ring be so damaged by the explosions as
to be fractured, it may become necessary to entirely remove it, which
must always be a work of difficulty ; and the absence of the cutting
ring in sinking would cause that operation to be conducted with no small
amount of danger to the cylinder should more obstructions be encountered.
Small charges of from one to two ounces of dynamite have been
used for aiding sinking operations, as well as for cutting away rock
or boulders that projected into a cylinder, the idea being to overcome
friction by tremor and vibration, and to cause the cylinder to sink with
a diminished load ; but in other than large caissons the use of explosive
agents is questionable, and the drilling of holes by divers is always
very tedious work. The hydraulic method, by means of water dis-
charged at considerable pressure, through perforated pipes on the surface
of the cylinder, is to be preferred in the case of moderate-sized
cylinders, or in a caisson, as it cannot injure the rings. To lessen the
chance of the cutting ring being damaged, broken, or blown out, the
charge has been placed in a pit excavated in the centre of the cylinder
and there exploded ; no deleterious effect follows, but a trembling
motion is imparted to the earth, the surface friction is reduced, and
the cylinder at once sinks. Only very small charges should be used,
the charge being increased according to the area of the base, it being
borne in mind that continued disturbance and easy regular sinking is to
be desired, and not intermittent, sudden, and violent penetration, which
will be difficult to control sufficiently to cause the cylinder to proceed in
a perpendicular direction, and may crush the cutting ring. When the
necessary apparatus for the adoption of the compressed air system is
not available, and the dredger machinery cannot remove the boulders,
other specially-devised apparatus, such as steel bars dropping from a
height in guides, can be tried ; but blasting may be the only agency by
which they can be shattered. As there are about two hundred different
explosive agents, the selection of the most fitted for the work required
to be done is best determined by an expert.
With regard to "righting" an inclined cylinder, a generally effective
way of getting it back to verticalness is to firmly wedge up the lower
edges of the column on the depressed side, and excavate the soil under
the uplifted portion. When this has been effected the compressed air,
.should that system be used, can be suddenly discharged, the con-
sequence being that the material around the bottom of the cylinder will
enter into it. The top of the column can also be propped up on the
lower side. In some cases, for general sinking purposes, and in order
to reduce the surface friction, numerous holes have been drilled through
REMOVING OBSTRUCTIONS, AND "RIGHTING." 57
the rings on the higher side of the cylinder ; the compressed air escaping
through them loosened the material outside and lessened the frictional
resistance.
In an instance where a cylinder was sunk 30 ft. in sand, and was con-
siderably inclined, the simple wedge plan did not succeed. The upper
edge had to be under-excavated, so that the escaping air passed through
and loosened the material on that side. The cylinder was also wedged
up on its lower side, and a battering-ram, made of a whole oak balk
suspended from shear-legs, was used to strike successive blows on the
top of the column on its higher side. During descent it was brought
into a vertical position. It is preferable to weight the cylinder on the
higher side, instead of driving it, but the weights must be arranged so
that they can be readily removed. If the segments are firmly bolted
together, and the cylinder has become inclined in loose soil before many
lengths of rings have been sunk, pulling it over by means of cables
and blocks and crabs may be tried in conjunction with any of the other
methods herein described ; but there may not be sufficient purchase or
hold if the river-bed is mud or silt.
Columns have also been " righted " by means of steam-hoists pulling
upon the side to which the cylinder inclines ; by screw-jacks, hydraulic-
rams, and other powerful lifting tackle ; by additional weighting upon
the higher side ; excavating the ground to a slope on the inclined side
to the lowest water level, if any part of the ground upon which the pier
rests is dry at any time, and by propping up the leaning side with rails,
sleepers, or other hard material so as to cause a large firm wedge-shaped
mass to press against and support it. Hollow pointed perforated iron
tubes may be driven in, or sunk by the water- jet system, around and
close to the cylinder on its higher side, to loosen sand and such soils
and to diminish surface friction by the aid of water discharged through
them. They can be withdrawn and inserted as desired, and may be
useful adjuncts not only in " righting " but also in sinking a
cylinder.
The internal raising of excavation in one direction, and the vibration
BO caused, have been found to make a cylinder incline towards the
,source of power of the hoisting apparatus of dredging machinery. This
can be soon noticed, and counteracted either by changing the position of
the machinery frequently, by propping, or by other means.
58 CYLINDER BRIDGE PIERS.
CHAPTER VIII.
KE.NTLEDGE.
THERE are several different ways of arranging the kentledge or tho
weights for sinking a cylinder. Its cost often amounts to a considerable
sum, and much time is required to remove it. Perhaps the cheapest
temporary kentledge is obtained by putting across the top of the
cylinder some balks, and evenly and equally packing upon them
medium-sized stones, afterwards used in the masonry of the bridge, or
by placing rails or pig iron upon timbers resting upon the horizontal
flanges or top, leaving sufficient space for working and excavating
operations. The weights should be so arranged that they do not in-
terfere with the internal excavation ; they should be equally distributed
throughout the cylinder to ensure uniform sinking ; and care should be
taken that the weight on the iron rings and flanges is not excessive, and
that the temporary loading does not cause a cylinder to tilt.
In placing kentledge upon the top of a cylinder the centre of gravity
is raised, and the column may not be stable. It is sometimes laid upon
stages slung within the cylinder, as being not so likely to tilt the column
as when placed outside, and as being more easily thrown off when the
requisite depth is reached. A method that has been adopted is to have
weights cast to the form of the cylinder, and so made that they fit into
the concave side of the column and rest on the horizontal joint-flanges.
The weights are cast in convenient sizes, such as 6 or 7 ft. in length, 1
ft. in height, and 6 in. in thickness. The dimensions most convenient
depend upon the size of the cylinders and the width of the flanges.
The weights can be lowered down the interior of the cylinder by a crane
on the staging. All the lengths of the column by this system are
weighted with the exception of the cutting-ring and the next above it,
and if the weights are properly placed they mutually support each other
as they act as arch stones. From 10 to 30 tons of kentledge can thus
be readily placed out of the way of operations on a 6 or 9 ft. length of
cylinder ring of ordinary diameter. These weights can remain upon
the cylinder during sinking, being removed as the hearting reaches
them, and there is no danger of tilting by unequal distribution of weight
which occurs when the load is on the top. It seems to be considered,
if the cylinders to be sunk are of considerable height and many columns
have to be erected, that the advantages gained by having the weights
cast amply compensate for the extra expense of such special kentledge,
the latter bling made to fit all the cylinders and being sold after use.
Sir Bradford Leslie, M.Council Inst.G.E., introduced a system of
weighting cylinders by means of a water-tank, which could be filled by
pumps in from ten to fifteen minutes, and when empty was lifted on the
top of the cylinder. When a column had sunk sufficiently for another
KENTLEDGE. 59
segment to be attached, the tank was emptied, swung off, let down on
the top of the next length, and refilled. The same tank does for any
number of cylinders, the delay and expense in placing rails and
weights are obviated, and the load is equally distributed all round the
cylinder ring. It was found that loading a cylinder with rails and iron
took twenty hours ; fixing and filling the tank occupied but one hour.
This system is decidedly preferable, if tackle is at hand for swinging
the tank off and on, to weighting by rails, etc. ; but it has not the
advantage that inside kentledge has, namely, that of distributing the
weight over the height of the cylinder and practically maintaining its
centre of gravity unaltered.
The comparatively new method of inside kentledge will now be
examined. As rapidity is generally to be desired in sinking cylinders,
and is often imperatively necessary, the value of using a casing of the
permanent hearting as a load for aiding sinking operations can hardly
be over estimated, for it can be done with but little extra expense to the
ordinary cost of the hearting. It leaves the top of the cylinder entirely
free to receive an additional load ; it causes the centre of gravity of the
cylinder to remain low, and saves the trouble, waste of time, and
expense of constant stacking and re-stacking weights ; and part of the
casing or hearting is built on land and is not subject to any pressure of
water before it is set. The chief precautions to observe in using as
kentledge such an internal casing are not to make it too heavy for
regular sinking, or to cause a cylinder to run down so quickly as to
crush the cutting edge should it come in contact with boulders, or a
hard stratum, or rock ; to be sure that the casing fits the flanges of the
cylinder, whether it is made of masonry, brickwork, or Portland cement
concrete, the latter material being preferable, as it can be made to fill
spaces between bolts, ribs, and other projections, but time should be
allowed for it to set ; and sufficient open space must always be left for
excavating and the other ordinary operations of sinking.
Experience in cylinder sinking indicates that it is prudent to, as it were,
pull a cylinder down, as well as to weight it, which can be done either,
(1) by building up a portion of the hearting on an annular ring,
having a sufficient opening for purposes of excavation ; (2) by specially
cast kentledge placed on the horizontal flanges ; (3) by having a stage
loaded with weights, and slung from the flanges at intervals. The load
is then much more equally distributed than can be the case in any
system of top loading, the compressive strain on the rings is reduced,
which lessens the possibility of fracture of the rings, and also conduces
to prevent tilting of the cylinder, for the effect of weighting at intervals
from the top of the cutting ring is to assist vertical sinking, provided
the weights are equally distributed. In small cylinders internal loading
may be difficult to arrange, because of the space being required for
60 CYLINDER BRIDGE PIERS.
purposes of excavation, but in cylinders from about 9 to 10 ft. in
diameter, a casing of the permanent hearting of the cylinder can be
built so as to leave sufficient space for excavating or dredging machinery,
and general operations. Much time and considerable expense is saved
by using a casing of the permanent hearting for kentledge, instead of
temporary loading, for it obviates the removing and restacking rails,
stones, or other weights, each time a ring of the cylinder has to be
added, which is always a slow, expensive, and weary process.
As a rule, with but few exceptions, large cylinders are to be preferred
to small columns. The reasons have been given. An objection
sometimes raised against large cylinders is that more kentledge is
required to sink them, which undoubtedly is true if considered merely
from the view of the gross weight requisite to sink a cylinder, but is
not if considered from that of the f rictional surface resistance that has to
be overcome as compared with the area of the base in order to cause a
column to sink ; see Chapter IV., on Surface Friction, pages 33 to
39 inclusive, in which it is named that " in a cylinder of large
diameter the proportion of its circumference to the area of the base is
small. On the contrary, where a cylinder is of small diameter, the
circumference is nearly equal to the area of the base."
For instance — Supposing it is found that a 12 ft. in diameter, 1£ in.
in thickness cylinder is required under each main beam of a bridge, 01
two for a single line railway-bridge.
The area (see Table A, column 2, Chap. II., page 18) of two 12 ft-
cylinders is 113-10x2=226-20 sq. ft.
The surface area of two 12 ft. cylinders, 1£ in. in thickness (see
Table B, column 4, Chap. II., page 20) is 38-48 x 2=76'96 sq. ft. per
lineal foot of the height of the cylinder.
Now an area of 226*20 sq. ft.=two 12 ft. cylinders, must be provided
in order to safely support the weight of the cylinders, superstructure,
and rolling load.
Assume that 12 ft. in diameter cylinders are considered to be too
large, and that 8 ft. 6 in, in diameter columns, 1£ in. in thickness,
would be handier to sink, are thought to give a better base, to reduce
the gross resistance of the surface friction of each cylinder, and there-
fore to require less kentledge than a larger cylinder, how many would
be required ?
bqita/e iect.
The area of two 12 ft. cylinders = 226-20
The area of an 8 ft. 6 in. cylinder = 56'75
consequently — ; =say, four 8 ft. 6 in. cylinders would be required.
o6'7o
The surface area of four 8 ft. 6 in. cylinders, 1£ in. in thickness, per
foot of the height is (see Table B, column 4, Chap. II., page 20) 27-49
KENTLEDGE. 61
X 4=109-96 sq. ft. The surface area of the four 8 ft. 6 in. in internal
1 f)Q-C)£
diameter cylinders per foot of their height would therefore be — — -—
76-yo
=1-43 times greater than the surface area of the two 12 ft. cylinders,
and the total weighting would be in round numbers 1£ times more than
that of the two 12 ft. in diameter cylinders, although one 8 ft. 6 in.
cylinder would only require ?~- 5=0'71 of the kentledge requisite
oo"4o
for sinking a 12 ft. cylinder under similar circumstances.
Assume the 12 ft. in diameter cylinders have to be sunk to a total
depth of 40 ft. in soil having a frictional resistance of 280 Ibs. per
square foot, or £th of a ton. How much kentledge would be required
when the cylinder had reached 30 ft. in depth ?
The frictional resistance of the 12 ft. in diameter, 1£ in. in thickness
cylinder,
Surface Area. Depth. Square Feet. Ton. Tons.
= 38-48 x 30 = 1,154-40 x £ = 144-30
The area of the cutting edge of the 12 ft. cylinder, 1£ in. in thickness
which is here taken to be flat, as being sufficiently near for purposes of
calculation, although of course it would taper, is 38*09 sq. ft. X 1^ in.=
4*76 sq. ft. This area has to be thrust through the earth, unless the
excavation always extends under it, which is unlikely. What weight
would be required to make it sink ? Although it might be estimated on
the surface, at such a depth as 30 ft. it cannot be known, but it may
be approximately determined by deductive reasoning. With a cutting
ring tapered to about £ in. in thickness, and the soil bared as the
cylinder descends, it would probably not exceed the normal pressure
of the soil, which would be at a depth of 30 ft., assuming it was
earth weighing 0'055 ton per cubic foot; 30xO'055=l-65 tons-
Consequently the force required under the conditions named would
probably be, area, 4-76 sq. ft. x 1/65 tons=say, 8 tons.
The total resistance to be overcome by the kentledge, disregarding
fractions, would therefore be :
Frictional resistance = 144 tons + cutting edge Tons.
resistance = 8 tons = ... ... ... 152
DEDUCT. — The weight of the cast iron rings of
the cylinder 12 ft. in diameter, 1^ in. in Ton.
thickness (see Table B, column No. 3) ... 0'95
Add 20 per cent, for flanges, ribs, etc 0'19
1-14
1-14 x 30= 34
Weight of kentledge required = 118
62 CYLINDER BRIDGE PIERS.
EEQUIRED. — The thickness of an annular casing of Portland cement
concrete to produce this weight.
118
A cubic foot of concrete weighs, say, 136 Ibs. =say, 0'06 ton- — ,
= the total cubic feet of concrete required = 1,966 cub. ft., or per
foot of height 1-2??? = say, 66 cub. ft.
30
The internal area of a 12 ft. cylinder = 113 '10 sq.ft.
DEDUCT. — Portland cement concrete
area required per foot of the height
of the cylinder
Leaving 47*10 area in square
feet or open space left for excavating operations.
By looking down column No. 2, Table A, the areas near this are
those for a 7 ft. 6 in. and 8 ft. cylinder. Take the former, which will
allow sufficient space for excavating operations. Consequently the
thickness of the annular ring would require to be
(12'Q"-7'6") _ 4' 6" _. „, y
2 2 '
to produce the necessary deadweight.
If four 8 ft. 6 in. in diameter cylinders were adopted instead of two
12 ft., the permanent hearting could hardly be used as temporary
kentledge, for there would not be a convenient open space left for
excavating and hoisting apparatus, and general sinking operations, as
the following calculations show : —
The surface area of an 8 ft. 6 in. cylinder, 1£ in. in thickness, per
foot of the height (Table B, column 4), is = 27*49 sq. ft.
Surface area. Depth. Sq. ft. Ton. Tons.
The frictional resistance = 27-49 x 30 = 824-7 X £ = 103-09
Cutting edge resistance to penetration, say = 5*57
108-66
DEDUCT. — The weight of the cast iron
1^ in. rings of the 8 ft. 6 in. in diameter Ton.
cylinders =0*68
Add 20 per cent, for flanges, ribs, etc. ... = 0' 14
0-82
0-82 X 30 =, say, 24-66
Weight of kentledge required 84*00
KENTLEDGE. 63
Proceeding as for the 12 ft. cylinders the total
cubic feet of Portland cement concrete
required = .§f = 1,400 cub. ft
or per foot of the height of the cylinder =i«g°= 47 „
The internal area of an 8 ft. 6 in. in diameter cylinder = 56*75 sq. ft.
DEDUCT. — Portland cement concrete casing area
required per foot of the height of the cylinder = 47*00 „
9*75 area in
square feet left for excavating and sinking operations.
A 3 ft. 6 in. in diameter opening would approximately give this area,
therefore, the thickness of the annular ring would be,
(8' 6' — 3' 6") _ 5^ = 2/ 6//
to produce the necessary deadweight.
The ratio of the diameter of the 12 feet cylinder
12
to that of open cylindrical space left ... = __ = 1*60
7*o
Ditto, ditto, of the 8 ft. 6 in. cylinder ... = ?^| = 2*43
3 * 5
an important difference, for according as it becomes greater so will
the difficulty of excavating over the area of the base of the cylinder
increase, and in any but very movable soil in the 8 ft. 6 in. diameter
cylinder it would be most difficult to excavate in tenacious earth, or to
make the earth fall into a central hole made below the base of the
cylinder. That is one objection. Another is that of the ratio of the
open area to the depth in each case. Taking the depth of 30 feet :
In the 12 feet cylinder, the open cylindrical space is 7 ft. 6 in., or
- — = ^ of the height.
In the 8 ft. 6 in. cylinder, the open cylindrical space is 3 ft. 6 in., or
3 '_?. say, 1 of the height.
The dimensions of the interior unobstructed area will be chiefly
regulated by the size of the dredger machinery and the depth of the
foundations. For tenacious earth, such as the clays, in which it is
desirable to have a heavier dredger in order to help penetration than in
light, loose soil having little tenacity, open space is of importance, and
the larger it is the better, and it should increase according to the depth
as the normal weight of the soil is likely to make it more compact, and
therefore the distance of the extended edges of the scoops of the
dredger from the metal ring of the cylinder should be less as the depth
increases, for the ground will generally be harder, and control of the
64 CYLINDER BRIDGE PIERS.
apparatus not so easy as at less depthe. Perhaps a minimum free
working area of 5 feet diameter for excavating operations is to be pre-
ferred in loose soils, and 6 ft. to 6 ft. 6 in. in tenacious soils. Taking
these as minimum dimensions, sufficient deadweight for sinking from
a casing of the permanent hearting, without other additional means, can,
therefore, not be obtained in cylinders of a less diameter than about 9
to 10 ft. respectively, when they are sunk to ordinary depths. If the
uncovered space commenced with a minimum of 5 ft. diameter for a
depth to be sunk of 25 ft., it is desirable to increase it as the square root
of the depth to be sunk ; thus for 25 ft. in depth it would be 5 ft. ;
for 50 ft., say, 7 ft. ; for 100 ft., 10 ft. In all cases the open area
should be as large as possible, sufficient thickness being allowed for the
annular ring of permanent hearting to act as kentledge.
When a free working area is provided for easy lowering and hoisting,
at little depths up to about 30 ft., the excavating apparatus may be
readily controlled, but with increasing depth it becomes important to
have more room in which to control it, and to provide for a diver to
descend in case it becomes fixed or broken, or will not penetrate,
especially at the base of the cylinder, and for this reason every care
should be taken that no projections are left in the rings for the excavat-
ing machinery to be caught, consequently the annular ring supporting
the casing of the hearting should have a triangular end with the point
downwards, so that the dredgers, if they come in contact with the sides
of the casing, will slide up on being hoisted. In case of the scoops
holding a boulder or being much open as in catching a log, it is
necessaiy that the unobstructed space is sufficiently large for them to
be hauled up when they .are fully extended from any cause, and
especially so in very deep foundations. If the size of the cylinder will
not admit of a sufficiently thick casing to produce the necessary dead-
weight for sinking it, as wide a casing as convenient oan be adopted,
but it is not advisable that it should be of less thickness than 1 ft. 3 in.
to 1 ft. 6 in. for depths not exceeding 25 ft., and 1 ft. 6 in. to 2 ft. are
preferable minimum thicknesses for foundations sunk to any ordinary
depths. However, the deadweight thus gained will much reduce the
quantity of movable kentledge required and steady the cylinder during
sinking operations.
The necessary quantity of kentledge will vary with the nature of the
soil through which the cylinder has to be sunk, and according to its size
and depth in the ground. For cylinders of from 8 to 14 ft. in diameter,
and sunk to ordinary depths up to about 60 ft., from 50 to 400 tons
may be required. The deeper a column is sunk, the more it will
want, the weight increasing as the surface area in contact with
the earth becomes greater. In mud, 50 to 100 tons will probably be
sufficient for cylinders of moderate diameters. In sand and tenacious
HEARTING. 65
soil, from 75 to 300 tons, and in tenacious and adhesive earth, 100 to
400 tons in addition to the weight of the cylinder, and the plant placed
thereon ; but the load required is much influenced by the continued
rapidity and regularity of the excavating operations. When the" com-
pressed air system is used, in calculating the quantity of kentledge, the
lifting power of the air-pressure must be added to the weight required
as it must be counteracted. Reference to the notes on "Surface
Friction " (Chapter IV., pages 33 to 39) will enable an approximate
estimate to be formed. Some methods of lessening the surface fric-
tion, and procuring easy sinking have been previously mentioned.
CHAPTER IX.
HEAKTINQ.
WITH regard to the hearting or internal filling of a cylinder bridge-
pier, it may be made to fulfil a three-fold purpose, namely : —
1. To support the weight of the superstructure and rolling load,
and that of the pier, i.e., the iron casing and its own weight.
2. To water-seal the bottom of a cylinder.
3. To act as a weight to sink a cylinder.
It is not within the scope of this book to refer to the fabrication
or construction of the material of which the hearting may be composed.
It usually consists of Portland cement, concrete, brickwork, or masonry,
sand being occasionally used for filling up cavities at the base, and also
as hearting in wells forming quay walls when the insistent weight is
moderate. The first question to determine is, which is the best and
cheapest hearting ? It cannot be said that any material is the best to
use under all circumstances, for rapidity of execution, cheapness,
durability, homogeneity, and strength, have all to be considered.
Bearing in mind that the hearting should be a thoroughly homoge-
neous mass, Portland cement concrete is to be preferred on this account
to brickwork or masonry, for the mortar holding them together has
generally a cementitious strength below that of the bricks or stones ;
therefore a strong Portland cement mortar having a high cementitious
value should be employed, its maximum strength being reached and
maintained within a reasonably short time of its being mixed, but care
should be exercised that the Portland cement has not too much lime in rt
in order to produce an early high tensile strength, for, if the concrete is
F
66 CYLINDER BRIDGE PIERS.
immersed, the excess of lime will sooner or later become slaked by
moisture, and then the mass will expand or crack, and the concrete
probably be more or less disintegrated. Lime mortar should not be
used in the hearting, as the decrease of strength, durability, and
cementitious value is considerable.
It is important that the deposition of the concrete hearting be done
equally ; it is therefore desirable that it be put in the cylinder in layers
not exceeding 1 ft. in thickness. Objections have been raised against
the adoption of concrete hearting when it has to be cast in among
an entanglement of temporary timbers, as then cavities are more
likely to occur than when brickwork or masonry in cement are used,
which has to be carefully built ; however, if ordinary care is taken in
depositing the concrete, it may be said that a few small cavities are
certainly not worse than a mass consisting of a conglomeration of hard
materials possessing great strength and durability, but joined together
by a weaker and less durable substance.
At the Dufferin Bridge, over the Ganges, at Benares, it was found that
the weight of the pier superstructure caused a settlement of nearly 3
in., and this was chiefly attributed to cavities occurring in the
hearting. The plan was then adopted of filling in the lower part of the
cylinder or well to the top of the conical base plate with sand before
depositing the concrete hearting. The sand settled more closely under
the slopes at the base than when concrete was used, and much reduced
the settlement, which was by no means excessive.
As foundations have been repaired by means of Portland cement
grouting, consisting of equal parts of Portland cement and clean sharp
sand, forced by a hand pump through pipes having a diameter of from 1^
to 2 in. in a continuous stream of 1 or 2 cubic yards for each pipe, time
being allowed for the grout to set before resuming operations, the grout
being injected until no more can be received, it might be used for filling
cavities round the cutting edge of a cylinder. The writer's book
*' Notes on Concrete and Works in Concrete " contains brief practical
information as to the composition, air-slaking, testing, proportions of
the ingredients, mixing, and deposition, etc., of concrete.
The earth at the base of a cylinder must be cleared and levelled by
divers or otherwise before the hearting is deposited, and the concrete
should be evenly spread and trodden down by a -diver or other means,
and until the hearting has thoroughly set it should be kept entirely free
from dripping water, and no pumping should be allowed when concrete
is being lowered through water. As the concrete in a cylinder is in a
considerable mass, and is often covered up as soon as deposited, it is
imperative that only quick-setting material be used, and that it possesses
increasing powers of resistance.
At the New Tay Bridge, in order to provide against the possibility of
HEARTING. 67
the wrought iron cylinder ringa of f in. in thickness, and 16 ft.
6 in. in diameter, enlarged to 23 ft., perishing from corrosion, the Port-
land cement concrete hearting is encased in a ring of hard brickwork
set in Portland cement as a second shield of protection.
It has been found that concrete will not set under hydrostatic pressure,
and that the water pushes its way through the interstices of the stone
before the cement has time to harden sufficiently to resist it. And with
compressed air it generally happens that the upper surface in contact
with air-pressure sets quickly, so that the rest of the mass derives very
little or no benefit from the air-pressure, unless means are taken to bring
it in contact, or opposition to, the force of the water. Small vertical
pipes leading downwards to the bottom of the concrete, and placed
within 1 ft. of each other over the whole area of the column, have
been used to obviate this difficulty. It is advisable in all cases to test
the setting powers of any concrete to be used under a similar pressure to
that it will have to sustain when being deposited. General experience
seems to show that concrete laid down under compressed-air sets quicker
and slightly increases in strength, provided it is deposited in thin layers
which allow any excess of water to escape.
In cylinder piers no danger is to be apprehended from the unequal
contraction of the iron rings and the concrete, if ordinary precautions
are taken. There are numerous iron cylinder bridge piers in all parts of
the globe filled with concrete, subject to temperatures ranging from
150° F. to a few degrees below zero, which have stood perfectly under
all conditions of traffic ; but it should not be forgotten that the unequal
contraction of cast or wrought iron and concrete by cold, and the
freezing of water in a cylinder, may produce internal strains on the
rings, for the occasional bursting of water-pipes shows that the limit of
elasticity of cast iron is sometimes insufficient to allow the metal to
make the necessary expansion or contraction, hence the exclusion of all
water inside the cylinder is of importance, ard consequently the joints
of the cylinders should be caulked, or rendered water-tight in some
manner, so as to prevent any strain from the expansion of water on
freezing, and also aid any pumping out of water before the cylinder
is filled with the hearting. At the South Street Bridge, Philadelphia,
U.S.A., where, as usual, no allowance was made for the contraction of
the cylinder during frost, four or five rings split horizontally or verti-
cally during the first winter, the worst crack, a vertical one, opening
nearly £ in. A lining of wooden staves is recommended to
prevent this occurrence, as the wood would be compressed sufficiently
to relieve the strain on the metal. It is advisable to make the top of
cylinders watertight so as to prevent any percolation of water between
the hearting and the rings, which may cause them to crack in frosty
weather, and any holes made in the rings for the purpose of aiding
F2
68 CYLINDER BRIDGE PIERS.
sinking operations should be carefully filled. Anchor bolts with
washers are occasionally embedded in the concrete hearting, and pass
rertically through the whole of it from the base to the capping-piece on
which the girder rests, with the view to produce additional strength and
solidity.
With respect to water-sealing a cylinder by depositing some of the
lower portion of the hearting, unless it is composed of Portland cement
concrete it cannot be done, but by the special adaptability of that
material for air-sealing a cylinder, the compressed-air system will
frequently not be required. In order to water-seal a cylinder, two chief
points are presented for consideration, the proportion of the aggregates
to the cement and the required thickness of the seal. A very small
head of water will cause it to rise through concrete made of 10 of
aggregates to 1 of Portland cement, but a considerable head is required to
make it percolate through such a mixture as 6 to 1 when it is properly
proportioned and mixed with a view to solidity and imperviousness.
With this object the Portland cement concrete seal might be made of 2
of sand to 1 of Portland cement for the first few feet, and then a 4 to 1
to 6 to 1 mixture, or 4 to 1 for the first few feet, and upon it a 6 to 1
mass, thus making a nearly impervious surface in contact with the
water, and causing the concrete to be in a condition to readily spread
and fill any cavities at the base, and be well distributed under the
cutting edge.
The strength and thickness of the seal must be increased according to
the head of water and porosity of the soil, but no rules can be fixed, for
the conditions vary. From 5 ft. to 15 ft. of Portland cement concrete
will generally seal a cylinder. The concrete should be allowed a week
or so to set thoroughly before the water is baled or pumped out, and
should be properly trimmed and trodden, or gently beaten solid, and if
it has to be lowered through water it should be made richer than if it
had to be deposited in the air, to compensate for any cement that may
be washed out during lowering it.
When a depth of about 15 ft. of concrete has been deposited in a
cylinder through deep water, the following plan is sometimes adopted :
A disc of planking from 3 to 4 in. in thickness, and a few inches
smaller in diameter than the cylinder, is let down upon the sur-
face of the concrete and weighted ; the space between the edge of the
disc and the sides of the column are next filled in with wooden wedges
driven in by divers. The concrete is thus prevented from being dis-
turbed by the pressure of water underneath, and the water can be baled
out without causing a flow or material agitation. This method is es-
pecially useful in bridge-well sinking, and where the head of water is
great. If the concrete is not weighted or prevented from moving, it
may be blown up by the pressure of the water underneath. Weighted
HEARTING. 69
thick tarpaulins or any practically impervious and suitable material can
be used for small depths. The Portland cement concrete can be put in
by divers, or by the usual shoot-boxes in two pieces, hinged and
fastened by a catch which can be released on pulling a rope attached
to it, or in bags, but the hearting must be made to act as a monolith.
Where the cylinder is erected on dry land, the concrete can be raised
and lowered by an endless ladder or other usual hoisting and lowering
apparatus, great care being always taken that the concrete is not
thrown down from a height, but gently emptied upon the base, or
much of the cement will be washed out ; the heavier material will fall
quickest, and the concrete be unequable in strength and character.
A few thicknesses of the Portland cement concrete water-seal that
have been sufficient to stop the ingression of water, are named to illus-
trate the variableness of the required mass. In the case of a cylinder
14 ft. in internal diameter, the greatest depth of water being 13 ft,
the depth sunk through the river bed 38 ft., and the ground gravel
and silt, 4 to 5 ft. of 4 to 1 Portland cement concrete, when set, suffi-
ciently sealed a cylinder so that it could be pumped dry. In another ex-
ample, a 12 ft. in diameter cylinder required 8 ft. of similar concrete to
seal it sufficiently for the water to be ejected. In each case seven days
were allowed for the concrete to set. In another instance, where a Port-
land cement concrete composed of 4 of stone, 2|- of sand, and 1 of Port-
land cement was used, no less than 18 ft. of concrete had to be deposited,
the depth of water being 50 ft. The necessary thickness varied very
much from a maximum of 18 ft. to a minimum of 4 ft. The soil was
sand for a depth of about 35 ft., and clay and sand and clay for 20 ft.
Some of the causes influencing variations in the required thickness of
the seal are, apart from the depth or head of water, the relative porosity
of the earth that is penetrated ; the close contact of the outside soil
with the surface of the iron rings ; fissures or depressions in the bed of
the river ; considerable range of tide, which tends to keep loose soil in a
state of unrest and insolidity ; the inclination of the strata which may
localise and augment the pressure ; the area of the cylinder, the required
thickness being greater as it increases ; and the composition and charac-
ter of the seal.
70 CYLINDER BRIDGE PIER 3.
CHAPTER X.
THE COMPRESSED-AIR METHOD OF SINKING CYLINDER
DR. POTT'S vacuum principle of sinking cylinders, which was practically
introduced in 1839, has been generally abandoned in favour of the com-
pressed-air method. This latter system was first adopted at the
Rochester Bridge, England, in 1851-2 ; but air-compressors were first
practically" used by Smeatonin 1788, etc., at Ramsgate Harbour, England.
They were there employed for diving apparatus.
The plenum or compressed-air method of sinking is all but certain in
its action, which can hardly be said of any other system if obstructions
are likely to be met with, or in a difficult situation ; it can be further
aided by the use of mechanical pressure or weight ; however, provided
it has been ascertained that no obstructions will be encountered, some
of the other methods of sinking previously described may be used with
economy.
In the early examples of the use of compressed air in sinking cylinders
the whole of the cylinder from the air-lock downwards was filled with
compressed air ; but the system of a working chamber at the bottom,
with a communication pipe sufficiently large for men and materials to
pass, and an air-lock at top, is now generally used, the space unoccupied
by the compressed air being filled with the atmosphere, water, masonry,
brickwork, or concrete, which assist in sinking the cylinder. Many im-
provements and modifications have been from time to time introduced,
such as placing the air-lock immediately over the working chamber at
the bottom instead of at the top of the cylinder, and by the working
chamber, air-lock, and column being suspended by links, and raised as
the pier is built, thus requiring no iron skin to the pier. The latter
method is practically a funnel-shaped diving bell. By the use of com-
pressed air such heavy weights as that of an iron cylinder, which will
frequently amount to from 40 to 100 tons, may be manipulated during
descent with ease, by the aid of simple and inexpensive apparatus and a
few men, who should be experienced, none but skilled foremen being
employed.
The main points in sinking by means of compressed air are to supply
sufficient air for the expulsion of the water, and for the men in the
working chamber ; to provide for the ready entrance and exit of the
men, for the introduction of plant and the hearting, and for the removal
and discharge of the material excavated. In sinking cylinders by the
compressed-air method, if the depth is considerable, the pressure of the
air necessary to exclude the water may be sufficient to overcome the
weight of the cylinder and the surface-friction ; if so, and provided the
cylinder is not weighted, it will be lifted until the pressure of the air
and the weight of the cylinder and the surface friction balance ; and care
SINKING BY COMPRESSED AIR. 71
must be taken that the pressure does not blow up the top of a cylinder
or floor of a caisson.
In order that a cylinder may not sink without some air being let off,
or the cutting edge being undermined, its total weight when loaded
must be less than the surface friction in addition to the flotation power
and the resistance of the ground to penetration by the cutting ring.
For motion to take place, the effective air pressure in addition to the
surface friction and the resistance of the ground to penetration by the
cutting ring, must be slightly less than the weight of the loaded
cylinder. The reading of the gauges should be recorded when motion
commences, and when it is arrested. By gently opening the safety-
valve, or by pumping in more air, the pressure may be lowered or raised
as desired. On the air-pressure being removed, or greatly lessened, a
cylinder will in ordinary soil go down many feet ; a sudden sinking as
much as 20 ft. has been caused by a large reduction of the air-pressure,
the surface friction being quickly overcome. When such a precipitous
depression takes place it will generally be found that the earth in the
interior of the cylinder will rise very considerably more than the depth
to which the column has sunk ; in many instances the excess of the
soil in the column has been found to be as much as from 50 to 100 per
cent., in very loose soil it would probably be greater, and may, perhaps,
entirely fill the cylinder. Such sudden sinking is not economical, or to
be desired.
It is doubtful whether a reliable comparison of the cost of the com-
pressed-air system with other methods of sinking can be made, as all
the conditions and circumstances require to be exactly alike, and as this
only occasionally occurs, the difficulty is to make correct additions and
reductions. However, with great ingenuity, attempts have been made,
with various results, to establish the depth at which each system is the
most economical and to be preferred. The least depth for the economic
adoption of compressed air has been stated to be as little as 16 ft. of
water, and again as 25 ft. The determination is replete with difficulties,
for it is not to be expected that the exact cost in detail of every item
of expenditure will often be stated, and without it any conclusions that
may be drawn will be misleading. Doubtless a reliable comparison can
be occasionally made, but the point is, is it of general application, and
would anybody be willing to be bound as an engineer, bridge-builder, or
contractor to erect a bridge-pier according to the estimates so formed.
Most probably not. To be financially interested in the correctness of an
estimate is a somewhat different operation to that of having but a
purely scientific regard for it. Comparative estimates made from fifteen
to twenty years ago between the cost of sinking by compressed air and
by other means, are hardly applicable at the present time, for the im-
provements made in dredger-excavators during about that period have
72 CYLINDER DBIDGE PIERS.
been most marked, whereas the general apparatus necessary to be used
in adopting the compressed-air system has been but slightly improved,
and been more confined to small details than improvements made with
the view of lessening the cost of that method of sinking cylinders or
caissons. A few of the advantages of the compressed-air system may
be said to be : — -
1. The excavation can be done on dry land, and therefore the much
greater certainty of sinking a cylinder.
2. The easy examination of boulders, logs, or other obstructions en-
countered in sinking.
3. The possibility of using means and methods of excavating tha
core, and especially the removal of obstructions in sinking, not
economically available except on dry land.
4. Greater control of the cylinder from the power to increase or lower
the air pressures, and therefore the additional means afforded of
causing a hanging cylinder to sink.
5. The laying bare the base of the cylinder for the hearting, which
need not be deposited through water.
Some of the disadvantages may be considered to be : — •
1. The deleterious effect of the compressed air on the men when the
pressure is more than 1£ to 2 atmospheres above the ordinary
atmospheric pressure, and the consequent shorter hours of labour,
which must be decreased with the increase of pressure.
2. The liability of sudden and fatal accidents occurring.
3. The prudential necessity of having much of the compressed-air
machinery in duplicate.
4. The employment of additional skilled labour.
5. The increased plant required, such as air-compressors, pumps, air-
locks, working-chamber, light, boilers, engines, smithies, etc.
6. The expense of making the cylinder as air-tight as possible.
The question of relative speed of excavation is not considered, as the
size of a cylinder and the working area will influence that operation.
LIMITING DEPTH, AIR-SUPPLY, AND LEAKAGE 73
CHAPTER XI.
LIMITING DEPTH, AIB-SUPPLY, AND LEAKAGE.
IN using the compressed-air system for depths such as 80 or 100 ft.
there is difficulty in making the cylinders air-tight without special care
in construction, and at the depth of 100 ft. below the water level it is
dangerous to the men unless special precautions are taken. Many
examples of cylinders sunk 80 to 85 ft. below the water-level by the
compressed-air system exist, and at the St. Louis Bridge the men des-
cended to a depth of 120 ft., which may be considered as about the
maximum advisable or even practicable depth ; the maximum air-pressure
above the ordinary atmospheric pressure was nearly 52 Ibs., or about
3£ atmospheres. It is certainly very questionable whether the com-
pressed-air method is the best system that can be used for depths greater
than from 80 to 100 ft. below water-level, nor is it usually economical
for depths less than about 25 ft. below water, except under special
circumstances, but the depth for ita economic adoption is not easy to
determine generally, as has been mentioned.
There is considerable waste of air in the pneumatic process, through
the air escaping under the bottom of the cylinder, and by leakage, and
much more power is required than that shown by actual work. Careful
construction of the cylinder, particularly of the joints, and caulking the
latter with tarred oakum, or other approved water-tight preparation, will
save expense by preventing leakage of air and the ingress of water.
Sometimes it has been found necessary to line the interior with cement
to make the cylinder sufficiently air-tight; but this is seldom requisite if
due care is taken in the construction of the cylinder.
Authorities somewhat differ as to the actual quantity of air consumed
by a man, but 220 to 240 cub. ft. per hour is sufficiently near for
practical purposes, and about one-twentieth of this amount, or 11 to 12
cubic ft. per hour for an ordinary candle. This is the net quantity of
air required without allowing for leakage. There is the leakage from
escape of air under a cylinder, through the column, air-pipes, lock, etc.,
and the constant loss of air during the passage of workmen and material
through the air-lock. The loss from leakage will almost always
determine the necessary supply, hence the importance of making an
approximate estimate of its amount. Unless the power of the air
apparatus greatly exceeds the amount of air theoretically required, it
will be necessary to continuously keep the pumps at work ; under or-
dinary circumstances and without great care, it is not advisable to stop
them. The leakage through and under the column will be found to be
much greater than that of the air-pipes and lock, and the point of leakage
can generally be discovered, and in great measure stopped, by attention
to the joints, and by covering them withsome impermeable material,
74 CYLINDER BRIDGE PIER3.
such as tempered clay, which will be forced into any cracks or crevices
by the pressure of the air, if considerable. Leakage may also be ex-
pected where the roof of the cylinder joins the rings. So long as the
water is above the level of the bottom of a cylinder, the air will be
prevented from escaping at the base ; but if the sinking of the column
is arrested during the progress of the excavation, the water may be
entirely driven out of the column ; there will then «be an escape of air
under the cutting edge, the effect of which is to make the soil around
the cylinder loose and spongy, thereby lessening the surface-friction,
but increasing the liability of the column to tilt ; still, in clay soils, not-
withstanding the earth being excavated under the cutting-ring of a
cylinder, it may not sink, and in addition to extra loading it may be
necessary to raise the air-pressure half or three-quarters of an atmosphere
above that required to exclude the water so as to disturb the soil pressing
upon the cylinder rings, to reduce the frictional resistance, and to cause
the cylinder to descend.
The loss of air during the expulsion of the water from a cylinder is
usually considerably less than when it has been expelled, and excavating
operations are in progress ; and it will vary according to the workman-
ship, the nature of the soil, the pressure, and whether the sinking of
the column is carefully arranged so that there is not much loss of air
under the cutting ring. In coarse gravel and clay the loss may be said
to be, all other conditions being similar, from 8 to 9 per cent, less than
in fine gravel and sand. Where there is leakage of air through any
timberwork, if not through the wood, it can generally be lessened by
watering, which will cause the wood to swell.
Both the air-lock and the shaft of an iron cylinder can be made
almost air-tight ; but it is nevertheless necessary that air be constantly
discharged into the cylinder so as to keep it comparatively fresh and
pure to live in, or respiration cannot be efficiently performed. The air
pressure should not be excessive, or the men may be inconvenienced,
but it should be sufficient to keep the air in a fresh and pure state, and
so that there is no want of air. This fresh air is wasted regarding it
from the point of view of pressure, but such extra air has been utilised
by an arrangement by which it is allowed to escape through pipes, and
to carry sand and loose soil with it to the top of the cylinder.
It has been found that when the natural skin, or surface left in casting
has been removed from cast-iron, water under pressure of about 3 to 3%
tons per square inch will pass through the pores of the iron ; such
pressures, however, can never occur in cylinder sinking. As air under
a pressure of about 40 Ibs. per square inch, or 2'72 atmospheres, will
penetrate most wood, if a timber roof on a cylinder should have to be
used in the pneumatic system, it is necessary to coat the wood with
some air-tight preparation, such as resin or euphorbia-juice. The
LIMITING DEPTH, AIB-SUPPLY, AND LEAKAGE. 75
experiments of Professor Doremus show that air can be easily forced
through sandstone, brickwork, and unglazed tiles, etc. A depth of a
few feet of water produces sufficient pressure to enable it to percolate
red sandstone. In using the compressed-air system with brickwork and
masonry, it is necessary to coat them with an impervious preparation.
or neat cement.
To calculate the pressure of air required to balance the water-pressure
the following formulae may be found useful : —
Let D = the depth in feet of the foundation below water level.
„ A = the ordinary atmospheric pressure=say, 14'71 Ibs. per
square inch.
NOTE. — Although the pressure of the atmosphere varies
between, say, 13'65 Ibs. per square inch at sea
level, and 15'06 Ibs., 14*71 Ibs. is generally taken,
which equals 29*92 inches of mercury.
,, N = number of atmospheres above the ordinary atmospheric
pressure, or gauge pressure.
„ W = weight of a column of fresh water 1 in. square and 1 ft.
in height=0'433 Ib.
„ P = pressure of air hi Ibs. per square inch required in the
cylinder to balance the water pressure, in addition to the
ordinary pressure of the atmosphere.
„ Pp = Pressure required above a vacuum in Ibs. per square inch,
then,
P=WD. N=, or as WD=P, N= .
Pp=P+A.
Example. — Let the greatest depth below the surface of the water=
50 ft. Eequired P, Pp, and N.
P=WD=0-4333x 50=21-66 Ibs.
Pp=P+A=21-66 + 14-71=36-37 Ibs.
The total pressure per square inch above a vacuum in the cylinder
Gauge Pressure. Atmosphere.
would therefore require to be ... ... 1'47 + 1 = 2'47
atmospheres, or 21'66 + 14'71 = 36'37 Ibs.
The quantity of air that will be wanted in a cylinder can be approxi-
mately ascertained by knowing the greatest number of men that will
be in the working chamber at one time, the number and nature of the
lights to be used, the loss of air from the air-lock, and the constant,
76 CYLINDER BRIDGE PIERS.
pumping to keep the air fresh, the probable leakage of the cylinder,
and the loss from the escape of air under its cutting-edge. On calcu-
lating the air required for workmen and lights, it is not prudent to
allow for that purpose alone less than an air-delivering capacity of
about three times that amount ; but the consequences of any temporary
failure of the air-supply must be considered. The quantity of air
required to keep that in a cylinder in a comparatively pure state, will
depend upon the nature of the soil through which the column passes,
the purity of the river water, and the system of lighting used. In
some situations, in very large cylinders, an equal number of, if not
more, compressors, may be required to keep the air fresh than for
leakage only.
It is advisable that the air be compressed equal to the full head of
water. In soils which do not allow easy percolation of water, some-
times the pressure required to exclude it is less than the calculated
force, the water being held back by the soil, but, as this may be only
for a short time, it is not safe to work without the calculated pressure.
For instance, it is recorded that a sudden increase of water pressure led
to a disastrous accident at the Rheinpreussen Mine by bursting the air-
lock, hence the importance of the air-pressure balancing the calculated
water-pressure, and no deduction being made for any diminishing
influence caused by capillary attraction or a retentive stratum. As soon
as the cylinder has been sunk, and there is no danger of it floating, the
air-lock floor door can be opened, and the compressors set to work.
These should be kept constantly pumping air in until the water is
forced out, when excavating operations can be commenced on dry land,
If the cylinder is situated in a tidal river, and it is well made and tight,
the loss of the head of water with the falling tide may counterbalance
the leakage without any pumping in of air. When the tide begins to
turn, the pumps must be set to work again. After a few days' ex-
perience, the amount of air required will be ascertained ; at the same
time it should not be forgotten that there is always a probability of the
fixed standard of air pressure not being maintained. With a declining
pressure, the atmosphere in a cylinder will become misty and foggy ;
but with a rising pressure it will clear ; if a considerable excess of
air is pumped in, the atiaosphere will be materially cleared ; but for
reasons previously mentioned, this cannot always be done.
When the cylinder enters a water and air-tight stratum, such as clay,
the variations of level of the river will have no effect on the internal
air-pressure, provided there is no leakage of water along the surface of
the cylinder. The pressure of the air should not be raised too much
above the pressure from the head of water on the stratum, or it may be
percolated or injuriously affected. Sometimes springs are met with in
sinking cylinders of large diameter ; the air-pressure required under
LIMITING DEPTH. AIR-SUPPLY, AND LEAKAGE. 77
such circumstances, it haa been found, will vary to an important
extent.
The pressure of the compressed air on the air-lock floor and roof is
considerable, taking a cylinder 10 ft. in diameter, and a pressure in it
above the ordinary atmospheric pressure of, for instance, 36'36 — 14*7
= 21-66 Ibs. = 50 ft. head of water, the upward strain on the air-lock
would be nearly 110 tons. It is advisable to test the floors and roof to
at least twice the pressure they will have to sustain in practice ; and
should they be thought weak they can be loaded to counteract the up-
lifting strain. The larger the cylinder, the less it is affected by sudden
rises or falls in the air-pressures, as the space occupied by the air is so
great that the loss or increase of a little air is not so perceptible as in a
smaller column.
If a constant and increasing supply of compressed air has to be
provided, the better plan appears to be to use a number of small air-
compressors, particularly if the cylinder is of large diameter, in
preference to one or two machines, so that if any get out of order they
can be repaired without very appreciably lowering the pressure. These
small compressors can all lead into one main air-pipe, and be provided
with valves, so that each can be shut off at any time from the main.
The main air-pipe for large works generally passes into an intermediate
reservoir or receiver, which sometimes is a boiler, and then by other
flexible pipes of rubber or pliable material to the cylinder. In some
recent examples of air-apparatus for large works, each engine driving
the air-compressing machines had its own boiler, and they were all so
connected that the stoppage of one boiler or engine did not affect the
rest. Precautions should be taken that the air-pipes do not foul any
sharp substance that may tear or injure them. All air-hose should be of
the best material, and should be tested before being used with a con-
siderably greater pressure than that it will have to sustain in regular
work. Frequently the engines and air-pumps are in duplicate, both sets
being ready for work at a moment's notice, although but one set is in
constant use ; so that should one apparatus break down or need
repairing it can be stopped, and the other set at work without delay.
The air-compressing machinery is generally placed near one of the
abutments on the most convenient side of the river, and the sheds for
the engines, the air-compressors, pumps, smithies, repairing shops,
dynamos, stores and offices are there erected. Sometimes a semi-tixed
engine of from 8 to 10 nom.h.p. is used for the shallow depths, and
perhaps two 25 to 30 nom.h.p. for the greater depths, such as 80 ft., to
drive the air-compressors, but, of course, the engine- power required
varies according to the depth of water, kind of soil, area of cylinder, and
other circumstances. The system of having two semi-portable engines
of say 15 horse-power instead of one, say, of twice that horse-power, to
78 CYLINDER BRIDGE PIERS.
supply the power necessary to compress the required quantity of air is
frequently preferred, each engine being entirely independent of the
other, the air-pipes communicating separately with the air-lock.
Elaborate and heavy air-compressing machinery is not to be desired,
but simple apparatus of moderate weight and size, combining efficient
working with comparative cheapness, always remembering, however,
that lightness and small bulk may perhaps only be obtained at the ex-
pense of economy in the production of the necessary power to compress
the air. The vertical and angular system of air-compressors seems
generally to be not so effective as the direct-acting steam power engine,
or that constructed on the principle of direct straight line compression,
i.e., one in which the steam and air cylinders are fixed on the same
horizontal line, and the piston rods attached to a crank working on a
fly wheel. In some of the latest air-compressors, the air is first com-
pressed to a comparatively low pressure, about 1 atmosphere above the
ordinary atmospheric pressure, or, say 29'40 Ibs. per square inch above a
vacuum; it is then passed through an intercooler, and further compressed
as desired. The great point is to reduce the strain on the machinery as
much as possible, but, as in cylinder bridge pier sinking by means of com-
pressed air a pressure exceeding 55 Ibs. per square inch above a vacuum
is not required to be maintained, and seldom so great a pressure exerted, it
generally being from 30 Ibs. to 50 Ibs. per square inch, the pressure re-
quired is very much below that necessary in the case of air-compressors
for tunnel work or other general purposes ; but that is no reason for
using old or much worn air-pumps which will probably repeatedly fail,
and consequently be dangerous to employ, as the air supply may be
suddenly reduced, and operations will necessarily be both slow and
expensive.
It is claimed that in air-compressors the single-acting is better than
the double-acting air-cylinder system, because the air is but once com-
pressed at every revolution, and that it is therefore kept cooler as there
is more time for the heat to be evolved. Unless the water for cooling
is introduced into the air-compressing cylinder in the form of spray, as
in Dr. Colladon's compressed air cooling arrangement, it is found to be
ineffective as a cooler of the air during the process of compression, and
unless it effects that object, it is better not introduced, the point being
to cool the air during compression. Compressed air cannot be produced
without generating heat, and the efficiency of an air-compressor is there-
fore reduced, but this loss is diminished by a cooling arrangement to a
very small percentage of the theoretical power ; however, the thermal
loss must be considered with the loss by friction of the engine, as the
former may be lessened by an increase of the latter.
It is necessary to cool the compressed air so as to maintain it at as
little above 60° to 70° F. as can economically be effected, for the
tSTKlVERsiTY
LIMITING DEPTH. AIR-SUPPLY. AND LEAKAGE.
increase of temperature of air at 60° F., it being taken at the ordinary
atmospheric pressure of 14*71 Ibs. per square inch above a vacuum,
when compressed to 2'50 total atmospheres, is no less than 158° F., or
the production of a temperature of 218° F. The free or atmospheric
air should be cold and moist when admitted to a compressor, a low
initial temperature being economical, as it not only reduces the rise of
temperature and requires the air to be less cooled during the process of
compression, but less power is necessary to compress moist than dry air.
It is unadvisable to keep air-compressors at a temperature below about
40° F. The object of any cooling arrangement is to take up the heat
generated during compression, or as much of it as possible. This can
be effected by blowing spray, at ordinary temperature, into the air-com-
pressing cylinder during the process of compression ; but if the
compressed air is used expansively, the injected fine spray at ordinary
temperature is employed for another purpose, namely, to prevent the
air approaching too closely that of a freezing temperature, and encum-
bering the valves, pipes, and other parts of the machinery.
Taking into consideration size and weight of apparatus, etc., a
reasonably high speed and short stroke appears to be better adapted for
air-compressing machinery for use in the compressed-air system of
bridge-pier sinking than the slow speed and long stroke.
One objection against hydraulic air-compressors is that the cylinders
wear quickly, and, therefore, become leaky, and require to be rebored ;
another is that only one side of a large body of air comes in contact
with the water, whereas in the spray system diffusion and equal cooling
is attained, but there are staunch advocates of both arrangements. The
air-pumps are sometimes immersed in a cistern, with a constant flow of
cold water round them, to cool the compressed air. It has been found
that air compressed in contact with water, and then discharged into a
reservoir, leaves the machine at a temperature but very little above that
of the water at any pressure likely to be required in sinking bridge-pier
cylinders ; also that by maintaining the temperature of the air constant
during the operation of compressing it, a saving is effected in the
amount of the work required for compressing and storing the air,
ranging from 20 to 25 per cent. Dr. Colladon's pulverised water-com-
pressors, i.e., by injecting spray into the air-cylinder during the process
of compression, were used at the St. Gothard Tunnel with so much
success that in compressing air to 8 atmospheres the increase of tem-
perature did not exceed 27° F., whereas the rise of temperature without
any cooling would have been about 430° F. A condensing vessel is
sometimes used to precipitate the moisture in the compressed air, in
order to deliver the latter in a dry state, and the air is also cooled in the
air-pumps by the injection of a fine spray of water into the cylinder
with every stroke of the pump.
80 CTLINDER BRIDGE PIERS.
The temperature of the water inside a cylinder will be greater thar
that of the river outside ; the greater the depth the higher the tempera
ture, other conditions being alike.
CHAPTER XII.
EFFECTS OF COMPRESSED AIR ON MEN.
A PRESSURE of about 2 atmospheres does not appear to injure mer
if in health, but it depends on their temperament ; those of a plethoric
constitution suffering the most. Above the pressure previously in-
dicated it is injurious to them. As the pressure of the air is increased
above 2 atmospheres, the working hours of. the men must be reduced ;
about a four-hours' shift for a pressure not exceeding 2 atmospheres,
decreasing to one-hour relays for a pressure of 3 atmospheres, is
usual. Many men work with comfort if the length of the shifts is
shortened. Men have remained under a pressure of 2£ atmospheres
for ten hours, but this is an exceptional time. At the St. Louis
Bridge, under a pressure of a little more than 3 atmospheres,
several men died, or were paralysed; and the working hours had
to be reduced to one per diem. It is recorded that at the Alexander II.
Bridge, over the Neva, where the air-pressure in the caissons was 2£
atmospheres, corresponding to about 85 ft. depth of water, the workmen
had three-hours' shifts, and yet suffered considerably from weakness
and pains in the legs and arms.
When the pressure is very considerable it is advisable to reduce the
working hours, for it is believed the chief cause of paralysis in men
employed in highly-compressed air is the length of time they work in
it, and not more than two hours' continuous labour should be allowed at
the pressures required at depths above about 85 to 90 ft. However,
under favourable circumstances of clean and pure soil, and where the
strength of the experienced men is not required to be constantly or much
exerted, at such a depth of water as about 25 to 30 ft., men have
frequently worked in compressed air in shifts of eight hours each, but
when the pressure exceeds about 2£ atmospheres, it has been found
necessary to reduce the working time to about six hours ; generally, if
the pressure is more than 2£ atmospheres, it is necessary to very con-
siderably lessen the duration of the working hours.
In the winter, to prevent congestion of the lungs, owing to the
sudden change of temperature on coming out of the cylinder into the
EFFECTS OF COMPRESSED AIR ON MEN. 81
air-lock, steam-coils or other means should be employed to warm the
air. At the East River Bridge, the difference of temperature between
the working-chamber and the air-lock was 40° F., the former being 80°,
and the latter 40°. Workmen should not be allowed to go suddenly
from the air-lock into the open air, especially if the pressure has been
high ; about one minute's rest per atmosphere is now usually allowed.
In all foundations where the plenum process is adopted there is risk
to both life and limb, depending greatly upon the precautions taken,
therefore duplicate or numerous safety-valves, pressure-gauges, alarm
vyhistles, and preventive measures against fire, explosions from lighting
apparatus, and accidents of all kinds, should be taken, not only to
ensure the safety of the men and to give them confidence while at
work, but also on the ground of true economy. To prevent the
mistakes which occasionally occur when line signals are used with
divers, an inexpensive speaking-apparatus has been introduced by Mr.
Gorman, so that vivd voce communication can be obtained with a diver.
It is claimed that it is less costly than the telephone, and having no
battery is much le&s liable to get out of order, and can be applied to any
form of diving-helmet. It has been used with success at depths as
great as 120 ft.
Cooling the compressed air is an important operation, which has
previously been briefly referred to, as the high temperature developed
when air is compressed makes it most trying for workmen. To obtain
a fair average amount of work from any man, he should obviously not
be placed in a heated or vitiated atmosphere, or in such a position that
he is not free to move his limbs.
The air can generally be kept pure while the cylinder is sinking
through permeable or porous soil, but when it is penetrating an
impervious stratum the atmosphere in it may quickly become foul, and
it may also be in the same condition when the bottom is covered by the
hearting. Means must be at once taken to remedy this ; a method that
has been adopted, when, after the bottom of the cylinder was over-
spread with concrete, the air became foul, was by inserting through the
centre of the hearting a small tube down to the permeable soil which
formed the base, the upper end of the pipe being always above the
hearting, the foul air thus passed through it to the bottom forced by
the compressed air. Diverse opinions are held as to the cause of the
pain and paralysis to which some men are subject when working under
a high pressure, but it seems that with each breath, the quantity of
oxygen inhaled is proportionate to the pressure, and that the inhalations
per minutG are voluntarily reduced nearly in the proportion between the
pressure of the normal state of the atmospheie and that of the
compressed air. Workmen who have been affected by compressed air,
it has been noticed, are very nervous upon entering the atmosphere.
G
82 CYLINDER BRIDGE PIERS.
Medical practitioners prohibit violent exertion, such as climbing ladders,
and severe work. Only men in good health, and of temperate and
regular habits, should be allowed to work in air compressed to more
than about 1£ atmospheres.
At the St. Louis Bridge, where the foundations were 100 ft. in depth,
the bad effect of the compressed air upon the men was mostly felt after
ascending the staircase of the shaft. A lift was therefore provided, and
it was made compulsory on the men to be raised by it ; they were only
allowed to work two shifts per day of forty-five minutes each ; they
were made to lie down in a hospital boat, and were given small doses of
stimulants for a short time after leaving off work.
Helmet-divers can work at a depth of 150 ft., but only for a short
period, the length of the working hours extending as the depth becomes
less. Depths from 80 to 100 ft. are the safe limits for most men. The
working hours for divers are about the same as those for men under the
compressed-air system, three quarters of an hour to one hour for great
depths, such as from 100 to 150 ft., and four or five hours for small and
medium depths. Native Indian divers have, without a diving dress, or
any aid beyond a guide-chain, picked up tackle, etc., at depths of from
45 to 50 ft. In muddy water the matter held in suspension prevents
the light penetrating, and the divers seeing ; and unless the air-pump is
on a fixed staging, and the ladder and air-hose protected, it is not safe to
work in rough weather.
The length of time a diver can remain submerged depends principally
upon the health of the man, the depth below water at which he has to
work, the temperature of the air and water, their purity, and the
apparatus used.
Great care is necessary in diving operations to prevent the air-hose
fouling any sharp substance that may tear or injure it. The air-pipe
should always be of the best material, and before being used should be
tested and carefully examined, and it should never be put to work
without testing after being in store. In some diving apparatus a
certain amount of vacuum must be produced by the lungs to open the
valve supplying fresh air ; this is a drawback, and tends to prevent the
divers working easily and long and with effect. Experiments have
shown that if the lungs be filled with compressed air, a healthy man can
easily remain under water from three to four minutes without any
apparatus. A greater pressure from the air-pump is necessary with
the pneumatic system of sinking cylinders than with divers at the same
depth, owing to the loss of air, principally through the bottom of the
cylinder and the air-lock. Divers are useful for clearing the ground of
loose stones and debris, and for inspecting the cause of obstruction in
sinking a cylinder by dredging, and for levelling and removing pieces
of rock, etc.
AIR-LOCKS. 83
Notwithstanding the deleterious effects of highly compressed air on
men, it has been noticed that a beneficial action has been produced when
they work at moderate pressures, not only in their general health, but
also in the chest in particular, because of the increased quantity of
oxygen inhaled under pressure ; and it has been said certain pulmonary
diseases have been so cured. Such curative baths have been used in
various hygienic establishments for many years.
CHAPTER XIII.
AIR-LOCKS.
TNT the compressed-air system an air-lock or chamber must be con-
structed in the cylinder for the entrance and exit of men and materials,
without allowing the egress of the compressed air in the working
chamber or shaft. The maximum working pressure allowed to be used
should be conspicuously indicated in large white indelible letters of
enamelled iron or some substance that cannot be easily erased, both in
the air-lock, gradual-pressure room, if there be one, working-chamber,
and in such other suitable places as may be convenient and advisable,
and the dates when the different pressures are applied should be care-
fully recorded ; and it is well to indicate the day of first application of
the air-pressure in a prominent place to give confidence to the men. In
addition to an air-lock, sometimes there is a room with two doors, the
first communicating with the outer air and opening inwards, the other
opening into the air-lock. It is also fitted with two cocks, with an index-
finger and plate, so that workmen may ascertain the pressures. The
air-lock in this arrangement is always filled with compressed air, A
workman wishing to go into it enters the gradual-pressure room through
the door, which he then closes, shuts the discharging cock and opens the
other, and allows the pressure to increase as he feels able to bear it.
When the pressure is equal to that in the air-lock he opens the door,
passes into the air-lock, and descends the shaft by a ladder or staircase
to the working-chamber. The operation is reversed on exit from the
cylinder.
A light air-lock is made by having everything but the doors, and
shoots if any, of wrought iron, and it is to be preferred to cast iron as
being a more reliable material. Every precaution should be taken
against bursting. The doors are liable to be especially strained, and there-
02
84 CYLINDER BRIDGE PIERS.
fore should be strengthened and supported by bar, angle or T irons riveted
on all round the frame and door to prevent distortion. The height of
an air-lock should not be less than 6£ or 7 ft., and there does not appear
to be any advantage in making it more than 8 or 9 ft. The doors of the
air-lock should be interlocked to prevent accidents, and to ensure that
the entrance door cannot be opened until the door leading to the descend-
ing shaft or steps is properly closed.
Economy of the compressed air is gained by having the air-lock
sufficiently large to allow all of the men forming one shift to enter at
one locking. It should also be made, if possible, of sufficient extent
to contain the whole quantity of material taken out by the men during
one relay, so that the air-lock only requires to be emptied or drawn
upon at the end of each shift. This expedites the work, and saves the
men from frequent changes of pressure. Bull's-eyes of glass, for light,
are often inserted in air-locks, but, owing to their being covered with
dirt, very little natural light penetrates through them. Reflectors are
also employed. The doors are made to open inwards, so that the in-
ternal air-pressure tends to keep them closed. The floor of the air-lock
usually consists of a wrought-iron plate with a man-hole cut in it, it
being firmly bolted to the cylinder, the flanges of which should be faced
in a lathe and packed with approved packing. The man-hole door in
the air-lock floor is sometimes fitted with an indiarubber washer, and
should open downwards. If simply for the passage of men, it need not
be above 2 ft. 6 in. in diameter ; if excavation and materials are to be
passed through it must be larger according to circumstances. The air
supply and equalising-pipes pass into the air-lock, and usually a pipe
for discharging any water which may percolate into the working-
chamber through any sudden lowering of the air-pressure. If brass or
copper pipes are used, 4 in. in diameter has been named as a prudent
limit of size, and that the working pressure should not exceed about one-
sixth that of the bursting pressure. Double air-locks have been used,
containing one large and one small compartment, the larger for the
workmen to pass, and the smaller o± sufficient size to contain a bag,
basket, or skip, and the necessary raising and lowering apparatus. If
the pressure of air is considerable, the air-lock can be gradually loaded,
so as to relieve the strain on the cylinder.
At the Argenteuil Bridge the air-lock had two diameters ; the outer
was 10 ft. 6 in., the inner, 4 ft. 7 in. The larger enclosed space was
divided into two by a partition. One compartment was put into com-
munication with the interior, and was thus filled with the excavated
material, while the other was being emptied by the outer door, so that
the loss of air in locking was diminished without interruption to the
work.
At the St. Louis Bridge the caissons had a circular open-air shaft 10
AIR-LOCKS. 85
X
ft. in diameter, which was continued to within 3 or 4 ft. of the lowest
part of the cornpressed-air or working-chamber, and it had a spiral
staircase. At its base there was an iron door, which opened into the
air-lock placed within the compressed-air or working-chamber. On the
air-lock entrance door being shut and the pressure equalised, the men
could descend to the working-chamber almost by one step, the distance
being only a few feet although the caisson was sunk to a depth of
about 125 ft. below high water. By locating the air-lock within the
compressed-air or working-chamber and at the bottom of the open-air
shaft, Capt. J. B. Eads claimed that it was much the most convenient
place for it ; and no extra exertion was required to reach the base or
ascend the shaft, descent or ascent being in the open air ; the shaft also
had not to be made air-tight, the air-lock and roof of the working-
chamber alone having to be so constructed, and those in and out of the
working-chamber were brought in comparatively close contact, which
facilitated the supply of tools and materials and the carrying out of in-
structions. However, only in the largest cylinders can such an arrange-
ment be adopted, especially if part of the permanent hearting of the
cylinder is utilised as kentledge, although it can be in nearly all
caissons.
A method of discharging material through a delivery pipe in an air-
lock frequently used may be thus described. A discharging pipe, with
closing flaps at each end, is placed through the side of the air-lock, it
being inclined outwards at a sufficient angle to shoot the excavation. The
process of discharging the soil is effected in the following manner.
The outlet-flap of the pipe is shut, and the pipe is filled ; the inlet
flap is then securely closed, and the outlet-flap opened, the material will
then discharge itself. Unless the air-lock is sufficiently large to contain
all the earth excavated during one shift, this method has advantages
over discharging material in the air-lock and opening the door for pur-
poses of delivery. Sometimes in addition to the discharging tubes there
are, in very large cylinders, tubes for shooting the concrete for the
hearting into the air-lock. The inclination of these latter pipes should
be the reverse of the excavation tubes. A code of signalling must be
arranged between the workmen in the air-lock and the men outside.
Signalling by means of an acoustic tube and vibratory diaphragm has
been employed with partial success, but is generally abandoned owing
to the noise made by workmen rendering it difficult to understand the
signals. Whistling signals have also succeeded, the compressed air being
allowed to escape through sonorous reeds. Electric signals are the best.
The telephone has been used, but, owing to noise, it cannot under toich
circumstances be considered thoroughly reliable.
At the Boom Bridge, over the Rupel on the Antwerp-Tournai Railway,
where the excavated material from the interior of the cylindei «/as
86 CYLINDER BBIDGE PIEB8.
discharged through the outer air-lock door, the inner end of the spout
opening inwards and the outer door of the pipe necessarily outwards, it
is obvious that if, by mistake between the men in the air-lock and those
outside, the outer door was opened at the wrong time, the flow of air
would be very dangerous, and perhaps fatal to the men in the air-lock.
An arrangement was therefore devised by which the safety of the men
was secured at trifling expense. It consisted in locking the fastening
bolt of the outside door by means of a sliding pin, which was worked
by a rod passing through a stuffing-box into the compressed-air
chamber, the pin being withdrawn only by the men inside the chamber,
and not until they had previously closed the door on the inner end of
the spout.
A discharging tube, consisting of buckets formed with india-rubber
lips, working in a perfectly true and smooth cylinder, has been employed
to save leakage of air by dispensing with the method of discharging
materials from the cylinder into the air-lock, and then outside ;
but the leakage of air was so great that it had to be abandoned. A
frequent rule, when the air-lock is also used as a spoil-lock, and will
contain all the material excavated during one relay, is for the men to
cease operations in the working-chamber half an hour or so before the
shift terminates, in order to remove the soil previously accumulated in
the air-lock.
In deciding upon the position of the air-lock in a cylinder, space
should be economised, the amount of air wasted should be caused to be
a minimum, and the safety of the men should be secured in case of an
accident to the cylinder. If an air-lock is placed in the cylinder below
the water-level outside it may be dangerous, especially if there is a con-
siderable range of tide, and also an uneven river-bed. On the other
hand, among the disadvantages of the upper air-lock system, the air-
lock must be sometimes taken off and replaced, and the air-shaft must
be ascended by the workmen when under pressure, a not unimportant
question if the air is compressed more than 2 atmospheres, for every
endeavour should be made to avoid unprofitable exertion of the men at
all pressures. If the air-lock be placed above the working-chamber,
although at the bottom of the air-shaft, it must be entered from the top,
and left through the bottom. Side doors cannot be used, but they can be
if the air-lock is within the working-chamber. Owing to the great
difference in area of the chamber of a cylinder and that of a caisson,
ranging generally from 1 to 100 to 1 to 200, these advantages and con-
veniences of access are of but little importance in the cylinder, but very
great in the caisson. As a matter of prudence, if the air-lock is close
to the working-chamber, or inside it, or below the water-level, it is
desirable to have an additional refuge or safety room. For cylinders, on
the whole, it would appear that it is preferable to place the air-lock on the
WORKING-CHAMBER, AND LIGHTING IT. 87
top, but in the case of caissons of considerable area, or of cylinders of
very large diameter, it is more conveniently situated at the bottom. It
is always advisable to provide for capping the cylinder, or shaft of a
caisson, so that, if necessary, it can be made a receptacle for compressed
air.
CHAPTER XIV.
WORKING-CHAMBER, AND METHOD OF LIGHTING IT.
THE height of the working-chamber, or chamber of excavation, should
not be less than 6 ft. 6 in., and from 7 to 8 feet is a preferable height.
Each man requires about an area of from 20 to 25 sq. ft. to enable him
to work freely. It is seldom that more than 8 to 10 men can simul-
taneously and profitably work in a cylinder of moderately large area.
To crowd the men is to waste labour. The chief aim should be to
equally excavate the material so as to prevent tilting of the cylinder,
and to manipulate the excavation so that the resistance of the ground
and the pressures are equal over the whole area of the cutting-ring, and
any outside local looseness of soil obviated. It is well to have the
working-chamber painted white, in order to obtain the greatest possible
amount of reflected light, and it must be thoroughly stayed in all
directions by angle-irons and gusset-plates.
When the air-lock is at the base of a cylinder, the air-supply pipefl\
should project about 3 ft. into the working-chamber, so that in the event
of an accident, and water rushing in as quickly as the air was forced
out, which would air-seal the bottom of the supply-pipe, the space
between the end of the air-supply tube and the roof of the working- \
chamber would contain a layer of compressed air, so that the men would
not, in that case, necessarily be drowned ; but it is questionable whether
many men would, under such circumstances, be sufficiently calm to avail
themselves of the refuge. The working-chamber sometimes alone
contains the compressed air, the air-chamber being fixed below its ceil-
ing.
Shafts for lowering the materials to the air-chamber, when the latter
is at the base of the cylinder, are generally arranged as follows : — A
tube or pipe, about 2 ft. in diameter, is fixed from the top of the air-
chamber to the summit of the cylinder, with doors at the top and bottom,
the lower opening into the air-chamber. When the upper door is open,
the lower is held in position by the pressure of the air in the working-
chamber, and by ordinary arrangements. The supply-shaft is then
88 CYLINDER BRIDGE PIERS.
nearly filled with material, or with as much as is desired, which being
effected, the upper doot is drawn up, compressed air is sent into the
pipe, and when the pressure in it is equal to that of the working-
chamber, the air-chamber is signalled, the fastenings of the working-
chamber door are removed, and the material is deposited. Many
accidents, however, have arisen through mistakes in the signals, and an
automatic arrangement from above is preferable ; but notice must, of
course, be given the men below that the material is about to be deposi-
ted, in order that they may keep away from the mouth of the supply-
shaft. To ascertain whether all the material put in the shaft at one
time has been discharged at the bottom, a rod, or other means, should be
employed. A thoroughly trustworthy foreman should see that the top
door is always shut, and that the requisite amount of compressed air is
let into the supply-shaft before the discharge door is opened, or the
shaft will be blown out, the compressed air in the working-chamber will
be set free, the water will immediately flow in, and the men in the
air-chamber will probably be drowned, all ordinary lights will be extin-
guished, and the moisture being, by the sudden absence of pressure, set
free from the compressed air, would cause a mist, and in addition there
would be the roar of the escaping air, which would render it almost
impossible for men to grope their way to the ladder. It is advisable
to conspicuously mark the ladder, whether by a phosphorescent plate,
luminous paint, or by other means, so that its position can be ascer-
tained in the dark.
The supply-shaft at the lower end should be gently splayed, and the
bottom door and fastenings must be made sufficiently strong to sustain
the weight of materials in it, and in filling the shaft it should be ascer-
tained that the material does not get jammed, or it may have a sudden
fall, and fracture the lower door. At low tide, owing to the decrease of
the hydrostatic head, there will be less chance of water getting into the
working-chamber than at high water. Any small agitation of the water
on the surface of the ground in the working-chamber will permit the air
to escape if the undulations allow the water to get momentarily below
the edge of the cylinder, therefore it should be kept as still as possible.
A strong light in the working-chamber is a necessity, not only to
penetrate the mists that prevail from time to time, but to illuminate the
whole internal base of the cylinder, in order that the excavation may
properly and equally proceed. At a pressure of two atmospheres above
the ordinary atmospheric pressure the wick of a candle will rekindle
when the flame has been blown out, therefore inflammable materials
should be kept from the vicinity of the lights in the working-chamber
of a cylinder. In a fire in the East River Bridge caisson, as soon as the
water-pipes were stopped playing upon the timber, it would re-ignite.
Candles produce much smoke, owing to their rapid, but incomplete,
WORKING-CHAMBER, AND LIGHTING IT. 80
combustion under an excess of air-pressure, and they are liable to be
extinguished by air-currents. The nuisance of smoke has been over-
come by reducing the size of the wick and the candle, and by n facing
alum with the tallow, and steeping the wick in vinegar. Candles iiave
been burnt in closed glass lamps, the air being brought from the surface.
Lamps are of but slight use, as they smoke more than candles, and ihe
oil, to a certain extent, is dangerous. The relative volume of oxyg< n
consumed should be considered in determining the kind of light to
adopt.
If gas is used for illuminating a cylinder, it is necessary to have its
pressure always 1 Ib. or 2 Ibs. above the air-pressure in the column ;
the pipes should therefore be of extra strength, so as to obviate the
possibility of their breaking, which would probably cause an explosion.
A gas pump is sometimes used for obtaining the necessary pressure.
At the St. Louis Bridge the gas tanks were filled with water from an
artificial reservoir having a head of water always slightly in excess of
the caisson pressure. Into these tanks the gas was discharged from small
cylinders under a pressure of 225 Ibs. The immediate effect was to force
the water from them back into the reservoir until the tank was full, when
the supply was stopped. The pipes leading to the caisson remained opened,
and the gas passed through them under the pressure due to the artificial
head of water. By means of glass gauges the contents of the tank
could be watched to be replenished as often as necessary. The gas
tank was placed below, in the air-chamber, so as not to require building
up as the caisson sank. If the gas is pumped directly into the tank,
the stroke of the pump creates an unpleasant jumping of the flame. As
danger will arise from leakage of the pipes, and from leaving any cocks
open, the lighting should be carefully supervised. The sense of smell
under compressed air is greatly lessened, and leakage is not easy to
detect.
At the St. Louis Bridge the gas burners kept the temperature below
at 80° to 85° F. Gas was found to cost one-fifth of the calcium or
limelight, and about one-third that of candles ; it, however, produced a
considerable amount of heat, and vitiated the air more than candles. A
candle when blown out was instantly relighted for twenty times
successively, and a woollen garment quickly ignited if brought
momentarily in contact with a flame. Candles with fine wicks had only
5 per cent, increased consumption at a pressure of 46 Ibs. per square
inch, but a cotton wick in alcohol no less than 200 per cent, at the
same pressure. The alcohol wick flame, instead of being blue, changed
to a white colour, giving three-fourths as much light as a coach candle.
The relative cost of candles as compared with alcohol was as
1 to 2. In the East River Bridge caisson, after reaching about
20 Ibs. pressure per square inch, the gas lights smoked very
90 CYLINDER BRIDGE PIERS.
badly ; the cause of the smoke was deemed to bo a lack of
ventilation of the flame, or circulation of air around it, the sixe of the
burners wad therefore reduced as the pressure increased, with the result
that there was but little smoke, less gas burned, and a better light. Mr.
F. Gollingwood, in a paper read before the Lyceum of Natural History,
U.S.A., stated that from numerous experiments on the burning of
/x"~3tearin caridLs when in compressed air, he found that " the amount of\
consumption at various pressures is approximately as the square roots !
\^pf those pressures," and a waste of one-third took place from flaring o^s*
the flame while in motion. The above rule shows the number of
candles that will be required at any depth, after the quantity wanted
has been determined at any other depth. General experience has
demonstrated that the electric light is the most suitable for the working-
chamber of cylinders, and that it should be used in preference to any
other yet devised, as, when properly arranged, it has invariably given
satisfactory results. The portable lamps are most useful for this
purpose ; however, great care should be exercised to prevent the men
being placed in darkness from any cause, as accidents may then arise,
and it is therefore advisable to have a light or lights continually burning
entirely independent of the electric illumination. In caissons it has
been found that a few arc-lights are not so suitable as a considerable
number of small 16-candle glow-lamps placed around the caisson,
chiefly because the height of the working-chamber is insufficient to
allow of the effective diffusion of light. The impediments that have
been experienced in adopting the electric light in caissons and cylinders
have been chiefly confined to the difficulty of preserving the insulation
of the wires, and keeping the lamps free from dirt and moisture.
CHAPTER XV.
EXCAVATING AND DREDGING APPARATUS FOR REMOVING THE EARTH
FEOM THE INTERIOR OF A CYLINDER OR WELL
IT may be said that the excavating or dredging apparatus has to per-
form the most important part in cylinder sinking, for without an efficient
means of removing the earth from the interior of a cylinder the latter
cannot be sunk to the required depth ; it is therefore a matter of much im-
portance to employ the best machinery for the soil that has to be excavated
and raised, as each kind of earth requires a cutting and disintegrating
apparatus that has been specially designed for it in order that it may be
EXCAVATING AND DREDGING APPARATUS. 91
completely successful, and the point to determine is, what is the best
machine to use under the particular circumstances. Some of the
advantages and disadvantages of using the compressed-air system for
sinking cylinders have been referred to in a previous chapter. A few of
the advantages of sinking cylinders by means of dredger apparatus
are now given : —
1. The hours of labour need not be reduced and are not regulated by
the depth of the foundations below water-level.
2. There is no danger to the men, and no liability of sudden and
fatal accidents occurring.
3. The comparatively small cost of the dredging apparatus.
4. No air-lock and working-chamber are required, and the cylinder
need not necessarily be made air-tight.
5. With the exception of the dredging apparatus and lifting machinery
no other special plant is required.
6. Less skilled labour is necessary.
7. Provided the dredging apparatus is adapted for the earth to be ex-
cavated and raised, it is independent of the depth of the foundation
below water-level.
8. The cost of working does not increase according to the depth, for
a dredger-excavator can be efficiently employed at any ordinary depth
with but little additional expense, that being principally due to more
time being occupied in raising and lowering the apparatus and conse-
quently to the fewer lifts that can be made.
9. Its portability and easy erection.
Some of the disadvantages may be considered to be : —
1. That as the foundations cannot be inspected in the open air when
the excavation is completed, and only by divers, or by means of a diving-
bell, it cannot be known whether or not the whole area of the base is
equally supporting the hearting of the cylinder.
2. That it is by no means easy to excavate the soil equally over the
whole internal area of a cylinder, and when the action of "the grabs or
buckets can only be in the same perpendicular line, the soil may not be
sufficiently loose to fall equally around a central hole made by the ex-
cavator, consequently, should the ground not be of the same character,
the cylinder may become inclined. Means will, however, be named by
which this may generally be prevented.
3. Unless the interior of the cylinder is so arranged that nothing can
be caught by any projections, the grabs or buckets may be held, and
the dredger have to be broken or abandoned from this cause, but it is in
great measure preventable.
4. The difficulty of excavating close to the cutting edge, especially in
cohesive soils such as clay, and sufficiently near to it to cause the earth
92 CYLINDER BRIDGE PIERS.
to fall into the central hole, or become loose enough to be excavated
and raised by the dredger-grabs or buckets.
5. The tediousness and difficulty of removing unexpected obstructions
such as tree-stumps, large boulders, or masses of conglomerate, and the
then perhaps necessary employment of the compressed-air system,
either by a diver, diving-bell, or by an air-lock, etc., so as to disintegrate
the obstruction sufficiently to enable the excavation to be raised.
6. The difficulty of excavating cohesive soils by dredgers, also clayey
silt, and compact sand and gravel, which latter, however, have seldom to
be excavated except in seams. NOTE. — Some means will be named by
which this difficulty may be much lessened and perhaps entirely
avoided.
7. The heavy strain on the hoisting apparatus and wear and tear
of the buckets and grabs, consequently the latter especially should have
as few parts as practicable, and those that come in contact with the
soil should be additionally strong.
Most of the principal advantages and disadvantages of dredger
machinery for excavating and raising the earth in the internal area of a
cylinder having been named, reference is made to some of the chief
points to be especially considered in grab or bucket-dredger machinery
to be used in cylinder sinking.
1. It should excavate the earth over the whole internal area of a
cylinder, or nearly so, and not be dependent upon the soil around a
central hole falling into it.
2. The grab or bucket should easily enter the ground, and sufficiently
to cause it, when closed, to be full of earth, and it should shut tightly
and readily, either pushing in or out any boulders or lumps of material.
3. Very little or no earth should be washed away or drop out during
the operation of raising or hoisting a bucket or grab through the water.
4. As little water as possible should be raised to the surface with the
excavation.
5. The grab or bucket should readily discharge its contents, and not
require to be cleared.
6. It should be simple in construction, with as few parts as possible,
be not liable to get out of order, be easily repaired, and occupy a com,
paratively small space.
7. Special provision should be made for extra strength in any closing
chains and in the bucket edges.
8. Any grab or dredger designed to excavate the earth under the
cutting ring should be capable of doing so under its whole area, so that
no lumps remain to be removed by divers, if they will not fall into the
central excavation pit, or any hollows that may be formed between
them.
EXCAVATING AND DREDGING APPARATUS. 93
9. Preferably, no special lowering or lifting apparatus should be
necessary ; but it is well to remember that such a quality may only
be obtained by a sacrifice of efficiency.
10. The arms or bent levers, which, on being moved, cause the grab
to excavate and hold the material, should not when opened project much
beyond the grab edges, in order that the scoops or grabs may penetrate
and excavate nearly the whole horizontal area over which they extend
on being lowered.
11. It should not require the constant removal of heavy plant when a
ring of the cylinder has to be added.
12. It should so perform the excavation that, as nearly as practicable,
only the net cubical contents of the subterranean portion of a cylinder
have to be removed ; and it should not disturb the surrounding earth or
cause " blows " or " runs " of soil, and so probably prevent vertical
sinking.
These may be stated to be the chief requirements, but there are
others that have to be considered, and they will be named. Here it is not
intended to describe in detail or illustrate the various machines that have
been introduced for the purpose of excavating the earth in a bridge-
cylinder well or caisson, as most of them have been illustrated and de-
scribed in the various engineering journals and the Minutes of Proceed-
ings of the Institution of Civil Engineers and other scientific societies, but
to comment upon some features to which attention should be directed in
almost all such machines and the soils for which they are considered to
be especially adapted. It would be most difficult to say which is the
best grab or bucket-dredger. Some are more suitable for one kind of
earth than another, and for comparatively little depths. For consider-
able depths it would appear that those actuated by a strong central rod
are to be preferred to those having looser means of opening and closing ;
and those which occupy, when fixed for descending, the least area and
have the simplest and most direct-acting parts should have the prefer-
ence.
From a study and analysis of many cases in which various kinds of
buckets and grab-dredging machinery have been used in bridge
cylinders and well foundations, almost all have been suocessful when
applied under the circumstances for which they were intended to be
used ; the chief difficulties to be overcome are those of penetration of
the scoops and equal excavation over the whole internal area of a
cylinder or well. When the material to be excavated and raised is
loose soil, there are many kinds of most efficient bucket-dredgers actu-
ated by chains, rods, bent levers, etc., the scoops acting on stationary
pivots or by means of other devices having one combined object,
namely : easy descent, penetration, gathering up, perfect closing, and
94 CYLINDER BRIDGE PIBR8.
gentle raising of the excavated material without allowing any earth to
fall over the sides of the bucket or grab. For considerable depths, and
in cohesive or hard compact soil the most certain plan of action, and
one that will seldom fail, appears to be to first sufficiently disintegrate
the earth by a separate apparatus, so that it can be expeditiously
gathered by a bucket or grab, rather than to proceed by attempting to
excavate, collect, and raise the material by one machine at one operation,
which may be ineffectual unless divers can be sent down to loosen the
earth ready for the grab or bucket to lay hold of and raise it. By first
separating the soil into sufficiently small pieces so as to be readily
gathered and raised to the surface by the grabs or buckets, any time
occupied by the first operation will be soon compensated by increased
speed and certainty of action, and by the dredger being full or nearly
so when it is lifted, instead of, as frequently is the case, only partly
filled. For removing boulders, cohesive or hard compact soil, the
ordinary dredger-buckets have too much surface to readily penetrate the
earth, and may be unable to do so, and a dredger is required that will
plough the soil. Sand also under a considerable head of water may be
difficult to penetrate with ordinary scoops, and in clayey or sandy silt
the scoop may not bite or enter it sufficiently to cause the bucket to
gather its proper quantity of soil, for it then often merely scrapes the
surface, its powers of penetration being insufficient to enable it to grasp
the earth.
Apparatus which may fail when unassisted, if aided by heavy jumpers
and sharp cutters will often remove earth of the usual description met
with in cylinder sinking, but generally simple quadrant bucket-dredgers
are ineffective in clay, tenacious, or moderately compact soils. If it is
found that the dredgers will not make their own holes, or enter the
ground, which they may not do in silt, sand having boulders in it, or in
clay, cutters or jumpers can be used. However, the boulders may be too
large to be moved by a dredger and too hard to be broken sufficiently
small by machinery working from a height in water ; it may then be
necessary to adopt the compressed-air method of sinking ; but divers
should be tried first, although excavating by means of helmet-divers is
not economical. On the Continent the tendency of late years has been
to abandon the dredger-system and adopt that of compressed air ; but
there is no reason, except the requirement that the foundations must be
laid dry, so often decreed in Continental specifications, and unless serious
obstacles are expected to be encountered in sinking, why it should be
renounced in favour of the compressed-air method, as great improve-
ments have lately been introduced in dredger-excavating machinery. If
obstructions, such as debris and large boulders, or other obstacles, which
cannot be readily broken by helmet-divers, are not likely to be met with
in sinking a cylinder, and if the column cannot be readily kept dry,
EXCAVATING AND DREDGING APPARATUS. 95
excavating the soil by machinery under water is the cheapest method to
adopt.
When the compressed-air system is used in sinking, or the excavation
effected by divers, ordinary excavating tools can be employed, but no
expense should be spared to procure the best, most efficient, and expe-
ditious tools that can be obtained, as any extra expense thereby incurred
will be quickly saved by the work being accelerated. Consequent upon
the short hours men can work in compressed air, or in a diving' dres^,
every effort should be made to economise their labour, as the actual
working time may be as little as one-thirteenth of the usual hours under
ordinary circumstances, and the wages considerably higher.
The means of lowering, closing, and raising bucket and grab-dredgers
have been well considered, and it is in the direction of increased
efficiency of the cutting and breaking-up apparatus so as to feed the
buckets and grabs, and cause them to become quickly and easily filled,
and the earth excavated over the entire internal area of the cylinder to
prevent any additional cutting of the earth from underneath the bottom
ring, that the greatest scope for improvement exists ; but, as has been
before stated, experience appears to point to the advisability of an
effective first use of the cutter and jumper tool to disintegrate the
ground, and a grab or bucket-dredger to raise the loosened soil, rather
than to attempt to effect too much with the grabs or buckets and so
court failure in cohesive soils and those difficult to penetrate ; whereas
by a combination of the two systems success will be almost certain.
It is impossible to be sure that logs, boulders, or tree trunks will not be
met in such variable soil as the beds of rivers, therefore in cylinder
sinking it is an advantage to have an apparatus ready in a few minutes
to break up any such obstruction should the work of the grabs or
buckets become unsatisfactory ; however, if the trunk of a tree or
a boulder be encountered, probably the quickest and most effective plan
is to send down a diver to direct the cutters or jumpers, and so shatter
the boulder, or by sawing, axing, chipping, barring, and by chains being
placed round the trunk, to pull it into the cylinder, and so enable it to
be raised.
Almost every kind of earth requires a specially shaped tool, grab, or
bucket, and the suitability of the form and capacity of the dredging
apparatus causes it to be successful or to fail, and entirely different
results will be obtained when these points are carefully considered. As
it is seldom certain that no hard or tenacious soil will occur in sinking a
cylinder, it is important in selecting a dredger-excavator for such work
that it be adapted to excavate and raise any such stratum, and the
question should always be initially determined whether a cutter or
jumper shall be employed simply for breaking up the soil and a dredger
for raising the material. When a cylinder has to be sunk to a moderate
96 CYLINDER BRIDGE PIERS.
depth and there is every probability of the soil being comparatively loose,
a bucket or grab-dredger may be sufficient ; but if the depth to be sunk
is considerable, say more than about 40 ft., and a hard stratum is
expected to have to be excavated, experience seems to indicate that it is
better to disintegrate the hard material independently of a dredger, and
only use that for collecting and raising the loosened earth, as then the
soil can be easily penetrated, and operations are likely to be successfully
accomplished without delay, while attempting to thrust a bucket, scoop,
grab, or spade-dredger through tenacious clay or hard soil may not only
be ineffectual but result in breaking the apparatus, for pronged spades
are liable to be bent, turned up, and broken ; therefore, as a precaution
against injuring the forks, it is advisable to first disintegrate the soil
with jumpers or cutters, or to send down divers to effect that operation.
When the force with which a dredger can be dropped into the soil is
simply that of its own weight falling tbrough a certain distance, it is
obvious, bearing in mind the extent of the cutting edges of the bucket,
that a sharp-pointed jumper or chisel having a penetrating area of, say,
less than 1 sq. in. must have a greater power of penetration than that
of a bucket blade, whether serrated or not, having a continuous flat or
inclined edge, which, although pointed, has a thickness of f or £ an inch
and a length generally exceeding 18 in. ; and if a small boulder should
happen to get under the cutting edge the apparatus is likely to tilt and
become ineffectual.
The defects of dredgers for undercutting the curb are that they do not
do so equally under the whole area of the curb or cutting edge, conse-
qn mtly, short pieces of earth remain between those portions excavated,
which induce " blowing " or " running " of the soil. These lumps of
earth have either to be excavated by divers, to be undermined, or left
unsupported in such a way that the central excavating hole can be
deepened sufficiently to cause the remaining pieces to slip in, a system
which is not conducive to eith?r economical, quick, regular, or vertical
sinking. This is one of the chfef difficulties with scoop-dredgers, as
many can only with certainty bo lowered in and near the ce.itre of a
cylinder or well, consequently in any cohesive soil a hole like an inverted
cone is excavated, and as the sides do not readily fall into it, unless the
hole is filled by other means, the quantity dredged at each lift is very
small, and progress necessarily slow and uncertain.
It not unfrequently happens, even when the dredger appliances are so
successful as to eqaally excavate the material over almost the whole
internal area of the cylinder, that it refuses to sink notwithstanding
additional weighting, and that it is necessary to excavate under tho
cutting ring of the cylinder or permanent ring of the hearting used ay
kentledge, or the curb, if the well system is used. When the under-
cutting apparatus fails, divers must be sent down to disintegrate the
EXCA.VATING AND DREDGING APPARATUS. 97
material under the cutting ring or curb, and cause it to fall into the
central hole. In clay, if the dredger apparatus only breaks up the earth
for a portion of the area and leaves a wall of 2 ft. or 2 ft. 6 in. in
thickness, it will generally not fall into the excavated central hole unless
it is disturbed or separated, and therefore the cylinder will not continue,
to sink. In either a cylinder bridge-pier or caisson any internal staging
or timbering should be so arranged that the excavation can extend to
the edges of the rings, so that it is not necessary to employ divers to
shovel the earth towards the centre in order that the dredgers may
gather and raise it. An instance may here be mentioned of the difficul-
ties caused by the excavation being effected over but a small portion of
the area of a caisson. At the Poughkeepsie Bridge, U.S.A., the founda-
tions of which are 124 ft. below high water, and were reached when
mud, clay, and sand had been excavated, and rest upon strong gravel
overlying rock, an open grillage of crib work was used for getting them
in, it being divided into pockets or cells from which the material was
excavated by dredging. The cribs were 104 ft. in height, and the top
finished 20 ft. below water. The cribwork was built on the shore and
towed out. It was divided into weighting and dredging pockets.
Fourteen dredger-cells were simultaneously worked, but their area only
amounted to one-fourth of that of the crib, therefore considerable
masses of earth were left under the cutting edges, and consequently the
wells or dredge-cells were often carried 30 ft. below the base before the
crib would sink, and the sinking was irregular; sometimes the crib went
down suddenly 10 ft., and did not then descend vertically.
With respect to buckets or grab-dredgers, cases have occurred in which
it was found that although the buckets were suitable for loose silty soil,
they were too large and blunt for pure sand, although it could be easily
excavated ; and also that in compact and viscous silt the form that is
effective in loose soft silt is unsuitable, it being necessary that the
bucket edge be more pointed so as to enter the earth and not merely
scrape it, and also discharge more easily the soil on the bucket being
tipped.
Opinions are somewhat divided as to the relative merits of dredgers
of large and small capacity ; however, in a large dredger the weight of
the excavator is less in proportion to that of the material raised than in
the case of a small bucket or grab, thus in a very large excavator its
weight may be as little as 0*75 of that of the earth lifted, whereas in
the small dredgers it may vary from 1*2 to 1-7 time the weight of
the earth, therefore in proportion much more dead weight has to be
raised each time, provided the large dredgers are always full, which
point has been previously referred to in this chapter. A dredger of small
capacity can excavate at almost any point in a cylinder, and is generally
raised full, whereas large dredgers are liable to be nearly empty. On
H
98 CYLINDER BRIDGE PIERS.
the other hand, in small cylinders, their capacity being as little as 2 to 3
cub. ft. instead of £ or f of a cubic yard or more, an additional number
of lifts have to be made, but the large machine can only act near the
centre of a cylinder, and when a " run " of soil occurs, the hole dredged
by it being generally much below the level of the inflowing soil, the
apparatus becomes buried, considerable delay is caused, and perhaps the
machine is broken. Under similar circumstances the small dredger can
be readily abandoned or pulled up as desired without interfering with
the working of other similar dredgers in the cylinder.
It is usually a serious matter when large grabs are caught in a
cylinder, for work is then entirely suspended ; but by having no projec-
tions or abrupt internal bends or splays, these accidents may be avoided
to a considerable extent, therefore a variation in the size of the interior
of a cylinder is a disadvantage in using dredger machinery. When the
dredging apparatus is light, and fresh rings are added to the cylinder,
no heavy hoisting machinery has to be removed and replaced ; however,
if there is independent staging, the lifting apparatus can be so arranged
as to allow of fresh lengths of the cylinder or well being added without
affecting the machinery for raising the grabs or buckets. Perhaps in
cylinders of small diameter the best plan is to have two sizes of
dredger-grabs or buckets, the smaller holding from as little as 2 to 4
cub. ft., and the larger 7 or 8 cub. ft. or more, according as the size of
the cylinder will permit, duly taking into consideration the depth
below water, the size of the cylinder, the nature of the soil to be
excavated, and all other circumstances. In a 6 ft. in diameter free
working space, a 7 to 8 cub. ft. capacity of the dredger, grab, or bucket
will probably be as large as can be conveniently worked, its dimensions
being increased as the available open area allows of easy operation-
Experience seems to indicate that a larger capacity than about f of a
cubic yard is of doubtful economy and efficiency in cohesive soil, because
of the difficulty of penetration, in brief, the capacity of the buckets will
be governed by the diameter of the free working space in the cylinder,
and the nature of the soil, but the bucket and grabs are usually made
to contain from £ to 2 tons weight of excavated material, and most
frequently between £ to 1 ton ; and at moderate depths as many as
fifteen grabs may be made in one hour, but Messrs. Bruce & Batho's
dredgers have successfully worked with a capacity of 5 cub. yards.
Much depends upon the lifting power available, for the larger the
capacity of the dredger and the more cohesive the earth to be excavated,
so will the power of the lifting apparatus require to be increased. The
excess of power advisable to employ may be as much as three times the
weight of the excavation to be lifted, for the weight of the dredger has
to be raised, and the excavator has to pull out the ground with it, so
the force required, in addition to friction, etc., is to some extent
EXCAVATING AND DREDGING APPARATUS. 99
dependent upon the tenacity of the earth. Although the full bucket
capacity of material may be occasionally raised in a dredger, from one
cause or another it is not prudent in cylinder sinking to rely upon more
than about half the full contents as the result realised in continuous
work performed by ordinary labour.
Some hard and stiff material, provided it will break in lumps, can be
excavated by dredger-grabs when the apparatus used is specially
designed for that purpose, but in tenacious clay and concreted or solid
gravel, i.e., with the particles joined by a cementing substance, or in
very compact firm sand, it is advisable to first separate the soil with
cutters or jumpers, and this may be absolutely necessary. Most bucket-
dredgers work well in loose sand, but when clay and compact soil are
encountered, they are usually not so successful. However, it is
generally agreed that the shape of the dredger causes the success or
failure of the apparatus. Simple bucket or quadrant-dredgers have
been incapable of excavating a soil, but when a prong was added, and
the cutting edge of the bucket was of a suitable shape for penetration,
it would excavate the ground. An instance may be here referred to.
In order to prevent a grab-dredger refusing to excavate below a certain
depth, and to ensure that a sufficient distance in the ground was
penetrated to cause the earth to fill the grab when it was closed
ready for raising, Mr. W. Matthews, M.Inst.C.E., had a few prongs
about 1 ft. in length riveted on the outside of a grab-bucket, with the
successful result that it descended to any required depth, the prongs
loosened the ground, and the bucket collected and raised the earth as
desired.
Although grab-dredgers do not excavate quite so evenly as bucket-
dredgers, it is seldom they so unequally do so as to cause inconvenience.
In boulder or pebbly soil, consisting of loose stones and silt, sand, or
sandy gravel, stones are liable to become fixed between the quadrants,
and also between the teeth of the grabs, and then the smaller material
falls out, and although the excavating operation is successful the lifting
is not so, as much of the material is dropped. Grab-dredgers are not
designed to be driven into the soil by a ram falling upon them, but, as
their name implies, to grab or lay hold of the earth on being lowered.
The best grab-dredgers are so framed as to penetrate the soil on the
lifting chain being drawn up, even when the grab is gently lowered
upon the ground, its weight being sufficient to cause it to enter the
earth. The single bucket and clam-shell dredgars succeed in loose
material having separate particles, but they are not adapted for firm
clean sand or hard tenacious earth, or clayey silt, or soil that possesses
some tenacity and viscosity although comparatively liquid.
In considering the dredger-bucket or grab, its size when opened for
descending, its power of penetration and excavating, capacity, easy
ii 2
100 CYLINDER BRIDGE PIERS.
raising, and also the unaided discharge of the lifted material have to be
considered. Buckets that will freely discharge clay and viscous earth
of all kinds are to be preferred, if not lessening the general efficiency
of the apparatus, to those requiring a man with a bar to free the soil
from the raised bucket. Experience has shown that large buckets
discharge the contents more freely than those of smaller capacity, and
that the bucket shoul 1 taper horizontally and vertically according to the
nature of the material to be discharged, and not have parallel sides. In
a case where there was great difficulty in discharging the material from
the bucket, the backs were made movable so as to throw out the
soil. The shape of the bucket when ready for raising should be
such that it will be filled entirely with earth and its contents be raised
without loss, and holes in the buckets should allow of the escape of any
water so that as little as possible is lifted with the earth.
In bucket-dredgers or excavators the wear of the closing-chains and
the edges of the buckets is considerable. All working parts should
therefore be of the strongest material and steel be used in preference to
iron. In the best dredger-excavators all holes are bushed, and the pins
and bushes made of case-hardened steel, the arms, sliding collars, and
the plates, etc., being of cast steel. Some special features of bucket
and grab-dredging apparatus may be thus described: — The buckets are
made of double-riveted steel plates having heavy replaceable steel jaw
plates. Clay-grabs consist of bent prongs, and form a combined bucket
and grab, in which the prongs fit in between each other ; their upper
part is an ordinary close bucket, the idea being to enclose the looser
material in the top portion of the bucket. As the clay becomes more
tenacious the distance between the prongs is increased, there being as
many as twelve or so in a combined bucket and grab for excavating
and raising loose and soft material, nine or ten for shingle and earth
that can be raised in lumps, but for hard clay soil only four or five
prongs in the same length of grab-bucket. In fine sand, difficult to
penetrate, the prongs or tines are fixed tightly together, or the bucket
has a serrated edge. For boulders and hard lumpy soils the prongs are
strengthened by a bar riveted on each side at a distance of about two-
thirds of their length measured from their points.
In bucket-dredgers, it would appear that when the blades of the buckets
are of spear or V form, there is considerably less chance of their tilting
than when they are simple quadrants, but buckets of segmental form
are much steadied by outside prongs being fixed as previously described.
Some of the most important and practical improvements in dredger-
excavators are those of Messrs. Bruce & Batho. 1. The introduction of
buckets shaped so that they present a pointed cutting blade, and form a
hemispherical bucket when closed, which may be familiarly described as
half an orange, instead of a semi-circular bottom with two flat sides.
UNIVERSITY
EXCAVATING .AND DREDGING APPARATUS.
Thus four pointed bladf ri are in simultaneous operation to disintegrate
the soil instead of two flat quadrant bucket edges. 2. One pair of
blades being larger than the other, they excavate a greater area than
the other two, consequently the excavator does not fit into the hole pre-
viously made. These are important improvements, as the power of
penetration is much increased and the central hole difficulty is prevented,
two of the principal drawbacks in dredger-excavators for cylinder-
bridge piers.
A slight change in the nature of the earth to be excavated may make
all the difference in the working of the dredging apparatus, for instance
grab-buckets have succeeded in excavating and raising hard quartz sand,
which had round grains, but were not so successful when the sand had
flat and pointed grains, as the particles became wedged and were conse-
quently riot easily penetrated or separated in their natural position. For
excavating close to the cylinder rings in soft soil, and at small depths, a
bag and spoon-dredger is very useful, as it cannot injure the rings or
become jammed, and if it breaks, it is not a serious obstruction. It
can either be worked by hand or by a small steam engine on the
staging.
A question to be considered is how many cubic yards of earth can be
taken out of the cylinder in a working day. The quantity of soil to be
removed is generally much more than the contents of the subterranean
portion of the cylinder, and according to the excess of material so will
be the disturbance of the outside earth, which will usually assume the
shape of an inverted cone, the base being at the level of the bed of the
river. In soft soil, in addition to the expense of excavating the excess
of material, there is the danger of the cylinder being for some time
feebly supported laterally, until the earth has become consolidated,
which, however, may be prevented by scour ; therefore, care should be
taken to preserve the external bed of the earth in order to prevent
" runs " of soil in the cylinder, and to reduce the required excavation as
near as possible to that of the cubical contents of the subterranean
portion of the column. When obstructions, such as logs and trunks of
trees, have occurred in loose soil as much as three to four times the
contents of the cylinder have been necessarily excavated, but this may
be considered an extreme case. Means have been named by which the
outside surface disturbance of the river-bed may be lessened or pre-
vented, and a method that might be frequently tried with little expendi-
ture is that of hardening suitable soil by injecting into it liquid
Portland cement. The area of the base that can be excavated by a
dredger should be compared with the total area of the cylinder, so as to
ascertain the width and mass of material left around and under the
cutting edge by the excavator, for the extent of this strip will influence
the speed of the excavating operations, and the smaller it is, the quicker
102 CYLINDER BRIDGE IMF.RS.
the removal of the earth and vice versd. It is advisable to have a large
and small dredger or some means of excavating close to, if not under,
the cutting ring in case of necessity.
With regard to the hoisting apparatus, it should be effectively worked
at any depth, in order that there may be no limit to its operation. To
mention in detail the hoisting apparatus that might be used would
cause reference to almost every known kind of lifting machine, and it
will here suffice to state that it should be simple ; should quickly raise the
dredger apparatus at an even speed and without jerking, or some of the
contents may be lost, and the dredgers be raised partly empty ; it
should have sufficient power to pull up the grab or bucket when it
penetrates the earth, so that it may be completely filled ; it should be
as light as possible consistent with the required strength, for it has to
oe raised at each lift ; it should be removable ; and, if it can be so
arranged, not necessarily fixed on any staging that rests upon or is
supported by the cylinder rings, so that on fresh rings being added it
need not be removed ; and it should not in working have any tendency
to pull the cylinder towards the source of power, and so perhaps be the
cause of the column not sinking vertically. Derrick-poles fixed on
staging, entirely independent of the cylinder, have therefore been used
so as to comply with the last two conditions, the excavation being raised
by a steam hoist.
In some examples of river bridge foundations sunk by compressed
air, a tube, projecting beneath the cutting-ring of the column, has been
inserted in the cylinder, an adjustable dredging-machine working in it,
t'ie bottom being sealed by the water, and the earth being raised
by the dredger. The material to be removed by dredging-machinery in
such a tube must be pushed under the lower edge of the shaft into the
pool of water underneath it, which must always be maintained, in order
that the dredger may be properly fed and no air escape. At the Forth
Bridge the hoisting of the material was done by a steam engine fixed
outside the air-lock, and working a shaft upon which there was a drum
inside the air-lock. By means of a stuffing-box passing through the air-
lock roof, there was no escape of the compressed air.
At the St. Louis Bridge, to facilitate the excavation in the caisson, an
extra tube was inserted in the centre, and down to the level of the
bottom of the air or working-chamber. The water in the tube was at
the same level as in the river, and in the pipe an endless chain, with
dredger-scoops attached, rotated round pulleys at the fop and bottom of
the tube. Thus the sand was raised without the escape of air from the
chamber, or passing the material through the air-locks. The men in the
working-chamber shovelled the material to the bottom of the tube,
which vTas in the water, where the dredger-scoopB took it an(J dis-
charged it at the top of the caisson. Somewhat similar apparatus was
EXCAVATING APPARATUS. 103
proposed by Mr. Wright in 1852 to be used at the Rochester Bridge
foundations, Kent.
At Chicago, dredging apparatus was fixed upon a traveller on the top
of the cylinder, and upon the platform of the traveller was a carriage
for removing the material ; the frame- work being adjustable, so that the
sand could be dredged to a depth of 6 ft. below the bottom of the
cylinder. The excavating-machinery consisted of two endless chains,
on which were placed fourteen iron buckets, each of about a capacity of
f of a cubic yard. The buckets were driven by a small portable engine
fixed on a traveller. This brickwork-in-cement cylinder was 31 ft. 6 in.
in internal diameter, and was sunk through 20 ft. of quicksand down to
solid clay.
The discharging spouts of dredging-machinery have been arranged in
the following manner : — The buckets delivered the sand into a mov-
able spout worked on a cam, so that the spout was brought forward to
receive the contents of a full bucket as it mounted the top ; the spout
was then drawn back, so that the empty bucket passed down clear. At
the new Prague-Smichow Bridge, the excavated material was emptied
from the dredgers into a shallow tray, having a lateral automatic motion
communicated to it by an arrangement of cranks and levers, and was
thence discharged into chambers, of which there was one on either side
of the air-lock, fitted with inlet and outlet sliding doors, from which it
was again removed, the outlet door being closed when the inlet was
opened, and vice versa. These doors or valves were actuated by vertical
rods passing upwards through stuffing-boxes and worked by manual
power from a platform above and outside the air-lock. At the bridge
over the Ticino, at Sesto Calende, Italy, the sandy clay excavation in
the cylinder was removed in wrought-iron buckets holding 0'39 of a
cubic yard each by a small three-cylinder engine, worked by compressed
air, placed above the air-lock, the material being discharged through a
pipe having suitable doors.
CHAPTER XVI.
NOTES ON SOME DREDGING APPARATUS USED IN SINKING BRIDGE
CYLINDERS AND WELLS.
WITH respect to the different apparatus generally used for removing the
internal earth from a bridge cylinder or well, a few notes of a practical
character are given under the head of each machine.
104 CYLINDER BRIDGE TIERS.
BAG AND SPOON DREDGER. — This is -very useful for mud, soft and
loose soil, if comparatively small quantities of excavation have to be
removed, and for clearing trenches for cofferdams, the site of piers, the
corners of caissons, or in any situation where a narrow trench has to be
dredged in such soil, and also for excavating close to the cutting-ring
of a cylinder. It may be used where grab or bucket-dredgers may be
either impracticable or unsuitable. If used in firmer soil than silt and
mud, instead of the ordinary bag, forked spades can be fixed to the end
of the long handle. The excavation at the Victoria Bridge, London*
Brighton and South Coast Kailway, was conducted in the following
manner. The bed of the river was levelled by bag and spoon dredgers
before the cylinder rings were pitched, then the excavation in the
column was effected by the same means until the clay was reached,
when the water was pumped out, and the excavation carried on in the
open air. At the Charing Cross Bridge, South Eastern Eailway, the
bed of the river over the site was levelled by dredging, a sufficient
height of rings of the cylinder were then pitched so that the top reached
above the water level, a bag and spoon dredger was used inside the
cylinder, and the mud and gravel so excavated until London clay was
reached ; the water was then pumped out, and sinking conducted by
ordinary open excavation. The bag and spoon dredger was found to be
a better system to use, in many ways, than excavating by helmet divers.
INDIAN JHAM, OR HOE-SCOOP WITH HANDLE. — This machine has been
very largely used in India, and is occasionally employed in loose sand
for small depths. For dense sand the scoop is made of thin plate-iron,
eo as to penetrate the ground. It is not well adapted for depths
exceeding about 25 ft. The process is slow, and only economical at
depths at which the bag and spoon, the earliest system of dredging, is
applicable. At the bridge over the Ems at Weener, the excavation was
done by steam-dredger, hand-dredger, and Indian scoop. This last,
2 ft. 1 in. by 1 ft. 7 in. by 7 in. in dimensions, was attached by a hinge to
a vertical guiding rod, and was dropped, edge first, into the sand to be
dredged, being pressed down by a man standing upon a step attached to
the rod. It was then wound up by a crab. By 140 lifts from a depth
of 13 ft., it excavated 9 cub. yards a day, the cylinder being 13 ft. 1 in-
in external diameter, and sinking 1 ft. 8 in. Although the steam
dredger was somewhat cheaper in its work, the scoop was preferred
because it excavated round the edges of the cylinder so much better,
and the columns consequently sank more evenly than when the dredger
was used. In the large cylinders of 18 ft. 4 in. in external diameter,
a steam-dredger and two scoops were worked together, excavating
15| cub. yards per day.
STEEL POINTED RAMMER FOR ROOK OR CONCRETED SOIL.— The steel
pointed ram system of excavating rock under water, introduced by Mr.
EXCAVATING APPARATUS. 105
Lobnitz, of Renfrew, in which in soft rock the points of fhe rock-
cutting rams become automatically, through work, at an angle of
\y and in hard rock \Y , and remain at those angles, has been used
with success on the Suez Canal for breaking up rock for dredging. The
rods were placed in a frame and allowed to drop about 18 ft. They
weighed four tons each and were about 40 ft. in length, and were
hoisted by a chain and let fall. This method might be used in cylinder
sinking to break up a hard stratum, or an obstruction, as its object is to
dispense with blasting, and to shatter the rock, etc., under water without
inspection of the surface.
STONE'S CHISELLED-RAIL JUMPER, used on the Delhi Railway. — It
was composed of rails chiselled at the lower end to a point, fished
together to make any required lengths. It was raised by a crab engine,
or by manual power, to a height of 8 to 10 ft. and dropped, and was
used in stiif clay with great success for separating the ground in masses
weighing a quarter to three-quarters of a hundredweight ready for the
bucket-dredgers to raise the loosened soil. It was found that it pos-
sessed the great advantage of enabling the earth to be broken up over
the whole area of the cylinder or well, and the jumper could be guyed
and made by tackle to fall in any place.
Generally, the solid bar or rail jumper, pointed at one end, is sufficient
for shattering any soil likely to have to be removed in cylinder sinking,
except when a thin stratum of a very hard nature is encountered ; more
powerful means may then be required.
STRONG'S CEYLON GOVERNMENT RAILWAY EXCAVATOR. — This consists
of a cylinder 4 ft. in diameter and 2 ft. in depth. The bottom is divided
into 6 parts of equal length fitting on and within a circular plate, the
latter being 5 in. in width. Six equi -distant sharp-pointed bent picks
are attached by pins to bars actuated by a central rod. The apparatus
is heavily weighted and lowered so that the sharp points pierce the clay,
and when they are drawn up the material is raised. It is only intended
for clay and tenacious soil that can be raised in lumps.
GATWELL'S EXCAVATOR. — Grab-dredgers in boulder soil, that is, those
which in closing form a kind of bucket thus U, bave sometimes failed ;
for instance, at the bridge over the Sutlej, Indus Valley State Railway,
Col. Peile, R.E., the engineer-in-chief, stated that at a depth of 35 to 45
ft. a band of compact, intractable clayey silt was encountered which
resisted various ordinary dredgers and sand pumps. Chisels and cutters
of various forms, applied to the ends of heavy bars, were used to cut up
the surface, and divers were kept continually at work, but no progress
was obtained in the sinking for many weeks. Then Gatwell's excava-
ting apparatus was employed. Two blades were used for excavating
the earth in the cylinder, and once they brought up 30 cub. ft. of clay
106 CYLINDER BRIDGE TIERS.
at one lift ; and One for cutting under the bottom ring or curb. It may
be described as a combination of the Indian jham and the ordinary
dredger. It consists of two pointed scoops which penetrate the ground
on being lowered in a vertical position. On touching the ground a hook
becomes disengaged, and by hauling chains the blades are drawn apart,
and, in excavating the soil, assume a horizontal position under the earth
excavated, the nearly flat scoops being then raised. Prongs are also
attached to the apparatus for breaking up clay, and a side excavator is
used for under-cutting the curb. This latter consists of a kind of spade
bucket fixed to a long rail lowered vertically by a chain, a rope being
attached to it below the hanging chain, it is then pulled over to such an
angle that it will undercut the curb, and raised. The Gatwell excavator
does not close inwards, like the ordinary grab and bucket-dredgers, but
forms a figure when being raised resembling two trays $ 1 I A ,thus it
cuts from the centre outwards, the material being on the ledges A A,
which are slightly rounded, and no boulders can prevent it raising the
material. An advantage in working with this apparatus in cylinders in
silty soil is that as the shelves turn outwards and are level when ready
for raising, no silt or loose sand can run out owing to the buckets not
being closed tightly. They occupy slightly more room when opened
for lowering than the inwardly-raising bucket-dredgers. These excava-
tors have succeeded where some ordinary inwardly-closing quadrant-
dredgers have failed in clay soils, and are generally successful.
BRUCE AND BATHO'S EXCAVATORS. — The special features are that they
are circular on plan and hemispherical in form, having three or four or so
V-shaped pointed blades, and therefore can be used nearly of the same
size as the cylinder, and so excavate close to the cutting edge or curb,
thus avoiding any undercutting. They have been employed with a
central pole or tube, which forced the blades into the soil, applied at the
end of the jib of a crane which held the apparatus in the centre of the
cylinder in a fixed position, and have been used with success at a depth
of ISO ft. below water level. They are especially designed for pene-
trating hard and tenacious material, and are usually worked by a chain
in soft earth, and by a spear in hard soil.
FOTJRACRE'S DREDGER AND SPIDER CLAY-CUTTER. — The former has
been used successfully in India for dredging sand and mud. It consists
of two segmental dredger-buckets hinged to a cross-head and worked
by lifting chains. The spider clay-cutter for loosening clay and other
soil so that it can be removed by dredging, consists of six picks hinged
at equal distances apart to a central shaft ; each pick has a connecting
rod hinged to a boss placed about 3 ft. 6 in. above the hinged end of the
six picks. On a pile-driving ram, made to slide in the central shaft,
descending, the boss is driven down with the connecting rods, the picks
EXCAVATING APPARATUS. 107
are thus forced into the soil and break it up sufficiently for raising. The
six picks are extracted from the clay by pulling a chain attached to the
boss, and are so lifted.
MILROY'S EXCAVATOR. — This apparatus, one of the earliest designed,
has been largely employed ; it usually has eight ordinary spades for
mud, sand, and loose permeable soils, pronged spades being used for
gravelly earth, marly and ordinary clays. It has excavated clay to a
sufficient depth for the water in the cylinder to be pumped out. A 5 ft.
in diameter apparatus, 2 ft. 3 in. in depth, has raised If cub. yard at
one lift. At the Caledonian Railway Viaduct over the River Clyde at
Glasgow, where the greatest depth of water was 23 ft., and the
cylinders were 15 ft. in diameter, the soil penetrated was principally
sand, clay, and mud, with a few small beds of gravel ; the foundations
being 85 ft. below high water. A steel digger was used, weighing 3 tons
16 cwt., arranged somewhat like the Milroy apparatus. It had 12
blades, each heavily weighted on the back to assist penetration, and was
8 ft. in diameter, 15 in. in depth at the sides, and 22 in. in the centre.
The blades were attached to the centre of the digger by a system of
bars similar to the framework of an umbrella, and were drawn up by
four chains. The blades, suspended from a monkey hook, were sunk
in a vertical position, so that the moment they struck the bottom, the
hook was detached ; they were then drawn together and the machine
raised. The digger sank into the ground by its own weight. When
raised, the original hook was attached to the blades, which, on being
lifted, fell apart and deposited the earth in a waggon. In favourable
soil the average lift occupied five minutes, .and 1£ cub. yard was
raised. The digger frequently brought up boulders weighing from 7 to
8 cwt. each.
IVES'S EXCAVATOR. — Especially introduced for excavating in stiff clay
as well as all less cohesive soils. It is driven vertically into the earth
by a pile-driving monkey. The lower portion is hinged and forked with
six or more prongs, which penetrate the ground on the hinge-catch being
withdrawn, the prongs are pulled round till they are at right angles to
the vertical rod, and then the whole apparatus is raised. Instead of a
pronged fork, a scoop is used for loose soil such as sand. In recon-
structing some bridges on the Delhi Railway, Mr. Charles Stone,
M.Inst.C.E., stated it was found a perpendicular position was necessary
to give effect to the driving power, and it was somewhat difficult to
keep it vertical, and that the apparatus could not be lowered to work at
any great depth except in the centre of a cylinder, but this comment
applies to most excavators.
Among simple devices used for loosening clay may be mentioned that
employed at the Ravi Bridge on the Punjab Northern State Railway,
which consisted of a screw 9 in. in diameter fixed to a 2{ in. gas tube.
108 CYLINDER BRIDGE PIERS.
This was repeatedly screwed into the soil, and was successful in loosen-
ing clay so that it could be raised by the dredger-buckets.
At the Katzura Bridge, near Kioto, the foundation was compact gravel
and sand, and could not be raised by ordinary excavators. DIACK'S
EXCAVATOR was used. It consisted in a flange rail being hammered to a
point, and two iron bars of the same width as the web of the rail being
fixed to it by three bolts, and bent so as to form a quadrant of a circle
like a fishing net, the projecting length being about 2 ft., and the width
1 ft. 4 in. ; the bottom of one ring had a cutting edge, and to the other
five teeth were attached to loosen the gravel. Two canvas bags were
fastened by cords looped through holes in the bar. The required length
of shaft was obtained by joining lengths of rails by fish plates. The
apparatus having been lowered into position was worked round by man-
power being applied to a lever attached to the rail shaft. About | of a
cub. yard was brought up at each lift, and six to twelve lifts were
made in one hour.
At the Bookree Bridge, Great Indian Peninsula Railway, when a
hard conglomerate stratum of marl and gravel and impacted sand and
hard clay or marl was reached, bucket-dredgers would not penetrate it.
Mr. R. Riddell therefore employed a long vertical iron rake, the shaft
being made of old rails bolted together, pointed at the end, which sunk
into the ground at the centre of the cylinder. About 3 ft. above the
bottom a cross-piece armed with strong steel prongs was bolted, and the
rake was revolved by the capstan bars from the top. This apparatus
loosened the hard soil and enabled the dredger to lift the excavation.
There was no difficulty after the boulders, debris, and conglomerate had
been so disintegrated. When large stones were met, they were shattered
by divers with hammer and bar, and then raised in the bucket-dredgers.
At the Rokugo river-bridge, Japan, Mr. R. V. Boyle, C.S.I.,
M.Inst.C.E., has stated that Bull's hand-dredger was first used and
answered well in brick cylinders, 12 ft. in diameter and 2 ft. in thick-
ness, in fine sand near the surface, but in coarse gravel and soft mud
the efficiency of the hand-dredger became much reduced. Kennard's
improved sand pump was used and did good service in the coarse gravel
but was not found suitable for dealing with the mud. A double bag
excavator was then tried. It consisted of two bags, each being
fastened to a frame of iron, the lower part of which formed a cutting
edge. These frames were fixed on opposite sides of a vertical bar, by
which they were made to rotate and dredge a circular hole. In deep
bridge- wells, the two frames were bolted to a square intermediate socket
fitted loosely on a vertical rod, which remained suspended in the
cylinder while the frame and bags were lifted and emptied at the sur-
face.
Any required pressure upon the bottom to make the cutting edges
EXCAVATING APPARATUS. 109
effective was obtained by loading the frame with weights slipped into a
cross-bar attached to it. Eight men were able to turn the excavator by
bearing on tillers keyed to the vertical rod, and under favourable cir-
cumstances, four to six lifts were made in an hour, and 5 or 6 cub. ft.
of mud were raised in the smaller apparatus, and 12 to 16 cub. ft. in
the larger dredger.
Many of the grab-dredgers designed for excavating clay or tenacious
soil, follow the principle of ordinary bucket-dredgers, the chief
alteration being that the buckets instead of being made of curved plates
are formed entirely of ribs or prongs having pointed ends, the lowering
and raising apparatus being almost identical. When clay, boulders,
hard or tenacious soils, such as compact gravel veins, have to be
excavated, ordinary bucket-dredgers are not adapted for effecting the
excavation. Briefly, simple bucket-dredgers are useful in loose earth,
grab-bucket-dredgers for moderately hard soil readily penetrated, and
especially designed dredger-excavators, such as those that have been
described, for clay and compact earth; or the cutter and jumper
system of first separating the ground, the bucket-dredgers being simply
used for gathering and raising the loosened soil.
SIMPLE BUCKET-DREDGERS. — Almost all form a nearly semicircular
bucket when closed. Bucket-dredgers are so well and favourably known
for excavating and gathering all kinds of loose material that there is
no occasion to describe them. The one great objection to them is that
they are only adapted for loose soils. The buckets have been raised full
in certain loose deposits, but when the earth is harder to penetrate, they
are only partly full or nearly empty. Much depends on the character
of the earth. The varieties of sandy, silty, and clayey soils are very
numerous. It is necessary to know the nature of each before deciding
as to the suitability of the dredger. Impure loamy or argillaceous
sand, or sand derived from soft sandstone rock, or that has round
grains, will generally be readily raised ; but sand derived from quartz
or hard sandstone rock, rough, angular, hard sand which is clean, clear,
and translucent, and consists of fragments of the most durable rocks,
will usually be difficult to penetrate ; as also clean fine sand, i.e.,
sand almost wholly comprised of minute particles of hard rock.
In silty soil it will generally be found that the clayey silts are difficult
to penetrate by bucket-dredgers, as the edges of the buckets slide on
the surface or do little more than scrape it ; whereas, if the silt is of a
decidedly sandy nature it is more easily separated, and therefore pene-
trated. In the former case, the tendency will be for the bucket, as it
were, to float on the surface, in the latter, to press the harder particles
into the muddy clay or softer portion of the mass, and so penetrate it.
Clayey silt is by no means a satisfactory earth to excavate and raise,
its viscidity preventing both easy penetration ^H|J^S5iajrffl — -'-
iL. OF THE
^UNIVERSITY
110 CYLINDER BRIDGE PIERS.
sandy soft silt is usually raised with so much water, that although a
bucket may be full, only about one-half of its contents can be called exca-
vated material, and the greater the depth of water through which it
has to be raised, the more charged with water the earth is likely to be.
Small openings in the dredge-buckets will allow the water to a certain
extent to drain away, but it is very difficult to separate the water from
the earth without some loss of the soil. Those who have had difficulty
in excavating soft silt at a considerable depth below water, say from 30
to 70 ft., have stated that it was not only advisable, but cheaper, to
adopt the pneumatic system, and put men in to excavate such material
in the ordinary way, especially so when the earth is very soft and the
cylinders of small or moderate diameter.
'In clayey soils all depends on the nature of the clay. If it will
readily fissure or break into lumps, or has much sand in it, penetration
will be easier than if it is comparatively pure clay of any kind. Except
in loose soils it is generally advisable to serrate the edges of the buckets,
but perhaps the most important recent improvements in bucket-dredgers
are, (1) the introduction of the pointed hemispherical form of scoop ; (2)
the attachment of prongs or bent forks to the outside of the buckets so
that they are able to penetrate the earth, and can be drawn together by
the closing bars or chain, and, (3) loading the buckets so as to cause them
to descend with greater force. The first two improvements are the
most important.
With regard to the use of a bucket or grab-dredger actuated by two
chains, one for opening the bucket, or grab, and the other for closing
and raising the load, they are worked by a special form of crane ;
whereas the single chain bucket or grab-dredgers, i.e., those having one
chain for lowering, closing, and raising, can be worked by an ordinary
crane ; but the latter when closed at the bottom of a cylinder, or in the
earth cannot be opened until they are raised, and therefore if boulders
or other obstructions are encountered, the chains may break, the dredger
become fixed, or the catch hooks that release the grabs or buckets on the
latter reaching the ground may not act properly through being obstructed
by lumps of earth, debris, or loose stones.
One of the best known and most successful dredgers for bridge cylin-
ders, it having been largely used in India, is BULL'S SIMPLE QUADRANT
DREDGER. It is specially adapted for sand and loose fine sandy gravel,
and possesses the advantage of having few working parts, and of being
very simple. The buckets are fixed to curved arms. In lowering they
are kept open by a catch, and when lowered it is released by a rope,
the closing and hoisting chains pass round a pulley attached to the ends of
the lower arms. There are two arms, and each extends over the opposite
quadrant during lowering, thus, on their being pulled together, a
considerable grip of the earth is obtained.
DREDGING APPARATUS. Ill
Among some other dredgers may be named Sir Bradford Leslie's
rotary plough, or boring head, referred to in the next chapter under sand-
pumps, suction, water-jet and compressed-air dredgers ; Molesworth's
dredger ; Stoney's helical excavator ; Furness & Slater's telescopic
dredger, used on the Thames Embankment works at shallow depths
from 18 to about 30 ft. below water, and described as suitable for sand,
compact sand, and porous gravel.
When the excavation in the cylinder is completed, the interior should
be cleared, and the bed levelled by a diver, and all earthy matters that
may adhere to the sides and flanges should be removed. To prevent
sandy soil becoming impregnated with mud or muddy water before
the hearting is deposited, arrangements should be made that, as soon as
the cylinder is free from debris, and the base properly levelled, the
hearting is deposited over the entire internal area of the column, and
any "runs" of earth or percolation of water prevented.
CHAPTER XVII.
SAND PLMPS, SUCTION, COMPRESSED AIR, AND WATER-JET
DREDGERS.
WITH regard to sand pumps, subaqueous-dredging on the suction or
water-jet system, and compressed-air dredgers as applied to excavating
the earth in the interior of a cylinder or well, it is not here intended to
describe in detail the various apparatus, but to refer to some few points
connected with them. In the sand pump, the suction-pipe draws in
water with the material, the proportions of sand or mud to water being
different according to the nature of the earth. A mixture of 5 of water
to 1 of sand has worked well. The cohesive properties of clay soils
prevent the employment of excavator-pumps, but, when they are helped
by cutters disintegrating the earth, they have been used in loose ground
of that nature. Sand and fine gravel are the most suitable earths for
them, but they have been employed with radiating cutters on the lower
part of the movable bottom, which, being rotated sufficiently, break up
seams of clay or tenacious soil for raising by pumping, i.e., into pieces
somewhat smaller than the suction-pipe. Their chief disadvantage is
that they lift a large quantity of water with the sand, and consequently
much of the power applied is wasted, and perhaps a " run " of earth is
induced by a flow of water being caused. Experience has shown that
it is better to work sand-pumps by bands and not by gearing, i.e., by a
112 CYLINDER BRIDGE PIERS.
yielding medium in preference to rigid driving, because, should the
pumps become choked, which is sometimes the case, the power being as
it were elastically communicated prevents injury to the machinery.
Some consider that hydraulic dredgers should preferably be worked
by a centrifugal pump, because of its comparatively few working
parts ; and as the action is continuous and in one direction, there is no
stoppage or change of the stroke, and the material is steadily ejected
and therefore cannot settle. These are important advantages. A reversal
of the flow which induces settling should always be avoided as much as
possible. Among the pumps especially adapted for pumping sandy
water may be named the centrifugal, rotary, pulsometer, and chain.
For such purposes pumps having complex or delicate parts, or pistons
which fit closely, or that have other than ball or clack valves should
not be used, and it is well if any pump valves and seats can
be removed so that they can be inspected. The wear of the cylinders
in a direct-acting pump in sandy water is very considerable, and it may
be advisable to use some other kind.
Boring with hollow rods and a continuous current of water might
perhaps be occasionally used to break up sand difficult to dredge by
ordinary bucket-dredgers, but the current of water must be continuous
or the tube and the cutter may become fixed, the object of the machine
being to flush out the earth as it is excavated by the cutting-tool. The
necessary velocity of the current is ascertained by the ease with which
the tube penetrates, and the force-pump preosure can be so regulated as
to produce the desired velocity. This method, it has been claimed,
possesses advantages over that of other boring systems. For soft
ground the flushing current passes down an inner line, of pipe forming
the boring rods, and rises to the surface through the lining pipe. On
the contrary, in boulder ground, the water is admitted through the
lining tube and passes out loadod with the material through the central
hollow rod, the diameters being increased ; a 3£ in. tube being con-
sidered the maximum working sizs. The pressure required usually
varies from about three to five atmospheres for ordinary depths. The
blades of the cutting-tools should be perforated so as to allow the water
to circulate. When the flushing tube becomes plugged, a method of
clearing is to raise it 10 or 15 ft. and pump rapidly for some
time.
Some devices for breaking up the soil sufficiently small for dredger
pumping will now be considered.
At the foot of the suction or dredger pipe, which is flexible to allow
of its being spread around, a scraper is fixed ; when this is dragged over
the bottom it loosens the material sufficiently for the earth to be drawn
into the sue i ion-pipe with the flowing water.
Sir Bradford Leslie's rotary -plough or boring-head is a combined com-
DREDGING APPARATUS. 113
pressed air, boring, excavating, and lifting apparatus. It was used at
the Gorai River Bridge, on the Eastern Bengal Eailway, in very hard
clay as well as in ordinary earth and sand, the soil being discharged by
a constant current of water in a pipe. The average daily sinking of a
14-ft. cylinder was 4 ft. 6 in., but 9 ft. was really done in one day, the
other being occupied in removing and refixing the apparatus on an
additional ring of the pier being added.
The quantity o£ earth raised depends upon the power applied to
drive the plough and the volume of water flowing up the pipe, and is
quite independent of the depth. It raised and discharged anything that
could pass through the discharge pipes. The apparatus consisted of a
horizontal disc-plate, with four triangular blades at right angles to each
other, projecting underneath, and armed with cutters, which, when
revolved, excavated a conical hole 9 ft. in diameter. The plate was
bolted to an annular pipe of 13 in. inside and 26 in. outside diameter.
The spaje between the inner and outer pipes was made air-tight by
annular flange plates riveted into the ends of each 9-ft. length of pipe.
The shaft therefore consisted of a vertical pipe surrounded by a series
of air-jackets The boring head was worked by a small compressed air
engine. The earth was removed by a current of water constantly flow-
ing up the pipe For this purpose a 12-in. syphon pipe was provided,
the inner leg of which was immersed in the boring-shaft, and the outer
leg in the water of the river ; then, by connecting the suction of the air-
pumps with the syphon, the air was exhausted from it, and, being
replaced by water, a flow of water from the cylinder into the river was
immediately established proportionate to the quantity thrown into the
cylinder by the two 13-in. centrifugal pumps.
At the Hooghly Bridge the dredging was effected by a special boring
gear, one set in each of the three excavating chambers, similar to that at
the Gorai Bridge ; but it was driven by steam instead of by air-pressure
or turbines, and the syphons through which the earth was discharged
into the river were charged by Korting ejectors instead of by air-pumps.
Hutton's sand pump, and Burt & Freeman's sand and mud pump
were used on the Amsterdam Ship Canal works, St. Petersburg-Cron-
stadt Canal, and on the Lower Danube. The latter machine had
stirrers or knives on the vertical pump shaft, and by means of jets of
water from a force pump impinging under great pressure on the
dredged material, it was disintegrated before it entered the pump, thus
the scope of this appliance has been largely extended, and clay of
moderate consistency was successfully dredged in the new cutting of
the Sulina branch of the Danube.
Colonel Schmidt's is another form of dredger for excavating clay as
well as loose earth by the aid of cutting knives and a special arrangement
of centrifugal pump, suction, telescopic suction, and discharge pipes.
i
114 CYLINDER BRIDGE PIERS.
At the new Tay Viaduct the soil was chiefly silty sar.d,. with
occasional beds of gravel, boulder stones, clay, and red sandstone ; it
was found that the steel digger of the Milroy pattern lost a considerable
quantity of the material while being hoisted through the water. This
led to trials being made with various kinds of pumps in order to raise
it without loss. The best results were obtained from a 12-in. centri-
fugal pump, the suction connections of which were thus arranged
Two flexible hose-pipes, each 6 in. in diameter, and 20 ft. in length;
were placed in the bottom of the cylinder, the ends being brought
together and joined into one 12-in. pipe leading to the pump on
the platform. A diver was then sent down who manipulated the
suction pipes, so that while one 6-in. pipe threw up sand, the other
kept the pump free by drawing clear water only. As much as 40 cub.
yds. had been pumped up in one hour, causing a subsidence of over 2
ft. in a 23-ft. cylinder. When the tide was too low for pumping, the
digger was used. In clay strata, as the material could not pass up the
pump, the two flexible hose-pipes were removed, and the water was
pumped down as far as possible, giving additional pressure on the
bottom owing to the difference of level of the water. In this manner
cylinders had been sunk as much as 11 ft. in thirty minutes, and the
material was afterwards taken out with the digger.
At Dunkirk Harbour the dredging was effected by the two-fold
action of streams of water injected under pressure into the sand and
by exhaustion, ».<?., by injection and suction, for each of which
operations a separate centrifugal pump was used. One pump was
employed for driving the water into the air-chamber, and thence to a
hydraulic injector or sand-pump, similar to that used for excavating the
foundations of the St. Louis Bridge, which required only two pipes,
one passing down to the sand-pump, and the other brought the materials
to the surface. Thus there was no obstruction to the use of the air-
locks, etc., in the caisson at that bridge. The lower end of the injector,
which rested on the bottom, was made of cast iron so as to sink readily
into the sand. The water was injected under pressure down one pipe,
and passed out of three small tubes, which projected slightly from the
casting and stirred the sand, the sand and water being drawn up a
separate pipe by the action of the other centrifugal pump. Both of
these pipes were flexible at their extremities. The apparatus is more
suitable for comparatively large areas, as in a caisson, than for a
cylinder bridge pier.
At the Alexander II. Bridge over the Neva, a Korting hydro-ejector
was erected to pump up the mud, and it acted satisfactorily. The water
pressure used was 10 atmospheres, and the issuing water contained 26
per cent, of solid matter, as much as 38 cub. yds. of mud being
raised in one day.
DREDGING APPARATUS. 115
Reeve's vacuum excavator was used at the first Tay and Severn
bridges, etc., etc. It was considered suitable for sand, silt, mud, loose
clay, and small gravel. The material was excavated by means of a
flexible suction-pipe discharging it into receivers, from which the air
had been exhausted. It was worked under water, the tide rising and
falling within the cylinders.
At the new quay walls at Calais Harbour, where the soil is very fine
and movable sand, vertical square built masonry walls on a strong
concrete curb were sunk by the pressure of water. The depth of the
foundation was 8 to 11 metres. The walls were 1 metre in thickness
and 8 by 8 in dimensions, with an octagonal shaft 4 metres in diameter.
They were sunk side by side, leaving 0'4 of a metre between them.
The first, third, and fifth well were first erected of one series, then the
intermediate, and lastly the 0'4 of a metre space was excavated by a
water-jet, and filled with concrete, which dove-tailed the whole series
together by filling two pairs of grooves which had been formed in the
sides of the contiguous masonry wells. The wells were sunk by
injecting water under their cutting edge by means of wrought-ircn
pipes carried down through a central shaft, and splayed outwards so as
to direct the jet upon the sand beneath. Thus loosened, the material
was brought up by a centrifugal pump, whose suction-pipe descended in
the centre of the shaft and drew sand and water from the bottom of
the conical cavity which was gradually formed by the disengagement
of the sand around its sides. The necessary pumping machinery was
mounted on wheeled trucks, which ran upon a tramway parallel to the
line of the wells. For the water-jets, four Tangye pumps were used?
supplied with steam from two small vertical boilers, while a centrifugal
pump was driven by a separate portable engine and boiler. Twelve
wrought-iron pipes were used as water-jets, and were divided into four
groups ; the three pipes of each group were connected with one of the
pumps by flexible rubber tubes. The jets were so directed around
the cutting edge as to excavate the sand regularly, and in general the
verticalness of the wells was easily maintained. Sinking a well 4 to 4£
metres took twelve to fourteen hours, being equal to 20 cubic metres of
excavated material per hour. In a bed of clay the operation was difficult
and tedious, but succeeded in beds 1 metre in thickness. The system was
also used for smaller wells 4 metres by 4 metres, but although the rate
of descent was faster, it was not easy to sink the wells vertically.
Some difficulty was experienced in working the centrifugal pump owing
to the settlement of sand in the suction-pipe, which tended to choke the
valve at the foot of the pipe, when pumping was temporarily stopped.
It was remedied by attaching to the valve box one of the wrought-iron
pipes, through which a jet of water was at such times delivered into
the valve box just above the valve, and by means of the circula-
i2
116 CYLINDER BRIDGE PIERS.
tion of a continuous stream of water the deposit of the sand was
prevented.
AIR-LIFT EXCAVATING APPARATUS, AND THE WATER-JET SYSTEM. —
Sand, mud, and loose soil can be raised by the escape of compressed air
through a discharge pipe leading into the open air at the top of the
cylinder, and can be emitted in a continuous stream. Where the air
space is small, as in a cylinder, this method of ejecting sand, etc., by
direct force of the air may be difficult to keep in regular work ; but in a
caisson, because of its size, the objection vanishes. At the St. Louis
bridge sand was forced up under a pressure of 10 atmospheres, or about
150 Ibs. per square inch, one 3^-in. pipe raising 20 cub. yds. per
hour 125 ft. in height when continually worked. At the East River
bridge, at a depth of 60 ft., sand was continuously discharged through a
3 -in. pipe for thirty minutes at the rate of 1 cub. yd. in two minutes,
and fourteen men, standing in a circle round the pipe, shovelling as fast
as they could, were required to supply the mouth of the air-discharging
pipe with sufficient material. General Smith stated that with this
apparatus men need only enter the compressed-air chamber to remove
an unusual obstruction, and that such an appliance is required in sinking
cylinders to very great depths, and necessarily the greater the depth
the more efficient the air-lift. Of course this method can only be used
when the material will yield and flow with an air current, unless it is
previously separated. At the Glasgow bridge over the Missouri, Kansas
City, St. Louis, and Chicago Railway, some of the excavation in the
c;ti<son was removed by means of an Ead's sand-pump, but it was found
that the most economical and rapid method, when sand and gravel had
to be excavated, and the pressure exceeded 5 Ibs. per square inch, was
the air-lift, for here it simply consisted in a 4-in. pipe passing down
through the roof of the caisson being provided with a valve within the
air-chamber, and terminating in a short goose-neck. The ^and being
piled round the lower end of the pipe, and the valve being opened, the
escaping air raised it with great velocity. It only required a moderately
increased supply of air, which is always desirable for changing and
keeping fresh that contained in the air or working chamber.
Dredgers for the removal of sand or silt by an injection of compressed
air, instead of by suction, have been used successfully in soft silt, sand,
and gravel. Jandin's apparatus was used at Havre and Saumur. The
principle of it is that of forcing air through a number of holes in a
pipe surrounding a main pipe, the compressed-air being sent into the in-
ternal raising tube by an injector. The pressure causes the water to rise
in it, thus dredging the loose soil at the bottom, and lifting a mixture of
water and sand, the latter being 25 to 40 per cent, of the volume. This
apparatus is actuated on the same general principle as Sir Bradford
Leslie's boring-head previously described. At the bridge over the Po
DREDGING APPARATUS. 117
at Casalmaggiore, Parma-Brescia Railway, the earth, which was of a
sandy nature, was cast by men into a box holding about 7 to 8 cub.
ft., and water was pumped through a pipe to mix with it. The mixture
was then forced out by another pipe in an almost continuous stream by
the pressure of the compressed air in the chamber. About 30 per cent,
of sand and 70 of water were so discharged, the volume being about 5£
cub. yds. per hour.
Sir F. Bramwell, many years ago, suggested that at the bottom of a
cylinder a massive plate, sufficiently heavy that the water-pressure
underneath could not raise it, should be fixed ; that a pipe reaching to
the top to force water might be attached to the seal plate, and a worm
wheel fitted to the pipe to cause it to rotate, or that motion be imparted
by a hand spike. In brief, that the hydraulic method of sinking piles
by forcing the sand outside, as used in disc piles sunk by the water-jet,
might be applied to sinking cylinders in loose sandy soils capable of
being forced outwards by water-pressure from the interior. Advantages
claimed for this system are that no " blows " or " runs " of soil into the
cylinder can take place, and therefore the outside earth is not nearly so
much disturbed, a cylinder is better supported laterally, and any move-
ment of the surrounding ground is likely to extend equally in all
directions.
Experience with the water- jet system has shown that although very
efficient and economical in sand, silt, mud, or soft clay, when the sand
is clayey or gravelly it loses much of its efficiency, and in gravel it is
not a desirable method to use. In its application to cylinder sinking the
jets should be so arranged that they discharge the water under pressure
in such a way as to ensure regular and vertical sinking. The reason of
the ineffectualness of the water-jet in gravel and gravelly sand is that
although the sand and any earthy matter are washed out, the stones of
the gravel remain and accumulate until they form a barrier which the
water-jet cirmot remove, it forcing any sand or earthy particles through
the interstices of the stones, the result b^-ing a layer similar to a pebbly
beach. The water-jet is almost useless in such soil, or when large timber
chips, so often found embedded in the earth near docks and piers, have
to be removed.
When water is forced vertically in the direction of the axis of a pile
by means of an oblique hole being made in it near its point, down
which the water is injected into a hole made for a short distance along
the axis of the pile, sinking is much faster than when a pipe jet is
brought to the point of a pile, therefore if water-jets are used in
cylinder sinking it is well to remember that the vertical action of the
water is the most effective in increasing the fluidity of sandy soil ; for
that is the principal effect of the water-jet, the especial object of the
appliance being to produce such a state of fluidness that the pressure
118 THE WELL SYSTEM OF FOUNDATIONS.
necessary to cause effluxion is as little as possible ; thus there are two
actions, and obviously the more water the greater fluidity, and conse-
quently the less pressure required; therefore a considerable jet discharged
with moderate force is more effective than a small jet emitted at a high
pressure ; still an excess of water is undesirable, a sufficient fluidity of
the earth being all that is necessary. As the necessary fluidness of a
mass of gravel, pebbles, or solid clay cannot be attained by the applica-
tion of a water-jet under ordinary pressure, it is in sandy soil having
fine particles easily transported under slight pressure, or in loamy soils
which on water being forced into them quickly become liquid mud, that
the water-jet system is particularly successful. The nozzles of the dis-
charging jet should be properly formed in accordance with the most
approved shape, and it is important that the pumps have ample power
and capacity to fully and continuously feed the jets.
CHAPTER XVIII.
THE WELL SYSTEM OF FOUNDATIONS FOR BRIDGE-PIERS, ABUTMENTS,
QUAYS, AND DOCK-WALLS, ETC.
THE well system is particularly adapted for loose sand, mud, and silt,
but practice shows it is not suitable for soil harder than ordinary sand,
unless under exceptional circumstances. It is an especially good method,
if the mud is sufficiently watertight, for the well to be pumped dry, so
that the excavation can be executed without dredging machinery. It
has many important advantages over a timber pile foundation in sand,
silt, or mud, and in warm climates should be preferred. Brick walls
have been sunk through clay, boulder sand, and solid beds of shingle.
If boulders or debris are expected to be encountered in sinking, masonry,
concrete, or brick cylinders should not be used, but iron, as they are
stronger and more air-tight, as neither dredging nor divers may be
able to remove the obstruction, and the compressed-air system may have
to be adopted. The well system has failed when boulders and
obstruction in sinking have been encountered. The modern practice of well
sinking is to diminish the number of wells and to increase the diameter
or area of each, as the larger wells are more stable, and the resistance
opposed to the lateral force of winds and currents tending to overturn
them increases with the diminished number of sub-divisions. The re-
sistance has been stated to be approximately as inversely as the square
THE WELL SYSTEM OF FOUNDATIONS. 119
root of the number of separate parts into which the foundation is
divided. It is important that the diameter of a well should bear a
sufficiently large proportion to its height. If they are in groups, the
wells should be securely tied at the level of the river bed.
Wells have been sunk of 40 ft. diameter, their internal diameter
being about 32 to 33 ft. General experience seems to show that, within
reasonable limits, the larger the diameter of the well, the less
difficulty there is in sinking it, and the height should not exceed about
one-fourth of the diameter.
Large brick cylinders are more likely to crack than small wells, but
this defect is readily overcome by substantial construction, by having
numerous holding-down bolts, and by taking care that the wells sink
evenly, and do not hang from surface friction, which resistance may
be distributed unequally. Many of the remarks made with respect to
the cylinder system and sinking are obviously applicable to the well
method of foundations, and therefore are not here repeated.
Trouble has been experienced when two rows of wells have been
sunk close together, as they tilt and often become jammed against
either the top or bottom of the opposite well ; and in the process of
removing the material from under the curb, in order to bring it to
perpendicularity, the adjacent well tilts, from the earth moving from
under its curb at the nearest part. One row of cylinders of large
diameter is decidedly preferable to two rows of small wells sunk close
together.
Kectangular and oblong wells have been used, and for dock or quay
walls it may be necessary to adopt them to produce a straight face,
but the circular has been proved by long experience to be the best
form, especially in India, where the course of a river may, during floods,
be at right angles to the centre line of the usual channel, showing that
piers should have equal bases in all directions, and therefore be circular.
One of the principal objections to rectangular wells is that in excavating
the soil a circular hole is formed, and therefore the wells hang on the
four corners, instead of equally all round, and therefore fractures often
occur ; they are also much more difficult to " right " than cylindrical
wells, should they become inclined in sinking. There is less material
or steining in a circular than in any other form of well of equal area,
and it is also the best for resisting lateral pressure, because a strain at
any point in the ring is communicated to the whole.
GENERAL CONSTKUCTION. — As wells may be severely strained during
sinking, special attention must be given to their construction. They
have to withstand the external pressure of the soil and the head of
water, the strains arising during unequal sinking, the tensional strain
from surface friction, which may act upon only a small surface of the
well, the compressive load from the weight of the well and any kent-
120 THE WELL SYSTEM OF FOUNDATIONS.
ledge, and rushes of water or soil ; for brickwork wells have been burst
because of a sudden rise of water inside them ; the reason of such a
rush of water is frequently that the diggers and dredgers have only
excavated a central hole, and because this has extended from 7 to 9 ft.
below the cutting edge before the surrounding earth would fall into it.
In order to counteract the pressure due to a considerable head of water,
it may be prudent, even if the internal excavation can be effected in the
open air, to execute it by dredgers or divers, but sinking will then not
be so easy, and kentledge may be required. The weight of the super-
structure should be equally distributed over the whole area of the top of
the well.
The thickness of a well will depend upon the nature of the material
used in the steining, the height and diameter of the well, and character
of the soil to be sunk through ; and sufficient space must be left in the
interior for the excavating machinery. It is an ad vantage if it ran be
of sufficient thickness so that its w sight will cause it to penetrate the
earth. Wells of less outside diameter than about 10 ft. are now but
seldom used. The thickness of the steining usually varies from 2 ft.
3 in. to about 4 ft., but, for quay walls, masonry in Portland cement
mortar wells, 33 ft. by 22 ft., 7 ft. 3 in. in thickness, have been sunk at
Havre, and are exposed to the sea. When brickwork is used, it is some-
times made to gradually increase in thickness by half-brick projections
on the inside to its maximum at the curb seat, but the corbelling is
objectionable if dredger-machinery has to be employed for excavating
the interior earth, as the dredgers may be caught by the projections.
The brickwork is often tapered towards the shoe, so as to offer the least
obstruction to penetration. Ordinary bricks, not radiated, are sometimes
used for the steining ; but radiated bricks are preferable, and they
require less cement in the joints. It has been found that bricks exceed-
ing 9-in. ordinary bricks are too large to be economical for the
steining. The bricks are sometimes made so that the angle of divergence
at the ends, and the radius of curvature of the sides are of the mean
radius of the steining. Vitrified face bricks are occasionally introduced
if ordinary bricks are likely to be injuriously affected by the salt water
in the soil. The brickwork should be thoroughly bonded together, and
its outer cylindrical surface smoothly plastered with Portland cement, so
as to lessen the surface friction. It is sometimes bonded with hoop-iron
laths, at intervals of 3 or 4 ft. On adding fresh brickwork to that
already made, in order to get a good joint, care should be taken that a
clean surface is obtained to which the cement mortar can firmly
adhere.
The steining should be allowed to stand until the masonry, concrete,
or brickwork is thoroughly set. Cases have occurred in which fracture
and failure of a well have arisen because the material had not had time
THE WELL SYSTEM OF FOUNDATIONS. 121
to fully set. Concrete made of about equal portions of cement and
other constituents should have at least six or seven days to consolidate
and set ; and masonry, brickwork, and Portland cement concrete in the
proportion of 5 to 1, not less than fifteen days, and one month is to be
preferred. The cement should always have a high cementitious
strength. Good Portland cement concrete steining appears to be a pre-
ferable material to brickwork or masonry, on account of its homogeneity,
and it is also cheaper and heavier than brickwork. The thickness of
the concrete is usually from one-fourth to one-fifth of the outside dia-
meter, a minimum thickness being 2 ft. to 2 ft. 6 in.
An objection to brickwork, unless the bricks are of a non-porous
nature, is that when such a well is empty, water percolates from the
surrounding earth through the steining if the depth sunk is considerable.
It is therefore advisable to test any bricks before using them in the
steining in order to ascertain the head of water they can resist. An out-
side thick rendering of Portland cement may prevent any percolation.
Masonry wells have been sunk from 8 to 10 ft. into the ground in
shallow depths of water, such as from 10 to 15 ft. The masonry being
about one-fourth of the diameter in thickness or 3 ft. 3 in. for a 13 ft.
outside diameter well, the lower portions being set in cement, the curb
being of wood, 4 to 6 in. in thickness, strengthened by angle-irons bolted
to the steining.
Tie- bolts are an essential in the steining. The probable strain on
these bolts would be, during the forcing-down operations, if the wells
hung, that of the surface friction less the weight of the well, the kent-
ledge, and the tensional resistance of the steining in some measure. It
usually happens, when a cylinder is suspended by surface friction, that
the resistance is almost entirely on the ring of the well just added. The
vertical tie-bolts are mostly from 1 to 1 ^ in. in diameter, and are placed at
intervals of from 3ft. 6 in. to 6 ft. round the whole central circumferential
line of the steining. They must go through the steining from the curb
seat to the top of the well, and be securely attached to the curb. Rings
of flat iron, 4 to 6 in. in width, and about f in. in thickness, through
which the tie- bolts pass, are sometimes introduced at intervals of 8 to 10
ft., in the height of the well. This plate is also occasionally of a width
equal to the thickness of the steining, and can be cottered down to the
tie-bolts ; or the latter can be in lengths, with a nut or coupling 6 or 8 in-
in length, with a large washer, the nut or coupling being screwed down
tight on the completion of each length of the well, additional lengths
being screwed on as fresh rings are added. The latter method is to be
preferred to any cotter arrangement, and there is an advantage in this
system of tie-rod, nut, and washer, because each length of well is compact
in itself, and is also joined to other rings. If from any reason, such as
grooving the joints of the different lengths, it should be inconvenient to
122 THE WELL SYSTEM OF FOUNDATIONS.
place the tie-bolts in the centre of the steining, they should be fixed
nearer the outer circumference than the inner surface, as the greatest
resistance is encountered on the outer circumference owing to surface-
friction. On the upper surface of the highest length of the well, a plate
about f in. in thickness should be placed, upon which to screw up the
tie-bolts tightly ; the well is then complete. In order to prevent any
fracture caused by iron bolts, bars, etc., being built in the steining, it
miy be necessary to provide for alterations in their length, consequent
upon variations in the temperature.
The remarks made on the best form of cylinders are applicable to
wells, but there are even stronger reasons for the adoption of the
circular form for wells. Oblong and elliptical wells have been sunk,
and a straight face for a wall may be necessary ; if not, the general
testimony is decidedly in favour of the cylindrical form. Circular are
far preferable to oblong wells, and elliptical are better than the latter,
although that form is much inferior to the cylindrical. Among the
objections to oblong, and in a lesser degree to elliptical wells, are the
great practical difficulties of obtaining a thorough bond at the corners ;
the long, straight side walls which have to resist the pressure of the soil,
the great trouble experienced in sinking them evenly, and righting them
should they tilt as frequently happens. This form should therefore not
be adopted, unless a straight face must be afforded ; but of course, if
the depth to which the wells have to be sunk is small, as is usually the
case in quay or dock walls as compared with bridge-piers, these objec-
tions are not nearly so important. If it is absolutely necessary to approach
such a figure, the elliptical should be used ; but, if possible, the circular.
There is seldom any necessity for the employment of any other form
than the circular for bridge piers, as several wells can be sunk in a line,
which can be built upon in the usual shape of a pier, but the wells must
not be too close together. When large wells are sunk, with only about
3 ft. clearance, small arches are sometimes turned over them, so as
to make a continuous surface, upon which the pier is built, or the wells
are corbelled out at the top, and are connected by two or three thick
courses of ashlar being placed upon them. The difficulty of sinking is
much increased by grooving the wells or interlocking them, as the
slightest divergence from perpendicularity retards the sinking.
CURBS. — The curb should not present a large flat surface in order that
the resistance to descent may not be great. In the previous notes on
the cylinder system a union of the metallic and non-metallic methods is
referred to ; a modification of this combination might be effected by
a lengthening of the outer edge of the curb, which would then not only
give a more pointed cutting edge, but would to some extent prevent the
exterior soil being forced into the well. Cast-iron are heavier than
wrought-iron curbs, but in material which admits of easy penetration,
THE WELL SYSTEM OF FOUNDATIONS'
such as sand and mud, a heavy curb is a disadvantage, because in ad-
dition to the expense of construction, it brings more weight on the
foundation with no corresponding gain. Curbs require to be sharper and
longer, according to the compactness and hardness of the soil to be pene-
trated. The form of the curb is usually an inverted right-angled
triangle for soft soils, the perpendicular being about 1^ to lj time the
width of the base, upon which latter the steining is built. If the stein-
ing is Portland cement concrete, the thickness is sometimes reduced by
one-half at the curb seat, it being bevelled for about 2 ft. upwards from
it on the outside, thus lessening the width of the curb.
The curb should be strengthened and stiffened by gusset-plates and
angle and T-irons, and should not be very thin, so that it may be heavily
loaded ; and should it meet with boulders or obstructions, that it may
be of sufficient strength to resist them, as the expense of a little extra
iron is nothing as compared with the cost entailed by fracture of a well
during sinking operations. Iron is the best material for a curb, but it
may not always be obtainable, and time rnay be saved by using some
other substance ; if such should be the case, either wood or concrete
can be adopted, both of which should, however, be shod with iron. The
triangular open space formed in an iron curb is generally filled with
concrete. In designing the curb it should be borne in mind that if it
bends it will most probably be destroyed, or cause an entire suspension
of operations for a time. Its dimensions and thickness will vary
according to the thickness of the steining, height and diameter of the
well, the hardness of the soil, and the probability of obstruction being
encountered during sinking. In wells of moderate diameter, the
pressure per square foot on the curb, assuming it acts equally over the
whole surface, seldom exceeds from about 3 to 5 tons. To bind the
steining to the curb, the cutting-plate should be carried up above the
level of the horizontal plate, from 3 to 6 in., which will prevent the
steining slipping off on the outsidei; an angle-iron riveted to the hori-
zontal plate on its inside diameter will hold it internally. Such a curb
of ordinary diameter weighs about 3 to 4£ tons. Cast iron curbs are
generally constructed in segments bolted together.
If the curb is made of timber, the wood should be hard, and have a
comparatively high resistance to crushing, such as oak, beech, ash,
American plane, sycamore. The usual method is to build up wedge-
shaped segments, which should break joint and be fastened together
with strong bolts. The end of the wedge, which can be about 3 in. in
width, should be protected by plates, and a cutting-plate should project
for about 1 ft. below the wedge-end, upon which a strong angle-iron
should be bolted, and the cutting-plate be riveted to it so as to make it
as rigid as possible. The area of the wedge-end must be regulated
according to the strength of the timber used, and the weight that it
124 THE WELL SYSTEM OF FOUNDATIONS.
will have to bear, not only from the well, but also from the kent-
ledge.
SINKING NON-METALLIC CYLINDERS. — When wells have to be sunk in
a waterway, the simplest mode of pitching the curbs is to form an arti-
ficial island. It may not be always necessary to make such islands if
the water is of less depth than 5 or 6 ft. ; and, with plenty of tackle, the
curbs and first lengths of the well might be pitched in an ordinary current
where the depth of the stream does not exceed 10 ft., but much will
depend upon the diameter of the well ; if of small size, it would very
probably upset should the diameter be less than the depth of the water ;
and rather than risk this, it may be advisable to raise a bank by simply
casting earth into a river until it reaches above the water level. There
are several methods of making these artificial islands. In still water,
circles of sandbags can be deposited by divers, or other means around
the site of the wells forming the pier, and when the circle is completed,
sand can be deposited until a level of about 1 ft. above the water is
reached. If the river has a gentle current, sandbags can be laid on the
down stream end of the site of the pier, and on the two sides of the site,
forming a three-sided wall ; sand must then be deposited at or about
the centre of this enclosure, and the current wilt throw it against the
down stream sandbags, at which end a bank will be gradually raised to
the surface of the water ; when this occurs, it is usual to deposit the
material on the upstream open end of the enclosure, whence the current
transfers it to that part of the bank previously formed, and gradually
the artificial island is completed ready for the wells to be pitched. In
a swift current, this system would scarcely afford sufficient stability.
Piles must then be used as a protection and auxiliary to the sandbags.
Spurs made of trees and stones, etc., are sometimes placed in swift
rivers to divert or slacken the current during the construction of
an artificial island. There are obviously many different ways of
making an artificial island of sandbags and piles. A successful
method is to drive piles on the upstream side of the river, which are
also used as staging ; these piles are driven so as to make a cut-water ;
gunny bags are then placed by divers on the remaining sides until the
whole area of the pier is enclosed. On the down-stream side there is no
danger of the bags being washed through, but the sides parallel with
the stream should have piles driven about 2 to 3 ft. apart for the bags
to rest against. The island is then completed by bags being placed by
divers, the interstices between the bags being filled with loose sand
until the water level is reached.
At the river bridge over the Ems at Weener, wells which were 13 ft.
1 in. diameter for a height of 8 ft. 3 in. from the curb were built inside
a wooden sheathing, and the bolts suspending them from the stage
during construction and lowering were built into the brickwork. They
THE WELL SYSTEM OF FOUNDATIONS. 125
were circular at the bottom and gradually tapered inside towards the top,
which is at low-water mark. The depth of water was only 7 ft. 6 in.
The thickness of the well on the curb seat was 2 ft. 1 in., at the top
1 ft. 3 in. At low-water mark the ordinary brick well begins. They
were built in cement brickwork, one of cement to two of sand, faced in
river piers above bed of river with alternate courses of whole and half
bricks in cement, one of cement to one of sand. The piers stand on the
filled up wells and are faced with hard brickwork. The wells were
sunk from a floating stage carried by two barges, between which there
was just room for the cylinder. They were hung by bolts and links
from a circular timber frame and were sunk on the ebb tide. This
example is mentioned, as it is an alternative method to adopt to that of
erecting wells on an artificially formed island. Circumstances must
decide which plan of operations is to be preferred.
Wells for foundations are often sunk in the silty or sandy bed of
rivers, which become dry in summer, and where there is therefore no
running water to contend with. The usual method of sinking wells is
first to excavate the ground to the water level, and then to lay a curb
on the soil. To keep the curb in place it is advisable to sink it to the
level of its top plate, or seat, before commencing building operations,
after which the tie-rods can be fixed and the first length built. In
order to obtain a perfectly vertical descent, and to enable the direction
of the sinking of the well to be easily corrected, it is prudent to build
the first or curb length of much less height than the remaining lengths ;
the second length can be made of greater height, and the third and
other rings of a convenient length. The first or curb length can there-
fore be about 5 ft. in height, the second 8 to 10 ft., and not exceeding
the latter dimension, and the third not higher than 15 ft. These heights
are for wells from about 12 ft. in diameter. It is generally agreed
among engineers experienced in well sinking that it is of paramount
importance the curb and the first two lengths should be perfectly
vertical ; the after sinking is then a comparatively easy matter with
ordinary care. To ensure the curb being always vertical, the steining
should be equally built around its whole circumference ; and in sinking
the curb and the first and subsequent lengths, the material from the
interior should be methodically excavated either evenly over the whole
internal area, or in the centre, the former being the better system.
There are objections to increasing the height of the wells in order to
obtain greater dead weight for sinking purposes, which become more
cogent in the case of wells of small diameter. Among them may be
named the additional height of the staging for building the lengths, the
increased range of the tackle required in lifting the material for the rings,
the greater difficulty of righting the well should it tilt, the augmented
height through which the excavating machinery has to act, and the
126 THE WELL SYSTEM OF FOUNDATIONS.
less stability. At the Plantation Quay on the Clyde, Messrs. Bateman
& Deas instead of first depositing the curbs and then building upon
them when in situ, constructed the concrete rings in frames on a plat-
form near the line of quay, and had them put together on the curb after
they were consolidated. By the adoption of this latter method of
adding lengths much time is saved, and the rings can be attached
almost as quickly as iron rings, the joints being simply cemented
together. If proper joints are made between the lengths, it appears
to be the better system to adopt, especially after the first length.
The number of wells commenced in one season should be such that
they can be completed before the time of deep flow or floods, so as to
avoid running the chance of their overturning, but should any be incom-
plete, the tops should be taken off at low-water level, and the site
indicated.
In well sinking the use of compressed air is exceptional, the soil being
removed by dredging. The pneumatic system of sinking is generally
only used when all other methods have failed to remove unexpected
obstructions met with in sinking, and no other course is open. Every
endeavour should be made to stop the leakage of the air by the use of
impermeable coatings. The concrete, or, if the well is of brickwork or
masonry, the cement mortar should be allowed ample time to set and
harden, and the joints and steining should be thoroughly grouted with
liquid cement. Records do not show many successful applications of
the pneumatic system to sinking non-metallic cylinders under a pressure
of more than about 40 ft. head of water. At Rochefort, the rubble-
masonry-set-in-cement-mortar-wells were so constructed that the com-
pressed-air system could be used when there was a rush of silt ; a recess
was made round the inside of the well at a height of about 16 ft. from
the bottom ; this was used as the springing of a vaulted roof of masonry
in cement 3 ft. 3 in. in thickness. Concrete was deposited upon the top
of the arch, a circular 2 ft. 4 in. opening being left in the centre. The
space below the roof provides a working chamber to which the hollow
cylinder gives access, an air-lock being fixed at the top of the wall over
the cylinder. The soil was soft alluvium.
Until a depth of water of about 5 or 6 ft. is reached, the soil can be
excavated by men with scoops or a jham, then, if necessary, by
dredger-excavating apparatus. (See Chapters XV., XVI., and XVII.)
The notes on cylinder sinking are generally applicable to well sinking.
Should firm strata be encountered in sinking, the well must be weighted
in order to make it descend. Kentledge placed upon the well is to be
preferred to building the well to an additional height. When water
percolates through the steining of a well it has the effect of drying the
earth around it, the consequence being that surface friction is increased
and the well harder to sink, and in some soils the result may be that
THE WELL SYSTEM OF FOUNDATIONS. 127
around the outer circumference of the well the earth may become
dried, detached from the wetter earth, and adhere to the well in its
descent. On meeting with obstructions in sinking, the water, if pos-
sible, should be removed from the well ; this may perhaps be effected
by bags or pails, if not, by pumping. As stated under the head of
cylinder sinking, clearing the well of water will often make the sand
move at the bottom because of the unbalanced exterior pressure, and
" blows " may occur which may be attended with danger to the well.
Perhaps the quickest plan to adopt is to send down helmet divers with
picks and jumpers when satisfactory progress is not made in the sinking.
It will usually occur that the quantity of material excavated from a
well is from about 60 to 100 per cent, more than the cubic contents of
the subterranean portion of the well, although this excess may be much
more in very unstable earth ; but if wells sink freely, and the water-
levels inside and outside are about equal, the extra excavation may not
exceed 30 to 40 per cent. It is advisable to proceed with the sinking
continuously by day and night shifts in rivers where the working
suason is short.
From an analysis of many works, the rate of sinking appears to
decrease according as the depth increases. The rate of sinking in sand
with ordinary obstacles, of some wells 13 ft. 6 in. in outside diameter,
was from 12 to 18 in. per day at starting, up to about 10 ft. deep, and
6 in. per day for a depth of 20 ft. Of course the rate will vary
considerably according to many circumstances, which have been
mentioned in cylinder sinking, and the progression is frequently very
variable. Ten to twelve men and a foreman will be sufficient to effect
this amount of sinking for a well 10 to 12 ft. in diameter, or one man
for every foot of diameter of the well. After a depth of about 30 ft. has
been reached, unless the soil is favourable, the amount of sinking in a
day of twenty-four hours will often become tedious, perhaps not
exceeding 2 in. and even 1 in. Wells 8 to 13 ft. 6 in. in diameter have
been sunk at the rate of from 3 to 6 in. per hour. At the Sone Canal,
where most of four thousand wells were sunk from 8 to 10 ft. in the
sand, a well 10 ft. by 6 ft. was sunk 10 feet in nine hours ; but this
is an exceptional rate, and in any soil other than most open sand, it is
hardly ever reached. Wells sometimes go down as much in one hour
as shortly after will take a day, therefore they require to be thoroughly
watched ; but progress of course much depends on the efficiency of the
excavating apparatus employed.
From an examination of several examples where seams of clay have
been encountered after sinking in sand, and a comparison of rates
of the same diameter of well and depths in clay and in sandy soil
under analogous circumstances, it appears that the rate of sinking in
the former is from about one-fourth to one-fifth of the latter.
128 THE WELL SYSTEM OF FOUNDATIONS.
In sinking groups of wells joined together, it has been found that
the excavation in all the wells of one cluster sho ild be carried on simul-
taneously and equally, and then there is no difficulty in sinking them
evenly, and that less kentledge is required to force them down.
To " right " or bring back to perpendicularity, a well which has
tilted after the second length has been sunk, is an operation necessita-
ting great care, hence the importance of the descent always being kept
vertical. Wells have been righted when the third length has been built,
by pulling them over during sinking operations. After they have
penetrated more than 20 ft. it is very difficult to right them, and after wells
of ordinary diameter have sunk to a depth equal to twice their diameter,
it is almost impossible. Among the expedients used and suggested for
bringing wells back to perpendicularity are, the insertion of perforated
pipes from which water is discharged under pressure on the higher
side to diminish the surface-friction, additional weights on that side of
the well, which must be done very carefully so as not to unduly strain
the steining, excavating by a dredger outside the elevated portion, by
having a pulling-strain in the direction in which the well is to be righted,
by excavating under the curb, by strutting on the lower side, and by
depositing stiff material on the surface of the ground outside and close
to the well. (See also Chapter VII.)
After a well has been sunk, in depositing the hearting a thorough
connection must be effected between it and the steining, so that the
whole may act as a monolithic mass. This can be attained by toothing
the internal face of the steining, if of brick, or by set-offs if of brick-
work or concrete, arid in the interior diameter of the well the concrete
face should be rough, so as to bind and bond with the hearting, but, of
course, the external face must be as smooth and as even as possible, to
lessen surface-friction during sinking. The concrete should not be
simply thrown in from the top of the well, if the latter is dry, but be
gently deposited from a moderate height, so that in the descent, the
heavier may not separate from the lighter constituents, and it is best
when merely shovelled from a stage practically on the level with the
surface ; or it should be lowered in self-acting discharging skips if it
has to be passed through water. (See Chapter IX.) When the wells are
finished, the spans should be measured to ascertain what provision must
be made for lateral and longitudinal divergence.
For quay and dock walls not subject to very heavy loads, it is not
necessary that the whole of the hearting of the wells should be of
concrete, as, provided the bottom of a well is sealed from water, which
a layer of from 5 to 12 ft. of cement concrete generally effects, and the
concrete bottom has a proper bearing, sand will do; but it should be damp
when deposited, and well rammed, and water should be prevented from
accumulating behind the wall of wells, as then the pressure may become
THE WELL SYSTEM OF FOUNDATIONS. 129
that of the head of water. For practical information on concrete, see
the second edition of the author's book "Notes on Concrete and
Works in Concrete."
At Pallanza, Lake Maggiore, brickwork wells 23 ft. apart, centre to
centre, 7 ft. 6 in. external, and 5 ft. 3 in. internal diameter, were used.
They were sunk into hard compact sand, 20 to 30 ft. below low water,
and filled with concrete. Upon them nearly semi-circular arches were
turned, and the quay wall built. It was stated that whereas all the other
walls on the shore in the neighbourhood were more or less damaged,
and some collapsed, this system has proved entirely satisfactory. Quay
walls on this principle have among other places been erected at Bor-
deaux, St. Nazaire, and Rochefort, where semi-circular arches, 30
ft. span, were turned on piers 16 to 20 ft. in thickness, sunk to a depth
of 50 to 90 ft. in soft alluvium. The wells were of rubble masonry
in cement mortar, and were built in a trench to a height of 10 ft., and
allowed fifteen days to set, when the excavation was commenced by
which means they were sunk.
Bridge abutments have, especially in India, also been built on arches
turned upon well-piers a few feet below the ground.
UNIVERSITY
INDEX.
A.
Abutments, Well System of, 129.
Air, Compressed, Effect on Men,
81-83.
Cooling, 78, 79, 81.
— Noxious, in Cylinder Sinking, 49.
— Penetrating Pressure on some Sub-
stances, 74, 75.
— Quantity required, 73, 75, 76, 78.
— Temperature, Precautions. 80, 81.
Air-Compressors, Arrangement and
Character, 77-79, 81.
— Hydraulic, 79.
— Old, 78.
— Number of, 77.
Air Escape, Effect of, 74.
Air-Lift, Excavating Apparatus, 116.
Air-Lock, Arrangement and Purpose,
83-87.
— Doors, Interlocking, etc., 84-86.
— Floor, 77, 84,
— Height, 84.
— Light, 83.
— Lighting, 84,
— Position of, 86, 87.
— Removal of Excavation in, 86.
— Roof, 77.
— Signalling Apparatus, 81, 85, 86.
— Size of, 84, 85.
- Temperature, 80-81.
Air-Pipes, 84.
Air-Pressure, Advisable, 73-76.
— Declining, Effects of, 76.
— Formula, 75.
— when Injurious to Men, 80, 81.
— when Springs Encountered, 76.
— Working-hours in, 80.
Air-Pumps, Working Continuously,
73.
Air-Supply, Constant Discharge, 74.
— Purifying it, Necessity of, 74, 81.
Air-Tightness of a Cylinder, 73.
Air-Waste in Sinking Cylinders, 73,
74.
Areas of Cylinder, Table of, 18, 19.
Artificial Islands, Pitching Wells upon,
124.
B.
Bag and Spoon Dredger, when Useful,
101, 104.
Base of Cylinder Piers, Load on,
24-31.
" Blows " of Soil during Sinking, 46-48,
54, 71, 101.
Bracing Cylinder-Piers, 3, 4.
Brickwork, Penetrating Air-Pressure,
75.
Bruce and Batho's Excavators, 106.
— Special Features, 101, 106.
Bucket-Dredgers, Construction, 100.
— Defects, 96, 97, 99, 101.
— Discharge, 100.
— Form, 1UO.
— v. Grab-Dredgers, 99.
— Hoisting Apparatus, 102.
— Improvements in, 101, 106, 110.
— when Ineffectual, 94, 97, 106, 108,
109.
— v. Jumpers, 96.
— Lifting Power required, 98.
— Shape of, causes Success or Failure,
99-101.
— Size of, 97, 98, 100.
— Suitability of Earth for, 95, 96, 99
101, 109, 110.
— Working Capacity, 99, 101.
K2
132
INDEX.
Bull's Dredger, 108, 110.
Bursting of an Air-Lock, 83.
C.
Compressed-Air System of Sinking,
70-72.
— Adoption, 94.
— Advantages, 72.
— Dangerousness, 73.
— Depth of Economic Adoption,
71-73.
— Disadvantages, 72.
— and Dredging, 94, 95.
— Effects of, 70, 71, 81, 83.
— Limiting Depth, 73.
— Old and New, 70.
— Precautions, 81.
— Requirements, 70, 71.
— Signalling Apparatus, 81.
— Waste of Air in, 73.
Compressors, Air, Arrangement and
Character, 77-79.
— Number, 77.
Cooling Compressed Air, 78, 7£, 81.
Cutting-Edge, Excavating around and
under, 96, 97, 102, 104, 106.
Cutting-Ring, 5, 6.
Cylinder-Piers, Advantageous Applica-
tion, 1, 2, 4.
— Area required for Excavating, 63,
64, 97, 98.
— Compressed- Air, Method of Sinking,
70-72.
— Cost of Different Methods of Sink-
ing, 71.
— and Cribwork, to Resist Ice-Floes,
2.
— Diameter required, 10-17.
— Distance between, 5, 44, 45.
— Forces Governing Stability, 23,
24.
— Increased Stability, 4, 5.
— Large v. Small, 5, 8, 9.
— Limiting Height, 13, 14.
— Load on Base, 24-33.
— and Opening-Bridges, 4.
— Position, 5, 8.
— Shortening Spans, 5.
— Sinking, 40-50.
Cylinder - Piers, Surface Friction,
33-39.
— Unsuitableness, 3.
— Water-tightness, 67.
— Weights, Diagrams and Formulae,
11, 12.
Table of Areas, etc., 17-23.
— v. Welis, 1, 2.
D.
Design of Bridge-Pier, Determining, 1,
2, 24, 25.
Diack's Excavator, 108.
Diameter required, Cylinder Bridge-
Pier, 60-62.
Dimensions of Rings, 6, 7.
Discharging Material through Air-Lock,
85, 86.
Distance between Cylinder-Piers, 5.
Diver's Helmet, Muddy Water, 82.
— Precautions, 82.
— Rough Weather, 82.
— Signalling, 81.
Dock Walls, Well System of, 116, 126,
129.
Doors, Interlocking Air-Lock, 85, 86.
Dredging Apparatus for Cylinders and
Wells (see also Excavating Appa-
ratus).
— Advantages, 91.
— Bag and Spoon, Useful Application,
101, 104.
— Bucket, when Ineffectual, 94-97,
106, 108-110.
— v. Compressed-Air System, 94, 95,
110.
— Construction, 100, 101.
— Defects, 96-98.
— Design and Purpose, 90 - 93,
95.
— Disadvantages, 91, 92.
— Expulsion System, 117.
— Grab-Dredgers, 99.
— Hoisting and Discharging Appara-
tus, 102, 103.
— Improvements in, 100, 101, 106,
110.
— Jumper and Bucket System com-
bined, 93-95, 99, 105, 109.
INDEX.
133
Dredging Apparatus, Lifting Power re-
quired, 98.
— Shape of, causes Success or Failure,
99-101.
— Single v. Double Chain, 110.
— Size of, 97-100.
— Suitable Earth for, 95, 96, 99, 101,
109, 110.
— Water-jet, 116-118.
— Working Capacity, 99, 101.
E.
Excavating, Working Area for, 63,
64.
— by Compressed Air, 116.
— Effective Action, 116.
— Expulsion System, 117.
— Water-pressure System, 117, 118.
when Ineffectual, 117.
Excavating Apparatus for Cylinders
and Wells (see also Dredging Ap-
paratus).
— Adoption, 94, 95, 110.
— Advantages, 91, 92.
— Defects, 91, 92, 96, 97.
— Design and Purpose, 90-93, 95.
— Hoisting and Discharging Appara-
tus, 102, 103.
— Improvements in, 101, 102-106,
110.
— Jumper and Bag Dredgers, 108-109.
— — and Bucket System combined,
93-95, 99, 105, 109.
— Lifting Power required, 98.
— Screw for Loosening Soil, 107.
— Shape of, causes Failure or Success,
99-101.
— Size of, 97-100.
— Suitability of Earth for, 95, 99,
101.
— Various, Notes on, 103-111.
— Working Capacity, 101.
Excavation, Discharging Pipe through
Air-Lock, 85, 86.
— Method of, in Cylinder, 87.
— Removal of, in Air-Lock, 86.
Excavator-Pumps, 111, 112.
Explosives for Removal of Obstruc-
tions, 55.
F.
Floor of Air-Lock, Pressure on, 77.
Flotation Power of Cylinder, 19-23.
Form of Cylinder Rings, 5, 8, 9.
Foul Air in Cylinders, 49.
Fouracre's Dredger and Spider Clay
Cutter, 106.
Frictional Resistance, Earth on Cylin-
ders, 33-39.
G.
Gatwell's Excavator, Special Features,
105, 106.
Grab-Dredgers v. Bucket-Dredgers, 99-
100.
— Construction, 100, 109.
— Object, 99, 109.
Gradual Pressure Room in Air-locks, 83.
H.
Hearting, Contraction, etc., 67.
— Depositing in Compressed Air,
67.
under Hydrostatic Pressure, 67.
— Deposition, 66, 69.
— Grout, for filling Cavities round the
Cutting Edge, 66.
— Purpose of, and Material for, 65,
66.
— Surface of Base before Deposition,
66, 111.
— Watertight, Importance of, 67,
68.-
Height, Limiting, of Cylinder Pier,
13, 14.
Hoe-Scoop, or Indian Jham, Usefulness
of, 104.
Hoisting and Discharging Apparatus
for Dredging Machinery, 102-103.
Hydraulic Method of Removing Obstruc-
tions, 56.
Inclined Cylinders, A Cause of, 57.
— " Righting," 56, 57.
134
INDEX.
Iron, Cast, Penetrating Air Pressure,
74.
Iron Cylinders, Advantages of, 1, 2.
— v. Well System, 1, 2.
Iron Rings, Dimensions of, 3, 4.
— Object of, 3.
Islands, Artificial, for Pitching Wells
upon.
Ive's Excavator. 107.
J.
Jham, Indian, or Hoe-Scoop, Useful-
ness, 104.
Joints, Cylinder Rings, 6, 7.
Jumper, Chiselled Rail, 105.
— Rail, 108.
K.
Kentledge, Calculation, 60-65.
— Cast, 58.
— Large and Small Cylinders, 59,
60.
— Methods and Precautions, 58, 59.
— Permanent Hearting for, 59, 60.
— Quantity required, 64, 65.
— Resistance to be Overcome, 61,
62.
— Thickness and Weight of Casing
required, 62, 63.
— Top, Inside, and Outside, 58, 59.
— Unobstructed Area required in
Cylinder, 63, 64.
— Water-tank, 58, 59.
L.
Large Cylinders v. Small, 5.
Leakage of Air in a Cylinder, 73, 74.
Leslie's, Sir Bradford, Rotary Plough
and Boring-head, 111-113.
Lifting Apparatus, Dredging Ma-
chinery, 102, 103.
Lighting, Air-Lock, 84.
— Working Chamber, 88-90.
Limiting Depth, Compressed-Air Sys-
tem, 73.
— Height of Cylinder, 13.
Load on the Base of a Cylinder Founda
tion, 24-28.
- Safe. 26-31.
— Table of Safe Loads, 31-33.
M.
Machinery, Air-Compressing, 77.
— Character and Arrangement, 78.
Making-up Ring, 7.
Milroy's Excavator, 107.
Molesworth's Dredger, 111.
Mooring Pontoons, 51, 52.
O.
Obstructions in Sinking,
— Advantage of Compressed-air
System, 54.
— " Blows " of Soil caused by,
101.
— Explosives, Use of, Questionable,
55, 56.
— Hydraulic Method of Removal,
56.
— Methods of Removal, 53-57.
— Removal of, 54, 95.
P.
Pipes, Air, 84.
Pontoon System of Floating-out Cylin-
ders, 51, 52.
— Improvement in, 52.
— Precautions necessary, 51-53.
— Small Cylinders, 52.
— Top and Bottom Guidance neces-
sary, 51.
Portland-cement Concrete Cylinders, 3.
Position of Air-lock, 86, 87.
— Cylinder Piers, 5.
Pressure, Normal, of Soil, 28.
Pumps for Sandy Water, 111, 112.
Purification of Compressed Air, 81.
Q.
Quay Walls, Well System of, 116, 126
129.
INDEX.
135
R.
Rammer for Hard Soils, 104. 105.
Reducing Ring of Cylinder, 4.
" Righting " an Inclined Cylinder, 56, 57.
- an Inclined Well, 125, 128.
Rings of Cylinder, Contraction of, 67.
— Cutting-Ring, 7.
— Dimensions of, 6, 7.
— Form of, 5.
— Making-up Ring, 7.
— Thickness of, 6.
Roof, Air-Lock, Pressure upon, 77.
S.
Sand-Pumps, Arrangement and Use of,
111, 112,114.
— Combined with Cutters, 111, 112.
— Ead's,H6.
- Kennard's, 108.
— Working, 111, 112.
Sandstone, Penetrating Air-Pressure,
75.
Shafts to Working Chamber, 85, 87, 88.
Signalling Apparatus, Air-lock, 85.
— Compressed- Air System, 81.
Sinking Cylinders, " Blows " of Soil
during, 46, 49.
— Close together, 44.
— Comparing Cost of, 40.
— Compressed- Air Method, 70, 72.
— Cost of Different Methods, 40, 71, 73.
— Danger of Sudden Sinking, 44.
— Earthbound, 48, 49.
— General Notes, 40.
- Loose Soils, 48, 49.
— Methods of, 40-42.
— Noxious Gases Encountered in, 49.
— Obstructions in, 53.
— Outside Subsidence caused by, 46,
48.
— Pontoon, System of Floating-out,
51, 52.
— Precautions in, 45, 46.
— Staging, 50, 51, 102.
— Suddenly to be Avoided, 71.
— Vertical Sinking Important, 43, 44.
— Water-levels, Inside and Outside
47, 48.
Sinking Wells by Compressed Air, 126.
— Discontinuing, When Incomplete,
126.
— General Notes, 124-128.
— Rate of Sinking, 127.
— " Righting " Them, 125, 128.
Small v. Large Cylinders, 5, 8, 9, 44.
Spider Clay Cutter and Dredger,
Fouracre's, 106.
Stability of Cylinder-Bridge Piers,
Forces Governing, 23, 24.
Staging, 9, 50, 51, 97.
— in Exceptional Circumstances, 50,
51.
— Fixed, when Impracticable, 50.
— Use of, 50.
Stoney's Helical Excavator, 111.
Strong's Excavator, where Useful, 105.
Subsidence of Ground during Sinking
Cylinders, 46.
Supply Shafts, 87, 88.
Surface Areas of Cylinders, Table of»
19-22.
Surface Friction, on a Cylinder Pier,
33-39.
— Depth, Influence, 37, 38.
Reliable, 38.
— Dry and Wet Surface, 37.
— Large v. Small Cylinders, 38.
— Table of Values, 39.
T.
Furness and
Telescopic Dredger,
Slater's, 111.
Temperature of Air, Precautions, 80,
81.
Thickness of Rings, 5, 6.
Timber, Penetrating Air-Pressure, 74.
Top Ring of Cylinder,.?.
W.
Water-jet Excavators, 112-118.
Water-sealing a Cylinder, 68, 69.
— Thickness required, 69.
Weight of Cylinder Piers.
— Diagram and Formulae, 10-12.
— Tables of, 17-23.
136
INDEX.
Well System, Abutments, 129.
— Advantageous Application, 1,4,118.
— Conditions when it may Fail, 1,
118.
— Curbs, 122.
Heavy v. Light, 122.
Material for, 122, 123.
Securing Steining to, 122.
— Excavation, Internal, 127.
— Form of Wells, 119, 122.
— Grooving and Interlocking Wells,
Objections to, 122.
— Hearting, 128.
— Height of Rings, 125.
— Large v. Small Wells, 118, 119.
— Methods of Sinking, 124, 125.
— Modern Practice, 118.
Well System, Quays and Dock Walls,
116, 126, 129.
— Sinking Wells, 124.
Close together, 119, 128.
— Steining, 120-122.
— Strains on Wells, 119.
— Tie Bolts, 121, 122.
Wood, Penetrating Air-Pressure, 74.
Working Chamber, Arrangement and
Construction, 87.
— Height and Size, 87.
— Lighting, 88-90.
— Purpose of, 87.
— Supply Shafts to, 87, 88.
— Temperature, 80, 81.
— Water Ingression, 88.
Working-hours under Air-Pressure, 80.
WERTMEIMSB. LEA * CO~ PRINTERS. LONDON.
Crown 8f0, cloth, 2s. 6d.
SCAMPING TRICKS
AND
ODD KNOWLEDGE
OCCASIONALLY PRACTISED UPON PUBLIC WORKS
CHRONICLED FROM THE CONFESSIONS OF SOME
OLD PRACTITIONERS.
BY JOHN NEWMAN,
Assoc.M.lNST.C.E.
OIF THE
ENGINEERIXG NEWS (New York).
'•This readable and interesting book is arranged as a conversation
between two old sub-contractors, in the course of which they deliver
themselves of numerous yarns relating to methods practised on various
kinds of works, to deceive the engineers and obtain the much-desired
' extras,' thus indicating some of the points to be especially looked after
in superintending the construction of works. A still more interesting
and valuable feature of the book, however, is that it is full of practical
hints and notes upon different methods of carrying out different kinds
of work under varying circumstances, giving also advice as to the merits
of the different methods."
THE BRITISH ARCHITECT.
" We take the following story from a series of amusing narratives of
' Scamping Tricks and Odd Knowledge occasionally practised upon
Public Works.' "
INDUSTRIES.
" This book is out of the run of ordinary professional works, inasmuch
as it is intended, not so much for the purpose of showing how public
works are to be carried out, as to point out some of the tricks which are
practised by those who do not wish to carry them out properly, and to
name some methods, founded on practical experience, adopted by sub-
contractors and others to cheaply and quickly execute work.
"The young engineer or inspector will find many things in the book
which will at least cause him to pay attention to special points in the
different departments of civil engineering construction. Such matters
as piles, which are chiefly hidden from view, seem to require careful
inspection, and in fact all work which is covered up when the structure
is completed."
INDIAN ENGINEERING.
" This is an entertaining little book. It abounds with stories of gross
cheating. Its publication is not likely to corrupt the morals of native
contractors, some of whom could give points to Bill Dark (who is re-
counting his ' dodges '), inasmuch as that worthy claimed to own a
conscience, though it is not very prominent, and always to draw the line
somewhere — always put some lime in his mortar, and some headers in
his masonry.
" The ingenuity displayed in hiding the results of some of the frauds
may be useful in setting young engineers on their guard against the
over-plausible."
THE ENGINEER AND IRON TRADES ADVERTISER (Scotland).
u The somewhat uncommon title of this book will in itself prove a
ready attraction to the ordinary student of current literature. The title
page alone is characterised by a curious vein of humour. The author
has, however, a serious and a most important object in view.
"There is a peculiar charm in it not usually found in works where
technical details require to be recorded. The many 'dodges' indulged
in by these ideal contractors will come as 'eye-openers' to those unac-
quainted with the subject. We have no hesitation in saying that the
volume before us is likely to serve a good purpose, and it is deserving
of a wide circulation."
E. & F. N. SPON, 125, STRAND, LONDON.
( iii )
Crown Svo, cloth, 7s. 6d.
EAETHWOEE SLIPS AND SUBSIDENCES
UPON PUBLIC WOEKS,
BY JOHN NEWMAN, Assoc.M.lNST.C.E.
REVIEWS OF THE PRESS.
ENGINEERING NEWS (New York).
" The book is of a practical character, giving the reasons for slips in
various materials, and the methods of preventing them, or of making
repairs and preventing further slips after they have once occurred. The
subject is treated comprehensively, and contains many notes cf practical
value, the result of twenty-five years' experience."
THE BUILDEE.
" We gladly welcome Mr. Newman's book on slips in earthworks as an
important contribution to a right comprehension of such matters.
" There is much in this book that will certainly guard designers of
engineering works against probable, if not against; possible, slips in
earthworks.
" The capital cost of a work and the cost of its maintenance may both
be very sensibly reduced by attention to all the points alluded to by the
author.
" We are glad to see that the author enters at some length into the
subject of the due provision of drainage at the backs of retaining walls,
a matter so often neglected or overlooked, and carries this subject to a far
larger one, the causes which tend to disturb the repose of dock walls.
His remarks on these matters are well worthy of consideration, and are
thoroughly practical, and the items which have to be taken into account
in the necessary statical calculations very well introduced.
" In conclusion, we may say that there is plenty of good useful
information to be obtained from this work, which touches a subject
possessing an exceedingly scanty vocabulary.
u It contains an immense deal of matter which must be swallowed
sooner or later by every one who desires to be a good engineer. "
BUILDING NEWS.
" Mr. John Newman, Assoc.M.Inst.C.E., has written a volume on a
subject that has hitherto only been treated of cursorily.
"Useful advice is given, which the railway engineer and earthwork
contractor may profit by.
" The book contains a fund of useful information."
BUILD EES' REPORTER AND ENGINEERING TIMES.
" The book which Mr. John Newman has written imparts a new interest
to earthworks. It is, in fact, a sort of pathological treatise, and as such
may be said to be unique among books on construction, for in them
failures are rarely recognised. Now in Mr. Newman's volume the
majority of the pages relate to failures, and from them the reader infers
how they are to be avoided, and thus to form earthworks that will endure
longer than those which are executed without much regard to risks.
'; The manner of dealing with the subsidences when they occur, as well
as providing against them, will be found described in the book.
"It can be said that the subject is thoroughly investigated, and con-
tractors as well as engineers can learn much from Mr. Newman's book."
E. & F. N. SPON, 125, STRAND, LONDON.
NOTES ON CONCRETE AND WORKS
IN CONCRETE.
By JOHN NEWMAN,
Assoc.M.lNST.C.E.
REVIEWS OF THE PRESS.
FIRST EDITION.
ENGINEERING.
" An epitome of the best practice, which may be relied upon not to
m islead.
" The successful construction of works in concrete is a difficult matter
to explain in books.
" All the points which open the way to bad work are carefully pointed
out."
IRON.
" As numerous examples are cited of the use of concrete in public
works, and details supplied, the booh will greatly assist engineers engaged
upon such works"
THE BUILDER.
" A very practical little book, carefully compiled, and one which all
writers of specifications for concrete work would do well to peruse.
" The book contains reliable information for all engaged upon public
works.
" A perusal of Mr. Newman's valuable little handbook will point out
the importance of a more careful investigation of the subject than is
usually supposed to be necessary."
AMERICAN PRESS.
BUILDING.
" To accomplish so much in so limited a space, the subject-matter has
been confined to chapters.
" We take pleasure in saying that this is the most admirable and
complete handbook on concretes for engineers of which we have knowledge."
E. & F. N. SPON, 125, STRAND, LONDON.
1893.
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General — Linear Measures — Square Measures — Cubic Measures — Measures of Capacity —
Weights — Combinations — Thermometers.
Elements of Construction for Electro- Magnets. By
Count TH. Du MONCEL, Mem. de 1'Institut de France. Translated from
the French by C. J. WHARTON. Crown 8vo, cloth, 4^. 6d.
A Treatise on the Use of Belting for the Transmis-
sion of Power. By J. H. COOPER. Second edition, illustrated, 8vo,
cloth, 15-r.
A Pocket-Book of Useful Formula and Memoranda
for Civil and Mechanical Engineers. By Sir GuiLFORD L. MOLESWORTH,
Mem. Inst. C.E. With numerous illustrations, 744 pp. Twenty-second
edition, 32mo, roan, 6s.
SYNOPSIS OF CONTENTS:
Surveying, Levelling, etc. — Strength and Weight of Materials — Earthwork, Brickwork,
Masonry, Arches, etc. — Struts, Columns, Beams, and Trusses— Flooring, Roofing, and Roof
Trusses — Girders, Bridges, etc. — Railways and Roads — Hydraulic Formulae — Canals. Sewers,
Waterworks, Docks — Irrigation and Breakwaters — Gas, Ventilation, and Warming — Heat,
Light, Colour, and Sound — Gravity : Centres, Forces, and Powers — Millwork, Teeth of
Wheels, Shafting, etc. — Workshop Recipes — Sundry Machinery — Animal Power — Steam and
the Steam Engine — Water-power, Water-wheels, Turbines, etc. — Wind and Windmills —
Steam Navigation, Ship Building, Tonnage, etc. — Gunnery, Projectiles, etc. — Weights,
Measures, and Money — Trigonometry, Conic Sections, and Curves — Telegraphy — Mensura-
tion— Tables of Areas and Circumference, and Arcs of Circles — Logarithms, Square and
Cube Roots, Powers — Reciprocals, etc. — Useful Numbers — Differential and Integral Calcu-
lus—Algebraic Signs — Telegraphic Construction and Formulae.
8 CATALOGUE OF SCIENTIFIC BOOKS
Hints on Architectural Draughtsmanship. By G. W.
TUXFORD HALLATT. Fcap. 8vo, cloth, is. 6d.
Spons Tables and Memoranda for Engineers ;
selected and arranged by J. T. HURST, C.E., Author of 'Architectural
Surveyors' Handbook,' * Hurst's Tredgold's Carpentry,' etc. Eleventh
edition, 641110, roan, gilt edges, is. ; or in cloth case, is. 6d.
This work is printed in a pearl type, and is so small, measuring only 2^ in. by if in. by
i in. thick, that it may be easily carried in the waistcoat pocket.
" It is certainly an extremely rare thing for a reviewer to be called upon to notice a volume
measuring but 2^ in. by if in., yet these dimensions faithfully represent the size of the handy
little book before us. The volume — which contains 118 printed pages, besides a few blank
pages for memoranda — is, in fact, a true pocket-book, adapted for being carried in the waist-
coat pocket, and containing a far greater amount and variety of information than most people
would imagine could be compressed into so small a space The little volume has been
compiled with considerable care and judgment, and we can cordially recommend it to our
readers as a useful little pocket companion." — Engineering.
A Practical Treatise on Natural and Artificial
Concrete, its Varieties and Constructive Adaptations. By HENRY REID,
Author of the ' Science and Art of the Manufacture of Portland Cement.'
New Edition, with 59 woodcuts and 5 plates, 8vo, cloth, 15^.
Notes on Concrete and Works in Concrete; especially
written to assist those engaged upon Public Works. By JOHN NEWMAN,
Assoc. Mem. Inst. C.E., crown 8vo, cloth, ^s. 6d.
Electricity as a Motive Power. By Count TH. Du
MONCEL, Membre de 1'Institut de France, and FRANK GERALDY, Inge-
nieur des Pontset Chaussees. Translated and Edited, with Additions, by
C. J. WHARTON, Assoc. Soc. Tel. Eng. and Elec. With 113 engravings
and diagrams •, crown 8vo, cloth, Js. 6d.
Treatise on Valve-Gears, with special consideration
of the Link-Motions of Locomotive Engines. By Dr. GUSTAV ZEUNER,
Professor of Applied Mechanics at the Confederated Polytechnikum of
Zurich. Translated from the Fourth German Edition, by Professor J. F.
KLEIN, Lehigh University, Bethlehem, Pa. Ilhtstrated, 8vo, cloth, \2s. 6d.
The French - Polishers Manual. By a French-
Polisher; containing Timber Staining, Washing, Matching, Improving,
Painting, Imitations, Directions for Staining, Sizing, Embodying,
Smoothing, Spirit Varnishing, French-Polishing, Directions for Re-
polishing. Third edition, royal 32m o, sewed, 6d.
Hops, their Cultivation, Commerce, and Uses in
various Countries. By P. L. SIMMONDS. Crown 8vo, cloth, 4^. 6d.
The Principles of Graphic Statics. By GEORGE
SYDENHAM CLARKE, Major Royal Engineers. With 112 illustrations.
Second edition, 4*0, cloth, I2s. 6d.
PUBLISHED BY E. & F. N. SPON.
Dynamo Tenders Hand-Book. By F. B. BADT, late
1st Lieut. Royal Prussian Artillery. With 70 illustrations. Third edition,
i8mo, cloth, 4^. 6d.
Practical Geometry, Perspective, and ^Engineering
Drawing; a Course of Descriptive Geometry adapted to the Require-
ments of the Engineering Draughtsman, including the determination of
cast shadows and Isometric Projection, each chapter being followed by
numerous examples ; to which are added rules for Shading, Shade-lining,
etc., together with practical instructions as to the Lining, Colouring,
Printing, and general treatment of Engineering Drawings, with a chapter
on drawing Instruments. By GEORGE S. CLARKE, Capt. R.E. Second
edition, with 21 plates. 2 vols., cloth, IQJ. 6d.
The Elements of Graphic Statics. By Professor
KARL VON OTT, translated from the German by G. S. CLARKE, Capt.
R.E., Instructor in Mechanical Drawing, Royal Indian Engineering
College. With 93 illustrations, crown 8vo, cloth, $s.
A Practical Treatise on the Manufacture and Distri-
bution of Coal Gas. By WILLIAM RICHARDS. Demy 4to, with numerous
wood engravings and 29 plates, cloth, 28.?.
SYNOPSIS OF CONTENTS :
Introduction — History of Gas Lighting — Chemistry of Gas Manufacture, by Lewis
Thompson, Esq., M.R.C.S. — Coal, with Analyses, by J. Paterson, Lewis Thompson, and
G. R. Hislop, Esqrs. — Retorts, Iron and Clay — Retort Setting — Hydraulic Main — Con-
densers— Exhausters — Washers and Scrubbers — Purifiers — Purification — History of Gas
Holder — Tanks, Brick and Stone, Composite, Concrete, Cast-iron, Compound Annular
Wrpught-iron — Specifications — Gas Holders — Station Meter — Governor — Distribution —
Mains — Gas Mathematics, or Formulae for the Distribution of Gas, by Lewis Thompson, Esq.—
Services — Consumers' Meters — Regulators — Burners — Fittings — Photometer — Carburization
of Gas — Air Gas and Water Gas — Composition of Coal Gas, by Lewis Thompson, Esq. —
Analyses of Gas — Influence of Atmospheric Pressure and Temperature on Gas — Residual
Products — Appendix — Description of Retort Settings, Buildings, etc., etc.
The New Formula for Mean Velocity of Discharge
of Rivers and Canals. By W. R. KUTTER. Translated from articles in
the ' Cultur-Ingenieur,' by Lowis D'A. JACKSON, Assoc. Inst. C.E.
8vo, cloth, I2s. 6d.
The Practical Millwright and Engineers Ready
Reckoner; or Tables for finding the diameter and power of cog-wheels,
diameter, weight, and power of shafts, diameter and strength of bolts, etc.
By THOMAS DIXON. Fourth edition, I2mo, cloth, 3*.
Tin: Describing the Chief Methods of Mining,
Dressing and Smelting it abroad ; with Notes upon Arsenic, Bismuth and
Wolfram. By ARTHUR G. CHARLETON, Mem. American Inst. of
Mining Engineers. With plates •, 8vo, cloth, I2s. 6d.
io CATALOGUE OF SCIENTIFIC BOOKS
Perspective, Explained and Illustrated. By G. S.
CLARKE, Capt. R.E. With ilhtstrations, 8vo, cloth, 3^-. 6d.
Practical Hydraulics ; a Series of Rules and Tables
for the use of Engineers, etc., etc. By THOMAS Box. Ninth edition,
numerous plates , post 8vo, cloth, $s.
The Essential Elements of Practical Mechanics ;
based on the Principle of Work, designed for Engineering Students. By
OLIVER BYRNE, formerly Professor of Mathematics, College for Civil
Engineers. Third edition, with 148 -wood engravings, post 8vo, cloth,
7^. 6d.
CONTENTS :
Chap. I. How Work is Measured by a Unit, both with and without reference to a Unit
of Time — Chap. 2. The Work of Living Agents, the Influence of Friction, and introduces
one of the most beautiful Laws of Motion — Chap. 3. The principles expounded in the first and
second chapters are applied to the Motion of Bodies — Chap. 4. The Transmission of Work by
simple Machines — Chap. 5. Useful Propositions and Rules.
Breweries and Mailings : their Arrangement, Con-
struction, Machinery, and Plant. By G. SCAMELL, F.R.I.B.A. Second
editjon, revised, enlarged, and partly rewritten. By F. COLYER, M.I.C.E.,
M.I.M.E. With 20 plates, 8vo, cloth, I2s. 6d.
A Practical Treatise on the Construction of Hori-
zontal and Vertical Waterivheels, specially designed for the use of opera-
tive mechanics. By WILLIAM CULLEN, Millwright and Engineer. With
II plates. Second edition, revised and enlarged, small 4to, cloth, 12s. 6d.
A Practical Treatise on Mill-gearing, Wheels, Shafts,
Riggers, etc.', for the use of Engineers. By THOMAS Box. Third
edition, -with 1 1 plates. Crown 8vo, cloth, Js. 6d.
Mining Machinery: a Descriptive Treatise on the
Machinery, Tools, and other Appliances used in Mining. By G. G.
ANDRE, F.G.S., Assoc. Inst. C.E., Mem. of the Society of Engineers.
Royal 4to, uniform with the Author's Treatise on Coal Mining, con-
taining 182 plates, accurately drawn to scale, with descriptive text, in
2 VOls., Cloth, 3/. I2J.
CONTENTS :
Machinery for Prospecting, Excavating, Hauling, and Hoisting — Ventilation — Pumping —
Treatment of Mineral Products, including Gold and Silver, Copper, Tin, and Lead, Iron,
Coal, Sulphur, China Clay, Brick Earth, etc.
Tables for Setting out Curves for Railways, Canals,
Roads, etc., varying from a radius of five chains to three miles. By A.
KENNEDY and R. W. HACKWOOD. Illustrated 321110, cloth, 2s. 6d.
PUBLISHED BY E. & F. N. SPON. n
Practical Electrical Notes and Definitions for the
use oj Engineering Students and Practical Men. By W. PERREN
MAYCOCK, Assoc. M. Inst E.E., Instructor in Electrical Engineering at
the Pitlake Institute, Croydon, together with the Rules and Regulations
to be observed in Electrical Installation Work. Second edition. Royal
32mo, roan, gilt edges, 4^. 6d., or cloth, red edges, $s.
The Draughtsman s Handbook of Plan and Map
Drawing^ including instructions for the preparation of Engineering,
Architectural, and Mechanical Drawings. With numerous illustrations
in the text, and 33 plates (15 printed in colours). By G. G. ANDRE,
F.G.S., Assoc. Inst. C.E. 4to, cloth, gs.
CONTENTS :
The Drawing Office and its Furnishings — Geometrical Problems — Lines, Dots, and their
Combinations — Colours, Shading, Lettering, Bordering, and North Points — Scales — Plotting
— Civil Engineers' and Surveyors' Plans — Map Drawing — Mechanical and Architectural
Drawing — Copying and Reducing Trigonometrical Formulae, etc., etc.
The B oiler-maker s andiron Ship-builders Companion,
comprising a series of original and carefully calculated tables, of the
utmost utility to persons interested in the iron trades. By JAMES FODEN ,
author of ' Mechanical Tables,' etc. Second edition revised, with illustra-
tions, crown 8vo, cloth, 5^.
Rock Blasting: a Practical Treatise on the means
employed in Blasting Rocks for Industrial Purposes. By G. G. ANDRE,
F.G.S., Assoc. Inst. C.E. With 56 illustrations and 12 plates ; 8vo, cloth,
ioj. 6d.
Experimental Science: Elementary, Practical, and
Experimental Physics. By GEO. M. HOPKINS. Ilhistrated by 672
engravings. In one large vol., 8vo, cloth, i$s.
A Treatise on Ropemaking as practised in public and
private Rope-yards, with a Description of the Manufacture, Rules, Tables
of Weights, etc., adapted to the Trade, Shipping, Mining, Railways,
Builders, etc. By R. CHAPMAN, formerly foreman to Messrs. Huddart
and Co., Limehouse, and late Master Ropemaker to H.M. Dockyard,
Deptford. Second edition, I2mo, cloth, 3^.
Laxtoris Builders and Contractors Tables ; for the
use of Engineers, Architects, Surveyors, Builders, Land Agents, and
others. Bricklayer, containing 22 tables, with nearly 30,000 calculations.
4to, cloth, 5-r.
Laxtons Builders and Contractors' Tables. Ex-
cavator, Earth, Land, Water, and Gas, containing 53 tables, with nearly
24,000 calculations. 4to, cloth, 5*.
B 4
12 CATALOGUE OF SCIENTIFIC BOOKS
Egyptian Irrigation. By W. WILLCOCKS, M.I.C.E.,
Indian Public Works Department, Inspector of Irrigation, Egypt. With
Introduction by Lieut-Col. J. C. Ross, R.E., Inspector-General of
Irrigation. With numerous lithographs and 'wood engravings^ royal 8vo,
cloth, i/. i6s.
Screw Cutting Tables for Engineers and Machinists,
giving the values of the different trains of Wheels required to produce
Screws of any pitch, calculated by Lord Lindsay, M.P., F.R.S., F.R.A.S.,
etc. Cloth, oblong, 2s.
Screw Cutting Tables, for the use of Mechanical
Engineers, showing the proper arrangement of Wheels for cutting the
Threads of Screws of any required pitch, with a Table for making the
Universal Gas-pipe Threads and Taps. By W. A. MARTIN, Engineer.
Second edition, oblong, cloth, is., or sewed, 6d.
A Treatise on a Practical Method of Designing Slide-
Valve Gears by Simple Geometrical Construction, based upon the principles
enunciated in Euclid's Elements, and comprising the various forms of
Plain Slide- Valve and Expansion Gearing ; together with Stephenson's,
Gooch's, and Allan's Link-Motions, as applied either to reversing or to
variable expansion combinations. By EDWARD J. COWLING WELCH,
Memb. Inst. Mechanical Engineers. Crown 8vo, cloth, 6s.
Cleaning and Scouring : a Manual for Dyers, Laun-
dresses, and for Domestic Use. By S. CHRISTOPHER. i8mo, sewed, 6d.
A Glossary of Terms used in Coal Mining. By
WILLIAM STUKELEY GRESLEY, Assoc. Mem. Inst. C.E., F.G.S., Member
of the North of England Institute of Mining Engineers. Illustrated with
numerous woodcuts and diagrams^ crown 8vo, cloth, 5-r.
A Pocket-Book for Boiler Makers and Steam Users,
comprising a variety of useful information for Employer and Workman,
Government Inspectors, Board of Trade Surveyors, Engineers in charge
of Works and Slips, Foremen of Manufactories, and the general Steam-
using Public, By MAURICE JOHN SEXTON. Second edition, royal
32mo, roan, gilt edges, $s.
Electrolysis: a Practical Treatise on Nickeling,
Coppering, Gilding, Silvering, the Refining of Metals, and the treatment
of Ores by means of Electricity. By HIPPOLYTE FONTAINE, translated
from the French by J, A. BERLY, C.E., Assoc. S.T.E. With engravings.
Svo,, cloth, 9J.
PUBLISHED BY E. & F. N. SPON. 13
Barlow s Tables of Squares, Cubes, Square Roots,
Cube Roots, Reciprocals of all Integer Numbers up to 10,000. Post 8vo,
cloth, 6s.
A Practical Treatise on the Steam Engine, con-
taining Plans and Arrangements of Details for Fixed Steam Engines,
with Essays on the Principles involved in Design and Construction. By
ARTHUR RIGG, Engineer, Member of the Society of Engineers and of
the Royal Institution of Great Britain. Demy 410, copiously illustrated
•with woodcuts and 96 plates, in one Volume, half-bound morocco, 2/. 2s. ;
or cheaper edition, cloth, 2$s.
This work is not, in any sense, an elementary treatise, or history of the steam engine, but
is intended to describe examples of Fixed Steam Engines without entering into the wide
domain of locomotive or marine practice. To this end illustrations will be given of the most
recent arrangements of Horizontal, Vertical, Beam, Pumping, Winding, Portable, Semi-
portable, Corliss, Allen, Compound, and other similar Engines, by the most eminent Firms in
Great Britain and America. The laws relating to the action and precautions to be observed
in the construction of the various details, such as Cylinders, Pistons, Piston-rods, Connecting-
rods, Cross-heads, Motion-blocks, Eccentrics, Simple, Expansion, Balanced, and Equilibrium
Slide-valves, and Valve-gearing will be minutely dealt with. In this connection will be found
articles upon the Velocity of Reciprocating Parts and the Mode of Applying the Indicator,
Heat and Expansion of Steam Governors, and the like. It is the writer's desire to draw
illustrations from every possible source, and give only those rules that present practice deems
correct.
A Practical Treatise on the Science of Land and
Engineering Surveying, Levelling, Estimating Quantities, etc., with a
general description of the several Instruments required for Surveying,
Levelling, Plotting, etc. By H. S. MERRETT. Fourth edition, revised
by G. W. USILL, Assoc. Mem. Inst. C.E. 41 plates, with illustrations
and tables, royal 8vo, cloth, I2j. 6d.
PRINCIPAL CONTENTS :
Part i. Introduction and the Principles of Geometry. Part 2. Land Surveying; com-
prising General Observations — The Chain — Offsets Surveying by the Chain only — Surveying
Hilly Ground — To Survey an Estate or Parish by the Chain only — Surveying with the
Theodolite — Mining and Town Surveying — Railroad Surveying — Mapping — Division and
Laying out of Land — Observations on Enclosures — Plane Trigonometry. Part 3. Levelling—-
Simple and Compound Levelling— The Level Book— Parliamentary Plan and Section-
Levelling with a Theodolite — Gradients — Wooden Curves — To Lay out a Railway Curve-
Setting out Widths. Part 4. Calculating Quantities generally for Estimates— Cuttings and
Embankments — Tunnels— Brickwork — Ironwork — Timber Measuring. Part 5. Description
and Use of Instruments in Surveying and Plotting — The Improved Dumpy Level — Troughton's
Level — The Prismatic Compass — Proportional Compass— Box Sextant— Vernier— Panta-
graph — Merrett's Improved Quadrant — Improved Computation Scale — The Diagonal Scale —
Straight Edge and Sector. Part 6. Logarithms of Numbers — Logarithmic Sines and
Co-Sines, Tangents and Co-Tangents — Natural Sines and Co-Sines — Tables for Earthwork,
for Setting out Curves, and for various Calculations, etc., etc., etc.
Mechanical Graphics. A Second Course of Me-
chanical Drawing. With Preface by Prof. PERRY, B.Sc., F.R.S.
Arranged for use in Technical and Science and Art Institutes, Schools
and Colleges, by GEORGE HALLIDAY, Whitworth Scholar. 8vo,
cloth, 6s.
14 CATALOGUE OF SCIENTIFIC BOOKS
The Assayers Manual: an Abridged Treatise on
the Docimastic Examination of Ores and Furnace and other Artificial
Products. By BRUNO KERL. Translated by W. T. BRANNT. With 65
ilhtstrations, 8vo, cloth, I2J. 6d.
Dynamo - Electric Machinery : a Text - Book for
Students of Electro-Technology. By SILVANUS P. THOMPSON, B.A.,
D.Sc., M.S.T.E. {New edition in the press.
The Practice of Hand Turning in Wood, Ivory, Shell,
etc., with Instructions for Turning such Work in Metal as maybe required
in the Practice of Turning in Wood, Ivory, etc. ; also an Appendix on
Ornamental Turning. (A book for beginners.) By FRANCIS CAMPIN.
Third edition, with wood engravings, crown 8vo, cloth, 6s.
CONTENTS :
On Lathes — Turning Tools — Turning Wood — Drilling — Screw Cutting — Miscellaneous
Apparatus and Processes— Turning Particular Forms — Staining— Polishing— Spinning Metals
—Materials — Ornamental Turning, etc.
Treatise on Watchwork, Past and Present. By the
Rev. H. L. NELTHROPP, M.A., F.S.A. With 32 illustrations, crown
8vo, cloth, 6s. 6d.
CONTENTS :
Definitions of Words and Terms used in Watchwork — Tools — Time — Historical Sum-
mary— On Calculations of the Numbers for Wheels and Pinions; their Proportional Sizes,
Trains, etc. — Of Dial Wheels, or Motion Work — Length of Time of Going without Winding
up— The Verge— The Horizontal— The Duplex— The Lever— The Chronometer— Repeating
\Vatches— Keyless Watches — The Pendulum, or Spiral Spring — Compensation — Jewelling of
Pivot Holes — Clerkenwell — Fallacies of the Trade — Incapacity of Workmen — How to Choose
and Use a Watch, etc.
Algebra Self-Taught. By W. P. HIGGS, M.A.,
D.Sc., LL.D., Assoc. Inst C.E., Author of 'A Handbook of the Differ-
ential Calculus,' etc. Second edition, crown 8vo, cloth, 2s. 6d.
CONTENTS :
Symbols and the Signs of Operation— The Equation and the Unknown Quantity —
Positive and Negative Quantities — Multiplication — Involution — Exponents — Negative Expo-
nents— Roots, and the Use of Exponents as Logarithms — Logarithms — Tables of Logarithms
and Proportionate Parts — Transformation of System of Logarithms — Common Uses of
Common Logarithms — Compound Multiplication and the Binomial Theorem — Division,
Fractions, and Ratio — Continued Proportion — The Series and the Summation of the Series-
Limit of Series — Square and Cube Roots — Equations — List of Formulae, etc.
Spons Dictionary of Engineering, Civil, Mechanical,
Military, and Naval ; with technical terms in French, German, Italian,
and Spanish, 3100 pp., and nearly 8000 engravings, in super-royal 8vo,
in 8 divisions, 5/. 8j. Complete in 3 vols., cloth, 5/. $s. Bound in a
superior manner, half-morocco, top edge gilt, 3 vols., 6/. I2j,
PUBLISHED BY E. & F. N. SPON. 15
Notes in Mechanical Engineering. Compiled prin-
cipally for the use of the Students attending the Classes on this subject at
the City of London College. By HENRY ADAMS, Mem. Inst. M.E.,
Mem. Inst. C.E., Mem. Soc. of Engineers. Crown 8vo, cloth, 2s. 6d.
Canoe and Boat Building: a complete Manual for
Amateurs, containing plain and comprehensive directions for the con-
struction of Canoes, Rowing and Sailing Boats, and Hunting Craft.
By W. P. STEPHENS. With numerous illustrations and 24 plates of
Working Drawings. Crown 8vo, cloth, gs.
Proceedings of the National Conference of Electricians,
Philadelphia, October 8th to 13th, 1884. i8mo, cloth, 3*.
Dynamo - Electricity, its Generation, Application,
Transmission, Storage, and Measurement. By G. B. PRESCOTT. With
545 illustrations. 8vo, cloth, I/, is.
Domestic Electricity for Amateurs. Translated from
the French of E. HOSPITALIER, Editor of "L'Electricien," by C. J.
WHARTON, Assoc. Soc. Tel. Eng. Numerous illustrations. Demy 8vo,
cloth, 6s.
CONTENTS :
i. Production of the Electric Current— 2. Electric Bells — 3. Automatic Alarms — 4. Domestic
Telephones — 5. Electric Clocks — 6. Electric Lighters — 7. Domestic Electric Lighting—
8. Domestic Application of the Electric Light — 9. Electric Motors — 10. Electrical Locomo-
tion—n. Electrotyping, Plating, and Gilding — 12. Electric Recreations — 13. Various appli-
cations— Workshop of the Electrician.
Wrinkles in Electric Lighting. By VINCENT STEPHEN.
With illustrations. i8mo, cloth, 2s. 6d.
CONTENTS :
i. The Electric Current and its production by Chemical means — 2. Production of Electric
Currents by Mechanical means — 3. Dynamo-Electric Machines — 4. Electric Lamps —
. Lead — 6. Ship Lighting.
Foundations and Foundation Walls for all classes of
Buildings, Pile Driving, Building Stones and Bricks, Pier and Wall
construction, Mortars, Limes, Cements, Concretes, Stuccos, &c. 64 illus*
trations. By G. T. POWELL and F. BAUMAN. 8vo, cloth, IQJ. 6d.
Manual for Gas Engineering Students. By D. LEE.
i8mo, cloth, ij.
1 6 CATALOGUE OF SCIENTIFIC BOOKS
Telephones, their Construction and Management.
By F. C. ALLSOP. Crown 8vo, cloth, 5-r.
Hydraulic Machinery, Past and Present. A Lecture
delivered to the London and Suburban Railway Officials' Association.
By H. ADAMS, Mem. Inst. C.E. Folding plate. 8vo, sewed, is.
Twenty Years with the Indicator. By THOMAS PRAY,
Jun., C.E., M.E., Member of the American Society of Civil Engineers.
2 vols., royal 8vo, cloth, I2s. 6d*
Annual Statistical Report of the Secretary to the
Members of the Iron and Steel Association on the Home and Foreign Iron
and Steel Industries in 1889. Issued June 1890. 8vo, sewed, 5-r.
Bad Drains, and How to Test them ; with Notes on
the Ventilation of Sewers, Drains, and Sanitary Fittings, and the Origin
and Transmission of Zymotic Disease. By R. HARRIS REEVES. Crown
8vo, cloth, y. 6d.
Well Sinking. The modern practice of Sinking
and Boring Wells, with geological considerations and examples of Wells.
By ERNEST SPON, Assoc. Mem. Inst. C.E., Mem. Soc. Eng., and of the
Franklin Inst., etc. Second edition, revised and enlarged. Crown 8vo,
cloth, los. 6d.
The Voltaic Accumulator : an Elementary Treatise.
By EMILE REYNIER. Translated by J. A. BERLY, Assoc. Inst. E.E.
With 62 illustrations, 8vo, cloth, 9*.
Ten Years Experience in Works of Intermittent
Downward Filtration. By J. BAILEY DENTON, Mem. Inst. C.E.
Second edition, with additions. Royal 8vo, cloth, 5-r.
Land Surveying on the Meridian and Perpendicular
System. By WILLIAM PENMAN, C.E, 8vo, cloth, 8j. 6d.
The Electromagnet and Electromagnetic Mechanism.
By SILVANUS P. THOMPSON, D.Sc., F.R.S. Second edition, 8vo,
cloth, 15-r.
PUBLISHED BY E. & F. N. SPON. 17
Incandescent Wiring Hand-Book. By F. B. BADT,
late ist Lieut. Royal Prussian Artillery. With 41 illustrations and
5 tables. iSino, cloth, qs. 6d.
A Pocket-book for Pharmacists, Medical Prac-
titioners, Students, etc., etc. (British, Colonial, and American). By
THOMAS BAYLEY, Assoc. R. Coll. of Science, Consulting Chemist,
Analyst, and Assayer, Author of a 'Pocket-book for Chemists,' 'The
Assay and Analysis of Iron and Steel, Iron Ores, and Fuel,' etc., etc.
Royal 32010, boards, gilt edges, 6s.
The Fireman s Guide ; a Handbook on the Care of
Boilers. By TEKNOLOG, foreningen T. I. Stockholm. Translated from
the third edition, and revised by KARL P. DAHLSTROM, M.E. Second
edition. Fcap. 8vo, cloth, 2s,
The Mechanician : A Treatise on the Construction
and Manipulation of Tools, for the use and instruction of Young Engineers
and Scientific Amateurs, comprising the Arts of Blacksmithing and Forg-
ing ; the Construction and Manufacture of Hand Tools, and the various
Methods of Using and Grinding them ; description of Hand and Machine
Processes ; Turning and Screw Cutting. By CAMERON KNIGHT,
Engineer. Containing 1147 illustrations, and 397 pages of letter-press.
Fourth edition, 4to, cloth, i&y.
A Treatise on Modern Steam Engines and Boilers,
including Land Locomotive, and Marine Engines and Boilers, for the
use of Students. By FREDERICK COLYER, M. Inst. C.E., Mem. Inst. M.E.
With -^plates. 4to, cloth, 12s. 6d.
CONTENTS :
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Method of representing the actual pressure
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Painting in Oils, in Water
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Photography.
Plastering.
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MECHANICAL MANIPULATION,
THE MECHANICIAN:
A TREATISE ON THE CONSTRUCTION AND MANIPULATION OF TOOLS,
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. and Grinding them ; the Construction of Machine Tools, and
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By CAMERON KNIGHT, Engineer.
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Of the six chapters constituting the work, the first is devoted to forging ; in
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are the elements of machine-making in general. The processes described in
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Adhesion
.. I
Agricultural Engines
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.. 2
Air- Pump ..
2
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Alloy
.. 2
2
Aluminium
.. 2
Amalgamating Machine . .
2
Ambulance
2
Anchors
.. 2
Anemometer
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3 and 4
Angle-iron
•• 3
Angle of Friction
Animal Charcoal Machine
•• 3
.. 4
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•• 4
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• • 4
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.. 4
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4 and 5
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•• 5
•• 5
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.. 6
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•• 7
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•• 7
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7 and 8
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.. 8
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.. 8
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Bismuth
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Body Plan..
Boilers
Bond
Bone Mill..
Boot-making Machinery
Boring and Blasting
Brake
Bread Machine
Brewing Apparatus
Brick-making Machines
Bridges
Buffer
Cables
Cam, 29 ; Canal . .
Candles
Cement, 30 ; Chimney
Coal Cutting and Washing Ma-
chinery .. .. .. -.31
Coast Defence .. .. 31, 32
Compast.es.. .. .. ..32
Construction .. .. 32 and 33
Cooler, 34 ; Copper .. ..34
Cork-cutting Machine .. .-34
Nos.
8 and 9
9 and 10
.. 10
10 and 1 1
.. II
11 and 12
.. 12
12 and 13
I3» 14. 15
15 and 16
.. 16
.. 16
16 to 19
19 and 20
.. 20
20 and 21
.. 21
21 tO 28
.. 28
28 and 29
29
29 and 30
30
PUBLISHED BY E. & F. N. SPON.
Corrosion ..
Cotton Machinery
Damming ..
Details of Engines
Displacement
Nos.
•• 34 and 35
•• 35
• - 35 to 37
-• 37, 38
38
Distilling Apparatus . . 38 and 39
Diving and Diving Bells .. 39
Docks 39 and 40
Drainage .. .. .. 40 and 41
Drawbridge .. .. -.41
Dredging Machine .. ..41
Dynamometer .. .. 411043
Electro-Metallurgy .. 43, 44
Engines, Varieties .. 44, 45
Engines, Agricultural .. I and 2
Engines, Marine .. .. 74, 75
Engines, Screw .. ... 89, 90
Engines, Stationary .. 91, 92
Escapement .. .. 45, 46
Fan .. .. .. ..46
File-cutting Machine . , . . 46
File-arms .. .. .. 46, 47
Flax Machinery .. .. 47, 48
Float Water-wheels .. ..48
Forging . . . . . . . . 48
Founding and Casting . . 48 to 50
Friction, 50 ; Friction, Angle of 3
Fuel, 50; Furnace .. 50, 51
Fuze, 51 ; Gas .. .. .. 51
Gearing .. .. .. 51, 52
Gearing Belt .. .. 10, II
Geodesy 52 and 53
Glass Machinery .. .. . . 53
Gold, 53, 54; Governor.. .. 54
Gravity, 54 ; Grindstone . . 54
Gun-carriage, 54 ; Gun Metal . . 54
Gunnery .. .. .. 541056
Gunpowder .. .. ..56
Gun Machinery .. .. 56,57
Hand Tools ' .. .. 57, 58
Hanger, 58; Harbour .. . . 58
Haulage, 58, 59; Hinging .. 59
Hydraulics and Hydraulic Ma-
chinery . . . . . . 59 to 63
Ice-making Machine . . . . 63
India-rubber
Indicator . .
Injector
Iron
Iron Ship Building
Irrigation . .
.. 63 and 64
.. 64
64 to 67
.. 67
.. 67 and 68
Nos.
Isomorphism; 68; Joints .. 68
Keels and Coal Shipping 68 and 69
Kiln, 69 ; Knitting Machine .. 69
Kyanising .. .. .. ..69
Lamp, Safety .. .. 69, 70
Lead 70
Lifts, Hoists .. .. 70, 71
Lights, Buoys, Beacons .. 71 and 72
Limes, Mortars, and Cements .. 72
Locks and Lock Gates . . 72, 73
Locomotive .. .. • • 73
Machine Tools .. .. 73,74
Manganese .. .. ..74
Marine Engine . . . . 74 and 75
Materials of Construction 75 and 76
Measuring and Folding . . . . 76
Mechanical Movements . . 76, 77
Mercury, 77 j Metallurgy .. 77
Meter' 77,78
Metric System 78
Mills .. 78, 79
Molecule, 79 ; Oblique Arch .. 79
Ores, 79, 80 ; Ovens . . . . 80
Over -shot Water-wheel .. 80, 8 1
Paper Machinery .. .. .. 81
Permanent Way .. .. 81,82
Piles and Pile-driving . . 82 and 83
Pipes 83,84
Planimeter .. .. ..84
Pumps . . . . . . 84 and 85
Quarrying .. .. .. -.85
Railway Engineering .. 85 and 86
Retaining Walls . . . . " . . 86
Rivers, 86, 87 ; Rivetted Joint . . 87
Roads 87, 88
Roofs 88,89
Rope-making Machinery .. 89
Scaffolding 89
Screw Engines .. .. 89, 90
Signals, 90; Silver .. 90, 91
Stationary Engine .. 91, 92
Stave-making & Cask Machinery 92
Steel, 92 ; Sugar Mill .. 92,93
Surveying and Surveying Instru-
ments .. .. ' .. 93,94
Telegraphy .. .. 94, 95
Testing, 95 ; Turbine .. "95
Ventilation .. 95, 96, 97
Waterworks .. .. 96, 97
Wood-working Machinery 96, 97
Zinc .. .. .. 97
CATALOGUE OF SCIENTIFIC BOOKS.
In super-royal 8vo, 1168 pp., with 2400 illustrations, in 3 Divisions, cloth, price 13*. 6</.
each ; or i vol., cloth, a/. ; or half-morocco, 2/. 8s.
A SUPPLEMENT
TO
SPONS' DICTIONARY OF ENGINEERING.
EDITED BY ERNEST SPON, MEMB. Soc. ENGINEERS.
Abacus, Counters, Speed
Indicators, and Slide
Rule.
Agricultural Implements
and Machinery.
Air Compressors.
Animal Charcoal Ma-
chinery.
Antimony.
Axles and Axle-boxes.
Barn Machinery.
Belts and Belting.
Blasting. Boilers.
Brakes.
Brick Machinery.
Bridges.
Cages for Mines.
Calculus, Differential and
Integral.
Canals.
Carpentry.
Cast Iron.
Cement, Concrete,
Limes, and Mortar.
Chimney Shafts.
Coal Cleansing and
Washing.
Coal Mining.
Coal Cutting Machines.
Coke Ovens. Copper.
Docks. Drainage.
Dredging Machinery.
Dynamo - Electric and
Magneto-Electric Ma-
chines.
Dynamometers.
Electrical Engineering,
Telegraphy, Electric
Lighting and its prac-
ticaldetails,Telephones
Engines, Varieties of.
Explosives. Fans.
Founding, Moulding and
the practical work of
the Foundry.
Gas, Manufacture of.
Hammers, Steam and
other Power.
Heat. Horse Power.
Hydraulics.
Hydro-geology.
Indicators. Iron.
Lifts, Hoists, and Eleva-
tors.
Lighthouses, Buoys, and
Beacons.
Machine Tools.
Materials of Construc-
tion.
Meters.
Ores, Machinery and
Processes employed to
Dress.
Piers.
Pile Driving.
Pneumatic Transmis-
sion.
Pumps.
Pyrometers.
Road Locomotives.
Rock Drills.
Rolling Stock.
Sanitary Engineering.
Shafting.
Steel.
Steam Navvy.
Stone Machinery.
Tramways.
Well Sinking.
UNIVERSITY OF CALIFORNIA LIBRARY
THIS BOOK IS DUE ON THE LAST DATE
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