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EARTH DAMS
A STUDY
BY
BURR BASSELL, M. Am. Soc. C. E.
Consulting Engineer
New York
THE ENGINEERING NEWS PUBLISHING COMPANY
1904
COPTBIQHT, 1904 I
By
The Enoineebinq News Publishino Co.
ACKNOWLEDGMENTS.
The writer wishes to acknowledge his appreciation of the assist-
ance given him by Mr. Jas. D. Schuyler, M. Am. Soc. C. E., Con-
sulting Hydraulic Engineer, in reviewing this paper, and in making
suggestions of value. Appendix II. contains a list of authors
whose writings have been freely consulted, and to whom the
writer is indebted ; the numerous citations in the body of the paper
further indicate the obligations of the writer.
CONTENTS.
CHAPTER I.
PAGE
Introductory i
CHAPTER II.
Preliminary Studies and Investigations -. . . 3
CHAPTER III.
Outline Study of Soils. Puddle 12
CHAPTER IV.
The Tabeaud Dam, California 17
CHAPTER V.
Different Types of Earth Dams 33
CHAPTER VI.
Conclusions • • 63
APPENDIX I.
Statistical Descriptions of High Earth Dams 67
APPENDIX II.
Works of Reference 68
V
ILLUSTRATIONS.
PAGE
Fig. I . Longitudinal Section of Yarrow Dam Site lo
2. Cross-Section of the Yarrow Dam lo
3. Plan of the Tabeaud Reservoir 17
4. Tabeaud Dam: Plan Showing Bed Rock Drains 18
5. Details of Drains 18
6. View of Drains 19
7. North Trench 20
8. South Trench 21
9. Main Central Drain.... 21
10. Embankment Work ....23
11. Dimension Section 26
12. Cross and Longitudinal Sections 27
13. View of Dam Immediately After Completion 29
14. Cross-Section of Pilarcitos Dam 34
15. San Andres Dam 34
16. Ashti Tank Embankment 35
17. Typical New England Dam 40
18. Two Croton Valley Dams Showing Saturation 41
19. Studies of Board of Experts on the Original Earth Portion of
the New Croton Dam 43
20. Studies of Jerome Park Reservoir Embankment 46
21 to 24. Experimental Dikes and Cylinder Employed in Studies
for the North Dike of the Wachusett Reservoir 49
25. Cross-Section of Dike of Wachusett Reservoir 49
26. Working Cross-Section of Druid Lake Dam 53
27 to 29. Designs for the Bohio Dam, Panama Canal 55
30. Cross-Section of the Upper Pecos River Rock-Fill Dam 59
31. Developed Section of the San Leandro Dam 59
VI
EARTH DAMS
CHAPTER I.
Introditctory .
The earth clam is probably the oldest type of dam in existence,
antedating the Christian Era many hundreds of years. The litera-
ture upon this subject is voluminous, but much of it is inaccessible
and far from satisfactory. No attempt will here be made to collate
this literature or to give a history of the construction of earth dams,
however interesting such an account might be. The object will
rather be to present such a study as will make clear the application
of the principles underlying the proper design and erection of this
class of structures. In no way, therefore, will it assume the
character or dignity of a technical treatise.
Dams forming storage reservoirs, which are intended to impound
large volumes of water, must necessarily be built of considerable
height, except in a very few instances where favorable sites may
exist. Recent discussions would indicate that a new interest has
been awakened in the construction of high earth dams. As related
to the general subject of storage, it is with the high structure rather
than the low that this study has to do. To the extent that "the
greater includes the less," the principles here presented are ap-
plicable to works of minor importance.
Many persons who should know better place little importance
upon the skill required for the construction of earthwork embank-
ments, considering the work to involve no scientific problems. It
is far too common belief that any ordinary laborer, who may be able
tc use skillfully a scraper on a country road, is fitted to superintend
the construction of an earth dam. It has been said that the art of
constructing earth dams is purely empirical, that exact science fur-
nishes no approved method of determining their internal stresses,
and that in regard to their design experience is much more valua-
ble than theory. When the question of stability is fully taken into
consideration, it certainly requires a large amount of skill success-
fully to carry out works of this character.
Extreme care in the selection of the site, sound judgment in the
choice of materials and assiduity in superintending the work while
in progress, are all vitally essential.
2 EARTH DAMS.
Classification of Dams.
Dams may be classified according to their purpose as diverting
dams or weirs and as storage dams. The former may be located
upon any portion of a stream where the conditions are favorable,
and the water used for manifold purposes, being conveyed by means
01 canals, flumes, tunnels and pipe lines to places of intended use.
These dams are generally low and may be either of a temporary
oi permanent character, depending upon the uses to which the wa-
ter is put. Temporary dams are made of brush, logs, sand bags,
gravel and loose rock. The more permanent structures are built of
stone and concrete masonry.
Storage dams may be classified according to the kind of material
entering into their structure, as follows : (i) Earth ; (2) Earth and
Timber ; (3) Earth and Rock-fill ; (4) Rock-fill ; (5) Masonry ; (6)
Composite Structures.
Low dams forming service reservoirs for domestic water sup-
plies and for irrigation comprise by far the most numerous class.
They are not designed to impound a large volume of water and
therefore may be built across a small ravine or depression, or even
upon the summit of a hill, by excavating the reservoir-basin and
using the material excavated to form the embankment. These res-
ervoirs may be used in connection with surface or gravity systems,
artesian wells, or underground supplies obtained by pumping. The
dams forming these reservoirs being of moderate size and height
may vary greatly in shape and dimensions. The form may be made
to suit the configuration of the dam site. When the earthwork re-
quires it, they may be lined with various materials to secure water-
tightness. Often such dams are made composite in character,
partly of earth and partly of masonry or some other material. They
are also frequently accompanied by numerous accessories, such as
settling-basins, aerating devices and covers, which present a diver-
sity in form and appearance. A presentation of the different types
of dams thus employed, with a discussion of the questions pertain-
ing to utility in design and economy in construction, would be ex-
ceedingly valuable and of general interest. Service-reservoirs will
receive only a passing notice, with the hope expressed that some
competent authority will discuss them in the future.
CHAPTER II.
Preliminary Studies and Investigations.
The preliminary studies and investigations which should be made
prior to the construction of any dam for the storage of water have
to do with (i) the Catchment Area, (2) the Reservoir basin, and (3)
the Dam site.
Catchment Area.
It is thought desirable to define a number of terms as we proceed,
for the purpose of correcting erroneous usage and for a clearer
understanding of the subject. The catchment area of a reservoir
i.s that portion of the country naturally draining into it. The water-
shed is the boundary of the catchment area and may be correctlv
defined as the divide between adjacent drainage systems. In re-
gard to the catchment area it is necessary to determine :
1. Its extent and area in square miles.
2. Its topography or the character of its surface.
3. Its hydrography or precipitation and run-ofif.
4. Its geology, or the character of its soils and subsoils, and the
nature and dip of its rock strata.
5. Its flora, or the extent to which it is clothed with forest trees
or other vegetation.
All of these elements afifect the volumes of maximum run-ofif,
which is the one important factor in the construction of earth dams
that must not be underestimated.
If the proposed dam or reservoir is to be located upon a main
drainage line; that is, upon a river or stream, it is necessary to
know both the flood and low-water discharge of the stream. Fre-
quently no reliable data on this subject are available, and the engi-
neer must then make such a study of the whole situation as will en-
able him to estimate the minimum and maximum flow with con-
siderable accuracy.
There are numerous factors entering into the solution of this first
problem, such as the shape and length of the catchment area, its
general elevation, the character of its surface, whether mountainous,
hilly or flat, barren or timbered.
Good topographic maps, if available, furnish valuable data on
4 EARTH DAMS.
these subjects and it is to be regretted that only a comparatively
small portion of the United States has been thus mapped in detail.
The results of stream measurements, if any have been made in
the catchment basin, are especially important: These are usually
few in the high areas, on account of their inaccessibility. The year
1902 marked a notable beginning of such measurements in Califor-
nia. In many parts of the arid region of the United States, the
best storage-sites are situated in the upper or higher portions of
the drainage systems. This is especially true of the streams on the
Pacific Slope having their source in the High Sierras. As regulators
of stream-flow and for power purposes such storage is peculiarly
valuable, while storage for irrigation and domestic uses may be lo-
cated nearer the valleys and the centers of population.
Frequently the engineer is required to build his dam where no
such data are available. In such instances he should endeavor to
secure the establishment of rain gages and make measurements of
the flow of the main stream and its principal tributaries at various
places to obtain the desired information. Even this may not suffice,
owing to the limited time at his disposal, and he must resort to the
use of certain empirical rules or formulas, and make such compari-
sons and deductions from known conditions and results as will best
answer his purpose.
The engineer should know, approximately at least, the normal
yield of the catchment area, the duration of the minimum and max-
imum seasonal flow, and the floods he may have to provide against
during the construction of his dam. These data are absolutely nec-
essary to enable him to provide ample wasteways for his reservoirs.
Many of the failures of earth dams have been the result of over-
topping the embankment, which would have been averted by an
ample wasteway. The most notable example of this kind in recent
years was that of the South Fork Dam, at Conemaugh, Pennsyl-
vania, in 1889, resulting in what is generally known as the "Johns-
town Disaster."
There are several empirical rules and formulas for calculating
the run off from catchment areas and for determining the size of
spillways necessary to discharge this flow with safety to the dam.
The proper formula to apply in any given case, with the varying
coefficients of each, involves a thorough knowledge on the part of
the designing engineer of the principles upon which the different
factors are based.
It is unwise and often hazardous to make use of any important
PRELIMINARY STUDIES AND INVESTIGATIONS. 5
hydraulic formula without knowing the history of its derivation.
Experiments are not always properly conducted, and often the de-
ductions therefrom are unreliable. A presentation and discussion
of these formulas would require more space than can be given in
this study, and the technical reader must therefore consult for him-
self, as occasion may require, the various authorities cited. Form-
ulas for the discharge or run-ofif from catchment areas, as deter-
mined by Messrs. Craig, Dickens, Ryves and others, are given by
most writers on the subject of hydraulics.
Reservoir Basin.
The next subject of inquiry relates to the reservoir basin. It is
necessary that its area and capacity at different depths should be
definitely known, and this information can only be obtained by hav-
ing the basin surveyed and contoured. A map should be made
showing contours at intervals of 2 to 10 ft., depending upon the
size of the basin and the use to which the reservoir is to be put.
Reservoir basins have been classified according to their location
as follows:
1. Natural lakes.
2. Natural depressions on main drainage lines.
3. Natural depressions on lateral drainage lines.
4. Arbitrary and artificially constructed basins.
Natural lakes may need to be investigated more or less thorough-
ly to determine the character of their waters, whether saline, alka-
line or fresh. It may also be necessary to know their normal depth
and capacity, and to make a study of their outlet if they have one.
In some instances the storage capacity of a lake may be enormous-
ly increased by means of a comparatively low and inexpensive em-
bankment.
The area of reservoir basin, mean depth, temperature of the
water, exposure of wind and sunshine, losses by seepage and evap-
oration, all have a bearing upon the available water supply and in-
fluence the design of the dam and accessories to the reservoir.
In determining the character and suitability of materials for con-
structing a dam it is necesary to make a careful study of the soil
and geological formation. This is best accomplished by digging
numerous test pits over the basin, especially in the vicinity of the
proposed dam site ; borings alone should never be relied upon for
this information. For such an investigation the advisability of bor-
rowing material for dam construction from the reservoir basin is
6 EARTH DAMS.
determined. The porous character of the subsoil strata, or the
dip and nature of the bed rocls, may forbid the removal of material
from the floor of the basin, even at a remote distance from the dam
site.
The area to be flooded should be cleared and grubbed more or
less thoroughly, depending again upon the use for which the water
i.s impounded. In no instance should timber be left standing below
the high water level of the reservoir ; and all rubbish liable to float
and obstruct the outlet tunnel and spillway during a time of flood
should be removed.
The accessories to a reservoir, to which reference has been made,
may be enumerated as follows :
1. Outlet pipes or tunnel.
2. Gate tower, screens and controlling devices.
3. Sluiceways for silt or sand.
4. Wasteway channel or weir.
5. Cover, settling basin, aerating devices, etc.
Some of these are necessary and common to all classes of reser-
voirs, while others are employed only in special cases, as for
domestic water supplies. All reservoirs formed by earth embank-
ments must have at least two of these, namely a wasteway, which
is its safety valve, and outlet pipes or outlet tunnel.
It may be stated that the proper location and construction of
the .outlet for a reservoir are of vital importance, since either to
improper location or faulty construction may be traced most of the
failures of the past. It is almost impossible to prevent water
uiider high pressure from following along pipes and culverts when
placed in an earth dam. The pipes and culverts frequently leak,
and failure ensues. Failure may result from one or -more of the
following causes :
1. By improper design and placement of the pudddle around the
pipes.
2. By resting the pipes upon piers of masonry without continu-
ous longitudinal support.
3. By reason of subsidence in the cuts of the embankments and
at the core walls, due to the great weight at these points.
4. Leakage due to inherent defects, frost, deterioration, etc.
Mr. Beardsmore, the eminent English engineer who built the
Dale Dyke embankment at Sheffield which failed in 1864, and who
was afterwards requested to study and report upon the great reser-
voirs in Yorkshire and Lancashire, said, after examination and care-
PRELIMINARY STUDIES AND INVESTIGATIONS. 7
ful study of reservoir embankment construction, that "in his opin-
ion there were no conditions requiring that a culvert or pipes
should be carried through any portion of the made bank." The
writer would go even further and say that the only admissable out-
let for a storage reservoir formed by a high earth dam is some
form of tunnel through the natural formation at a safe distance
from the embankment.
Dam Site*
The third preliminary study (that relating to the dam site itself)
will be considered under three heads :
1. Location.
2. Physical features, materials, etc.
3. Foundation.
LOCATION. — The location for a dam is generally determined
by the use which is to be made of it, or by the natural advantages
for storage which it may possess. If it be for water power it is
very frequently located upon the main stream at the point of great-
est declivity. If for storage it may be, as we have seen, at the
head of a river system, on one of its tributaries, or in a valley
lower down.
The type of dam which should be built at any particular local-
ity involves a thorough knowledge, not alone of the catchment-area
and reservoir basin, but also accurate information regarding the
geology of the dam site itself. It would be very unwise to decide
definitely upon any particular type of dam without first obtaining
such information. Too frequently has this been done, causing
great trouble and expense, if not resulting in a total failure of the
dam.
The conditions favorable for an earth dam are usually unfavor-
able for a masonry structure, and vice versa. Again, there may
be local conditions requiring some entirely different type.
Dams situated upon the main drainage lines of large catchment
areas are usually built of stone or concrete masonry, and designed
with large sluiceways and spillways for the discharge both of silt
and flood waters. It need scarcely be remarked that, as a rule, such
sites are wholly unsuited to earthwork construction. It is said,
however, that "every rule has at least one exception," and this may
be true of those relating to dam sites, as will appear later under
the head of new types.
In a general way, the location of high earth dams is governed
8 EARTH DAMS.
by the configuration of the ground forming the storage basin. It
may not be possible, however, to decide upon the best available site
without careful preliminary surveys and examinations of the geo-
logical formation.
All earth dams must be provided with a wasteway, ample to dis-
charge the maximum flood tributary to the reservoir. Whatever
type of wasteway be adopted, no reliance should ever be put upon
the outlet pipes for this purpose. The outlet should only figure as
a factor of safety for the wasteway, insuring, as it were, the accuracy
of the estimated flood discharge. The safety of the dam demands
that ample provision be made for a volume of water in excess of
normal flood discharge. This most necessary adjunct of earth
dams may be an open_chaniiel, cut through the rim of the reservoir
basin, discharging into a_sideTaviDe which enters the main drainage
way some distance below the dam. It may be necessary and possi-
ble to pierce the rim by means of a tunnel where its length would
not prohibit such a design. Lastly, there may be no other alter-
native than the construction of an overfall spillway, at one or both
ends of the embankment. This last method is the least desirable
of any and should be resorted to only when the others are imprac-
ticable ; even then, the volume of water, local topography, geology,
and constructive materials at hand must be favorable to such a
design. If they are not favorable it may be asked, "what then?"
Simply do not attempt to build an earth dam at this site.
PHYSICAL FEATURES, MATERIALS, ETC.— An investiga-
tion of the location and the physical features of the dam site should
include a careful and scientific examination of the materials in the
vicinity, to determine their suitability for use in construction. An
earth embankment cannot be built without earth, and an earth
dam cannot be built with safety without the right kind of earth
material.
Test pits judiciously distributed and situated at different eleva-
tions will indicate whether there is a sufficient amount of suitable
material within a reasonable distance of the dam. The type of earth
dam best suited for any particular locality, and its estimated cost,
are thus seen to depend upon the data and information obtained
by these preliminary studies. Economical construction requires
the use of improved machinery and modern methods of handling
materials, but far more important even than these are the details of
construction.
PRELIMINARY STUDIES AND INVESTIGATIONS. g
FOUNDATION. — We may now assume that our preliminary
studies relating to the location and physical features of the dam
site are satisfactory. We must next investigate the foundation up-
on which the dam is to be built. This investigation is sometimes
wholly neglected or else done in such a way as to be practically
useless. To merely drive down iron rods feeling for so-called bed
rock, or to make only a few bore-holes with an earth auger should
in no instance be considered sufficient. Borings may be found
necessary at considerable depths below the surface and in certain
classes of material, but dug pits or shafts should always be re-
sorted to for moderate depths and whenever practicable. Only by
such means may the true character of the strata underlying the
surface, and the nature and condition of the bed rock, if it be
reached, become known. If a satisfactory stratum of impermeable
material be found it is necesary also to learn both its thickness and
extent. It may prove to be only a "pocket" of limited volume, or
if found to extend entirely across the depression lengthwise of the
dam site it may "pinch out" on lines transversely above or below.
Shafts and borings made in the reservoir basin and below the dam
site will determine its extent in this direction, knowledge of which
is very important.
Fig. I, showing a longitudinal section of the site of the Yarrow
Dam of the LiverpoolWater-Works, England, illustrates the neces-
sity of such investigation. A bore hole at station 2 + 00 met a large
boulder which at first was erroneously thought to be bed rock.
The hole at station 3 + 50 met a stratum of clay which proved to
be only a pocket.
The relative elevation of the different strata and of the bed rock
formation, referred to one common datum, should always be deter-
mined. These elevations will indicate both the dip and strike of the
rock formation and are necessary for estimating the quantities of
material to be excavated and removed, including estimates of cost.
They furnish information of value in determining the rate of perco-
lation or filtration through the different classes of material and
the amount of probable seepage, as will appear later. The cost
of excavating, draining and preparing the floor or foundation for
a dam is often very great, amounting to 20 or 30% of the total cost.
Fig. 2 is a transverse section of the Yarrow Dam. This partic-
ular dam has been selected as fairly representative of English prac-
tice and of typical design. It is one of the most widely known earth
dams in existence.
10
EARTH DAMS.
PRELIMINARY STUDIES AND INVESTIGATIONS. II
At the Yarrow dam site it was necessary to go 97 ft. below the
original surface to obtain a satisfactory formation or one that was
impermeable. A central trench was excavated to bed rock, par-
allel to the axis of the dam, and filled with clay puddle to form a
water-tight connection with the rock, and prevent the water in the
reservoir from passing through the porous materials under the
body of the embankment. This interesting dam will be more fully
described later, when the different types of earth dams are dis-
cussed.
CHAPTER III.
Outline Study of Soils. Puddle.
The following study of soils is merely suggestive and is here
given to emphasize the importance of the subject, at the risk of
being considered a digression. Soil formations are made in one
of three ways:
1. By decomposition of exposed rocks.
2. By transportation or sedimentation of fine and coarse mater-
ials worn from rocks.
3. By transformation into humus of decayed organic matter.
The transforming agencies by which soils succeed rocks in geo-
logical progression have been classified as follows :
1. Changes of temperature.
2. Water.
3. Air.
4. Organic life.
Heat and its counter agent frost are the most powerful forces in
nature, their sensible physical effects being the expansion and con-
traction of matter.
Water has two modes of action, physical and chemical. This
agent is the great destroyer of the important forces, cohesion and
friction. Cohesion is a force uniting particles of matter and resists
their separation when the motion attempted is perpendicular to the
plane of contact. Friction is a force resisting the separation of
surfaces when motion is attempted which produces sliding. The
hydrostatic pressure and resultant efifect upon submerged surfaces
need to be kept constantly in mind. When the surface is imper-
meable the line of pressure is normal to its plane, but when once
saturated there are also horizontal and vertical lines of pressure.
Since the strength of an earth dam depends upon two factors,
namely, its weight and frictional resistance to sliding, the effect of
water upon different materials entering into an earth structure
should be most carefully considered. This will therefore occupy a
large place in these pages. An earth embankment founded upon
rock may become saturated by water forced up into it from below
through cracks and fissures, reducing its lower stratum to a state
U U TUNE STUDY OF SOILS. 13
of muddy sludge, on which the upper part, however sound in itself,
would slide. The best preliminary step to take in such a case is
to intersect the whole site with wide, dry, stone drains, their depths
varying according to the nature of the ground or rock.
Air contains two ingredients ever active in the process of decom-
position, carbonic acid and oxygen.
Organic Life accomplishes its decomposing effect both by physi-
cal and chemical means. The effect of organic matter upon the
mineral ingredients of the soil may be stated as follows :
1. By their hydroscopic properties they keep the soil moist.
2. Their decomoosition yields carbonic acid gas.
3. The acids produced disintegrate the mineral constituents, re-
ducing insoluble matter to soluble plant food.
4. Nitric acid results in nitrates, which are the most valuable
form of nutritive nitrogen, while ammonia and the other salts that
are formed are themselves direct food for plants.
Vegetable Humus is not the end of decomposition of organic mat-
ter, but an intermediate state of transformation. Decay is a pro-
cess almost identical with combustion, where the products are the
same, and the end is the formation of water and carbonic acid, with
a residue of mineral ash. The conditions essential to organic de-
composition are also those most favorable to combustion or oxida-
tion, being (i) access of air, (2) presence of moisture, and (3) appli-
cation of heat.
Now the cooperation of these chemical and physical forces, which
are ever active, is called "weathering." Slate rock, for instance,
weathers to clay, being impregnated with particles of mica, quartz,
chlorite and hornblend. Shales also weather to clay, resulting of-
ten in a type of earth which is little more than silicate of aluminum
with iron oxide and sand.
In the vicinity of the Tabeaud Dam, recently built under the per-
sonal supervision of the author, the construction of which will be
described later, there is to be found a species of potash mica, which
in decomposing yields a yellow clay (being ochre-colored from the
presence of iron), mixed with particles of undecomposed mica. This
material is subject to expansion, and by reason of its lack of grit
and its unctuous character it was rejected or used very sparingly.
Analysis of this material gave, Silica, 54.1 to 59.5%; potash, 1.5 to
2.3% ; soda, 2.7 to 3.7%.
Soil analysis may be either mechanical or chemical. For pur-
poses of earthwork, we are most interested in the former, having to
14
EARTH DAMS.
deal with the physical properties of matter. Chemical analysis,
however, will often afford information of great value regarding cer-
tain, materials entering into the construction of earth dams. The
most important physical properties are :
(i) Weight and specific gravity.
(2) CoefHcient of friction and angle of repose.
(3) Structure and coloring ingredients.
(4) Behavior toward water.
There are two distinct methods of mechanical analysis : (i) Gran-
ulating with sieves, having round holes. (2) Elutriating with water,
the process being known as silt analysis.
It would require a large volume to present the subject of soil
analysis in any way commensurate with its importance. Experi-
ments bearing upon the subjects of imbibition, permeability, capil-
larity, absorption and evaporation, of different earth materials, are
equally interesting and important.*
The permeability of soils will be discussed incidentally in connec-
tion with certain infiltration experiments to be given later.
Puddle.
Puddle without qualification may be defined as clayey and grav-
elly earth thoroughly wetted and mixed, having a consistency
of stiff mud or mortar. Puddle in which the predominating in-
gredient of the mixture is pure clay, is called clay puddle. Gravel
puddle contains a much higher percentage of grit and gravel than
the last-named and yet is supposed to have enough clayey mater-
ial to bind the matrix together and to fill all the voids in the
gravel.
The term earthen concrete may also be applied to this class of
material, especially when only a small quantity of water is used
in the mixture. These different kinds of puddling materials may
be found in natural deposits ready for use, only requiring the
addition of the proper amount of water. It is usually necessary,
however, to mix, artificially, or combine the different ingredients
in order to obtain the right proportions. Some engineers think
grinding in a pug-mill absolutely essential to obtain satisfactory
results.
Fudd le is handled very much as cement concrete, which is so>
.'The writer had intended to present a table of physical properties of different ma-
terials givmg their specific gravity, weight, coefficient of friction, angle of ren"l
percentage of imbibition percentage of voids, etc., but found it impossible to harmo-
nize the various classifications of materials given by different authorities
OUTLINE STUDY OF SOILS. 15
well understood that detailed description is hardly necessary. In-
stead of tampers, sharp cutting implements are usually employed
in putting puddle into place. Trampling with hoofed animals is
frequently resorted to, both for the purpose of mixing and com-
pacting.
As has been stated, clays come from the decomposition of crys-
taline rocks. The purest clay known (kaolin) is composed of
alumina, silica and water. The smaller the proportion of silica
the more water it will absorb and retain. Dry clay will absorb
nearly one-third of its weight of water, and clay in a naturally
moist condition 1-6 to 1-8 its weight of water. The eminent
English engineers, Baker and Latham, put the percentage of ab-
sorption by clayey soils as high as 40 to 60%. Pure clays shrink
about 5% in drying, while a mixture by weight of i clay to 2
sand will shrink about 3%. It follows, then, that the larger the
percentage of clay there may be in a mixture the greater will
be both the expansion and the contraction.
Clay materials may be very deceptive in some of their physical
properties, being hard to pick under certain conditions, and yet
when exposed to air and water will rapidly disintegrate. Beds of
clay, marl and very fine sand are liable to slip when saturated,
becoming semi-fluid in their nature, and will run like cream.
The cohesive and frictional resistances of clays becoming thus
very much reduced when charged with water, a too liberal use of
this material is to be deprecated. The ultimate particles forming
clays, viewed under the microscope, are seen to be flat and scale-
like, while those of sands are more cubical and spherical. This is
a mechanical difference which ought to be apparent to even a
superficial observer and yet has escaped recognition by many who
have vainly attempted a definition of quicksand.
Mr. Strange recommends filling the puddle trench with mater-
ial having three parts soil and two parts sand. After the first
layer next to bed rock foundation, which he kneads and compacts,
he would put the layers in dry, then water and work it by tread-
ing, finally covering to avoid its drying out and cracking.
Prof. Philipp Forchheimer, of Gratz, Austria, one of the high-
est authorities and .experimentalists, affirms that if a sandy soil
contains clay to such an extent that the clay fills up the inter-
stices between the grains of sand entirely the compound is pract-
ically impervious.
Mr. Herbert M. Wilson, C. E., in his "Manual of Irrigation En-
l6 EARTH DAMS.
gineering," recommends the following as an ideal mixture of
materials :
Cu. yds. Cu. yds.
Coarse gravel i.oo Clay 0.20
Fine gravel 0.35
Sand 0.15 Total 1.70
This mixture, when rolled and compacted, should give 1.25 cu.
yds. in bulk, thus resulting in 26^% compression.
Mr. Clemens Herschel suggests the following test of "good bind-
ing gravel :" "Mix with water in a pail to the consistency of moist
earth ; if on turning the pail upside down the gravel remains in the
pail it is fit for use, otherwise it is to be rejected.'' For puddling
material he would use such a proportion as will render the water
invisible.
CHAPTER IV.
The Tabeaud Dam, California.
The Tabeaud Dam, in Amador County, Cal., built under the
supervision of the author for the Standard Electric Co., is an ex-
ample of the homogeneous earth dam. A somewhat fuller descrip-
tion and discussion will be given of this dam than of any other, not
on account of its greater importance or interest, but because it ex-
FIG. 3.— PLAN OP TABEAUD iRESBRVOIR, WITH COXTOURS:
cmpliiies certain principles of construction upon which it is desired
to put special emphasis. This dam was described in Engineering
News of July lo, 1902, to which the reader is referred for more
complete information than is given here.
Fig. 3 is a contour map of the Tabeaud Reservoir, showing the
relative locations of the dam, wasteway and outlet tunnel. Fig. 4
shows the bed rock drainage system and the letters upon the draw-
i8
EARTH DAMS.
PIG. 4.-1PLAN OF TABE3AUD DAM, SHOWING BED ROCK DRAINAGE SYSTEM.
■t-DraIn
Rock Dram. Interior Puddle Trench.
FIG. 5.— 'DETAILS OF BED ROCK DRAINS AT THE TABEAUD DAM.
THE TABEAUD DAM.
19
ing will assist in following the explanation given in the text. The
whole up-stream half of the dam site was stripped to bed rock. As
the work of excavation advanced pockets of loose alluvial soil were
encountered, which were suggestive of a refill, possibly the result
of placer mining operations during the early mining days of Califor-
nia. In addition to this were found thin strata of sand and gravel
deposited in an unconformable manner. The slate bed rock near
the up-stream toe of the dam was badly fissured and yielded consid-
erable water. A quartz vein from i to 2 ft. in thickness crossed the
dam site about 150 ft. above the axis of the dam. The slate rock
FIG. 6.— VIEW OF BED ROCK TRENCHES, TA'BiBAUD DAM.
and
above this vein or fault line was quite variable in hardness
dipped at an angle of 40 degrees toward the reservoir.
The rear drain terminates at a weir box (Z) outside of the down-
stream slope at a distance of 500 ft. from the axis of the dam. This
drain branches at the down-stream side of the central trench, (Y),
one branch being carried up the hillside to high-water level (W) at
the North end of the dam, and the other to the same elevation at the
South end (X).
20
EARTH DAMS.
Figi 5 shows how these drains were constructed. After the re-
moval of all surface soil and loose rock, a trench 5 to 10 ft. wide
was cut into the solid rock, the depth of cutting varying with the
character of the bed rock. Upon the floor of this trench a small
open drain was made by notching the bed rock and by means of
selected stones of suitable size and hardness. The stringers and
cap-stones were carefully selected and laid, so that no undue settle-
ment or displacement might occur by reason of the superincumbent
Haw
FIG. 7.— VIEW OF NORTH TRENCH, TABEAUD DAM,
v.'cight of the dam. All crevices were carefully filled with spawls
and the whole overlaid 18 ins. in depth with broken stone i to 3
ins. in diameter. Upon this layer of broken stone and fine gravel
was deposited choice clay puddle, thoroughly wetted and com-
pacted, refilling the trenches.
These drains served a useful purpose during construction, in
drying off the surface of the dam after rains. The saturation of the
outer slope of the dam by water creeping along the line of contact
THE TAB BAUD DAM.
21
FIG. 8.— VIEW OF SOUTH TRENCH, TABEAUD DAM.
FIG. !).-VIEW OF MAIN CENTRAL DRAIN, TABEAUD DAM.
22 EARTH DAMS.
should thus be prevented, and the integrity or freedom from sat-
uration of the down-stream half should be preserved. It is be-
lieved that the puddle overlying these rock drains will effectually
prevent any water from entering the body of the embankment by
upward pressure and that the drains will thus forever act as ef-
ficient safeguards.
The main drain was extended, temporarily during construction,
from the central trench (Fig. 4), to the up-stream toe of the dam.
This was cut 5 or 6 ft. deep into solid rock, below the general
level of the stripped surface. Fig. 6 is reproduced from a photo-
graph of this trench. An iron pipe 2 ins. in diameter was im-
bedded in Portland cement mortar and concrete, and laid near
the bottom of the trench.
At the point (B) where the quartz vein (already described) in-
tersected this drain, two branch drains were made, following the
fault well into the hill on both sides. Figs. 7 and 8 are views
of the North and South trenches, respectively. These trenches
were necessary to take care of the springs issuing along the
quartz vein. This water led to a point (N, Fig. 4) near the up-
stream toe, by means of the drain shown in Fig. 9.
The lateral drains and that portion of the main central drain
extending from their junction (B) to a point (N) about 230 ft.
from the axis of the dam have pieces of angle iron or wooden
Y-fluming laid on the bottom of the trenches immediately over
the 2-in. pipe, as shown in Figs. 7, 8 and 9. These are covered in
turn with Portland cement mortar, concrete, clay puddle and
earth fill. The water will naturally flow along the line of least re-
sistance, and consequently will follow along the open space be-
tween the angle irons and the outside of the pipe mitil it reaches
the chamber and opening in the pipe, permitting the water to enter
and be conveyed through the imbedded pipe line to the rear drain.
This point of entry is a small chamber in a solid cross-wall of rich
cement mortar, and is the only point where water can enter this
pipe line, the two branches entering the wells and the stand-pipe
at their junction (soon to be described) having been closed.
That portion of the foundation between the axis of the dam and
the quartz vein, a distance of about 160 ft., was very satisfactory,
without fissures or springs of water. In this portion the 2-in.
pipe was imbedded in mortar and concrete without angle irons,
and the continuitv of the trench broken by numerous cross-
trenches cut into the rock and filled with concrete and puddle. It
THE TABEAUD DAM.
23
24
EARTH DAMS.
is believed that no seepage water will ever pass through this por-
tion of the dam. If any should ever find its way under the puddle
and through the bed rock formation, the rear drain, with its hill-
side branches, will carry it away and prevent the saturation of the
lower or down-stream half of the dam.
At the up-stream toe of the embankment, two wells or sumps
(shown at "S" and "K," Fig. 4) were cut 10 or 12 ft. deeper than
the main trench, which received the water entering the inner toe
puddle trench during construction. This water was disposed of
partly by pumping and partly by means of the 2-in. branch pipes
leading into and from these wells. At their junction (J) a 2-in.
stand-pipe was erected, which was carried vertically up through
the embankment, and finally filled with cement. The branch pipes
from the wells were finally capped and the wells filled with broken
stone, as previously mentioned.
EMBANKMENT. — As has been said, the upper surface of the
.<5late bed rock was found to be badly fissured, especially near the
upstream toe of the dam, and as the average depth below the sur-
face of the ground was not very great, it was thought best to lay
bare the bed rock over the entire upper half of the dam site. Had
the depth been much greater, it would have been more economical
and possibly sufficient to have put reliance in a puddle trench,
alone, for securing a water-tight connection between the founda-
tion and the body of the dam.
At the axis of the dam and near the inner toe, where the puddle
walls abutted against the hillsides, the excavation always ex-
tended to bed rock. Vertical steps and offsets were avoided and
the cuts were made large enough for horses to turn in while
tramping, these animals being used, singly and in groups, to mix
and compact the puddle and thus lessen the labor of tamping by
hand. In plan, the hillside contact of natural and artificial sur-
faces presents a series of corrugated lines, as is clearly shown in
Fig. 4. After all loose and porous materials had been removed,
the stripped surface and the slopes of all excavations were thor-
oughly wetted from time to time by means of hose and nozzle, the
water being delivered under pressure. Fig. 10 is a view of the
dam taken when it was about half finished and shows the work
in progress.
The face puddle shown in Fig. 11 was used merely to "make
assurance doubly sure" and was not carried entirely up to the
top of the dam. The earth of which the dam was constructed may
.ight of
CU.
U 4t
(1 H
tC It
" "
tt it
THE TABEAUD DAM. 25
be described as a red gravelly clay, and in the judgment of the
author is almost ideal material for the purpose. Physical tests
and experiments made with the materials at dififerent times during
construction gave the following average results :
Pounds.
ft. earth, dust dry 840
" saturated earth 101.8
" moist loose earth 76-6
" loose material taken from test pits on the dam 80.0
" earth in place taken from the borrow pits 116.5
" earth material taken from test-pits on the dam. 133.0
Per cent.
Percentage of moisture in natural earth 19
" " voids in natural earth 52
" " grit and gravel in natural earth 38
" " compression on dam over earth at borrow-pit 16
" " compression on dam over earth in wagons 43
Degrees.
Angle of repose of natural moist earth 44
Angle of repose of earth, dust dry 36
Angle of repose of saturated earth 23
CONSTRUCTION DETAILS.— The materials forming the bulk
of the dam were hauled by four-horse teams, in dump-wagons,
holding 3 cu. yds. each. The wagons loaded weighed about six
tons and were provided with two swinging bottom-doors, which
the driver could operate with a lever, enabling the load to be
quickly dropped while the team was in motion. If the material
v/as quite dry, the load could be dumped in a long row when so
desired.
After plowing the surface of the ground and wasting any objec-
tionable surface soil, the material was brought to common earth-
traps for loading into wagons, by buck or dragscrapers of the
Fresno pattern. In good material one trap with eight Fresno-
scraper teams could fill 25 wagons per hour. The average length
of haul for the entire work was about 1,320 ft.
The original plans and specifications were adhered to through-
out, with the single exception that the central puddle wall was not
carried above elevation 1,160, as shown on Figs. 11 and 12, more
attention being given to the inner face puddle. This modification
in the original plans was made because of the character of the ma-
terials available and the excellent results obtained in securing an
honiogeneous earthen-concrete, practically impervious.
EARTH DAMS.
The top of the embankment
was maintained basin-shaped
during construction, being low-
er at the axis than at the outer
slopes by i-io, to the height be-
low the finished crown. This
gave a grade of about i in 25
from the edges toward the cen-
ter, resulting in the following
advantages :
(i) Insuring a more thorough
wetting of the central portion of
the dam ; any excess of water in
this part would be readily taken
care of by the central cross
drains.
(2) In wetting the finished
surface prior to depositing a
new layer of material, water
from the sprinkling wagons
would naturally drain towards
the center and insure keeping
the surface wet ; the layers be-
ing carried, as a rule, progres-
sively outward from the center.
(3) It centralized the maxi-
mum earth pressure and en-
abled the depositing of material
in layers perpendicular to the
slopes.
(4) It facilitated rolling and
hauling on lines parallel to the
axis of the dam, and discour-
aged transverse and miscellane-
ous operations.
(5) It finally insured better
compacting by the tramping of
teams in their exertions to over-
come the grade.
The specifications stipulated
that the body of the dam should
THE TABEAUD DAM.
27
, Jtog JiaM
daid uizuQ Jo pu3
28 EARTH DAMS.
be built up in layers not exceeding 6 ins. in thickness for the first
60 ft., and not exceeding 8 ins. above that elevation. The finished
layers after rolling varied slightly in thickness, the daily average
per month being as follows :
April 4 ins. August S ins.
May S'A" September 6
June 4 " October 7
July 4J4" November and December. . 8 "
During the last few months more than one whole layer consti-
tuted the day's work, so that a single layer was seldom as thick
as the daily average indicates.
It was stipulated in the specifications that the up-stream half
of the dam was to be made of "selected material" and the lower
half of less choice material, not designated "waste." "Waste ma-
terial" was described as meaning all vegetable humus, light soil,
roots, and rock exceeding 5 lbs. in weight, too large to pass
through a 4-in. ring.
It may be well to define the expression "selected material," so
commonly used in specifications for earth dams. In England, for
instance, it is said to refer to materials which insure ivatcr-tight-
ncss, while in India it refers to those employed to obtain stability.
It ought to mean the best material available, selected by the engi-
neer to suit the requirements of the situation.
The method employed in building the body of the embankment
may be described as follows :
,(i) The top surface of every finished layer of material was
sprinkled and harrowed prior to putting on a new layer. The
sprinkling wagons passed over the older finished surface imme-
diately before each wagon-row was begun. This insured a
wetted surface and assisted the wheels of the loaded wagons, as
well as the harrows, to roughen the old surface prior to deposit-
ing a 'new layer.
(2) The material was generally deposited in rows parallel to
the axis of the dam. However, along the line of contact, at the
margins of the embankment, the earth was often deposited in
rows crosswise of the dam, permitting a selection of the choicest
materials and greatly facilitating the work of graders and rollers.
(3) Rock pickers with their carts were continually passing along
the rows gathering up all roots, rocks and other waste materials.
(4) The road-graders drawn by six horses leveled down the tops
of the wagon-loads, and if the material was dry the sprinkling
THE TABEAUD DAM.
29
30 EARTH DAMS.
wagons immediately passed over the rows prior to further grad-
ing. When the material was naturally moist the grader continued
the leveling process until the earth was evenly spread. The depth
or thickness of the layer could be regulated to a nicety by prop-
erly spacing the rows and the individual loads. The grader brought
the layer to a smooth surface and of uniform thickness, and noth-
ing more could be desired for this operation.
(5) After the graders had finished, the harrows passed over the
new layer to insure the picking out of all roots and rocks, fol-
lowed immediately by the sprinkling wagons.
(6) Finally the rollers thoroughly compacted the layer of earth,
generally passing to and fro over it lengthwise of the dam. Along
the line of contact at the ends, however, they passed crosswise.
Then again they frequently went around a portion of the surface
until the whole was hard and solid.
Two rollers were in use constantly, each drawn by six horses.
One weighed five tons and the other eight tons, giving respectively
166 and 200 lbs. pressure per lin. in. They were not grooved, but
the smooth surface left by the rollers was always harrowed and cut
up more or less by the loaded wagons passing over the surface pre-
viously wetted. The wagons when loaded gave 750 lbs. pressure
per Un. in., and the heavy teams traveling wherever they could do
the most eiifective work compacted the materials better even than
the rollers.
, Several test pits which were dug into the dam during construc-
tion showed that there were no distinct lines traceable between
the layers and no loose or dry spots, but that the whole mass was
solid and homogeneous.
A careful record is being kept of the amount of settlement of
the ;Tabeaud Dam. It will be of interest to record here the fact
that just one year after date of completion the settlement
amounted to 0.2 ft., with 90 ft. depth of water in the reservoir.
Water was first turned into the reservoir five months after the
dani was finished. The very small amount of settlement here
shojwn emphasizes more eloquently than words the author's con-
cluding remarks relating to the importance of thorough consolida-
tion, by artificial means, of the embankment. (See p. 64, Sees.
6 to 8.)
OUTLET TUNNEL.— The outlet for the reservoir is a tun-
nel 2,903 ft. in length, through a ridge of solid slate rock forma-
tion, which was very hard and refractory. At the north or res-
THE TABEAUD DAM.
31
ervoir end of the tunnel, there is an open cut 350 ft. long, with a
maximum depth of 26 ft.
Near the south portal of the tunnel and in the line of pressure
pipes connecting the "petty reservoir" above with the power-
house below, is placed a receiver, connected with the tunnel by
means of a short pipe-line, 60 ins. in diameter.
A water-tight bulkhead of brick and concrete masonry is placed
in the tunnel, at a point about 175 ft. distant from the receiver.
In the line of 6o-in. riveted steel pipe, which connects the reser-
voir and tunnel with the receiver, there is placed a cast iron cham-
ber for entrapping silt or sand, with a branch pipe 16 ins. in diam-
eter leading into a side ravine through which sand or silt thus
collected can be wasted or washed out. By the design of construc-
tion thus described, it will be seen that all controlling devices,
screens, gates, etc., are at the south end of the tunnel and easily
accessible.
WASTEWAY. — The wasteway for the reservoir is an open cut
through its rim, 48 ft. in width and 300 ft. long. The sill of the
spillway is 10 ft. below the crown of the dam. The reservoir hav-
ing less than two square miles of catchment area, and the feeding
canals being under complete control, the dam can never be over-
topped by a flood. Fig. 3 shows the relative location of the dam,
outlet tunnel and wasteway channel.
Almost the whole of the embankment forming the Tabeaud
Dam, not included in the foundation work, was built in less than
eight months. The contractor's outfit was the best for the pur-
nose the writer has ever seen. After increasing his force from
time to time he finally had the following equipment:
1 steam shovel (l^ yds. capacity),
37 patent dump wagons,
II stick-wagons and rock-carts,
39 buck-scrapers (Fresno pattern),
21 wheel scrapers,
3 road-graders,
3 sprinkling-wagons,
2 harrows,
2 rollers (5 and 8-ton),
233 men,
416 horses and mules.
8 road and hillside plows,
32 EARTH DAMS.
STATISTICS.— The following data relating to the Tabeaud
Dam Reservoir will conclude this description ;
DAM.
Length at crown °3" ''■
Length at base crossing ravine 5° to lOO
Height to top of crown (El. 1,258.) 120
" at ends above bedrock ii7
" at up-stream toe 100
" at down-stream toe 123
Effective head US
Width at crown 20
Width at base 620
Slopes, 2j4 on i with rock-fill 3 to I.
Excavation for foundations 40,000 cu. yds.
Refill by company 40,000
Embankment built by contractor 330,350 "
Total volume of dam 370,35° "
Total weight 664,778 tons.
Length of wasteway (width) 48 ft.
Depth of spillwav sill below crown 10 "
Depth of spillway sill below ends 7 "
Height of stop-planks in wasteway 2 "
Maximum depth of water in reservoir 92 "
Area to be faced with stone i,933 sq. yds.
RESERVOIR.
Catchment area (approximate) 2 sq. miles.
Area of water surface 36. 75 acres.
Silt storage capacity below outlet tunnel 1,091,470 cu. ft.
Available water storage capacity 46,612,405 "
Elevation of outlet tunnel i, 180 ft.
" " high-water surface 1,250 "
" " crown of dam 1,258 "
Fig. 13 is a view of the finished dam, taken immediately after
completion.
CHAPTER V.
Different Types of Earth Dams.
There are several types of earth dams, which raay be described as
follows :
1. Homogeneous earth dams, either with or without a puddle
trench.
2. Earth dams with a puddle core or puddle face.
3. Earth dams with a core wall of brick, rubble or concrete
masonry.
4. New types, composite structures.
5. Rock-fill dams with earth inner slope.
6. Hydraulic-fill dams of earth and gfavel.
The writer proposes to give an example of each type, with s^uch
remarks upon their distinctive features and relative merits as he
thinks may be instructive. v'
Earth Dams nritb Pnddle Core, Wall or Face.
YARROW DAM.— The Yarrow clam of the Liverpool Water-
Works is a notable example of the second type, a section of which
is shown in Fig. 2. An excavation 97 ft. in depth was made! to
bed rock through different strata of varying thickness, and a
trench 24 ft. wide was cut with side slopes i on i for the first! 10
ft. in depth below the surface. The trench was then carried
down through sand, gravel and boulders with sides sloping i in
12. The upper surface of the shale bed rock was found to be soft,
seamy and water-bearing. Pumps were instailled to keep the water
out of the trench while it was being cut 4 or 5 ft. deeper into the
shale. The lower portion was then walled up on either side \yith
brickwork 14 ins. in thickness, and the trench betWeen the walls
was filled with concrete, made in the proportion of i of cem,ent,
I of sand and 2 of gravel or broken stone. By so doing a dryjbed
was secured for the foundation of the puddle wall. Two line^; of
6-in. pipes were laid on the bed rock, outside of the walls, 'and
pipes 9 ins. in diameter extended vertically above the top of the
brickwork some 27 ft. These pipes were filled with concrete, after
disconnecting the pumps. After refilling the trench with puddle
to the original surface, a puddle wall was carried up simultan-
34
EARTH DAMS.
DIFFERENT TYPES OF EARTH DAMS. 35
eous with the embankment, having a decreasing batter of i in 12,
which gave a width of 6 ft. at the top. This form of construction
is very common in England, and Figs. 14 and 15 show two Cali-
fornia dams, the Pilarcitos and San Andres, of the same general
type.
ASHTI EMBANKMENT.— This is not a very high embank-
ment, but being typical of modern dams in British India, where
the puddle is generally carried only to the top of the orig-
inal surface of the ground, and not up through the body of the
dam, it is thought worthy of mention. Fig. 16 shows a section of
this embankment, which is located in the Sholapur District, India.
The central portion of this dam above the puddle trench is made
of "selected black soil;" then on either side is placed "Brown
Soil," finishing on the outer slopes with "Murum." Trap rock
decomposes first into a friable stony material, known in India as
"Murum" or "Murham." This material further decomposes into
SCALC in TccT
KIG. 16.— OROSS-SBCTIO.V O'P ASHTI TANK BMBANKMENT.
various argillaceous earths, the most common being the "black
cotton soil" mentioned above.
This particular dam has been adversely criticised on account of
the lack of uniformity in the character of the materials composing
the bank. It is claimed that the materials being of different den-
sity and weight, unequal settlement will result, and lines of sep-
aration will form between the different kinds of materials.
Earth materials do not unite or combine with timber or mason-
ry, but there are no such distinct lines of transition and separation
between different earth materials themselves as Fig. 16 would
seem to indicate.
Puddle Trencli.
In the last three dams mentioned (Figs. 14, 15, 16) the puddle
trenches are made with vertical sides or vertical steps and offsets.
A wedge-shaped trench certainly has many advantages over this
36 EARTH DAMS.
form. Puddle being plastic, consolidates as the dam settles, fill-
ing the lowest parts by sliding on its bed. It thus has a tendency
to break away from the portion supported by the step, and a fur-
ther tendency to leave the vertical side, thus forming cracks and
fissures for water to enter. The argument advanced by those
holding a different view, namely, that it is difficult to dress the
sides of a trench to a steep batter and to timber it substantially,
has in reality little weight when put to practical test. Mr. F. P.
Stearns, in describing the recent work of excavating the cut-off
trench of the North Dike of the Wachusett reservoir, Boston,
said it was found to be both better and cheaper to excavate a
trench with slopes than with vertical sides protected by sheeting.
He favored this shape in case of pile-work and for the purpose
also of wedging materials together.
Mr. Wm. J. McAlpine's "Specifications for Earth Dams," repre-
senting the best practice of 25 years ago, which are frequently
cited, contain the following description of how to prepare the
up-stream floor of the dam :
Remove the pervious and decaying matter by breaking up the natural soil
and by stepping up the sides of the ravine; also by several toothed trenches
across the bottom and up the sides.
One of Mr. AlcAlpine's well known axioms was, "water abhors
an angle." The "stepping" and "toothed" trenches above speci-
fied need not necessarily be made with vertical planes, but should
be made by means of inclined and horizontal planes. The writer's
experience and observation leads him to think that all excavations
in connection with earth dams requiring a refill should be made
v.- edge-shaped so that the pressure of the superincumbent mater-
ials in settling will wedge the material tighter and tighter together
and fill every cavity. A paper by Mr. Wm. L. Strange, C. E., on
"Reservoirs with high Earthen Dams in Western India," pub-
lished in the Proceedings of the Institution of Civil Engineers,
Vol. 132, (1898), is one of the best contributions to the literature
on this subject, known to the writer. Mr. Strange states that
the rate of filtration of a soil depends upon its porosity, which governs the
frictional resistance to flovvr, and the slope and length of the filamentary
channels along which the water may be considered to pass. It is evident,
therefore, that the direct rate of infiltration in a homogeneous soil must de-
crease from the top to the bottom of the puddle trench. The best section
for a puddle trench is thus a wedge, such as an open excavation would give.
It is true that the uppermost infiltrating filaments when stopped by the
puddle, will endeavor to get under it, but a depth will eventually be reached
DIFFERENT TYPES OF EARTH DAMS. 37
when the frictional resistance along the natural passages will be greater
than that due to the transverse passage of the puddle trench, and it is when
this occurs that the latter may be stopped without danger, as the filtration to
it will be less than that that through it. This depth requires to be determined
in each case, but in fairly compact Indian soils 30 feet will be a fair limit.
Puddle 'Wall vs. Fuddle Xrencb.
There is a diversity of opinion among engineers in regard to the
proper place for the puddle in dam construction. Theoretically,
the inner face would be preferable to the center, for the purpose of
preventing any water from penetrating the embankment. It is
well known that all materials immersed in water lose weight in pro-
portion to the volume of water they displace. If the upper half of
the dam becomes saturated it must necesarily lose both weight and
stability. Its full cohesive strength can only be maintained by mak-
ing it impervious in some way. The strength of an earth dam de-
ponds upon three factors :
1. Weight.
2. Frictional resistance against sliding.
3. Cohesiveness of its materials.
These can be known only so long as no water penetrates the body
of the dam. When once saturated the resultant line of pressure is
no longer normal to the inner slope, for the reason that there is now
a force tending to slide the dam horizontally and another due to
the hydrostatic head tending to lift it vertically. When the water
slope is impervious the horizontal thrust is sustained by the whole
dam and not by the lower half alone. When once a passage is
made into the body of the dam, the infiltration water will escape
along the line of least resistance, and if there be a fissure it may
become a cavity and the cavity a breach.
For practical reasons, mainly on account of the difficulty of main-
taining a puddle face on the inner slope of a dam, which would re-
quire a very flat slope, puddle is generally placed at the center as
a core wall.
It was thought possible at the Tabeaud dam to counteract the
tendency of the face puddle to slough ofif into the reservoir by use
of a broken stone facing of riprap. This covering will protect the
puddle from the deteriorating efifects of air and sun whenever the
water is drawn low and also resists the pressure at the inner toe
of the dam.
38 EARTH DAMS.
Percolation and Infiltration.
The earlier authorities on the subject of percolation and infiltra-
tion of water are somewhat conflicting in their statements, if not
confused in their ideas. We are again impressed with the import-
ance of a clearly defined and definite use of terms. The temptation
and tendency to use language synonymously is very great, but it is
unscientific and must result in confusion of thought. Let it be ob-
served that filtration is the process of mechanically separating and
removing the undissolved particles floating in a liquid. That in-
filtration is the process by which water (or other liquid) enters the
interstices of porous material. That percolation is the action of a
liquid passing through small interstices ; and, finally, that seepage
is the amount of fluid which has percolated through porous mater-
ials.
Many recent authorities are guilty of confusion in thought or
expression, as will apoear from the following:
One says, for instance, that a
rock is water-tight when non-absorbent of water, but that a soil is not water-
tight unless it will absorb an enormous quantity of water.
This would seem to indicate that super-saturation and not pres-
sure is necesary to increase the water-tightness of earth materials.
Again, in a recent discussion regarding the saturation and perco-
lation of water through the lower half of a reservoir embankment,
it was remarked, that
the more compact the material of which the bank is built, the steeper will
be the slope of saturation.
Exception was taken to this, and the statement made, that
with compact material, the sectional area of flow is larger below a given level
with porous material, and as the bank slope is one determining factor of the
line of saturation, this line tends to approach the slope line; while with por-
ous material in a down-stream bank, the slope of saturation is steeper and
the area of the flow less.
In reply to this, it was said,
that it is obvious that if the embankment below the core wall is built of ma-
terial so compact as to be impervious to water, no water passing through
the wall will enter it, and the slope of saturation will be vertical. If it be
less compact, water will enter more or less according to the head or press-
ure, and according to its compactness or porosity, producing a slope of sat-
uration whose inclination is dependent on the frictional resistance encoun-
tered by the water. And the bank will be tight whenever the slope of sat-
uration remains within the figure of the embankment.
DIFFERENT TYPES OF EARTH DAMS. 39
Further,
that it was necessary to distinguish between the slope assumed
by water retained in an embankment and that taken by water passing
through an embankment made of material too porous to retain it; where the
rule is clearly reversed and where the more porous the material the
steeper the slope at which water will run through it at a given rate.
These citations are sufficient to emphasize the importance of
exact definition of terms and clear statement of principles.
The latest experiments relating to the percolation of wziter
through earth materials and tests determining the stability of soils
are those made during the investigations at the New Croton Dam
and Jerome Park Reservoir, New York, and those relating to the
North Dike of the Wachusett Reservoir, Boston. These are very
interesting and instructive, and it is here proposed to discuss the
results and conclusions reached in these cases, after some intro-
ductory remarks reciting the order of events.
NEW CROTON DAM.— In June, 1901, the Board of Croton
Aqueduct Commissioners of New York requested a board of ex-
pert engineers, consisting of Messrs. J. J. R. Croes, E. F. Smith
?nd E. Sweet, to examine the plans for the construction of the
earth portion of the New Croton Dam, and also the core wall and
embankment of the Jerome Park reservoir.
This report was published in full in Engineering News for Nov.
28, 1901. It was followed in subsequent issues of the said journal
by supplemental and individual reports from each member of the
board of experts, and by articles from Messrs. A. Fteley, who orig-
inally designed the works, A. Craven, formerly division engineer
en this work, and W. R. Hill, at that time chief engineer of the
Croton Aqueduct Commission.
After describing the New Croton Dam, the board of experts pref-
ace their remarks on the earth embankment by saying that
it has been abundantly proven that up to a height of 60 or 70 ft. an embank-
ment founded on solid material and constructed of well-selected earth, prop-
erly put in place, is fully as durable and safe as a masonry wall and far- less
costly.
There are, in fact, no less than 22 earth dams in use to-day
exceeding 90 ft. in height, and twice that number over 70 ft. in
height. Five of the former are in California, and several of these
have been in use over 25 years. The writer fails to appreciate the
reason for limiting the safe height of earth dams to 60 or 70 ft.
The New Croton Dam was designed as a composite structure of
masonry and earth, crossing the Croton Valley at a point three
40
EARTH DAMS.
miles from the Hudson River. The earth portion was to join the
masonry portion at a point where the latter was 195 ft. high from
the bed rock. The Board thought there was no precedent for such
a design and no necessity for this form of construction. The point
to be considered here was whether a dam like this can be made suf-
ficiently impermeable to water to prevent the outer slope from be-
coming saturated and thus liable to slide and be washed out.
The design of the embankment portion was similar to all the
earth dams of the Croton Valley. In the center is built a wall of
rubble masonry, generally founded upon solid rock, and "intended
to prevent the free seepage of water, but not heavy enough to act
alone as a retaining wall for either water or earth."
Fig. 17 shows a section which is typical of most New England
earth dams ; and Fig. 18, the sections of two of the Croton Val-
FIG. 17
SOVLE IW fEET
-CROSS-SECTIOX OF A TYPICAL NEW ENGLAND DAM.
ley dams. New York water supply. These dams all have masonry
core walls, illustrating the third type of dams given on page 33.
The board of experts made numerous tests by means of borings
into the Croton Valley dams to determine the slope of saturation.
The hydraulic laboratory of Cornell University also made tests of
the permeability of several samples of materials taken from pits.
All the materials examined were found to be permeable and when
exposed to water to disintegrate and assume a flat slope, the sur-
face of which was described as "slimy."
Pipe wells were driven at dififerent places into the dams and the
line of saturation was determined by noting the elevations at which
the water stood in them. In all the dams the entire bank on the
water side of the core wall appeared to be completely saturated.
Water was also found to be standing in the embankment on the
down-stream side of the core wall. The extent of saturation of the
outer bank varied greatly, due to the difference in materials, the
DIFFERENT TYPES OF EARTH DAMS.
41
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care taken in building them, and their ages. Fig. 19 gives the aver-
age slopes of saturation as determined by these borings.
The experts stated
that the slope of the surface of the saturation in the bank is determined by
the solidity of the embankment: The more compact the material of which
the bank is built, the steeper will be the slope of saturation.
As a result of their in-
vestigations, the experts
were of the opinion that
the slope of saturation in
the best embankments
made of the material found
in the Croton Valley is
about 35 ft. per 100 ft., and
that with materials less
carefully selected and
placed the slope may be
20 ft. per 100 ft.
Further, that taking the
loss of head in passing
through the core wall, and
the slope assumed by the
plane of saturation, the
maximum safe height of an
earth dam with its top 20 ft. above wa-
ter level in the reservoir and its outside
slope 2 on I, is 63 to 102.5 ft. This is a re-
markable finding in view of the fact that
the Titicus Dam, one of the Croton Valley
dams examined, has a maximum height
above bed rock of no ft. and has been in
use seven years. This dam is not a fair ex-
ample to cite in proof of their conclusion,
because its eifcctivc head is only about
46 ft.*
Mr. Fteley gave as a reason for
the elevation of the water slope
♦The effective head at any point of an ea-rth dam, has
been defined as the difference in elevation of high Tvater
surface in the reservoir and that of the intersection of
the down-stream slope with the natural or restored sur-
face of the ground below the dam.
42 EARTH DAMS.
found in the outer bank of the Croton dams the fact of their being
constructed of fine materials and stated that with comparatively
porous materials they would have shown steeper slopes of satura-
tion.
Mr. Craven argued that all dams will absorb more or less water,
and that porosity is merely a degree of compactness ; that slope im-
plies motion in water, and that there is no absolute retention of
water in the outer bank of a dam having its base below the plane
indicated by the loss of head in passing through the inner bank
and then through a further obstruction of either masonry or pud-
dle; that there is simply a partial retention, with motion through
the bank governed by the degree of porosity of the material.
Fig. 19 is a graphical interpretation of the conclusion reached
by the board of experts, as already given on page 41. "A" is an
ideal profile of a homogeneous dam with the inner slope 3 on i and
the outer slope 2 on i. The top width is made 25 ft. for a dam hav-
ing 90 ft. effective head, the high water surface in the reservoir
being 10 ft. below the crest of the dam. This ideal profile is a
fair average of all the earth dams of the world. Not haying a core
wall to augment the loss of head, it fairly represents what might
be expected of such a dam built of Croton Valley material, com-
pacted in the usual way. It should be noted that the intersection
of the plane of saturation with the rear slope of the dam at such
high elevation as shown indicates an excessive seepage and a dan-
gerously unstable condition.
Preliminary Study of JProfile for Dam.
The preliminary calculations for desiging a profile for an earth
dam are simple and will here be illustrated by an example. Let
us assume the following values :
a. Central height of dam, 100 ft.
b. Maximum depth of water, 90 ft,, with surface 10 ft. below
crest of dam.
c. Effective head, 90 ft.
d. Weight of water, 62.5 lbs. per cu. ft.
e. Weight of material, 125 lbs. per cu. ft.
f. Coefficient of friction, i.oo, or equal to the weight.
g. Factor of safety against sliding, 10.
The width corresponding to the vertical pressure of i ft. is,
62.5 X 10
=5 ft.
125
DIFFERENT TYPES OF EARTH DAMS.
43
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44 EARTH DAMS.
The hydrostatic pressure per square foot at 90 ft. depth is, 62.5 x
90=5,625 lbs.
The dam, having a factor of safety of 10, must present a resist-
ance of, 5,625 X 10^56,250 lbs., or 28 tons per square foot.
The theoretical width of bank corresponding to 90 ft. head and a
factor of 10 is shown by the dotted triangle (A-B-B) to be 450 ft.,
(B, Fig. 19) with slopes 2^ on i.
To this must be added the width due to the height of crest above
the water surface in the reservoir and the width of crest.
The former would be, 2 (2^ x 10)^50 ft., and the latter by Traut-
v/ine's rule, 2 + 2\/ 100=22 ft., giving a total base width of 522 ft.
Let us now assume that the slope of saturation may be 35 ft. per
100 ft. We observe that this intersects the base 40 ft. within the
outer toe of the bank slope. If the plane of saturation was 33 ft.
per 100, it would just reach the outer toe. It would be advisable
to enlarge this section by adding a lo-ft. berm at the 50-ft.level,
having a slope not less than 3 on i for the up-stream face, and two
15-ft. berms on the down-stream face, having slopes 2^ on i. The
additional width of base due to these modifications in our profile
amounts to 65 ft., giving a total base width of 587 ft., and increas-
ing the factor of safety from 10 to 13. It should be remembered
that if the bank becomes saturated this factor of safety may be re-
duced 50%, the coefficient of moist clay being 0.50.
The loss of head due to a core wall of masonry, as designed for
the New Croton Dam, was assumed by the board of experts to be 21
ft., or 17% of the depth of water in full reservoir. It has been
stated by several authorities that the primary object of a masonry
core wall is to afford a water-tight cut-off to any water of perco-
lation which may reach it through the upper half of the embank-
ment. It appears that absolute water-tightness in the core wall
is not obtained, although the core walls of the Croton dams are said
to be "the very best quality of rubble masonry that can be made."
Mr. W. W. Follett, who is reported to have had considerable ex-
perience in building earth dams, and who has made some valuable
suggestions thereupon, is emphatic in saying,
that the junction of earth and masonry forms a weak point, that either a
puddle or masonry core in an earthen dam is an element of weakness rather
than strength.
He also thinks the usual manner of segregating and depositing
materials different in density and weight, and thus subject to differ-
DIFFERENT TYPES OF EARTH DAMS. 45
ent amounts of settlement, as bad a form of construction as could
be devised.
Core walls may prevent "free passage of water" and "excessive
seepage," but are nevertheless of doubtful expediency.
EartbTTorlic Slips and Drainagre.
Mr. John Newman, in his admirable treatise on "Earthwork Slips
and Subsidences upon Public Works," classifies and enumerates
slips as follows :
Natural causes, 7.
Artificial causes, 31.
Additional causes due to impounded water, 7.
After describing each cause he presents 39 different means used
to prevent such slips and describes methods of making repairs.
Mr. Wm. L. Strange has had such a large and valuable experi-
ei/ce and has set forth so carefully and lucidly both the principles
and practice of earth dam construction, that the writer takes pleas-
ure in again quoting him on the subject of drainage, of which he is
an ardent advocate. He says that,
thorough drainage of the base of a dam is a matter of vital necessity, for
notwithstanding all precautions, some water will certainly pass through the
puddle.
It is at the junction of the dam with the ground that the maxi-
mum amount of leakage may be expected. The percolating water
should be gotten out as quickly as possible. The whole method of
dealing with slips may be summed up in one word — drainage.
The proper presentation of these two phases of our subject would
in itself require a volume. The interested reader is therefore re-
ferred to the different authorities and writers cited in Appendix II.
Jerome Park Reservoir £inbaiil(ineuts>
The Jerome Park reservoir is an artificial basin involving the ex-
cavation and removal of large quantities of soil, and the erection of
long embankments with masonry core walls, partly founded on
rock and partly on sand. The plan and specifications call for an
embankment 20 ft. wide on top, with both slopes 2 on r, and pro-
vide for lining the inner slope with brick or stone laid in concrete,
and for covering the bottom with concrete laid on good earth com-
pacted by rolling.
45
EARTH DAMS.
smmni
DIFFERENT TYPES OF EARTH DAMS. 47
Wherever bed rock was not considered too deep below the sur-
face the core walls were built upon it. In other places the founda-
tion was placed 8 to 10 ft. below the bottom of the reservoir and
rested upon the sand.
It appears that the plans of the Jerome Park embankment were
changed from their original design, prior to the report of the board
of experts, on account of two alleged defects, namely, "cracks in
the core wall" and "foundation of quicksand," and incidentally on
account of the supposed instability of the inner bank.
In describing the materials on which these embankments rest
the experts remarked
that all these fine sands are unstable when mechanically agitated in an ex-
cess of water, and that they all settle in a firm and compact mass under the
water when the agitation ceases. That they are quite unlike the true quick-
sands whose particles are of impalpable fineness and which are "quick" or
unstable under water.
Fig. 20 is a graphic exhibit of the results of tests made at "Sta-
tion 76 + 20," and at "Station 99," to determine the flow line of
water in the sand strata underlying the embankment and bottom of
the Jerome Park reservoir.
The experts reported that there was no possible danger of slid-
ing or sloughing of the bank ; that the utmost that could be expect-
ed would be the percolation of a small amount of water through the
embankment and the earth ; and that this would be carried ofif by
the sewers in the adjacent avenues; that a large expenditure to
prevent such seepage would not be warranted nor advisable.
In concluding their report, however, they recommended chang-
ing the inner slope of 2 on i to 2^ on i, and doubling the thickness
of the concrete lining at the foot of the slope to preclude all
possibility of the sliding or the slipping of the inner bank in case of
the water being lowered rapidly in the reservoir.
Mr. W. R. Hill, then chief engineer of the Croton Aqueduct
Commission, favored extending the core walls to solid rock. He
took exception to the manner of obtaining samples of sand by
means of pipe and force-jet of water, claiming that only the coarsest
sand was obtained for examination. He did not consider
fine sand through which three men could run a f-in. rod 19 and 20
ft. to rock without use of a hammer, very stable material upon
which to build a wall.
48 EARTH DAMS.
North Dike of the Wacbnsett Beservotr, Boston.
The North Dike of the Wachusett Reservoir is another large pub-
lic work in progress at the present time. It is of somewhat unusual
design and the preliminary investigations and experiments which
led to its adoption are interesting in the extreme.*
The area to be explored in determining the best location for the
dike was great, and the preliminary investigations conducted by
means of wash drill borings, very extensive. A total of 1,131 bor-
ings were made to an average depth of 83 ft., the maximum depth
being 286 ft. The materials were classified largely by the appear-
ance of the samples, though chemical and filtration tests were also
made. The plane of the ground water was from 35 to 50 ft. below
the surface, and the action of the water-jet indicated in a measure
the degree of permeability of the strata.
In addition to these tests experimental dikes of different mater-
ials, and deposited in different ways, were made in a wooden tank
6 ft. wide, 8 ft. high and 60 ft. long. The stability of soils when in
contact with water was experimented with, as shown in Fig. 21, in
the following manner :
An embankment (Fig. 21) was constructed in the tank of the ma-
terial to be experimented with, 2 ft. wide on top, 6 ft. high, with
slopes 2 on I, and water admitted on both sides to a depth of 5 ft.
The top was covered with 4-in. planks 2 ft. long and pressure ap-
plied by means of two jack screws resting upon a cross beam on
top of the planks.
With a pressure of three tons per square foot, the 4-in. planks
were forced down into the embankment a little more than 6 ins.,
resulting in a very slight bulging of the slopes a little below the
water level. Immediately under the planks the soil became hard
and compact. A man's weight pushed a sharp steel rod, f-in. in
diameter, only 6 to 8 ins. into the embankment where the pressure
was applied, while outside of this area the rod was easily pushed to
the bottom of the tank.
These results corroborate in a general way the practical experi-
ence of the author, both in compressed embankments, where he
found it necessary to use a pick vigorously to loosen the material
of which they were composed, and in embankments made by mere-
•This work is very fully described in the Annual Reports of the Metropolitan Water
Board of Boston: and by Mr. F. P. Stearns, Chief Engineer of the Metropolitan Water
and Sewerage Board, in the Proceedings of the American Society of Civil Engineers
for April, 1902. The latter description was reprinted, with the omission of some of
the illustrations, in Engineering News for May, 8, 1902.
DIFFERENT TYPES OF EARTH DAMS.
49
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50 EARTH DAMS.
]y dumping the material from a track, in which case the earth is so
slightly compressed that an excavation is easily made with a shovel.
The difference in the coefficient of friction of the same material
when dry and when wet greatly modifies the form of slope. The
harder and looser the particles, the straighter will be the slope line
in excavation and slips. The greater the cohesion of the earth, the
more curved will be the slope, assuming a parabolic curve near the
top — the true form of equilibrium.
RATE OF FILTRATION.— The rate of filtration through dif-
ferent soils was experimented with by forming a dike in the tank
previously mentioned, as shown in Fig. 22.
The dike was made full 8 ft. high, 7 ft. wide on top, with a slope
on the up-stream side of 2 on i, and on the doY/n-stream side 4
on I. This gave a base width of 55 ft. Immediately over the top
of the dike there was placed 3 ft. of soil to slightly consolidate the
top of the bank and permit the filling of the tank to the top without
overflowing the dike. The water pressure in different parts of the
dike was determined by placing horizontal pipes through the soil
cross-wise of the tank. These pipes were perforated and covered
with wire gauze, being connected to vertical glass tubes at their
ends. The end of the slope on the down-stream side terminated
in a box having perforated sides and filled with gravel, thus en-
abling the water to percolate and filter out of the bank without car-
rying the soil with it.
When the soil was shoveled loosely into the tank, without con-
solidation of any kind, it settled on becoming saturated and became
quite compact. It took five days for the water to appear in the
sixth gage pipe near the lower end of the tank. After the pressure,
which was maintained constant, had been, on for several weeks,
the seepage amounted to one gallon in 22 minutes. When the soil
was deposited by shoveling into the water, the seepage amounted
to one gallon in 34 minutes. ;
The relative filtering capacities of soils and sands were thought
to be better determined by the use of galvanized iron cylinders of
known areas.
Fig. 23 shows one of the cylinders. These latter experiments
confirmed those previously made at Lawrence, by Mr. Allen Hazen,
lor the Massachusetts State Board of Health. They showed that
the loss of head was directly proportioned to the quantity of water
DIFFERENT TYPES OF EARTH DAMS. 51
filtered and that the quantity filtered will vary as the square of the
diameter of the effective size of the grains of the filtering material.*
The material classed as "permeable" at the North Dike of the
Wachusett Reservoir has an effective diameter of about 0.20 mm.
A few results are given in the following table :
Amount of Filtration in Gallons per Day, Through an Area of 10,000 Sq. Ft.,
With a Loss of Head or Slope of i ft. in 10 ft.
Material. Unit ratios. U. S. gallons,
(i) Soil I Sio
(2) Very fine sand 14 7,200
(3) Fine sand 176 90,000
(4) Medium sand 784 400,000
(5) Coarse sand 4,353 2,200,000
To be sure that the accumulation of air in the small interstices
of the soil was not the cause of the greatly reduced filtration through
it, another series of experiments was conducted in the wooden tank,
as shown in Fig. 24.
A pair of screens was placed near each end of the tank, filled
with porous material, sand and gravel, and the 50-ft. space between
filled with soil. The soil was rammed in 3-in. layers, and special
care taken to prevent water from following along the sides and
bottom of the tank. One end was filled with water to near the top,
while the other end gave a free outlet.
After this experiment had been continued for more than a month,
the amount of seepage averaged 1.7 gallons per 24 hours, or about
32 drops per minute.
Filtration tests were also made through soil under 150 ft. head,
or 5 lbs. per sq. in., with results not materially different, it is stated,
from those already given. The soil used in all these tests con-
tained from 4 to 8% by weight of organic matter. This was burned
and similar tests made with the incinerated soil, resulting in an in-
crease of about 20% more seepage water.
PERMANENCE OF SOILS.— This last material experimented
with suggests the subject of permanence of soils. This was report-
ed upon separately and independently by Mr. Allen Hazen and
Prof. W. O. Crosby. These experts agreed in their conclusion,
stating
that the process of oxidation below the line of saturation would be ex-
tremely slow, requiring many thousands of years for the complete removal
*By effective size of sand grains is meant sucli size ot grain that 10% by weight oi
the particles are smaller, and 90% larger than itself; or, to express it a little differently,
the effective size is equal to a sphere the volume of which is greater than Vu that
forming the weight and is less than Vio that forming the weight.
52
EARTH DAMS.
of all the organic matter, and that the tightness of the bank would not be
materially affected by any changes which are likely to occur.
It has been remarked,
that of all the materials used in the construction of dams, earth is physically
the least destructible of any. The other materials are all subject to more
or less disintegration, or change in one form or another, and in earth they
reach their ultimate and most lasting form.
In speaking of the North Dike of the Wachusett Reservoir, Mr.
Stearns remarked that,
it was evident by the application of Mr. Hazen's formula for the flow of
water through sands and gravels, that the very fine sands found at a con-
siderable depth below the surface would not permit enough water to pass
through them if a dike of great width were constructed, to cause ar serious
loss of water, and it was also found that the soil, which contained not only
the fine particles or organic matter, but also a very considerable amount of
fine comminuted particles, which the geologist has termed "rock flour,"
would be sufficiently impermeable to be used as a substitute for clay puddle.
Fig-. 25 showfs the maximum section of the North Dike with its
cut-off trench. The quantities and estimated cost of the completed
structure are given in the table herewith :
I Cost, 1
Per cent.
Work. Quantities. Unit price. Actual. total.
Soil 5,250,000 cu. yds. $0.05 $262,500 34.7
Cut-oflf trench 542,000 " .20 108,400 19.3
Borrowed earth and gravel 200,000 " .20 40,000
Slope paving 50,000 " 2.20 110,000 14.6
Sheet-piling, pumping, etc 117,000 15.5
Engineering and preliminary investigations 120,000 15.9
Total cost $757>900 loo.o
Druid LiaKe Dam, Baltimore, md>
Another very interesting and instructive example of high earth
dam construction is that of the Druid Lake Reservoir embankment,
Baltimore, Md.
This dam was built under the supervision of Mr. Robt. K. Mar-
tin. Construction was begun in 1864, and the dam was finished in
1870. Mr. Alfred M. Quick, present chief engineer of the water-
works of the City of Baltimore has given a very lucid description
of this work in Engineering News of Feb. 20, 1902.
Fig. 26 is a cross-section of this dam, showing the method of
construction so clearly as to scarcely need further description.
The banks D-D on either side of the central puddle wall were car-
DIFFERENT TYPES OF EARTH DAMS.
53
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ried up in 6-in. layers with
horses and carts, and kept about
2 ft. higher than the puddle
trench, which always contained
water. The banks E-E were
made of dumped material, after
which the basins F-F were first
filled with water and finally filled
by dumping material into the
water from tracks being moved
in toward the center.
After reaching the top of this
fill, banks B-B-B were built up
in layers similar to D-D. The
second set of basins C-C were
then filled in a manner similar
to F-F. The remaining portion
A-A was constructed in layers
like D-D and B-B, with the ad-
dition of compacting each layer
with a heavy roller.
Finally the inner face slope
was carred up in 3-in. layers and
thoroughly rolled, after which 2
ft. of "good puddle" was put
upon the inner slope the latter
was rip-rapped, the crown cov-
ered with gravel and the rear
slope sodded.
Some years after completion,
a driveway was built along the
outer slope, as shown, which
had a tendency to strengthen
the dam, though not designed
expressly for that purpose.
It .is of interest to know that
the influent, efifluent and drain
pipes were originally con-
structed through or under
the embankment. These pipes
were laid upon solid earth,
and where they passed
54 EARTH DAMS.
through the puddle wall were supported upon stone piers 6 ft|
apart. As might be expected, they soon cracked badly and were
finally abandoned, new ones being placed in the original ground at
the south side of the lake. Mr. Quick states that so far as is known
there has never been any evidence of a leak through the embank-
ment during these 32 years of service.
T(ew Types of Dams; Bobto, Panama Canal.
A brief description will now be given of three dififerent dams
designed for Bohio, on the proposed Panama Canal. Mr. George
S. Morison's paper before the American Society of Civil Engin-
eers, on "The Bohio Dam," and the discussion thereon, especially
that by Mr. F. P. Stearns, were quite fully reported in Engineer-
ing News for March 13 and May 8, 1902. In constructing
the Panama Canal it will be necessary to impound the waters of
the Chagres River, near Bohio, to maintain the summit level of
this canal and supplv water for lockage.
THE FRENCH DESIGN.— Fig. 27 is an enlarged section of the
original design of the new French Co. This design has no core
wall, but at the up-stream toe a concrete wall was to be built across
the river between the two lines of sheet-piling. At the down-stream
toe a large amount of riprap was to be placed to prevent destruc-
tion of the dam during construction. In this case it would be nec-
essary to construct a temporary dam above and also to use the ex-
cavation for the locks as a flood spillway. This method would in-
volve considerable risk to the work, on account of the large volume
of flood waters it might be necessary to take care of during con-
struction.
ISTHMIAN CANAL COMMISSION.— The dam proposed by
the Isthmian Canal Commission is shown by Fig. 28. This was de-
signed to be an absolutely water-tight closure of the geological
valley, by using a masonry core wall carried down to bed rock.
The maximum depth being 129 ft., it was planned to rest the con-
crete wall on a series of pneumatic caissons reaching to rock. The
spaces between the caissons would be closed and made water-tight.
Both slopes of the earth embankment were to have horizontal
benches and be revetted with loose rock.
MR. MORISON'S DESIGN.— To appreciate fully the object
and aim of the third design. Fig. 29, which may be called a new type,
although similar in many respects to the North Dike of the Wachu-
sett reservoir already illustrated and described, it should be stated
that the equalized flow of the Chagres River is put at 1,000 cu. ft.
DIFFERENT TYPES OF EARTH DAMS.
55
56 EARTH DAMS.
per sec. Of this quantity it is estimated that 5CK) cu. ft. would be
needed for lockage and 200 cu. ft. for evaporation. This leaves
300 cu. ft. per sec. available for seepage and other losses or to
be wasted.
Tt will thus be seen that a scarcity of water is not in this instance
a condition demanding an absolutely water-tight dam. The amount
of seepage permissible without endangering the stability of the
structure is the real point now to be discussed.
The third design, which was proposed by Mr. Morison, is shown
by Fig. 29. The topography and configuration of this dam site is
not unlike that of the San Leandro Dam, California, soon to be de-
scribed, while the yeneral design is similar, as has been remarked,
to the North Dike of the Wachusett Reservoir.
This third design contemplates a compound structure, formed by
two rock-fill dams situated about 2,120 ft. apart, with the inter-
vening space filled with loose rock, earth and other availible ma-
terial. Immediately below the upper and higher rock-fill dam, it
:s proposed to place across the canyon' a puddle wall 50 ft. in width,
resting over two lines of sheet-piling 30 ft. apart. This piling
would probably not reach farther than 50 ft. below tidewater, the
solid rock floor being about 100 ft', deeper.
Mr. Morison made use of Mr. Hazen's filtration formula for
estimating the rate and quantity of seepage through the permeable
strata below the dam. This formula is :
h t + io"
V=cd2 — where
1 60
V=rate of flow in meters per day through the whole section.
c=constant varying from 450 to 1,200, according to cleanness of
the sand.
d="effective size" of sand in mm.
h=head in feet.
l^ength or distance water must pass.
t=temperature of the water (Fahr.)
This formula should be used only when the effective sizes of sands
are from o.io to 3.0 mm. and with uniformity coefficients below 5.0*
Mr. Morison used the following values : C>=i,ooo; d=i.o mm. ;
h=9o ft. ; 1=2,500 ft. ; t=90° ; for the solution of this problem, and
♦The term "uniformity coefficient" is used to designate the ratio of the size of the
grain which has 60% ot the sample finer than itself to the size which has 10% finer than
itself. The method ot determining the size ot sand grains and their uniformity coeffi-
cients, is fully explained in Appendix 3 of Mr. 'Hazen's book on "The Filtration ot
Public Water Supplies."
DIFFERENT TYPES OF EARTH DAMS. 57
cbtained a velocity of 0.002 ft. per sec. The bed of sand and gravel
was assumed to have a sectional area of 20,000 sq. ft. for 2,500 ft.
in length. This gives a seepage of 40 cu. ft. per sec.
It is believed that the above rate of 0.002 ft. per sec, equivalent to
I 3-8 ins. per minute, or 7 ft. per hour, is not sufficient to move any
of the material. The velocity of water percolating through sand
is found to vary directly as the head and inversely as the distance.
The value of "c" in the formula is larger for sands of filters fav-
orable for flow, and smaller for compacted materials and dams.
Mr. Morison thought it might be nearer the actual conditions
to assume d=o.5o mm. ; c^soo; and l^s,ooo ft. ; in which case the
seepage would only amount to 2.5 ft. per sec. In this last assumption
the "effective size" of sand grains is 2^ times that classed as "per-
meable material" at the North Dike of the Wachusett Reservoir.
Prof. Philipp Forchheimer, of Gratz, Austria, recommends the
use of the formula,
h
_=a V + b V ^
1
for the percolation through soils between loam and loamy sand.
Sellheim, Masoni, Smreker, Krober and other authorities on fil-
tration use still other formulas, to which the reader and student is
referred for further research.
The writer, having had occasion in his professional practice to
study quite carefully the subject of ground waters, and their per-
colation or flow through different classes of materials and under
varying conditions, is of the opinion that rarely does the cross-
section of a stream-channel, filled with sand, gravel and debris, pre-
sent, even approximately, a homogeneous or uniform mass ; and
that there are, almost w'ithout exception, strata of material much
coarser and more porous than the general average. In other
words, that it is extremely difficult to arrive at a uniformity coeffi-
cient. It is unwise to place much reliance upon an estimated flow
where this is the case. The formula may be used with confidence
where the layers are artificially made, and where there is no uncer-
tainty regarding the uniform character of the material. In most
natural channels there are distinct lines of flow, and under con-
siderable hydrostatic head or pressure these lines of flow would
sureiy enlarge. There is a wide difference between permissible and
dangerously excessive percolation through an earth embank-
ment. The local features, economical considerations and magni-
58 EARTH DAMS.
tude of the risks, all bear upon this question and must be considered
for each particular case.
It is of interest to compare the estimated cost of the three de-
signs proposed for the Bohio Dam, based upon the same unit
prices, as follows:
French Ensrineers' design $3,500,000
Isthmian Canal Commissioners' design 8,000,000
Mr. Morison's design 2,500,000
No comments will be made upon these figures, further than to
remark that the successful building of a stable dam, accomplished
by the use of an excessive quantity of materials and at a cost be-
yond reasonable requirements, is mainly instructive as illustrating
"how not to do it." It is creditable to execute substantial works
at a reasonable cost, but it reflects no credit upon any one to con-
struct them regardless of expense.
Combined Rock-fill and Eartb Dam.
Fig. 30 shows a section of the Upper Pecos River Dam near
Eddy, N. M.
This dam is quite fully described by Mr. Jas. D. Schuyler, in his
recent book on "Reservoirs for Irrigation, Water-Power and Do-
mestic Water-Supply," and need not be mentioned in this paper,
further than to call attention to the combination of rock-fill and
earth which constitutes its- particular type of construction. This
type of dam is believed to be for manv localities a vei-y good one,
but up to the present time has only been adopted for dams of
moderate height, under 60 ft.
The San lieandro Dam, California.
A section of the San Leandro Dam, near Oakland, Cal.,
is shown by Fig. 31. This section was supplied by Mr. W. F.
Boardman, hydratilic engineer, who superintended the construction
of the dam, from his own private notes and da'ta. It differs mater-
ially from sections heretofore published, and is 5 ft. higher, thus
making it rank as the highest earth dam in the world of which
we have an authentic record.
The dam was commenced in 1874, and brought up to a height
of 115 ft. above the bed of the creek in 1898. At the present time
it is 500 ft. in length on the crest and 28 ft. wide. The original
width of the ravine at the base of the dam was 66 ft.-TThe present
width of base from toe to toe of slopes is i,7og-ft. The height of
DIFFERENT TYPES OF EARTH DAMS.
59
P
M
o
o
«
g
3
o
o
"l^^i
I
m
>
■ •'$;'—
8
f
o
O
o
o
fM;
M,J-.
C
h
..Y..
'6o EARTH DAMS.
embankment above the original surface is 125 ft., with a puddle
trench extending 30 ft. below.
All that portion of the dam within a slope of 2^ on i at the rear
and 3 on I at the face is built of choice material, carefully selected
and put in with great care. The portion outside of the 2^ on I
slope line at the down-stream side of the dam, was sluiced in from
the adjacent hills regardless of its character, and is composed of
ordinary soil containing more or less rock.
This process of sluicing was carried on during the rainy season,
when there was an abundance of water, and it was intended to be
continued until the canyon below the dam had been filled to an av-
erage slope of 6.7 on i at the rear of the dam. It was thought that
the location was particularly favorable for this kind of construction,
the original intention being to raise the dam from time to time,
not only to increase the storage as the demand for water increased,
but to meet the annual loss in capacity caused by the silting up of
the reservoir basin. The latter has amounted to about i' ft. in
depth per annum.
METHOD OF CONSTRUCTION.— Under the main body of
the dam, the surface was stripped of all sediment, sand, gravel and
vegetable matter. Choice material, carefully selected, was then
brought by carts and wagons and evenly distributed over the sur-
face in layers about i ft. or less in thickness. This was sprinkled
with just enough water 'to make it pack well, not enough to make
it like mud. During construction a band of horses was led by a
boy on horseback over the entire work, to compact the materials
and assist in making the dam one homogeneous mass. No rollers
were used on this dam.
The central trench was cut 30 ft. below the original bed of the
creek. In the bottom of this trench three secondary trenches, 3
ft. wide by 3 ft. deep, were made and filled with concrete. These
concrete walls were carried up 2 ft. above the general floor of the
trench, to break the continuity of its surface.
The original wasteway, constructed at the north end of the dam,
has been practically abandoned, having been substituted by a tunnel
of larger capacity. The original wasteway was excavated in the
bed rock of the natural hillside, and although lined with masonry,
is not in the best condition. The author considers its location an
objectionable feature, as menacing the safety of the dam, and thinks
it should be permanently closed.
A wasteway tunnel, 1,487 ft. in length, was constructed in 1888,
DIFFERENT TYPES OF EARTH DAMS. 6l
through a ridge extending north of the dam. This has a sectional
area of about loxio ft., Hned with brick masonry throughout, hav-
ing a grade of 2^%.
The criticism might be made of the tunnel that it is faulty in
design at the entry or reservoir end, where the water must first
fall over a high spillway wall, aerating the water before entering
the tunnel proper. The water even then has not easy access to
the tunnel, and no adequate arrangements have been made for ven-
tilation, so as to insure the utilization of its maximum capacity.
The maximum depth of water in the reservoir is about 85 ft., and
the full capacity 689,000,000 cu. ft. of water. The catchment area
is 43 square miles, and the surface of the reservoir when full 436
acres. The outlet pipes are placed in two tunnels at different ele-
vations through the ridge north of the dam. There are no culverts
or pipes extending through the body of the dam itself.
Hydranlic-fill Dams.
No discussion of earth dams would be complete without some
reference being made to the novel type of construction developed
in western America in recent years, by which railroad embankments
and water-tight dams are built up by the sole agency of water. The
water for this purpose is usually delivered under high pressure, as
it is generally convenient to make it first perform the work of
loosening the earth and rock in the borrow pit, as well as subse-
quently to transport them to the embankment, and there to sort and
deposit them and finally part company with them after compacting
them solidly in place, even more firmly than if compressed by
heavy rollers. Sometimes, however, water is delivered to the bor-
row pit without pressure, in which event the materials must be
loosened by the plow or by pick and shovel by the process called
ground sluicing in placer mining parlance.
An abundance of water delivered by gravity under high pressure
is usually regarded as one of the essential factors in hydraulic-fill
dam building, but it is not essential that there be a large continu-
ous flow. The Lake Frances Dam, recently constructed for the
Bay Counties Co., of California, by J. D. Schuyler, is 75 ft. high,
1,340 ft. long on top, and contains 280,000 cu. yds. The dam was
built up by materials sluiced by water that was forced by a cen-
trifugal pump through a 12-in. pipe and 3-in. nozzle, against a high
bank, whence the materials were torn and conveyed by the water
through flumes and pipes to the dam. About 6 cu. ft. per sec. of
62 EARTH DAMS.
water was thus used, and at one stage of the work the supply
stream was reduced to less than o.i ft. per sec, the water being
gathered in a pond and pumped over and over again.
The chapter on hydraulic-fill dams in Mr. Schuyler's book on
"Reservoirs for Irrigation'' will be found to contain matter on the
subject interesting to those who desire to pursue it further, and
the reader is again referred to that work.
An ImperTious Diapbra^m in Eartli Dams*
As a result of the recent extended discussion concerning the de-
sign of the New Croton Dam and the Jerome Park Reservoir em-
bankments, the Engineering News of Feb. 20, 1902, contained a
very suggestive editorial entitled, "Concerning the Design of Earth
Dams and Reservoir Embankments." The opinion is given that
no type of structure that man builds to confine water can compare
in permanence with earth dams, after which the following pertinent
questions are asked :
1. How shall an earth dam be made water-tight?
2. What is the office and purpose of the masonry core wall ?
3. Would not a water-proof diaphragm of some kind be better
than a core wall of either masonry or puddle?
The article then suggests a number of designs of diaphragm con-
struction, with a special view of obtaining absolute water-tight-
ness, by use of asphaltum, cement-mortar, steel plates, etc. Special
emphasis was put upon the principle of constructing a waterproof
diaphragm. The matter of relative cost is advanced as an argu-
ment in favor of the diaphragm principle as against the usual ortho-
dox method. The saving in cost is to be accomplished by the use
of inferior materials and less care in the handling of them, or by
both. It is suggested that almost any kind of material available,
rock, sand or gravel, will answer every purpose where good earth
is not to be found. Further, that this material may be dumped from
the carts, cars or cableways, or be placed by th& hydraulic-fill
method.
The writer believes the diaphragm method of construction may
have some merits, but that it is attended by the very great risk of
neglecting principles most vitally important to the successful con-
struction of high earth dams, which will now be formulated and
advanced, as follows :
CHAPTER VI.
Conclusions.
The writer in concluding this study wishes to emphasize certain
pr inciples and apparently minor details of construction, which from
observation and personal experience, seem to him of vital import-
ance.
He believes firmly in the truth contained in the following re-
marks by Mr. Desmond FitzGerald, of Boston, germane to this
subject :
An engineer must be guided by local conditions and the resources at his
command in building reservoir embankments. His design must be largely
affected by the nature of the materials. There are certain general principles,
however, which must be observed and which will be applied by an engineer
of skill, judgment and experience to whatever design he may adopt. It is
in the application of these principles that the services of the professional man
becomes valuable, and it is from a lack of them, that there have been so
many failures.
The details and principles of construction, relating to high earth
dams, may be summarized or stated in order of their application,
as follows:
(i) Select a firm, dry, impermeable foundation, or make it so by
excavation and drainage. All alluvial soil containing organic mat-
ter and all porous materials should be excavated and removed
from the dam site when practicable ; that is, where the depth to a
suitable impermeable foundation is not prohibitive by reason of ex-
cessive cost.
Wherever springs of water appear, they must be carried outside
the lines of the embankment by means of bed rock drains, or a sys-
tem of pipes so laid and embedded as to be permanent and effective.
The drainage system must be so designed as to prevent the in-
filtration of water upward and into the lower half of the embank-
ment, and at the same time insure free and speedy outlet for any
seepage water passing the upper half. All drains should be placed
upon bed rock or in the natural formation selected for the foun-
dation of the superstructure. They should be constructed in such
a manner as to prevent the flow of water outside the channel pro-
vided for it, and also prevent any enlargement of the channel itself.
64 EARTH DAMS.
To this end, cement, mortar, broken stone, and good gravel puddle
are the materials best suited for this purpose.
(2) Unite the body of the embankment to the natural foundation
by means of an impervious material, durable and yet sufficiently
elastic to bond the two together. When the depth to a suitable
foundation is great, a central trench excavated with sloping' sides,
extending to bed rock or other impervious formation, refilled with
good puddling material, properly compacted, will suffice.
When clayey earth is scarce and expensive to obtain, a small
amount of clay puddle confined between walls of brick, stone oj-
concrete masonry, and extending well into the body of the embank-
ment and so built as to avoid settlement, will prevent excessive
seepage. This form of construction is not to be carried much
above the origin'al surface of the ground.
(3) The continuity of surfaces should always be broken, at the
same time avoiding the formation of cavities and lines of cleavage.
No excavation to be refilled should have vertical sides, and long
continuous horizontal planes should be intercepted by wedge-
shaped ofifsets, enabling the dovetailing of materials together.
All loose and seamy rock or other porous material should be
removed, and where the refill is not the best for the purpose, mix
the good and bad ingredients thoroughly, after which deposit in
very thin layers.
(4) Make the dimensions and profile of dam with a factor of
safety against sliding of not less than ten. The preliminary cal-
culations for designing such a profile have been given on p. 42.
(5) Aim at as nearly a homogeneous mass in the body of the em-
bankment as possible, thus avoiding unequal settlement and de-
formation. This manner of manipulating materials will eliminate
many uncertain or unknown factors, but it means rigid inspection
of the work and intelligent segregation of materials, no matter what
method of transporting them may be adopted. The smaller the unit
loads may be, the more easily a homogeneous distribution of ma-
terials will be obtained.
(6) Select earthy materials in preference to organic soils, with a
view of such combination or proportion of different materials as will
readily consolidate. Consolidation is the most important process
connected with the building of an earth dam. The judicious use of
soil containing a small percentage of organic matter may be per-
mitted, however, when there is a lack of clayey material for mixing
with sandy and porous earth materials. Such a mixture, properly
CONCLUSIONS. 6$
distributed and wetted, will consolidate well under heavy pressure
and prove quite satisfactory.
(7) Consolidation being the most important process and the only
safeguard against permeability and instability of form, use only the
amount of water necessary to attain this. Too much or too little
:ire equally bad and to be avoided. It is believed that only by ex-
periment and ex^^erience is it possible to determine just the proper
quantity of water to use with the different classes of materials and
their varying conditions. In rolling and consolidating the bank, all
portions that have a tendency to quake must be removed at once
and replaced with material that will consolidate ; it must not be cov-
ered up, no matter how small the area.
(8) In an artificial embankment for impounding water it is im-
practicable to place reliance upon time for consolidation; it must be
effected by mechanical means. Again we repeat, that consolida-
tion is the most vitally important operation connected with the
building of an earth dam. When this is satisfactorily attained it is
proof that the materials are suitable and that the other necessary
details have been in a large measure complied with. Light rollers
are worse than useless, being a positive harm, resulting in a
smoothing or "ironing process," deceptive in appearance and detri-
mental in many ways.
The matter of supreme importance in the construction of earth
dams is that the greatest consolidation possible be specified and
effected. To this end it is necessary that heavy rollers be em-
ployed, and that such materials be selected as respond best to the
treatment. There are certain kinds of earth materials which no
amount of wetting and rolling will compact. These must be re-
jected as unfit for use in any portion of an earth dam. Let the de-
sign of the structure be ever so true to correct engineering prin-
ciples, it is still necesssary to give untiring attention to the work of
consolidation. It is therefore according to the design of a thor-
oughly compacted homogeneous mass, rather than to the suggested
diaphragm type, to which modern practice should conform. This is
in harmony with Nature's own methods, and in conformity to cor-
rect principles.
(9) Avoid placing pipes or culverts through any portion of the
embankment. The writer considers it bad practice ever to place
the outlet pipes through a high earth dam, and fails to see any nec-
essity for so doing.
(10) The surface of the dam, both front and rear, must be suit-
56 EARTH DAMS.
ably protected against the deteriorating effects of the elements.
This may include pitching the up-stream face, the riprap work
at the toe of the inner slope, the roadway and covering of the
crown, the sodding or other protection of the rear slope, and the
construction of surface drains for the berms.
(ii) Ample provision for automatic wasteways should be made
for every dam, so that the embankment can never under any cir-
cumstances be over-topped by the impounded water. Earthquakes
and seismic disturbances will produce no disastrous effects upon
an earth dam. Its elasticity will resist the shock of water lashing
backwards and forwards in the reservoir.
(12) Finally, provide for intelligent and honest supervision dur-
ing construction, and insist upon proper care and maintenance
ever afterwards.
APPENDIX I.
High Earth Dams.
Name ot Dam or
Reservoir.
Location.
. — Embankment — «
Max. Top
height, width,
ft. it.
San Leandro California 125 28
Tabeaud California 123 20
Druid Hill Maryland 119 60
Dodder Ireland 115 22
Titicus Dam New York no 30
Mudduk Tank India 108
Cummum Tank. . .India 102
Dale Dike England 102 12
Marengo Algeria loi
Torside England 100
Yarrow England 100 24
Honey Lake California 96 20
Pilarcitos California 95 25
San Andres California 95 25
Temescal California 95 12
Waghad India 95 6
Bradfield England 95 12
Oued Meurad Algeria 95
St. Andrews Ireland 93 25
Edgelaw Scotland 93
Woodhead England 90
Tordofif Scotland 85 10
Naggar India 84
Vahar India 84 24
Rosebery Scotland 84
Atlanta Georgia 82 40
Roddlesworth England 80 16
QUdhouse Scotland 79 12
Rake England 78
Silsden England 78
Glencourse Scotland 77
Leeshaw England 77
Wayoh England 76 22
Ekruk Tank India 76 20
Nehr India 74 8
Middle Branch . . . New York 73
Leenaing Ireland 73 10
South Fork .. .Penna 72 20
Anasagur India 70 20
Pangran India 68 8
Harlaw Scotland 67
Lough Vartry Ireland 66 28
La Mesa California .... 66 20
Amsterdam New York 65
Mukti India 65 10
Snake River. . California 64 12
Stubken Ireland 63 24
Den of Ogil Scotland 60
Loganlea Scotland 59 10
Ashti India 58 6
Cedar Grove New Jersey... 55 18
Slopes ,
Water. Bear.
3 on I
4 on I
2 on I
3 on I
3 on I
2^ on I
3 on I
3 on I
25^ on I
3>5oni
3 on I
3 on I
2"^ on I
3 on I
3 on I
3 on I
3 on I
30a I
3 on I
3 on I
3 on I
3 on I
3 on I
3 on I
2 on I
4 on I
3 on I
i>^on I
3 on I
2 on I
3 on I
3 on I
3 on I
3 on I
2)^ on I
2 on I
30° I
2^ on I
2J^on I
I on I
2% on I
2 on I
2 on I
2J4 on I
3 on I
2 on I
2 on I
2% on I
2% on I
2^ on I
2% on I
2}i on I
2^ on I
2 on I
2 on I
2^ on I
2 on I
2 on I
Ij^on I
2% on I
1% on I
2 on I
1^ on I
2 on I
2% on I
2 on I
2 on I
Avail-
able
depths,
ft.
70
82
90
84
81
72
68
58
65
5°
42
64
60
60
41
50
55
42
5°
APPENDIX.— II.
Works of Reference.
Author. Title. Date.
Baker, Benj The Actual Lateral Pressure of Earthwork. . 1881
Baker, Ira O Treatise on Masonry Construction 1899
Bell, Thos. J History of the Water Supply of the World . 1882
Beloe, Chas. H Beloe on Reservoirs 1872
Bowie, Aug. J., Jr A Practical Treatise on Hydraulic Mining. . 1898
Brant, Wm. J Scientific Examination of Soils 1892
Brightmore, A. M The Principles of Water- Works Engineering. 1893
Buckley, Robt. B Irrigation Works in India and Egypt 1893
Cain, Wm Retaining Walls 1883
Chittenden, H. M Report and Examination of Reservoir Sites
in Wyoming and Colorado 1898
Courtney, C. F Masonry Dams 1897
Fanning, J. T Water-Supply Engineering 1889
Flynn, P. J Irrigation Canals and Other Irrigation
Works 1892
Frizell, Jos. P Water Power 1891
Gordon, H. A Mining and Mining Engineering 1894
Gould, E. S The Elements of Water-Supply Engineering. 1899
Hall, Wm. Ham Irrigation in California 1888
Hazen, Allen The Filtra.tion of Public Water Supplies 1895
Howe, M. A Retaining Walls for Earth 1891
Hughes, Saml Treatise on Water-Works 1856
Jackson, L. D. A Statistics of Hydraulic Works 1885
Kirkwood, J. P Filtration of River Waters 1869
Merriman, M Treatise on Hydraulics, Masonry Dams and
Retaining Walls 1892
Newell, F. H Irrigation in the United States. 1902
Newman, John Earthwork Slips and Subsidences Upon Pub-
lic Works 1890
Potter, Thomas Concrete 1894
Schuyler, J. D Reservoirs . for Irrigation, Water Power and
Domestic Water Supply 1901
Slagg, Chas Water Engineering 1888
Stearns, F. P Metropolitan Water- Works Reports 1897
Stockbridge, H. E Rocks and Soils 1888
Trautwine, J. C Earthwork; and Engineer's Pocket-Book. . . . 1890
Turner, J. H. T The Principles of Water- Works Engineering. 1893
Wilson, J. M Manual of Irrigation Engineering 1893
Annual Reports.
Massachusetts State Board of Health.
Geological Survey of New Jersey.
Metropolitan Water- Works, Boston and vicinity.
U. S. Geological Survey.
Transactions American Society of Civil Engineers.
Vols. 3, 15, 24, 32, 34 and 35.
Proceedings of the Institution of Civil Engineers.
Vols. 59, 62, 65, 66, 71, 73, 74, 76, 80, 115 and 132.
Engineering News. Vols. 19 to 46.
Engineering Record. Vols. 23 to 46.
Journal of the Association Engineering Societies. Vol. 13.
INDEX.
Page
Analyses, soil, Tabeaud Dam ...'... 25
Analyses of soils. 14
Tabeaud Dam 25
Borings, wash drill, Wachusett Dam 48
Catchment area 3
Clay for puddle 15
Contractors' outfit, Tabeaud Dam 31
Core wall, impervious diaphragm as substitute for 62
necessity for 44
(See puddle.)
Dam, Ashti, India 35
Bog Brook 41
Bohio, Panama Canal 54
Croton Valley, slope of saturation in 40
different types of earth _ 33
Druid Lake, Baltimore , 52
high earth, statistical table of 67
hydraulic fill 61
hydraulic fill, San Leandro 60
ideal profile of 42
Isthmian Canal Commission 54
Lake Frances hydraulic fill 61
New Croton 39
graphical study of original earth portion of 43
New England, typical section of 40
new types of 54
North Dike, Wachusett Reservoir. 48
rock-fill and earth combined, upper Pecos River 58
safe height of 39
San Leandro 58
site location 7
Tabeaud 13, 17
Titicus 41
Upper Pecos River rock-fill and earth 58
with puddle core wall or face 33
Yarrow, Liverpool water- works 9, 33
Diaphragms impervious for earth dams 62, 65
Dike, north of Wachusett Reservoir (see Dam; also reser-
voir).
Drainage and slips of earthwork 45
of dam sites 63
70 INDEX.
Page
Drains, bed rock, Tabeaud Dam 19
Earthwork slips and drainage 45
Embankment, Ashti, India 35
Embankments, Jerome Park Reservoir 45, 46
Factor of safety for dams 64
Filtration, experiments on filtration through soils at Wa-
chusett Reservoir 50
formula, Hazen's ._:.. 56
Foundations 9, 63
Gravel for puddle 15
Infiltration and -percolation 38
Isthmian Canal Commission, designs of dams for 54
Outlet pipes and tunnels 6
Percolation 38, 57
Profile, ideal for dams 42
Puddle 14
core wall, Ashti Dam 33
or face 33
trench 37
wall, Druid Lake Dam S3
for Yarrow Dam : 34
vs. puddle face^ 37
Reservoir basin 37
outlets 6
Wachusett 48
Rollers for dams ; 30, 65
Sands and gravels, flow of water through 52
(Also see percolation.)
Slips and drainage of earthwork 4S
Soil analyses, Tabeaud Dam 25
analysis 14
Soils, experiments on filtration through at Wachusett
Reservoir 50
outline study of 12
permanence of 51
selection of, for dams 64
studies, Wachusett Reservoir 50
Spillway or wasteway 8
Tabeaud Dam 31
Subsidences, earthwork 45
Test pits 5, 8, 9
Tunnel, outlet, Tabeaud Dam 30
Tunnels as outlets to reservoirs 6
Wasteway or spillway 8, 66
Tabeaud Dam 31
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