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Transactions of the American Society of Civil Engineers (Volume 81) online

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the same fundamental elements as those on which architecture
(building composition) is based, but emphasizing the structural fea-
tures of the engineering design to a much greater extent than is
common in architecture.

The fvmdamental considerations of unity of effect, balance, pro-
portion, harmony, and climax cannot be taken care of after the
structure has been planned and partly designed. They must be kept
in mind from the very first and receive their proper consideration
in the preliminary schemes, sketches, and plans for the work. The
only man who can do this is the engineer himself, who realizes the
structural and economic principles involved, and, it is hoped, may
soon come to realize the necessity for proper architectural composi-
tion as a basis for a final and simple decoration in which the struc-
tural features should be emphasized.

P. P. RuTENBERG,t EsQ. (by letter). — European engineers have ^^
learned much from their American colleagues, and the war proves the Rntenberg.
extent to which American methods of solving technical problems, of
their organization and realization, have been adopted and developed in
Europe. In the special field of dam building they have heard and
learned from such world-famous works as the Croton, the Roosevelt,
the Elephant Butte Dams, and many others.

* Engineering News, February 26th, 1914, p. 461.
t Petrograd, Russia.



1030 DISCUSSION : reconsteuction of stony eiver dam

Mr. If the writer now takes the liberty of criticizing the construction

Rutenbeig. ^^ ^^iq Stony River Dam, it is because this structure, in his judgment,
is lacking in just that efficiency which is characteristic of American
engineering.

Foundations. — As described by the author, the foundation soil at
the site of the dam is mainly of a clayey nature, heterogeneous, per-
vious, and of poor bearing value in general. The examination of the
old cut-off wall, and of the buttress footings remaining intact, showed
that abundant percolation and leakage existed in the foundation soil
of the original dam. "The contact between the original footings and
the foundation soil was in some places found to be faulty. * * *
Hollow spaces were found under the footings around the 4 by 12-in.
weep-holes." In some bays, it was discovered that "the foundation
soil had been washed away at the junction between the footings and
the cut-off wall. * * * The construction joint would naturally open
somewhat, due to the deflection of the foundation soil when loaded.
* * * Observations showed that grout under pressure traveled
under the footings for a distance of at least 100 ft.", etc. (pages
987-988).

All this was produced by the leakage under pressure during 65 days
only, the period in which the original dam ftmctioned, until it failed.

The faulty conditions of the foundation soil were remedied by
pressure grouting through the original weep-holes. In this way, the
original foundation soil under the footings was more or less com-
pacted, but there surely remained other hollow spaces and pockets
from which water under pressure passed, not to the weep-holes of
the footings, but in other directions of least resistance, not observed
in the reconstruction of the dam. It will be shown later that the
author himself admits it, and that his statement (page 988) that "the
foundation soil under the original footings was thoroughly compacted
so as to warrant the assumption that the footings are everywhere in
contact with the foundation soil", is not entirely correct. Percolation
and leakage will cause harmful and dangerous uplift pressure in
any dam, with any foundation soil, even the best.

The uplift pressure applied to the up-stream part of the base
increases the overturning moment of the dam and the unit stresses
in the structure and on the soil at the down-stream foot of the dam,
where, under the full load of the dam, the values of these stresses
are maximum. The uplift pressure on the up-stream part of the
base decreases, consequently, the resistance of the dam to overturning,
and may render insufficient the resistance of the structure and that
of the soil at the base to the efforts of compression and shearing
developing there. The same conditions created by the uplift pressure
decrease also the resistance of the dam to sliding. This has been



discussion: reconstruction of stony river dam 1031

tlie cause of the failure of many dams, even with good foundation Mr.
soils which have possessed the best frictional resistance.

Therefore, it is impossible to state, as Mr. Scheidenhelm does
(page 947), that "the smaller the coefficient of frictional resistance,
the less the net effect of the uplift pressure."

Consequently, it is clear that percolation and leakage must be
eliminated by all possible means in any dam, in general, and in the
Stony Eiver Dam, with its heterogeneous and pervious clay founda-
tions, in particular.

The interception of the leakage and percolation in this dam should
have been made directly and immediately on the up-stream face of
its cut-off wall and discharged down stream by special channels with-
out any pressure.

Now, the principles on which the Stony Eiver Dam was recon-
structed are quite different. On page 997 we read:

"It was believed to be preferable, therefore, to take such risk as
might result from the existence of pockets, as it were, of unrelieved
uplift pressure near the down-stream side of the cut-off wall rather
than to invite further leakage by tapping such relatively harmless,
deep-lying pockets of water under pressure."

This statement, it seems to the writer, does ngt tally with the most
vital principles in dam-building, namely, that water under pressure
in the foundation soil is never harmless.

According to the foregoing consideration, the system of drainage
adopted for the Stony River Dam consists of 3-in. wrought-iron pipes,
perforated with four f-in. holes per linear foot, one hole in each
quadrant; three pipes per bay, driven into the foundation soil ver-
tically, the first "about 20 ft. down stream from the cut-off wall,
except at the bays of lesser height, where they are at a minimum
distance of 12 ft. from it."

The writer believes that:

1. — A 3-in. pipe with four small perforations per linear foot for
a bay 15 ft. high is useless for drainage, even if the drainage pipes
described by the author function perfectly well.

2. — The small perforations in the pipes must undoubtedly have
been clogged with clay in the process of being sunk. Mr. Scheidenhelm
states (page 998) that "any considerable hydrostatic pressure near the
drain pipes would soon open the perforations." He admits the presence
in the foundation soil of considerable hydrostatic pressures at a dis-
tance of 20 ft. from the down-stream side of the cut-off wall, which
is about the middle of the base. Consequently, by the improper
location of the drainage pipes, alone, the up-stream half of the base
is exposed to dangerous uplift pressures, with all previously stated
consequences, viz., decrease of resistance by overturning, increase of



1032 DISCUSSION : keconsteuction of stoxy kivee dam

Mr. the unit stresses in the structure and on the foundation soil, saturation

^^^' of the clay foundation soil with water, and decrease of its resistance

to sliding; which, as the writer understands, cannot but be harmful,

and all this solely because the drainage pipes, even assuming that

otherwise they function perfectly well, are not in the proper places.

3. — Some of the drainage pipes have been driven vertically to a
depth of 20 ft. into the foundation soil. When they are filled with
drained water, it is clear that their lower perforations are submitted
to the pressure of a column about 20 ft. high, and at this lower stratum
of the foundation soil the leakage will not be able to penetrate into
the drainage pipes, unless it is of greater hydrostatic pressure. Only
a small part of the leakage will penetrate through the small per-
forations; the remainder will continue its way down stream into the
foundation soil, where the resistance is weaker. Besides, there is a
possibility that the drainage pipes will be filled through the higher
perforations from the higher strata of the foundation soil, and that
the collected water will be conducted through the pipes and their
lower perforations, by the water pressure thus formed, into the other-
wise dry lower strata of the foundation soil.

In fact, on page 1000, the author takes cognizance of such phe-
nomena, for which manifestation he "has been unable to advance any
explanation which is satisfactory to himself."

The writer, therefore, considers these pipes, not as a drainage
system, but rather as a means of introducing water into the founda-
tion soil, and not only useless, but dangerous to the safety of the dam.

Resistance to Sliding. — On page 908, we read:

"The method adopted [for increasing the resistance to sliding]
is believed to be new, and consists in the use of anchoring walls ex-
tending to a considerable depth into the underlying foundation soil,
and, in effect, utilizing the weight of that underlying soil as well as
the resistance (to horizontal movement) of the soil inamediately down
stream from the structure."

These anchoring walls are two: one at the heel, and another at
the toe, of the original structure which remained intact.

To render the above-mentioned service, the heel-wall must be
strong enough to be able, in case of a down-stream sliding of the dam,
to function as a cantilever which can overcome the resistance of the
underlying foundation soil to sliding and shearing.

The paper does not give the dimensions and calculations of the
anchoring walls, but, from Plate XII, it is clear that they are too weak
to serve this purpose. The heel-wall is not able to compact the
underlying foundation soil, and, therefore, make it less pervious by
any down-stream movement on the part of the dam, a^ the author
believes. It will simply be broken in this case, opening the joint



DISCUSSION : RECONSTRUCTION OF STONY RIVER DAM 1033

between the upper structure and the cut-off wall, as happened in Mr.
the original structure, according to the description on page 959.

The toe-wall, as constructed, will aid in collecting the leakage
under the dam. Consequently, it will increase the uplift pressures
and the quantity of water in the foundation clay, decreasing the
resistance of the dam to overturning and sliding.

Openings should have been made in the vertical part of this wall,
directly under the footing floor of the dam to provide a free exit for
the leakage.

As far as the two anchoring walls are concerned, the writer does
not agree with the author's assertion that "the reconstructed dam
acts essentially as a monolith" and, consequently, he does not agree
that "the horizontal member of the toe-wall in effect increases the
width of the base of the dam, thus decreasing the unit vertical load
on the foimdation soil." (Page 960.) The efforts transmitted by the
buttresses to the foundation soil have their maximum value at this
point, and, the writer believes, under the existing circumstances, will
rather break this horizontal member of the toe-wall.

The imder-cut slope of the heel-wall presents, besides, a surface
for the application of uplift pressures, which, with their big
moment arm, decrease also the stability of the original structure
against overturning.

In the reconstruction of the intact part of the dam, the only
things to do were : to fill, if possible, all the holes foimd in the founda-
tion soil; to repair the cut-off wall, and to build a reinforced con-
crete wall up stream from the old cut-off wall, bearing upon this by
concrete apertures, in order to form chambers which would be able
to maintain the percolation through this drainage wall and conduct
it without pressure down stream from the dam by convenient channels.

The two anchoring walls with the drainage pipes have weakened
the original stability of the dam.

The "new theory" of resistance to sliding, with the investigation
about the "plane of least resistance", with the tests, calculations, and
deductions of an "average" coefficient of frictional resistance of 0.61
in wet clay, is an interesting theoretical exercise, but without practical
value for the reconstructed dam. One is the frictional resistance
of a cubic foot of clay, pulled by two men under the conditions of
the improvised laboratory described; the other is the effective fric-
tional resistance of the wet clay of heterogeneous structure in the
real foundation soil loaded by a head of 90 ft. and more, or by about
6 000 lb. per sq. ft.

There are dams in which the necessary weight is obtained by
clay, sand, pebbles, even water, included in a reinforced coffer, the
bottom of which constitutes an elastic monolith with other coffers.



1034 dtso-ussion: reconstkuction of stoxy river dam

Mr. If percolation took place, it would be applied to the bottom and, con-
ers:. gg^^gj^^-jy^ ^^ ^]^g whole structure of the dam. The material of light
weight cannot be washed from them.

In the Stony River Dam, however, engineers cannot seriously con-
sider for its resistance to overturning and sliding, the "'weight" of
the underlying foundation soil, which can be and is, as is known,
washed away by the existing leakage and percolation.

Spillway. — ISTot being acquainted with the hydrological conditions
of America, the writer cannot give an opinion as to whether the spill-
way capacity provided in the reconstructed dam is adequate or exces-
sive; but one thing is clear: that by adding 3i ft. of water to the
original level in the reservoir, the horizontal water pressure and its
overturning moment are increased by about 20% for the typical
section indicated on Plate XII. The increase is greater for the sections
of less height.

The parapet-like addition to the original structure and the curtain-
wall and roof, contribute a vertical effort of important value,
which passes into the down-stream third of the base. Both conditions
increase the overturning moment, consequently, they also decrease
the safety of the original structure. The upper structure in the
new spillway is made heavier than in the original dam.

For each horizontal section the water loading is exactly the same
in the new and in the old structure. Thus, either the original struc-
ture is insufficient or the excess of the new is useless. In any case,
the subjection of the original structure to greater loadings and unit
stresses than those for which they were evidently designed is dan-
gerous; 22 000 lb. per sq. in. = 15.5 kg. per sq. mm. in the steel,
and 800 lb. per sq. in. = 56.5 kg. per sq. cm. in the concrete, are too
much, at least, according to European provisions. The paper does
not give the necessary data with which it would be possible to com-
pute the unit stresses in the structure and on the soil, but the writer
is sure that the load on the soil at the down-stream foot of the dam is
excessive. Since, under favorable circumstances, a part of the orig-
inal structure remained intact, it was advisable to maintain the
original maximum water level.

The allowed over-topping of 24 ft. of water from a height of 40 ft.
between Buttresses 19 and A is, it would seem, also dangerous. The
shock of the falling water will not only break the provided horizontal
and inclined reinforced mat, but, when that occurs, it will wash the soil
from under the dam footings.

On page 917, Mr. Scheidenhelm, criticizing the rupture of the
original dam, says: "The conditions obtaining at the Stony River dam
site are such that a safe dam could be built there. * * * The dam



DISCUSSION : RECONSTRUCTION OF STONY RIVER DAM 1035

should, and could, have been, designed and constructed so as to be '■ Mr.
absolutely safe." Rutenberg.

The writer believes the reconstructed dam is less safe than the
original structure.

The flaws in the foundation soil which had not been taken care
of by the constructors of the original dam, widened and became more
pronounced by the water pressure formed by the old dam. After the
rupture occurred, some of these flaws came to light and could not but
be remedied; so that the foundation soil was relatively reinforced,
thus giving it another short lease of life, longer than for the
original dam.

The writer is firmly convinced, however, that were the reservoir
now to be emptied and the foimdation soil examined it wovild be
found to be in a very bad state.

"Certain of the drainage openings yielded muddy water, instead
of the normally clear water. * * * Such openings were grouted
shut, rather than take any chances of harmful erosion under the
footings." (Page 1000.)

This "harmful erosion" has surely foin:id other ways, unobserved
by the author.

The writer is firmly convinced that the reconstructed dam will also
be broken, perhaps soon, if adequate repairs are not made in time. It
is a question of preventing a new disaster. These are the writer's
reasons for taking the liberty of criticizing the work done in the recon-
struction of the Stony River Dam.

Fred F. Moore,* M. Am. Sue. C. E. (by letter).— After study of Mr.
this excellent description of the interesting reconstruction of an unconi- •^^°*^'"^-
mon type of dam, two impressions stand out prominently :

First, that there is a dearth of information regarding sub-surface
conditions as a guide to the original designs. Even now, comprehen-
sive knowledge of the character of the foundation materials, and the
behavior of these materials under the conditions imposed, does not
appear to be sufficient to justify the conclusions reached by the author
as to the margins of security of the reconstructed dam. Tests of fric-
tional resistances of soils, as carried out in connection with this work,
are of doubtful value as an aid to the judgment, because of the small
areas in contact, and the values of frictional resistance adopted for
the design seem to be considerably larger than even the indications of
these experiments would justify.

Second, with reference to the function of the walls at "heel" and
"toe" in resisting movement of the structure as a whole, the analyses
which consider sliding and overturning independently would appear
to befog rather than to aid the judgment. Materials such as these,

* New York City.



1036 DISCUSSION : eeconstkuction of stony eiver dam

Mr. mixed with clay and saturated with water, perhaps under considerable
*'°''^" pressure, and subjected to large loads, would flow, or, at least, transmit
pressures in all directions like a liquid. In order that the cut-off wall
at the "heel" may aid in resisting sliding as described, there must be
a sensible movement of the structure as a whole, with consequent large
uplift on the base of the dam. Hence, the sliding and overturning, or,
perhaps better, the floating, of the structure must be considered with
reference to the effect or reaction of these tendencies one on the other.
That is, the materials under the dam, with reference to the function
of the cut-off wall in resisting sliding, must be considered as a flowing
medium rather than one in which a sliding may occur on certain
planes like one solid on another.

The wall at the "heel" does not appear to have sufficient strength
for the purpose contemplated. If this wall is fractured, water under
reservoir pressure in considerable quantity would have access to the
materials under the dam. The drainage provisions appear to be a
doubtful reliance for minimizing uplift pressure. The danger of por-
tions of the dam being floated off the foundations from leakage of
water under pressure through the cut-off at the "heel", and through,
or under, the cut-off at the "toe", at a time of large overflow, appears
not to have had sufficient consideration. Although the idea of using
the materials between the cut-offs and immediately down stream from
the "toe" to resist sliding is a good one, it is doubtful if the recon-
structed dam has a sufficient margin of security to warrant a conclu-
sion that it is not likely to fail again.

The run-off assumed for the design of the spillway appears to be
reasonable for the purpose, but the margin of 6 in. against over-
topping is too small. A flow of 2 ft. of water over the intermediate
spillway would not fall "well-nigh" vertically. Such a flow would
strike the slope of the fill (Plate XII), which is inadequately protected
for such a condition. Even water falling into the concrete channel
from the top of the dam would start serious trouble through erosion
of the bank by wash. Regardless of damage by falling water, the con-
crete channel is too small. Any considerable flow over the intermediate
spillway would be almost certain to start cutting of the materials at
the "toe".

The use of brittle steel pins for the flash-board support is unusual,
and would seem to be an expedient of doubtful value.

i>



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