American Society of Civil Engineers.

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

. (page 16 of 167)
Online LibraryAmerican Society of Civil EngineersTransactions of the American Society of Civil Engineers (Volume 81) → online text (page 16 of 167)
Font size
QR-code for this ebook


however, and not in terms of equivalent water, so that they are of
little use for water supply estimates.

The individual discussions will now be taken up in detail: Mr.
Grover suggests, as the reason that so few records have been obtained
by the Weather Bureau in mountainous regions, the difficulty in
devising self-regulating instruments. The Committee believes that,
due to the rapid development which has occurred in the West during
the past few years, there will be found many more reliable observers
in mountain areas than might be supposed. This has been the expe-
rience of the members of the Committee. The Committee respect-
fully suggests that, if the local officers of the Weather Bureau were
given more assistants and were allowed to become intimately familiar
with the mountain portions of their districts, many good observers
could be found, in areas from which records are at present lacking, by
obtaining the co-operation of such local residents and by the establish-
ment of stations in the isolated areas in charge of trained men. As
the Committee has suggested, it should be entirely feasible to obtain
the desired records within a reasonable cost without waiting for the
development of automatically recording instruments. The Commit-
tee has already commented on Mr. Grover^s reference to the possible
misinterpretation of its original report, and wishes here to express its
appreciation to Mr. Grover for having brought out this matter with
such clearness.

Mr. Post's discussion contains several very practical suggestions
which are especially valuable, as they are drawn from his experience
in making rainfall and run-off observations over a large area of moun-
tain drainage. With regard to the publication of early records, of
which, as Mr. Post states, many exist in California, it has been stated
to the Committee, by the Chief of the Weather Bureau, that if a suffi-
cient volume of such data be assembled and compiled by the Local
Association, and presented to the Weather Bureau, the latter will
undertake their publication in bulletin form under separate cover.
The Committee is still engaged in gathering data of this character,
and will appreciate any which members or others may be able to
furnish.

Mr. Charles T. Leeds, brings out very clearly the diversity of
work which has been assigned by law to the Weather Bureau, and the



188 DISCUSSION : weather bureau service in CALIFORNIA

Messrs. limitations under which it is working with respect to the needs of the
'and^^ water supply interests of the West. The force of his statements has
^^^' been brought home to the Committee by its own investigations, and
it fully agrees that the proper method of obtaining desired improve-
ments is through Congressional action; and furthermore, that, "The
Engineering Profession is probably in a better position to bring this
to the attention of Congress than any other body of men." Mr. Leeds
has done well to mention the many lines of special research work
undertaken by the Weather Bureau. With regard to the evaporation
studies made by that Bureau at Salton Sea about 6 years ago, however,
attention is drawn to the fact that the data thus obtained have never
been made available to the public. The Committee agrees with Mr.
Leeds that stations for the collection and distribution of climatic
information should be maintained in the centers of population. The
Committee believes, however, that fully equipped (or regular) observa-
tion stations should be at a distance from buildings and other objects
and influences which, in cities, cause abnormal conditions. The Com-
mittee suggests that both requirements could be met by establishing
regular stations in Government-owned buildings and on Government-
owned land, at the military and lighthouse reservations, of which
many exist on the Pacific Coast, for example, the Presidio at San
Francisco, Point Arguello near San Luis Obispo, Fort Rosecrans at
San Diego, etc. There are military reservations adjoining practically
all large coast centers of population, at which communication is fully
as good as in the congested business district. The maintenance of
such stations would, without doubt, be less than that of the expensive
office quarters usually occupied by the Weather Bureau, and, in addi-
tion, the abnormal conditions existing on top of office buildings would be
eliminated, without sacrificing the requirement of easy communication.
The Committee has not been unaware of the course traveled by
the typical storm centers of this continent, as suggested by Mr. Leeds,
but believes that, by reason of the large diameter of these storm cen-
ters, atmospheric changes occur no later on the west slopes of the
mountain ranges of the Pacific Coast than they do on the Coast itself,
and that records obtained from judiciously selected mountain stations
would be of just as great value in forecasting weather conditions. In
this matter, however, the Committee heartily agrees with Mr. Tibbetts,
that

"Two observation stations in the ocean would be of more value,
in predicting several days in advance the occurrence of heavy storms,
than all the present stations in California combined."

The Committee is indebted to Mr. Tibbetts for his valuable and
instructive suggestions, as they represent the experience and viewpoint



Discussioy : weather bureau service in California 189

of ail engineer familiar with conditions in Central and Northern Messrs.
California. ''''IfJi'^

In connection with Mr. Tibbett's suggestion, it is proper to call ^^^•
attention to the fact that, in the course of an oral discussion of the
matter at a meeting of the Southern California Association of Mem-
bers of the American Society of Civil Engineers, William MulhoUand,
M. Am. Soc. C. E., made the suggestion that naval vessels be used
for the purpose of observing and reporting by wireless weather condi-
tions off the coast. Though it seems to the Committee that the
primary objects of the naval establishment would probably interfere
with regular service of this character, such information as might be
given, incident to the position of the vessel, would certainly be of
high value. A much broader and more comprehensive service could
be obtained very readily, however, by establishing the practice of com-
municating, through the Government wireless stations, with all ship-
ping within range of the station, whether it be naval, coastwise, or
deep-sea. The simple request of the American Consvd at a foreign
port would be quite sufficient, in a vast majority of cases, to insure
the prompt attention of shipmasters to wireless inquiries from our
Government stations, as to their position, direction of wind, baro-
metric pressure, temperature, etc., and, with such a custom of com-
munication established, the reciprocal advantage to the shipmasters
"would be correspondingly great. The utilization of such a source of
meteorological data would involve practically no expense, would call
for no additional plaijt or labor, and, the Committee believes, would
result in a very great improvement in the advance with which condi-
tions could be forecast, and in forecasts of far greater reliability.

Mr. Lippincott has well expressed the administrative policy of the
Weather Bureau with respect to the West. The visit of the present
Chief of the Weather Bureau to the Pacific Coast in 1915, and the
recent extension of the mountain climatological work of that Bureau
in Southern California, would indicate, however, that an effort is
being made by the present administration to bring about a change for
the better. The Committee can agree with Mr. Lippincott that the
reason so few field inspection trips are made, by local officers of the
Weather Bureau, is because of the "system". Before a local officer
can leave his station for official business of any kind, no matter how
trivial, he must go through a long process of correspondence with the
Washington office. This sometimes consumes a month, and even then
the authorization is frequently curtailed, and is often denied. There
is small wonder, therefore, that co-operative records are often broken
or discontinued. Such stations should be visited at least once a year,
and at no pre-arranged time, in order to insure accurate results and
the active co-operation of the observer.



190 discussion: weathek bueeau service in califoenia
Messrs. As a result of the discussioBS and the Committee's further inves-

Bincklcv

and tigation of the subject, it is believed that the following' general con-
^^^' elusions are warranted:

1. — That the law creating the United States Weather Bureau pre-
scribes a wide range of duties, among which the gathering
of precipitation records is but incidental.

2. — That there is an urgent demand among engineers, throughout
the United States, for more complete precipitation data
throughout mountain drainage areas, to be used in conjunc-
tion with stream-flow data.

3. — That the present fiscal regulations, organization, and admin-
istrative policy of the Weather Bureau are not adapted to
the task of gathering complete precipitation data of the char-
acter desired by engineers.
4. — That Congressional action should be sought, either to change
the organization of the Weather Bureau, so that the desired
result can be accomplished, or else that the duty of observing
all factors affecting stream flow be turned over to the Water
Resources Branch of the United States Geological Survey,
with the appropriation of sufficient additional funds to carry
on the work efficiently.

The Committee is continuing its studies in this matter, and its
conclusions and suggestions, as just stated, are not to be considered
final. The question of the establishment of a Bureau of Public
Works, which shall co-ordinate all engineering activities of the Federal
Government, and prevent the present duplicati(i i of effort, is believed
worthy of careful study. Any further suggestions from the member-
ship of the Society bearing on these matters will be greatly appre-
ciated by the Committee.



AMERICAN SOCIETY OF CIVIL ENGINEERS

INSTITUTED 1852



TRANSACTIONS



This Society is not responsible for any statement made or opinion expressed
in its publications.



Paper No. 1384

EARTH PRESSURES: A PRACTICAL COMPARISON
OF THEORIES AND EXPERIMENTS.

By L. D. Cornish, M. Am. Soc. C. E.



With Discussion by Messrs. William Cain, G. M. Braune, F. ]^.
Menefee, and L. D. Cornish.



Synopsis.



Of all structures which the engineer of to-day is required to
design for conditions of static loading, there is probably none which
is so irritating as the ordinary retaining wall. This, of course, is
due to the lack of definite and correct data relative to the pressures
exerted by the various kinds of earthy materials and to the variety
of formulas which have been proposed for determining the amount
and direction of the resultant earth pressure which acts on a re-
taining wall.

The writer has studied with a great deal of interest all the books
and papers he could obtain concerning earth pressure theories, and
the formulas or graphical analyses derived therefrom. Such study
has been confined principally to a comparison of solutions based on
the Eankine theory with those based on the sliding-wedge theory,
and certain facts were developed which appear to discredit, in certain
particulars, these commonly accepted theories. It is quite probable
that other investigators have observed at least some of the same
results, but, as the writer had never seen them discussed, he thought



192 EARTH PRESSURES

the matter of sufficient importance to assemble the results of his
studies in this brief paper.

Frequent reference will be made to the theories and formulas as
either those of Rankine or Cain. A reference to Eankine is intended
to relate, not only to the theory and formulas for the special cases
as advanced by Rankine, but also to the solutions, based on his
theory, covering all cases of inclination of a wall, as developed and
published by Milo S. Ketchum* and M. A. Howe,f Members, Am.
Soc. C. E. A reference to Cain relates to the solution by William
Cain, M. Am. Soc. C. E., of the wedge theory as given in his paper:]:
and in Ketchum's book.

Formulas to express the resultant earth pressure, as derived from
the two theories, are similar, and in some cases identical; but the
direction of the resultant force is different in all eases, except for a
wall with vertical back and with the angle of surcharge equal to
the angle of internal friction. These formulas, particularly those
involving surcharge, are somewhat complicated, and it is impossible
to grasp mentally their entire significance relative to the dimensions
of a wall to resist the forces indicated by them. The writer has
endeavored to show graphically the results obtained in actual wall
design by the use of the different formulas and by values obtained
in certain experiments, so that the points of interest may be dis-
cussed without resorting to mathematics. To accomplish this, and
to avoid complications in equations, due to uneconomical distri-
bution of masonry in the walls, all wall sections discussed will be
triangular and designed as to width so that the resultant of the
external forces shall cut a horizontal plane of the wall at the outer
edge of the middle third.



Nomenclature. — The nomenclature used in Figs. 1 to 15, and dis-
cussion thereof is that used by Cain in his paper discussing Leygue's
experiments, and, for the remainder of this paper, is the same as
that used by Ketchum in his "Walls, Bins, and Grain Elevators".
The differences are few and should cause no confusion, and the use

• "The Design of Walls, Bins, and Grain Elevators."
t "Retaining Walls for Eartli."

t "Experiments on Retaining Walls and Pressures on Tunnels", Transactions,
Am. Soc. C. E., Vol. LXXII, p. 403.



EAETH PKESSURES



193




of both will facilitate quick comparison with the works of the authors
mentioned.

h = vertical height of wall ;
ch = " " to center of pressure on AB, Fig. 1,

1

p/i = width of base of
wall;
TP = ratio of base to

height ;
e = weight of earth per
cubic foot (Cain-
Leygue) ;

w = weight of earth per cubic foot (Ketchum) ;
1^ = total weight of earth per linear foot;
w^ = weight of wall per cubic foot ;
W^ = total weight of wall per linear foot :
F = resultant earth pressure per linear foot of wall;
P^andPfr = the horizontal and vertical components, respectively,
of P;
^j = Z^ e/i^ = normal component of P (Cain-Leygue) ;
E^ = E^ tan. cos. a COS. (p cos. a

By substituting this value of h^, the equations shown on Fig. 19
are obtained, which equations are in a convenient form for practical
problems.

It is somewhat easier to derive p by substituting for h^ its value,
h (1 -\- tan. a tan.



Online LibraryAmerican Society of Civil EngineersTransactions of the American Society of Civil Engineers (Volume 81) → online text (page 16 of 167)