EARTH PRESSURES 207 
EARTH PRESSURES. 
Eighth Interim Report of Committee on Earth Pressures (Mr. F. E. 
WENTWORTH-SHEILDS, Chairman; Dr. J. S. Owens, Secretary ; 
Prof. G. Coox, Mr. T. E. N. Farcuer, Prof. A. R. Futon, 
Prof. F. C. Lea, Prof. R. V. SourHwett, F.R.S., Dr. R. E, 
STRADLING, Dr. W. N. Tuomas, Mr. E. G. WaLkKer, Mr. J. S. 
WILson). 
SINcE the Committee’s last report, a meeting was held at Garston on 
June 22, 1933, when the Committee had the advantage of meeting Prof. 
Jenkin and hearing from him an account of the work he has done during 
the past year. A short report from him is appended. 
His work, of which the Committee would again express high appreciation, 
has been of great importance. The work has consisted almost entirely of 
investigations and experiments on the mechanical properties of clay, the 
experiments being carried out with apparatus devised by him. It is hoped 
that these investigations and experiments will lead to an understanding of 
the fundamental principles of the mechanics of clay, and that it will then 
be possible to estimate the forces exerted by clay, used, for instance, as a 
.foundation of a structure or as backing for a retaining wall. 
The Committee would endorse Prof. Jenkin’s conclusion that, although 
no definite results have been reached so far, the experiments are working 
well, and a promising theory is being worked out. 
They recommend that his and their work be carried on for a further 
period. 
REPORT FOR THE BRITISH ASSOCIATION EARTH PRESSURES COMMITTEE. 
May 15, 1933. 
Since my report dated July 1, 1932, the work on the mechanics of clay has 
been carried on continuously. 
The filter press has been improved so that samples of air-free clay can 
now be prepared under any load up to 1,000 Ib. (100 lb. per sq. in. in the 
largest cylinder). The pressure/moisture curve for China clay has been 
determined with this press. The result was quite unexpected : the mois- 
ture left in the clay is found to depend much more on the way the clay 
is handled than on the pressure. Rotating the piston in the press greatly 
reduced the water content, and rotation in alternate directions produces a 
still greater reduction in the water content. 
An apparatus for measuring conjugate pressures on clay cylinders has 
been made and a full series of tests with it carried out. The results were 
again unexpected. It is found that the hydraulic conjugate pressure is 
transmitted through the clay in a few seconds by the water in the clay, so 
that it has no effect; the compression strengths are not altered by the 
_ presence of the hydraulic pressures. Tests were made with positive con- 
jugate pressures up to about 1 atmosphere, and also with negative pressures 
approaching 1 atmosphere. 
This apparatus has also been used to measure the compression strengths 
of clays of all moisture contents, and a complete curve of strength against 
moisture content has been plotted. 
To extend this curve into the region of partially dry clay—i.e. clay into 
which air has penetrated—a simple compression testing machine has been 
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