288 REPORTS ON THE STATE OF SCIENCE. ETC. 



high, specially constructed so that the horizontal and vertical loads exerted 

 on it by an earth backing could be measured. 



The Connmittee consider that the research on which Prof. Jenkin is now 

 engaged is likely to be of great value, and they recommend that his and 

 their work be carried on for a further period. 



Building Research Station, 



July I, 1932. 



REPORT FOR THE BRITISH ASSOCIATION EARTH PRESSURES 



COMMITTEE. 



The investigation of earth pressures has been continued without 

 interruption during the past year. 



A very large number of measurements of sand pressures on retaining 

 walls has been made with the experimental apparatus, and a fairly complete 

 mathematical theory, which I call the revised Wedge Theory, has been worked 

 out, which agrees with the experimental pressures, but no mathematical 

 theory has been found to explain the heights of the centre of pressure. 



A general account of the work was given in a paper illustrated by 

 experiments read to the Engineering Section of the British Association last 

 year, and a discourse on ' The Mechanics of Shifting Sand ' was delivered 

 to the Royal Institution on February 19. 



The whole of the work was described in a paper to the Institution of Civil 

 Engineers, which was discussed on February 23 and March i. At the dis- 

 cussion an apparent disagreement between my results and those obtained by 

 Takabeya in Japan was pointed out ; this has been investigated, and an 

 article entitled ' Predicting the Internal Motion of Sand ' was published in 

 Engineering for May 13, which shows that my theory could actually predict 

 the results obtained by Takabeya. 



I am now engaged on the problem of the pressure exerted by clay. Some 

 six different ideal materials have been investigated, and their mathematical 

 equations worked out. Experiments with china-clay and oiled glass beads 

 and other substances have begun. The most promising method of testing 

 these materials appears to be the determination of their stress-strain diagrams 

 when subject to torsion (pure shear). Preliminary experiments have turned 

 out more successful than was expected, and a complete recording torsion 

 meter is in course of construction. 



Simple large-scale experiments on clay, sufficient to check the theoretical 

 calculations, are being considered, and do not seem to be impossible. 



I have received valuable assistance from Mr. Wentworth-Sheilds, who 

 obtained the opinions of a number of experienced engineers on a question 

 I submitted. 



The difficulties presented by clay are very great, and it is too soon to offer 

 any opinion as to the probability of the ultimate success of the investigation. 



C. F. Jenkin. 



