It is possible that the method used by Leygue may prove of service to experimenters in obtaining more accurately than hitherto the coefficient of internal friction. Increasing pressures could be obtained by adding weights on top of the sand in the box; but, unless the total weight sustained by friction along the sides of the box is determined carefully for each weight used, the results can have but little value. Further, for coherent earths, the method of Leygue is open to objections.
Admitting the hypothesis that cohesion and friction act at the same time, a general graphical method[Footnote 6] ] will now be given to find the thrust against the inner face,
, of a retaining wall or board, [Fig. 11], caused by the earth,
, tending to slide down some plane of rupture,
,
