Note Return to text — APPENDIX.

An additional note with respect to Equation (1) may not be inappropriate. Scheffler, in deriving this equation, considered the conditions of equilibrium of an infinitesimal wedge of earth at the depth, . It was found that the horizontal pressure at the depth, , given by Equation (3), was zero, and it was assumed by the writer that there was no pressure on a vertical plane for a less depth. Thus, in Fig. 21, there is no horizontal pressure on the plane, , where ; consequently, the weight of the wedge, , is supported entirely by the normal reaction of the plane, , with the cohesion and friction acting along it.[Footnote 20] To deduce , the total earth pressure on the vertical plane, , it is then admissible to treat the prism, , as the prism of rupture, the surface of rupture consisting of the plane, , making the angle with the vertical and the plane, . Therefore , the weight of the prism, , is in equilibrium with , , and , where is the normal reaction of , , and the total cohesion on .