Calculation of the strength of rigid diaphragms in earth dams

Abstract

In the author's previously published works a method was proposed for calculating the strength of rigid watertight diaphragms in earth dams without consideration of the friction of the earth of the shoulders on the surface of the diaphragm. The assumptions made by the author are confirmed by the data of experimental investigations conducted by him. However, experiments in a flume of comparatively small height (1.18 m) did not permit evaluating with certainty the effect of friction of-the earth of the soulder on the diaphragm. Recommendations on taking this effect into account are given in the present article.A correct determination of the direction of action of the frictional forces of the shoulder earth on the diaphragm surface is quite important. It is assumed that the following normal and tangential forces act on the surface of a rigid diaphragm (Fig. i).In the given calculation scheme, to the surface from the side of the upper pool are transmitted:the total hydrostatic pressure and the difference of the horizontal components of the active earth pressure of the upstream and downstream shoulders of the dam; these forces are expressed by the angular coefficient u of a triangular diagram of height H, which includes the pressure of the water, buoyed earth of the upstream shoulder, and dry earth of the downstream shoulder of the dam 0.5 ~H~; vertical component Pz,'of the pressure of the earth and water, defined as the weight of the water and earth wedge between the inclined surface of the diaphragm and vertical plane tangent to it; frictional force of the earth of the upstream shoulder of the dam on the diaphragm surface T~ directed down a vertical contacting the diaphragm at its base under the assumption that the settlement of the shoulder is greater than the settlement of the diaphragm, and moreover the diaphragm, moving, is displaced upward relative to the earth of the upstream shoulder; this force is expressed by the lateral pressure of the soil of the upstream shoulder submerged in water multiplied by the coefficient of friction tan ~z of the soil on the diaphragm surface, which is expressed by the equation

Calculation of foundations and earth dams

“…This assumption is proved by many experiments on site and in the laboratory [2][3][4][5][6][7]. The dimensions of the clay core are taken, as usual, from considerations of the seepage strength with respect to and admissible gradient of the seepage head.…”