Approximate calculation of flexible watertight diaphragms for earth dams

Abstract

In recent years there has been rather wide use of watertight devices (diaphragms, skim) made of bituminous concrete, and attempts have been made to use films of various polymeric materials. The most reliable in service and the simplest to accomplish are vertical diaphragms located in the center of the dam profile [1,2].The main problem in the calculation of diaphragms is the determination of their deformations, particularly horizontal displacements in the plane of the dam cross section. Diaphragms made of bituminous concrete or films have a negligible resistance to bending [2] and in calculations can be regarded as perfectly flexible elements. Coupling of the flexible diaphragm with the foundation can be by various means: free support, hinged, or embedded in the foundation. Diaphragms made of essentially extensible materials (bituminous concrete or film), regardless of the coupling with the foundation, can be regarded with sufficient accuracy in calculations as freely yietding flexible strips completely following the displacements of the inside face of the downstream shoulder. For a diaphragm of low-extensible material, its coupling with the foundation can be taken into account by introducing appropriate corrections into the diagram of displacements calculated for a diaphragm with a conditionally free lower end.Thus, determination of the horizontal displacements of a diaphragm amounts to a determination of such displacements for the inside vertical face of the downstream shoulder due to the action of the load from the upper pool, In a previous work [3] a similar problem was solved for the case of a triangular shoulder of noncohesive soil, where a comparison of experimental data with calculated values is given. We will consider herein an analogous problem for the more general and more frequently encountered case of a trapezoidal downstream shoulder. The solution is carried out for the case of plane strain under the following assumptions: a) within the part of the shoulder being compacted partial surfaces of sliding (upward yielding) are formed which coincide with the outline of the Surfaces of sliding in the presence of upward yielding; b) over the entire length of the partially formed surface of sliding a state of equilibrium occurs which is characterized by the Coulomb relation; c) the surfaces of sliding are taken to be plane. Of the three assumptions the last two have been used repeatedly in the literature and do not cause particular objections. We must add that in the case of the direct action of a distributed load normal to the face of the shoulder, analogous to the interaction of a smooth wall with the soil, the surfaces of sliding will actually be plane or closely so. As is known, in the case of a vertical smooth wall and horizontal backfilI the surfaces of sliding in V. V. Sokolovskii's rigorous theory are plane, coinciding with the plane surfaces of sliding according to Coulomb. The first assumption was advanced by V. A. Florin as a working hypothesis [4]. Later, this hypothesis was used by us when solvi...

Construction of impervious membrane elements for dams and cofferdams

“…The strains in the membrane cover can be calculated only approximately [5], by starting from the deformability of the downstream shell of the water'retaining structure:…”