Assessing the mechanical response of rock structures subject to water forces

Discontinuities are the essential rock features that determine the behaviour of rock masses. However, it has proved hard to foresee and evaluate the potential interactions of water in rock joints. Fluid pressures in a joint causes large forces on its rock walls with increasing aperture and then permeability. If more water enters the system, instability of block may ensue. The joint water forces may change rapidly in magnitude and in direction due to the deformation of the rock mass. To consider the mechanical effect of water in the rocks, the concept of effective stress which is introduced by Terzaghi is used. On the other hand, Biot introduced a general effective stress law which incorporates the volumetric porosity n and the ratio of the stiffness of solid Ks and that of Bulk K. The present study aimed to clarify this subject by considering some fundamental tests to find out a proper effective stress law for rock discontinuities. As a result of this study, a theoretical consideration on the mechanical effect of water on the behaviour of discontinuities and its interaction for the mechanical coupling phenomena between the water and discontinuities is presented. The applicability of Terzaghi-type and Biot-type coupling models to water containing discontinuities is discussed.