3. Joint stiffness and the deformation behaviour of discontinuous rock

Abstract

The stress-strain behaviour of a discontinuous rock mass depends crucially on the geometrical and mechanical properties of discontinuities such as joints, fissures, and cracks present in the rock mass. Therefore, it is very difficult adequately to evaluate its deformability. However, it is very important to establish the relation between the stress-strain behaviour of the rock mass and the component elements mentioned above. In this paper, a constitutive relation for evaluating deformation behaviour of regularly jointed rock is presented as the results of experimental and analytical studies. Based on the concept of joint stiffness, an equation to evaluate the deformation of jointed rock was derived, assuming that the amount of deformation of the rock mass equals the summated deformation of rock substance and joints. Joint shear and compression tests on single joints with several kinds of specimen size and surface roughness were carried out, and their effects to joint stiffness were investigated. Loading tests using jointed rock mass models were performed, and the effects of joint orientation/roughness on deformation behaviour were studied. From comparison with the experimental and numerical studies, the applicability of the constitutive equation to jointed rock mass was confirmed.