STUDY OF ROCK JOINTS UNDER CYCLIC LOADING CONDITIONS

A conceptual model for the behaviour of rock joints during cyclic shea r and under constant normal stresses was proposed according to results from shear tests with 50 concrete replicas of rock joints. The shear strength and deformability of joint samples were found to be both anis otropic and stress dependent. Based on these experimental results, a t wo-dimensional constitutive model was developed for rock joints underg oing monotonic or cyclic loading sequences. The joint model was formul ated in the framework of non-associated plasticity, coupled with empir ical relations representing the surface roughness degradation, appeara nce of peak and residual shear stresses, different rates of dilatancy and contraction, variable normal stiffness with normal deformation, an d dependence of shear strength and deformability on the normal stress. The second law of thermodynamics was represented by an inequality and used to restrict the values of some of the material parameters in the joint model. The new joint model was implemented into a two-dimension al Distinct Element Method Code, UDEC, and its predictions agreed well with some well-known test results.