Numerical method for determining contact areas of a rock joint under shear load

摘要

A numerical method to determine the contact areas of a rock joint under normal and shear loads is proposed. The method requires only three dimensional surface coordinates at the initial stage before shearing, while in other conventional methods disparate materials are inserted between joint surfaces or particular equipments are adopted for the test. In the proposed method, a joint surface is modeled as a group of triangular planes and each plane is examined on contact condition by calculating the relative displacements from initial locations of both surfaces. This joint surface model makes it possible to evaluate the distributions of size, location, and micro-slope of contact areaswhich greatly affect the shear behavior of the joint. The proposed method was verified by using PFC simulation of direct shear test, in which the locations of contact points along the simulated joint were observed and showed good agreement with those estimated by the algorithm. The direct shear tests on the replicas of joints in granite were analyzed for the distribution of contact areas at each of four shearing stages: pre-peak, peak, post-peak and residual stage. From the test results at 6 different conditions, the effects of normal stress and normal stiffness on the contact area distribution were discussed.