It is difficult to effectively grasp the mechanical behavior of rock joints since it depends on such factors as the confining conditions, the material strength, the material friction, and the joint surface roughness. In this paper, the authors propose a mechanical model for the shear behavior of rock joints. The model considers the influence of the normal confining conantions, the material strength of the intact rock, the basic friction angle, and the joint surface roughness. A simuiation of the direct shear tests is carded out. Comparing the experimental and the predicted results, the validity of the model is presented. The model shows typical shear behavior, namely, the shear stress increases, decreases (softening), and then gradually reaches the residual state. Moreover, variations in joint surface roughness are predicted with this model.
Barton's empirical equation for the shear strength of rock joints is the representative research work for the shear behavior of rock joints. In this equation, the estimation of joint surface roughness holds the key to successfully predicting shear strength (Barton, 1973). Barton introduced to JRC (joint roughness coefficient) value which represents the coefficient of joint surface roughness. However, JRC is determined from the experimental results using backward analysis. Therefore, it is thought that JRC itself cannot estimate the shape of the joint surface roughness on rock joints.