53 Numerical Test Research on the Shear Strength Parameters of Rock Joints Based on the Fractal Theory

Based on the fractal simulation of rock joints, two types of numerical direct shear test models of rock joints were established, and the scale effect and the infill effect of the shear strength parameters of the rock joint were studied by using the numerical test method. The results of the first type of numerical direct shear test show that the critical joint size (CJS) exists by which the scale effect of the shear strength parameters of the rock joint can be eliminated. With the increase of the fractal dimension of the rock joint, the scale effect becomes more outstanding and the critical joint size develops larger. The results of the second type of shear direct test show that when the ratio of the infill thickness t to the asperity height a of rock joints (abbreviated as the thickness-height ratio t∕a in the following of this paper) is less than 1, the shear strength parameters of rock joints are controlled by the joint roughness, the mechanical properties of rock wall and infill material, and the shear strength parameters of rock joints decrease rapidly as the t∕a ratio increase. When t∕a is bigger than 1, the shear strength parameters are mainly controlled by the mechanical property of infill material and the value of shear strength parameters indicates infill material.