Mechanical properties of rock joints

Abstract

Sliding on rock joints occurs in situ under various boundary conditions. A servo-controlled direct shear testing machine was constructed to simulate these boundary conditions in the laboratory. Thirty-one sandstone samples were tested with two varying loading paths: (a) constancy of the normal force and (b) restriction of the dilation. The dilation was restricted by introducing a stiffness normal to the joint plane. The results of the experiments indicate that shear force and normal displacement (dilation) are both functions of normal force and shear displacement. Furthermore, it could be proved for the investigated material that the frictional behaviour is independent of the loading path. Based on the interpretation of the experimental results, a constitutive law for rock joints was developed. The constitutive law allows the calculation of stresses and strains in a rock joint. • -Five material constants are needed. They are determined by testing one sample in two conventional normal force-controlled direct shear tests. • -The constitutive equations allow consideration of the non-linearity of the material behaviour. The constitutive law was implemented in a finite element program. The comparison of the experimental with the calculated results indicates good agreement.