Shear Behaviour of Rock Joints Under Constant Normal Stiffness Conditions

The assessment of the shear strength of rock joints is essential for many rock engineering projects. The shear behavior of rock joints is usually investigated in the laboratory by using a direct shear apparatus, where the normal load is kept constant (CNL) during the shear process. However, they may be quite inappropriate for the situations where the normal stress on the joints surfaces changes considerably during the shear process. In this study, a high-performance direct shear apparatus and computer control system have been developed to accommodate the change in normal stress with dilation under constant normal stiffness (CNS) condition. The shear test results of the artificially prepared joint specimens show that the normal stiffness has a significant influence on the shear strength of joints.