Effect of opening on the shear behavior of a rock joint

Irregularity of rock joints is an important parameter which can enhance the stability of potentially removable rock blocks or wedges around an underground opening. When irregular-sided blocks or wedges are bounded by joints, additional shear strength develops as a consequence of the confinement. With open joints, the interlock effect is reduced or lost and the shear strength drops, possibly to its residual value. A joint opening model has been developed that considers the effect of strength loss along the joint as a result of opening. The model relates the geometric parameters and stress-displacement and can easily be incorporated into existing joint models. Several numerical simulations of direct shear tests are presented to demonstrate the performance of the joint opening model.