Numerical direct shear tests to model the shear behaviour of rock joints

In this paper, the shear behaviour of rock joints are numerically simulated using the discrete element code PFC2D. In PFC, the intact rock is represented by an assembly of separate particles bonded together where the damage process is represented by the breakage of these bonds. Traditionally, joints have been modelled in PFC by removing the bonds between particles. This approach however is not able to reproduce the sliding behaviour of joints and also results in an unrealistic increase of shear strength and dilation angle due to the inherent micro-scale roughness of the joint surface. Modelling of joints in PFC was improved by the emergence of the smooth joint model. In this model, slip surfaces are applied to contacts between particles lying on the opposite sides of a joint plane. Results from the current study show that this method suffers from particle interlocking which takes place at shear displacements greater than the minimum diameter of the particles. To overcome this problem, a new shear box genesis approach is proposed. The ability of the new method in reproducing the shear behaviour of rock joints is investigated by undertaking direct shear tests on saw-tooth triangular joints with base angles of 15°, 25° and 35° and the standard joint roughness coefficient profiles. A good agreement is found between the results of the numerical models and the Patton, Ladanyi and Archambault and Barton and Choubey models. The proposed model also has the ability to track the damage evolution during the shearing process in the form of tensile and shear fracturing of rock asperities.