A new dilation angle model and a cohesion-weakening and friction-weakening model for simulating post-peak deformation of brittle hard rocks

The post-peak deformation of rock is nonlinear, accompanied by strain-softening, dilatancy, and plastic flow. Hence, it is important to better understand these aspects to accurately capture the post-peak deformation behavior. In this study, the developments of rock dilatancy models are reviewed, and it is seen that three major types of models, i.e., constant dilation angle models, constant rate dilation models, and variable dilation angle models, exist. Using Beishan granite as an example, the dilatancy response of the rock in different deformation stages under uniaxial and triaxial compressions is examined. Furthermore, the variations of the dilation angles under different confining pressures and plastic shear strains are analyzed, and a segmented confinement and plastic-shear-strain-dependent dilation angle model is proposed. In addition, a plastic-shear-strain-dependent cohesion and friction angle model, named the cohesion-weakening and friction-weakening (CWFW) model, is developed. Finally, the proposed models are implemented into FLAC, and numerical simulations are conducted. The simulation results are compared with laboratory test data with good agreement, indicating that the proposed models can capture the post-peak strain-softening and dilatancy deformation behaviors of brittle rock well.