Mesoscopic damage to rock under prestatic and cyclic disturbances: A grain-based model

In engineering practice, rock often experiences complex stress states. For example, during underground mining and tunnel excavation, rocks are subjected not only to in situ stresses but also to cyclic disturbance loads. Rock is a heterogeneous material. Its mesoscopic structures, such as the distribution, shape, and size of internal grains, are highly related to its failure behavior. Therefore, considering the structural characteristics of rock is important for investigating its damage features under complex stress conditions. In this study, an improved grain-based discrete element model (GBM) was used to simulate the failure process of rock under prestatic and cyclic disturbances. A novel cyclic stiffness degradation method and a plastic strain-dependent strength criterion were implemented to capture the nonlinear hysteretic behavior of rocks. Numerical Brazilian tests of granite and marble revealed that increasing the prestatic load ratio led to increased axial deformation at failure, and the tensile strength slightly decreased. The failure is dominated by tensile cracks, which outnumber shear cracks by approximately two to one upon failure. On the basis of two-dimensional digital image correlation, we further determined that granite failure is primarily transgranular. As the prestatic load ratio increases, the percentage of transgranular cracks gradually decreases. This study helps reveal the failure characteristics of rock under combined loading from a mesoscopic perspective and provides important information for the prevention and control of engineering geological hazards induced by rock failure.