Study on the Failure Mechanism of Prefractured Coal Samples under Stepwise Cyclic Loading Based on PFC2D Simulation

To investigate the dynamic instability of surrounding rock in mining faces caused by engineering disturbances in coal-rock masses with structural defects within gate roads, PFC2D numerical simulation was employed to replicate laboratory tests, with its reliability verified. Further analysis was conducted on the development of microcracks, the evolution of displacement fields, and contact force chains under cyclic loading. Finally, the influence of pre-existing fractures on the fatigue damage evolution of coal samples under cyclic loading was elucidated. This study provides insights for reinforcing fractured coal masses and preventing dynamic hazards in mining excavations. The key findings of this study are as follows: For pre-fractured specimens, microcracks initially emerge at the tips of pre-existing fractures and subsequently propagate outward. These microcracks predominantly concentrate in the vicinity of the pre-fractures.