Discrete Element Simulation on the Evolution Mechanism of Excavation Damage Zone in Deep-Buried Tunnels Under Confining Pressure and Comprehensive Structural Planes

The failure mechanism of fractured rock masses under high in situ stress is crucial to the stability of deep underground engineering. This study employs the discrete element method to investigate the evolution of the excavation damage zone (EDZ) in deep-buried tunnels. Numerical models of granite were developed to analyze how confining pressure influences single fractures with varying characteristics and to compare the behavior of filled versus unfilled fractures in double-fracture configurations. The results show the following: (1) confining pressure exerts a dual role, promoting crack initiation and EDZ expansion in intact rock and exposed fractures due to stress concentration while suppressing damage near hidden filled fractures through confinement; (2) EDZ geometry is governed by fracture orientation and filling condition, with filled fractures maintaining stress continuity and raising the crack initiation stress ratio to 0.3–0.4; (3) in multi-fracture setups, unfilled fractures facilitate stress release and crack coalescence, whereas filled fractures act as barriers, diverting cracks and promoting symmetric stress redistribution; and (4) models accurately reproduced failure patterns from real rockburst cases, validating the method for predicting fracture behavior, with filled fractures reducing EDZ area by up to 44%. These findings provide theoretical support for rockburst risk assessment and support design in complex geological conditions.