DEM simulation of the mechanical response and acoustic emission mechanisms of ice-filled open-fissure granite after freeze-thaw cycles

Freeze-thaw cycles (FTCs) significantly affect the mechanical integrity of granite, and the geometric orientation of open fissures plays a critical role in regulating damage evolution. This study investigates the coupled micro-macro fracture mechanisms of granite under varying fissure angles \:(0^∘\:,\:30^∘\:,\:60^∘\:,\:90^∘\:) and multiple FTCs (10, 20, 30 cycles) using discrete element modeling combined with acoustic emission (AE) analysis. Microcrack evolution reveals that tensile and shear cracks accumulate progressively with increasing FTCs, while fissure angle strongly influences crack initiation and propagation patterns at different stages. Particle force analysis indicates that stress concentration occurs preferentially at fissure tips, with low-angle fissures (particularly \:30^∘\: ) maintaining higher contact numbers and more stable force chains, whereas vertical fissures ( \:90^∘\: ) exhibit delayed stress concentration and failure. AE monitoring demonstrates that low-angle fissures predominantly generate small-scale, linearly distributed events, moderate-angle fissures ( \:60^∘\: ) show intense tensile shear coupled with branching larger AE magnitudes, and high-angle fissures display delayed failure with limited AE event expansion. Macroscopic fracture patterns corroborate these findings, showing that low-angle fissures fail mainly by tensile-driven through cracks, moderate-angle fissures form complex, multi-branch divergent networks, and vertical fissures produce highly fragmented blocks with constrained propagation. Overall, the results highlight that fissure orientation governs local stress concentration, microcrack accumulation, fracture propagation mode, and ultimate macroscopic damage under FTCs. Notably, \:30^∘\: fissures exhibit optimal stability, \:60^∘\: fissures are most prone to complex fracture expansion, and \:90^∘\: fissures display delayed failure. These insights provide a comprehensive understanding of frost-induced damage mechanisms in fissured granite and offer practical guidance for stability assessment and design of rock engineering in cold regions.