Experimental characterization and grain-based numerical modeling of multiscale fracture mechanisms in pre-fractured granite

The mechanical behavior of pre-fractured granite is primarily governed by pre-existing fractures, in which macro-crack evolution emerges from micro-crack accumulation. This study employs an integrated approach combining mechanical testing, acoustic emission (AE) monitoring, and multiscale numerical simulations to systematically investigate the deformation and failure mechanisms of granite containing single and double pre-existing fractures. Key findings reveal: (1) Fracture geometry dictates strength: Uniaxial compressive strength (UCS) increases with fracture inclination angle, whereas elastic modulus remains relatively constant. For double-fractured specimens, strength peaks at a rock bridge angle of 60°, at which collinear crack alignment induces minimal resistance; (2) Three-stage AE evolution: AE activity progresses through initial compaction (minor events), intensifies during peak stress (crack coalescence), and diminishes toward post-failure stabilization; (3) Divergent failure modes: Single fractures display progressive tensile-dominated failure with localized shear, while double fractures promote abrupt tensile-shear hybrid failure; (4) Multiscale crack progression: Under uniaxial compression, microcracks nucleate at inter-mineral boundaries, propagate along intra-mineral interfaces, and escalate to rapid intra-crystalline coalescence, ultimately forming macroscopic fracture surfaces. These findings establish fundamental insights into fracture-driven rock failure, linking microscale damage processes with macroscale engineering manifestations.