Multiscale Fracture Mechanisms in Granite with Pre- existing Cracks: Experimental Characterization and Grain- Based Numerical Modeling

The mechanical behavior of pre-fractured granite is critically influenced by primary fractures, where macro-crack evolution originates from micro-crack accumulation. This study systematically investigates the deformation and failure mechanisms of granite containing single and double pre-existing fractures through integrated mechanical testing, acoustic emission (AE) monitoring, and multiscale numerical simulations. Key findings reveal: (1) Fracture geometry controls strength: Uniaxial compressive strength (UCS) increases with fracture inclination angle, while elastic modulus remains stable. For double-fractured specimens, strength peaks at a rock bridge angle of 60°, where collinear crack alignment induces weakest resistance; (2) Three-stage evolution: AE activity transitions sequentially from initial compaction (minor events), peak activity (crack coalescence), to post-failure stabilization; (3) Contrasting failure modes: Single fractures exhibit progressive tensile-dominated failure with localized shear, whereas double fractures trigger abrupt tensile-shear hybrid failure; (4) Multiscale crack propagation: Under uniaxial compression, microcracks initiate at inter-mineral boundaries, propagate along intra-mineral interfaces, and culminate in rapid intra-crystalline crack coalescence, forming macroscopic fracture surfaces. These findings provide critical insights into fracture-driven rock failure, bridging microscale damage mechanisms to macroscale engineering behavior.