Numerical study of voids geometry effects on sandstone’s mesoscopic fracture Mechanism: Insights from acoustic emission and moment tensor inversion

Abstract

In the field of rock mechanics, the study of void shape on the mechanical properties and fracture mechanisms of sandstone is crucial for the progression of rock engineering practices. In this study, PFC3D is utilized to conduct numerical simulations of uniaxial compression on intact rock and brittle rocks containing five different shapes of voids (including circular, inverted U-shaped, trapezoidal, rectangular, and square). By employing acoustic emission and moment tensor inversion techniques, the microscopic fracture mechanisms of rocks with different void shapes are revealed. Our key findings reveal: (1) The PFC3D’s Soft-Bond Model is adept at simulating acoustic emissions with high accuracy, facilitating an authentic reproduction of the uniaxial compression process in sandstone, including the nonlinear compaction stage. (2) The presence of hole defects markedly undermines the structural strength and deformability of the sandstone, with circular holes having minimal impact, whereas rectangular holes exert the most significant detriment. (3) A thorough analysis of fracture mechanisms demonstrates that specimens with hole defects primarily undergo initial tensile, remote cracks, V-shaped notch, and shear fractures, with shear fractures being pivotal in leading to specimen failure by rapidly evolving into macroscopic fractures that merge with V-shaped notches. (4) Acoustic Emission (AE) analysis highlights the distribution of tensile stress around the upper and lower extremities of the holes and shear stress along the left and right sidewalls, establishing shear stress as the dominant factor in the failure of specimens with hole defects.