Investigation of Compressive–Shear Fracture in Rock Considering Flaw Distribution and Interaction via an Improved Energy-Stress-Based Peridynamics Model

Predicting compressive–shear fracture in rock masses containing complex flaw distributions remains a major challenge in rock engineering. We propose an improved non-ordinary state-based peridynamics (NOSB-PD) model to simulate rock fracture behavior in this work. A stabilized NOSB-PD formulation is developed by incorporating a bond-level deformation gradient strategy to effectively suppress the zero-energy mode inherent in conventional NOSB-PD formulations, thereby ensuring deformation compatibility and numerical robustness. More importantly, the triple-shear energy criterion is introduced into the PD framework for the first time, enabling a more accurate characterization of shear fracture in rocks under complex stress states. The proposed NOSB-PD model is validated using two examples, demonstrating its excellent capability in suppressing the zero-energy mode and capturing fracture behavior in rock under compressive–shear conditions. Subsequently, the proposed model is used to systematically investigate the influence of flaw distribution on crack propagation and failure modes in rocks. The results indicate that variations in flaw distribution alter the local stress field, leading to a change in the rock fracture mode. Consequently, the rock bridge failure mode transitions from shear-dominated direct coalescence to mixed tensile-shear failure, and finally to tension-dominated indirect failure. The overall rock specimen is more prone to tensile–shear-mixed failure under conditions of shorter rock bridges with larger inclinations, or longer rock bridges with smaller inclinations. These findings provide new insights into the role of flaw distribution on rock fracture behavior.