Macro-Mechanical Property and Microfracture Evolution of Layered Rock Mass: Effects of Confining Pressure and Bedding Direction

Understanding the mechanical responses of layered rock masses at both macro and micro scales, particularly under diverse confining pressures and bedding directions, is crucial for evaluating their stability and optimizing resource extraction. This study employs PFC2D numerical models, calibrated with laboratory data from Xinjiang Barkol oil shale, to investigate how confining pressure and bedding direction control the mechanical properties of layered rock masses during biaxial compression. The results demonstrate distinct failure modes, shifting from splitting in Per bedding (beddings perpendicular to the loading direction) to shear-tension and shear-slip failures in inclined bedding. A U-shaped distribution of compressive strength across bedding directions is observed, with strength increasing under higher confining pressure. A novel microfracture connection algorithm is proposed to quantify microfracture parameters, such as quantity, length, and angle, shedding light on the complex microfracture evolution mechanisms. Fewer persistent microfractures in Par (i.e., beddings are parallel to the loading direction) and Per beddings explain their higher compressive strength compared to inclined bedding. Additionally, microfracture length evolution demonstrates a shift from brittle to ductile macro-failure as bedding direction changes. Microfractures primarily develop parallel to the loading direction, while confining pressure slightly affects microfracture characteristics. These findings establish a new framework for predicting the behavior of layered rock masses under complex loading, providing theoretical insights and practical guidance for engineering applications.