Mechanical anchoring mechanism of prestressed bolt for rock-coal-bolt combination under uniaxial compression

Understanding the mechanical behavior of rock-coal-bolt systems is crucial for ensuring the stability and safety of coal mine roadways. This study presents uniaxial compression tests conducted on four rock-coal-bolt (RCB) and rock-coal-prestress bolt (RCPB) combinations, each with varying interface dip angles (β is 15°, 30°, 45°, 60°). Through acoustic emission (AE) monitoring, the influence of prestressed and non-prestressed bolts on mechanical properties, energy dissipation, and AE entropy characteristics was analyzed. Additionally, the microscopic mechanisms of prestressed bolt reinforcement were explored using PFC2D simulations. Results demonstrate that increasing β leads to a shift in failure mode, transitioning from tensile-shear failure within the coal to slip failure along the interface. Prestressed bolt induces secondary stresses through tensile or bending deformation, effectively hindering shear crack propagation and controlling slip failure, thereby enhancing the overall strength of the RCPB system. Furthermore, prestressed bolt improves energy storage capacity and order stability within the rock-coal system. Numerical findings reveal a spatiotemporal evolution of contact force chains within the RCPB system, leading to the formation of a prestressed anchorage zone characterized by a concentration of high-strength and high-density compressive force chains at the rock-coal-bolt interface. This zone acts as the primary load-bearing region within the system.