Mechanical behaviors and anchoring mechanism of coal-rock-bolt combinations under high strain rate conditions

Understanding the mechanical properties of coal-rock-bolt (CRB) combinations at high strain rates and the anchoring mechanism of bolts is crucial for ensuring the safety of coal mining operations. However, the dynamic behaviors of these combinations, especially the mechanism of action of prestressed bolts, still need to be further investigated. This study carried out split Hopkinson pressure bar (SHPB) tests on three sets of coal-rock (CR), CRB, and coal-rock-prestressed bolt (CRPB) combinations with different interface angles ( β = 15°, 30°, 45°, and 60°). The dynamic properties of the combinations were analyzed based on the stress-strain curve, energy dissipation, dynamic strength, fractal dimension of cracks, and failure mode of bolts. The test results show that a larger β will affect the stress transfer and anti-sliding ability of CR, resulting in a decrease in CR strength. The anchoring force of the bolt effectively suppresses the slip feature of CRB at the yield stage. As the strain rate increases, CRB shows a more pronounced 'sudden increase' in strength, and the bolt significantly enhances its dynamic strength. The prestressed bolts enhance the dynamic strength of CRPB while weaken the effect of β . The fractal dimension of the macrocracks increases with strain rate, with smaller variations in CRB and CRPB, indicating that the bolt reduces the complexity degree of CRB and CRPB. The anchoring force of CRB depends on bolt strength, which reduces the slip along the interface. The anchoring force of CRPB balances the coal-rock slip and suppresses crack formation, resulting in a more cohesive response under dynamic load.