Analysis of Interfacial Properties and Mechanical Mechanisms of Expansion-Type Bolts

As mining operations extend to greater depths, the high in-situ stresses and intense disturbances associated with deep mining present significant challenges for mining operations, including fractured rock masses, poor stability, susceptibility to water-induced softening and deformation, and difficulties in ground support. As one of the most critical support components in tunnels and mine roadways, the anchorage mechanism of bolts at the bolt-surrounding rock interface in deep fractured surrounding rock remains unclear. To gain deeper insight into the anchorage mechanism and failure evolution of the bolt-surrounding rock interface under deep surrounding rock conditions, this study conducts similar bolt pull-out tests to investigate the anchorage performance of the bolt-surrounding rock interface during pull-out under multiple experimental factors, and analyzes the mechanical properties, response stages, and failure characteristics of the anchorage interface using multiple evaluation indices. The results show that: (1) the anchorage length, the confining pressure, and the material strength act on the anchorage performance through distinct mechanisms; (2) the introduction of expansion points on the bolt surface alters the interfacial load-transfer path and markedly improves the anchorage performance, albeit with a marginal effect; (3) based on the measured load-slip responses, the pull-out process is interpreted as six consecutive stages, whose characteristics differ notably between conventional and expansion-type bolts.