Dynamic mechanical responses and debonding failure mechanisms of a bolt–resin–rock anchoring system subjected to cyclic shear loading

This study investigated the mechanical responses and debonding mechanisms of a bolt–resin–rock composite anchoring system subjected to cyclic shear loading. A systematic analysis was conducted on the effects of the initial normal load (F_sd), cyclic shear displacement amplitude (u_d), frequency (f), and rock type on the shear load, normal displacement, shear wear characteristics, and strain field evolution. The experimental results showed that as F_sd increased from 7.5 to 120 kN, both the peak and residual shear loads exhibited increasing trends, with increments ranging from 1.98% to 35.25% and from 32.09% to 86.74%, respectively. The maximum shear load of each cycle declined over the cyclic shear cycles, with the rate of decrease slowing and stabilizing, indicating that shear wear primarily occurred at the initial cyclic shear stage. During cyclic shearing, the normal displacement decreased spirally with the shear displacement, implying continuous shear contraction. The spiral curves display sparse upwards and dense downward trends, with later cycles dominated by dynamic sliding along the pre-existing shear rupture surface, which is particularly evident in coal. The bearing capacity of the anchoring system varies with the rock type and is governed by the coal strength in coal, resin–rock bonding in sandstone#1 and sandstone#2, combined resin strength and resin–rock bonding in sandstone#3 (sandstone#1, sandstone#2 and sandstone#3, increasing strength order), and resin strength and bolt–resin bonding in limestone. Cyclic shear loading induces anisotropic interfacial degradation, characterized by escalating strain concentrations and predominant resin–rock interface debonding, with the damage severity modulated by the rock type.