Shear Behaviors and Failure Mechanisms of Anchored/unanchored Rock-concrete Interfaces Under Constant Normal Stiffness Conditions

This study investigated the effects of interface roughness and bolt anchoring on the shear behavior and failure mechanisms of rock-concrete composites under constant normal stiffness (CNS) conditions, with implications for deep tunnel support design. Direct shear tests were conducted on unanchored and anchored rock-concrete specimens featuring four regular roughness levels, assisted by acoustic emission (AE) monitoring. A calculation model for anchor contributions was also established, incorporating shear-dilation effects. Results indicated that increasing roughness enhanced peak shear strength, shear stiffness, residual strength, and post-peak stress drop for all specimens. Anchored specimens outperformed unanchored ones at equivalent roughness, showing higher strength, delayed failure, and suppressed shear dilation. The damaged area of the concrete section increases with increasing roughness, and the vertical displacement ΔH, horizontal displacement ΔL, and deflection angle θ of the anchor bolt increased monotonically with roughness. AE analysis revealed that peak AE energy and ringing counts rose with roughness, occurring later and with higher magnitude in anchored specimens. RA-AF distribution indicated that tensile failure dominated, though shear cracks increased with roughness. An empirical formula was developed to predict the peak shear strength of anchored rock-concrete interfaces, offering a practical reference for engineering design and practice.