Experimental insights into anchorage performance of en-echelon joints under cyclic shear loading

Understanding the anchorage performance of en-echelon joints under cyclic shear loading is crucial for optimizing support strategies in jointed rock masses. This study examines the anchorage effects on en-echelon joints with various orientations using laboratory cyclic shear tests. By comparing unbolted and bolted en-echelon joints, we analyze shear zone damage, shear properties, dilatancy, energy absorption, and acoustic emission characteristics to evaluate anchoring effects across shear cycles and joint orientations. Results reveal that bolted en-echelon joints experience more severe shear zone damage after cycles, with bolt deformation correlating to shear zone width. Bolted en-echelon joints exhibit faster shear strength deterioration and higher cumulative strength loss compared to unbolted ones, with losses ranging from 20.04% to 72.76%. The compressibility of en-echelon joints reduces the anchoring effect during shear cycles, leading to lower shear strength of bolted en-echelon joints in later stages of shear cycles compared to unbolted ones. Bolts reinforce en-echelon joints more effectively at non-positive angles, with the best performance observed at 0° and –60°. Anchorage accelerates the transition from rolling friction to sliding friction in the shear zone, enhancing energy absorption, which is crucial for rock projects under dynamic shear loading. Additionally, rock bolts expedite the transition of the cumulative AE hits and cumulative AE energy curves from rapid to steady growth, indicating that strong bolt-rock interactions accelerate crack initiation, propagation, and energy release.