Cumulative damage and bearing capacity attenuation law of anchorage structure interface under cyclic loading and unloading

The specimens of anchorage structures bonded by different anchoring materials are prepared to study the damage and reduced safety and reliability caused by the cyclic loading and unloading stress to the roadway anchorage structure. Using Fiber Bragg grating, acoustic emission monitoring and ANSYS, the anchorage structures' bearing properties, interface failure characteristics, overall failure mode and internal influence mechanism are obtained under cyclic loading and unloading stress path. Results show that the cracks at the anchorage interface would develop and expand rapidly under this path, and the cumulative damage to anchorage structures is primarily caused by repeated residual deformation, periodic opening-expanding-closing of internal cracks, and impact vibration resulted from large-scale cyclic loading and unloading. Compared with the results under single pull-out stress, the ultimate loads of the anchorage structures bonded by H and S materials are reduced by 30.8% and 45.5%, respectively, and the radii of inner damage are increased by 1.64 and 1.67 times, respectively, showing a significant decrease in the bearing capacity of anchorage structures under cyclic loading and unloading. The anchorage structures bonded by these two materials have more prominent brittleness and weaker post-peak bearing capacity than those bonded by resin anchoring agent. Therefore, the balance between bonding strength and brittle-plastic extension characteristics shall be fully considered for the selection of anchoring materials. Five failure modes of anchorage structure are summarized: failure of the bolt-anchoring material interface, failure of the anchoring material-surrounding rock interface, fracture of the anchoring material, fracture of the bolt, and integral bulging of the anchorage structure. Besides, under the action of stress disturbance, the anchorage structure of bolt group can mobilize adjacent bolts to restrain the continuous damage and bearing capacity attenuation of the middle bolt, thus guaranteeing the overall safety and stability.