Disturbance mechanical behaviors and anisotropic fracturing mechanisms of rock under novel three-stage true triaxial static-dynamic coupling loading

The surrounding rock in deep underground engineering is often subjected to true three-dimensional high-stress conditions. Excavation unloading results in changes in the stress state and induces damage in the surrounding rock, subsequently, dynamic disturbance triggers catastrophic in the damaged surrounding rock and increases the risk of engineering. Therefore, it is necessary to elucidate the dynamic mechanical behavior and fracture evolution mechanisms of deep surrounding rock. In this study, a novel three-stage true triaxial static-dynamic coupling loading test method was proposed to model stress paths experienced by the rock during disturbance failure after excavation damage in deep engineering. With acoustic emission (AE) monitoring, a set of true triaxial tests was conducted to investigate the influence of initial damage degree on the disturbance mechanical properties and failure mechanisms of monzogabbro, including bearing capacity, deformation, macro and mesoscopic fracture characteristics, and anisotropic disturbance fracture evolution mechanisms. AE activity can reflect the disturbance failure processes (decay stage, steady stage, and accelerated stage), and tensile-shear mechanisms evolution based on AE parameters AF/RA are well investigated. The disturbance critical stress is defined and calculated based on the disturbance life, and it can be used as the criterion for rock disturbance failure. The transition conditions of disturbance deformation in three stages can be linked with static strains corresponding to damage stress and peak strength under true triaxial stress. When initial damage degree increases from 80 to 93% of peak strength, disturbance life of monzogabbro decreases by 98%, deformation differential index DI values increases by 31%, and the disturbance failure mode changes from localized tensile splitting failure/ tensile-shear mixed failure to macroscopic shear failure. The study also explores the implications of initial damage degree on the disturbance fracture mechanisms of different buried depths and deteriorated surrounding rock.