Evolution of Deformation Failure and Energy of Siltite and Significant Shear Fracture Structure Under Cyclic Loading

The investigation of the shear fracture mechanism under cyclic loading holds significant implications for controlling instability in the surrounding rock of roadways. Both uniaxial constant amplitude and stepwise linear loading and unloading tests were carried out to reveal the fatigue damage and shear fracture mechanisms of the coal–rock mass under cyclic stress disturbance. The rock samples for the tests were taken from the lane side of the coal mine’s haulage trough, and the evolution of microcrack extension and shear damage were analyzed from the perspective of deformation modulus and energy evolution using the CT scanning technique and excavating the hidden stress–strain information. The results indicate that the microcracks undergo intermittent expansion under constant amplitude cyclic loading and unloading, while they exhibit progressive expansion under stepwise linear cyclic loading and unloading. In both cases, the cumulative damage caused to the rock samples is irreversible. The test discovered a rarely reported phenomenon of shear fracture oscillation, showing a process of “hysteresis–reciprocation–hysteresis–reciprocation,” and the corresponding fracture zone formed by shear fracture exhibited a pronounced domino structure. The results also show that the shear oscillation phenomenon is a unique stress–strain state of domino structural evolution. During the failure process of the rock sample, the trends of deformation modulus, energy, stress–strain rate, and rebound strain rate show a high spatial and temporal correlation and spatial synergy. The process of shear fracture oscillation can be subdivided into six stages: initial crack micro-extension, initial crack extension, main shear fracture extension, metastable fracture extension, rapid fracture extension, and accelerated failure. The rotation–gyration motion of the domino structure can slowly release and dissipate excessive energy, providing a potential coping strategy for optimizing the supporting system and controlling the stability of surrounding rock in coal mines by fully utilizing the structure.