Microdynamic mechanical properties and fracture evolution mechanism of monzogabbro with a true triaxial multilevel disturbance method

The far-field microdynamic disturbance caused by the excavation of deep mineral resources and underground engineering can induce surrounding rock damage in high-stress conditions and even lead to disasters. However, the mechanical properties and damage/fracture evolution mechanisms of deep rock induced by microdynamic disturbance under three-dimensional stress states are unclear. Therefore, a true triaxial multilevel disturbance test method is proposed, which can completely simulate natural geostress, excavation stress redistribution (such as stress unloading, concentration and rotation), and subsequently the microdynamic disturbance triggering damaged rock failure. Based on a dynamic true triaxial test platform, true triaxial microdynamic disturbance tests under different frequency and amplitudes were carried out on monzogabbro. The results show that increasing amplitude or decreasing frequency diminishes the failure strength of monzogabbro. Deformation modulus gradually decreases during disturbance failure. As frequency and amplitude increase, the degradation rate of deformation modulus decreases slightly, disturbance dissipated energy increases significantly, and disturbance deformation anisotropy strengthens obviously. A damage model has been proposed to quantitatively characterize the disturbance-induced damage evolution at different frequency and amplitude under true triaxial stress. Before disturbance failure, the micro-tensile crack mechanism is dominant, and the micro-shear crack mechanism increases significantly at failure. With the increase of amplitude and frequency, the micro-shear crack mechanism increases. When approaching disturbance failure, the acoustic emission fractal dimension changes from a stable value to local large oscillation, and finally increases sharply to a high value at failure. Finally, the disturbance-induced failure mechanism of surrounding rock in deep engineering is clearly elucidated.