Multi-scale study on dynamic damage characteristics and energy dissipation of deep rock under thermal-hydro-mechanical coupling

The thermal-hydro-mechanical (THM) coupling and a strong mining disturbance environment all have a significant impact on deep ground engineering excavations, which increases the risk of a rock burst disaster. The independently developed THM multi-physics coupling apparatus enables replication of intricate geological conditions in engineered rock formations, with high-strain-rate compression experiments on deep-buried rock specimens being implemented through a split Hopkinson pressure bar testing platform. The fracture surface microstructure and the pore structure of the rock after impact are characterized by SEM and NMR. Results show that the dynamic stress-strain curve exhibits nonlinear behavior, accompanied by a significant 'plastic platform area.' Under the same temperature and pre-static stress, the energy time-history evolution distribution of rock in the process of dynamic compression has the characteristics of synchronous and different amplitudes. The energy reflection coefficient and energy dissipation coefficient obey a good exponential function and a Gaussian function relationship with water pressure, respectively. 'Compression-shear crushing failure → inclined shear boundary failure → fracture failure' is the development trend of the overall failure mode of rock when temperature and water pressure increase. The dynamic damage threshold is between 0.35 and 0.36. Microscopically, it shows a transformation trend of intergranular fracture, complex fracture, and transgranular fracture. NMR analysis reveals that elevated water pressure enhances the structural integrity of rock pores, accompanied by a reduction in pore dimensions and a progressive decline in overall porosity. A mechanical model of sliding microcrack propagation under THM coupling and impact load is constructed. By analyzing the variation patterns of crack initiation points under different operating conditions, the accuracy and adaptability of this model were validated.