Abstract: Based on the engineering environment of the wellbore surrounding rocks in the energy storage areas during deep geothermal energy mining, the methods of high temperature heating, water immersion at different temperatures, heating-cycle times and radial impact loading were used to simulate the physical and mechanical conditions of wellbore surrounding rocks, such as dynamic disturbance caused by high temperature, water encounter, cyclic heat extraction and thermal impact. Meanwhile, the concentric perforated rock samples with different inner-hole diameters were used to simulate deep geothermal wells, and the dynamic mechanical tests of concentric perforated granite samples under the thermal-hydro-mechanical coupling were carried out by SHPB test system. VIC-3D non-contact strain measurement and numerical simulation analysis technology were used to monitor the history of fracture initiation and formation and the surface strain evolution law of concentric perforated granite samples during the impact process so as to reveal the dynamic damage mechanism of concentric perforated granite under the thermal-hydro-mechanical coupling. The results showed that the concentric perforated granite under radial impact load experienced three typical stages, i.e., elastic deformation, plastic deformation and structural instability failure successively. The four factors of inner hole diameter, heating temperature, immersion temperature and the number of heating-soaking cycles all weakened the ability of concentric perforated granite to resist external loads, but did not change its overall deformation evolution law. The failure mode of concentric perforated granite samples was dynamic tensile failure. Firstly, from inner hole wall to outer wall of rock samples along the impact direction, and then from outer wall of rock sample to inner hole wall in perpendicular impact direction, cracks initiate and coalesce, forming two sets of vertical fracture surfaces nearly perpendicular to each other. Finally, based on the damage deformation characteristics and history of the concentric perforated granite, a dynamic damage structure model was established on the basis of certain assumptions, the structure equations were deduced, and the parameters of the equations were determined by combining the test results. Comparative analysis demonstrated that the theoretical fitted curve was in good agreement with the tested curve, which verified the constructed dynamic damage structure model of concentric perforated granite was reasonable. The results not only reveal the damage and failure mechanism of concentric perforated rock samples, but also provide theoretical reference for predicting the damage and deformation law of geothermal wellbore surrounding rock in deep energy storage areas, which have certain scientific and engineering practical significance.

Key words: thermal-hydro-mechanical coupling, concentric perforated granite, dynamic damage, peak load, numerical simulation, structural model