Experimental Study on Shear Failure Characteristics and Crack Propagation Laws of Rocks with Various Joint Angles under Hydro-Mechanical Coupling

Abstract

With the increasing depth of coal resource extraction, the surrounding rock in deep engineering faces a geological-mechanical environment characterized by high in-situ stress and elevated water pressure. Investigating the damage evolution and crack propagation patterns in jointed rock masses under the coupled effects of water and stress is crucial for understanding the destabilization and failure mechanisms of deep rock masses. This study employs equipment such as the ROCK TEST SYSTEM 816.01 shear apparatus and a force-thermal-water coupled shear test system to conduct a comprehensive investigation into the damage characteristics and shear crack propagation patterns of granite with varying joint angles under hydraulic coupling conditions.The research findings indicate that the injection of water pressure can effectively reduce the peak shear strength of granite by lowering the effective normal stress. As the joint angle increases, the peak shear strength of the specimens exhibits an overall "n"-shaped trend, with shear displacement showing a reversed "s"-shaped pattern, initially increasing, then decreasing, and increasing again at the peak. Both joint angle and water pressure significantly influence the damage incurred during the granite fracture process. With an increasing joint angle, the damage in the specimens demonstrates an initial increase, followed by a decrease, and then another increase. However, under the influence of water pressure, the damage in the specimens is higher compared to those without water pressure. The damage growth rate under water pressure follows a trend of initially increasing and then decreasing, with the maximum damage growth rate occurring at a joint angle of 30°.Furthermore, numerical simulations using the FRACOD software are conducted to simulate shear fracturing for the Yangba well in Enhanced Geothermal Systems (EGS) geothermal engineering. The results of the simulation calculations hold significant guidance for selecting wellbore positions in the target area of hot dry rocks.