Experimental Study on the Influence of a Small-Scale Single Structural Plane on Rockburst in Deep Tunnels

To investigate the influence of a small-scale single structural plane with hard fillings in the surrounding rock of deep tunnels on the rockburst process, a series of biaxial compression tests were conducted on granite specimens (200 mm × 200 mm × 30 mm) with a circular hole of 50 mm in diameter. The characteristics of the rockburst process, acoustic emission (AE) and the corresponding energy release characteristics under different conditions of the structural plane (existence or not, exposure or not and inclination angle) were investigated. The test results show that the existence of the structural plane significantly influences the evolution characteristics of rockburst, such as the occurrence time and severity of the rockburst, the AE, and the energy release. The exposure condition of the structural plane also has a significant impact on the occurrence of the rockburst. Compared with the condition of the exposed structural plane, the unexposed structural plane can promote the occurrence of the rockburst, resulting in larger AE characteristic parameters and energy release. The inclination angle of the unexposed structural plane has a certain influence on the failure mode and intensity of the rockburst. The rock specimens containing unexposed structural planes with inclination angles of 30°, 45° and 60° are prone to shear failure and exhibit violent rockburst, while the rock specimens containing unexposed structural planes with inclination angles of 0° and 90° are prone to slabbing failure and exhibit relatively slight rockburst. In addition, the energy release increases first and then decreases as the inclination angle of the unexposed structural plane increases, while the inclination angle of the exposed structural plane has no apparent influence on the energy release. The results of this study can enhance the understanding of the influence mechanism of a small-scale structural plane on the rockburst in deep underground engineering.