Experimental Study on the Influence of Structural Planes on Rockbursts in Deep-Buried Hard-Rock Tunnels.

To study the influence of structural planes on rockbursts in the rock surrounding deep tunnels, a series of true triaxial compression tests were carried out on 100 mm × 100 mm × 100 mm red sandstone specimens (including 50 mm diameter circular holes and prefabricated structural planes). The characteristics of the rockburst process and acoustic emission under different structural plane conditions were studied, and the microscopic characteristics of the fracture surface were observed by scanning electron microscope (SEM). The test results show that: (1) The location of the initial damage and the mode and scale of the damage have changed significantly, regardless of the location of the structural plane and its exposure status. The existence of the structural plane will promote the occurrence of rock burst, and the intensity of the structural plane rock burst has also been greatly enhanced, but after the occurrence of the structural plane rock burst, the number and intensity of the rock burst are weakened. The failure process of the specimen with exposed symmetrical structural plane is dominated by slab spalling, and the initial failure position of the unexposed structural plane specimen is the corresponding position of the structural plane. (2) The existence of a structural plane changes the structure of the rock mass, and the transfer path of internal stress in the rock mass changes, It accelerates the overall failure of the specimen, has a significant "weakening effect" on the strength of the specimens, and the final damage of the specimen is more serious.According to the fracture behavior dominated by the structural plane, structural plane rockburst is divided into structural plane–plane pressure/column pressure rockburst and structural plane-buckling rockburst. Note that this failure mode may change with the distance between the structural plane and the hole and the nature of the rock. (3) According to the acoustic emission (AE) events, the existence of structural planes changes the scale of rockburst, the activity of acoustic emission is obviously enhanced, but the number of events is reduced, the generation of microcracks in the rock is reduced, and the proportion of shear cracks is increased. (4) Through SEM observation, the structural plane changes the energy transfer inside the rock mass, showing different micro-crack morphologies. A variety of crack morphologies are observed in the test samples containing structural planes, showing complex crack propagation modes, which means that the internal energy transfer path and scale have changed. The results of this study can enhance the understanding of the influence mechanism of structural planes on the rockburst in deep underground engineering. Highlights: A true triaxial physical simulation test of the rockburst process of surrounding rock with a structural plane near the boundary of a deeply buried tunnel was carried out. The existence of structural planes has significantly changed the development process of rockburst in deep tunnels. The existence of structural planes weakens the structural effect of circular holes in a rock mass. The existence of structural planes promotes the occurrence of rockburst, and an unexposed structural plane significantly increases the intensity of rockburst. [ABSTRACT FROM AUTHOR]