Influence of excavation stress paths on failure feature of deep hard rocks

The fracture of the surrounding rock in deep hard rock engineering is influenced by the stress path during excavation. Taking the stress path as the only variable, a true triaxial experimental system was used to study the loading-unloading stress path during excavation and the loading stress path with constant stress state after excavation, and combined with acoustic emission, 3D laser scanning and SEM to investigate the differential mechanisms of the two stress paths on the strength, energy storage and fracture of the rock. The results show that the strength, deformation and ultimate energy storage capacity of the rock under the loading-unloading stress path are greater than those under the loading stress path with constant stress state. Compared with the loading stress path with constant stress state, with the loading-unloading stress path, the rock fractures are more fragmented, the failure angles are slightly smaller, and the development of shear cracks is delayed, occurring closer to rock failure. This is due to the influence of the true triaxial stress state on rock fracture expansion. The changing direction and location of rock fracture expansion under the loading-unloading stress path inhibits crack penetration, which in turn delays the development of shear cracks. The effect of the stress path is influenced by the rate of loading and unloading; the greater the rate of loading and unloading of the rock is, the greater the strength and ultimate energy storage of the rock. Finally, the evolution characteristics of the tensile and shear cracks formed in the rock under the loading-unloading stress paths during excavation provide new understanding for the prevention and control of deep engineering hazards.