Stress-path dependency of rock shear strength influenced by shear surface integrity: Experimental and numerical investigations

Excavation causes stress redistribution and affects the stress path during the shearing process of rock. The shear strength of rock varies under different stress paths, and the presence of defects reduces the shear strength. To further investigate this phenomenon, this study investigates the shear behaviour of rocks with different shear surface integrities under the influence of different stress paths through laboratory tests and numerical simulations. The results indicate that the shear strength depends on the stress path and a decrease in the shear surface integrity reduces the degree of dependence. The cohesion and friction angle of the Mohr‒Coulomb criterion decrease with weakening of the shear surface integrity. For different stress paths, the direct shear strength is always greater than that of other shear stress paths. The pattern of changes in the acoustic emission count and cumulative count indirectly reflects the above findings. Numerical simulations further indicate that the different principal stress states and normal suppression effects during the shearing process lead to changes in the factors of crack propagation, resulting in different mechanical behaviours under various stress paths. For rocks with different integrity levels, the main reason for the different path dependences of shear strength is that the size of the area affected by shear is different. Shear failure will concentrate on the shear plane when the normal inhibition effect is greater. This study explores the mechanism of rock shear behaviour, providing a theoretical basis for establishing more accurate constitutive models and strength criteria.