Shear failure behaviors and fracturing mechanisms of rockmass bedding under true triaxial static-disturbance

Mechanical and blasting excavation of mining, transportation and hydropower engineering tunnels or caverns under three-dimensional geostress frequently impose dynamic waves on layered surrounding rock, inducing shear failure along bedding. However, the mechanisms of shear failure in slate bedding caused by disturbances under true triaxial stress remain poorly understood. Accordingly, a novel true triaxial shear disturbance approach was designed and applied to examine the fracture precursors and failure mechanisms of slate bedding subjected to shear disturbance. A comprehensive investigation was conducted to clarify how normal and lateral stresses affect the shear strength, deformation, strain rate, damage evolution and fracturing mechanics and precursor characteristics of slate bedding. The findings revealed that with increasing lateral stress, the disturbance shear critical strength of slate bedding initially increased and then decreased, with a maximum increase of 26.32%. Under the same stress-intensity ratio, the disturbance damage and irreversible strain rate in slate bedding decrease and then increase as lateral stress increases. An improved acoustic emission spatialization algorithm was used to reveal the gradual shear cracking process of slate bedding and the tensile-shear microcrack mechanism. As failure approached, the acoustic emission b -value continuously decreased, reaching a minimum at failure, with main frequencies characterized by high amplitude and mid-low frequency. • Fracture roughness and shear strength of slate bedding increase with normal stress. • Lateral stress strongly affects roughness, strength, strain rate and damage. • At disturbance shear failure, b -value drops and low-frequency AE events increase remarkably.