Energy-driven fracture and instability of deeply buried rock under triaxial alternative fatigue loads and multistage unloading conditions: Prior fatigue damage effect

Abstract

Rock failure subjected to respective cyclic loading or unloading have been well investigated, however, the energy mechanism of deeply buried rock under alternative cyclic loading and unloading are not well understood. This work aims to reveal the effect of prior fatigue damage on rock fracture and energy evolution characteristics subjected to triaxial alternative cyclic loads and unloading confining pressure. Testing results show that rock stress strain responses, deformation, energy dissipation, and mesoscopic crack pattern are all impacted by the prior fatigue damage. The incremental radial and volumetric strain at the unloading confining pressure stage (UCPS) is larger than the cyclic loading stage (CLS), and their relationships and the confining pressure are revealed. The total energy, elastic energy, and radial strain energy increases and dissipated energy decreases with the increase of disturbed cycles. The relationship between strain energy and confining stress was established at both the UCPS and CLS, it is found that dissipated energy at the UCPS is larger than at the CLS. A series of post-test CT images reveal the internal failure modes and confirm the effect of the number of disturbed cycles on energy release and dissipation. It is suggested that the consumed energy is not proportional to the crack scale, the formation of shear cracks consumes much more energy than those of tensile cracks.