Experimental study on shear behavior of rough fractured granite under true triaxial monotonic and cyclic loading

To analyze the fault slip mechanism under static and cyclic disturbance loads during construction, a series of true triaxial monotonic and cyclic loading tests on rough fractured granite were conducted. The effects of confining pressure and loading path on the slip characteristics of fractured granite with a 60° fracture angle were explored. Based on stress, strain monitoring, and acoustic emission techniques, the shear stress, shear displacement, friction coefficient, and energy release process during the fracture slip of fractured granite were analyzed. Meanwhile, macroscopic and microscopic observations were made to examine the morphological evolution of the fracture surface before and after slip. The results show that confining pressure is a key factor that limits the fracture slip of fractured granite. Compared to the intermediate principal stress, the increase in the minimum principal stress has a more significant effect on the increase in the peak shear stress of the fractured granite. Under true triaxial cyclic loading, the peak strength, shear stress, and static friction coefficient of fractured granite are higher than those under monotonic loading. As the confining pressure increases, the precursor AE characteristics of fractured granite specimens before slip become more pronounced. During the frictional sliding of the fracture surface, asperities on the surface are compressed and ground in the form of transgranular cracks, and both the roughness and the fractal dimension decrease. Compared with monotonic loading, under true triaxial cyclic loading, the fracture surface and the surrounding rock matrix are severely damaged after fracture slip, and transgranular and intergranular cracks develop. The debris and powder produced by fracture slip form fault gouge, which adheres to the fracture surface and accumulates in micro-pores and micro-cracks.