Influence of Microroughness on Stick-Slip Characteristics of Fault Under Constant Normal Stiffness

Under the high geo-stress conditions, the stick-slip instability of faults or rock discontinuities might lead to earthquakes or rock bursts, and then significantly affects the stability of rock engineering. The surface roughness is an important factor influencing the sliding stability and nucleation characteristics. In this study, considering the constant normal stiffness (CNS) conditions of a deep rock mass around a fault plane and fault heterogeneity, a series of shear tests were conducted. The effects of the microroughness of basalt fault on its shear strength, normal stress, normal displacement, and friction sliding stability were analyzed, and the spatio-temporal evolution characteristics of acoustic emission (AE) events and the strain during the loading process were explored. The results showed that: (1) Under CNS conditions, with the increase in the shear displacement, the samples with different microroughness exhibited vastly different slide characteristics in the friction sliding process, where smoother samples were more prone to stick slip than rougher samples. (2) During the stick-slip process, the smooth basalt fault sample exhibited a nucleated fracture on the side close to the upper loading end, and the fracture gradually propagated to the other side. The fracture speed was high in the loading end, and the degree of fracture damage was significant. (3) The AE data better reflected the occurrence and expansion of damage on the fault surface. The test results provide a basis for understanding the influences of normal stiffness and microroughness of basalt fault on the sliding characteristics of smooth fault planes.