Frictional sliding of infilled planar granite fracture under oscillating normal stress

This paper investigates the frictional behavior of the infilled rock fracture under dynamic normal stress. A series of direct shear tests were conducted on saw-cut granite fractures infilled with quartz using a self-developed dynamic shear apparatus, and the effects of normal load oscillation amplitude, normal load oscillation period and sliding velocity were studied. The test results reveal that the shear response can be divided into three stages over a whole loading-unloading process, characterized by different time spans and stress variations. Generally, a smaller oscillation amplitude, a longer oscillation period and a fast shear velocity promote the stability of the friction system, which is also confirmed by the Coulomb failure criterion calculated based on the observed periodic apparent friction coefficient. The dynamic strengthening/weakening phenomenon is dependent on the oscillation amplitude and product of sliding velocity and oscillation period ( vT ). Also, the rate and state friction law incorporating the parameter α that characterizes the normal stress variation is employed to describe the dynamic friction coefficient but exhibits an incompetent performance when handling intensive variation in normal stress. Finally, the potential seismicity induced by oscillating normal stress based on the observed stress drop is analyzed. This work helps us understand the sliding process and stability evolution of natural faults, and its benefits for relative hazard mitigation.