Shear Rate Effects on the Post-peak Shear Behaviour and Acoustic Emission Characteristics of Artificially Split Granite Joints

Rock joints may be sheared at different rates under quasi-static or dynamic loading. Understanding the mechanical response of rock joints at different shear rates is of great importance for the mitigation of dynamic geo-hazards such as earthquakes, fault slip rockbursts and landslides. In this study, direct shear tests at various shear rates (0.001-0.1mm/s) under different normal stresses (3-40MPa) are conducted on split granite joints, and the influences of shear rates on the shear strength, post-peak shear behaviour and acoustic emission (AE) characteristics are analysed and discussed. The research findings suggest that both peak and residual shear strengths tend to decrease with increasing shear rate. Stick-slip occurs on all the joints, during which stress drop values increase with increasing shear displacement and normal stress. The stress drop magnitudes during stick-slip decrease with shear rate, while the time intervals between stress drops during stick-slip increase with shear rate. Further, the energy rate tends to increase while the AE events decrease with increasing shear rate, which is caused by the time-dependent deformation behaviour. The AE b value decreases linearly with the shear rate on a logarithmic scale, and the influence is more significant under high normal stress conditions. The variations in the b value can reflect the evolution process (first loading at lower and then higher shear rates) of dynamic geo-hazards and can be used as an effective indicator to predict the dynamic shear failure of granite joints in a temporal sequence. The results of this study will encourage better understanding of the rate-dependent shear behaviour of rough granite joints, particularly under high normal stress, and will provide some references for the monitoring and prediction of dynamic geo-hazards with respect to the AE (or micro-seismic) technique.