Slip behaviors of rock joints subjected to weak shear disturbances: An experimental study

Frequent weak disturbances can induce dynamic shear slip along rock joints and potentially trigger dynamic hazards in rock masses. This study experimentally investigates the dynamic slip, failure, and instability behavior of jointed rocks under repeated shear disturbances. A custom dynamic shear testing apparatus was used to examine sawtooth-shaped rock joints subjected to weak shear disturbances, normal stress, and initial shear stress. The results reveal that the shear displacement of the joint progresses through three distinct stages: decelerated slip, constant-rate slip, and accelerated slip, forming an inverse S-shaped curve. Both the dynamic slip displacement caused by the disturbance and the post-disturbance deformation due to stress recovery in each cycle are captured. As disturbance cycles increase, a progressive instability process is identified, characterized by a transition from initial instability to stable damage accumulation, and finally to accelerated damage accumulation. Notably, all instabilities occurred during the stress recovery phase following the final disturbance. The effects of normal stress and joint undulation angle on these behaviors are also discussed. A combined linear- exponential model is proposed to quantify the shear slip in jointed rocks, incorporating a damage variable index. The p/a ratio in this model effectively describes the transition from stable to accelerated damage accumulation, which may also indicate the intensity of energy release. These findings provide guidance for the assessment of dynamic slip instability in jointed rock masses, particularly under far-field seismic events.