(1. Key Laboratory of Rock Mechanics and Geohazards of Zhejiang Province, Shaoxing University, Shaoxing, Zhejiang 312000, China;
2. School of Civil Engineering, Shaoxing University, Shaoxing, Zhejiang 312000, China; 3. Zhejiang Collaborative Innovation Center for Prevention and Control of Mountain Geologic Hazards, Shaoxing University, Shaoxing, Zhejiang 312000, China;
4. Department of Civil Engineering, Tongji University, Shanghai 200092, China; 5. Key Laboratory of Geotechnical and Underground Engineering of Ministry of Education, Tongji University, Shanghai 200092, China)
Abstract：The shear strength and stability of rock joints are critical factors in ensuring the safety of surrounding rock in underground engineering. To investigate the shear behavior and destabilization mechanisms of rock joints under the combined effects of roughness, shear rate, and normal stress, we developed rock joint models with varying roughness levels (low-order roughness JRC = 0.42, medium-order roughness JRC = 11.12, and high-order roughness JRC = 18.96) using the particle flow code (PFC2D). Subsequently, we conducted numerical direct shear tests on these models under varying normal stresses (2–6 MPa) and shear rates (50–200 mm/s). By quantitatively analyzing the evolutions of contact area, energy, and acoustic emission (AE) characteristics during joint shearing, we systematically revealed the macro-mechanical responses and associated micro-mechanisms of shear failure in rock joints. The main conclusions are as follows: (1) the peak shear strength of rock joints significantly increases with both JRC and normal stress. However, for the residual shear strength of high-order rough joints (JRC = 18.96) subjected to high normal stress (＞4 MPa), there is a decrease of approximately 30% due to brittle failures at the contact asperities caused by stress concentration. (2) Under constant shear rates, joints exhibit consistent velocity-strengthening behavior, where shear strength increases with an increase in shear rate. Nevertheless, in velocity-stepping tests, an increase in both JRC and normal stress promotes the transition of rock joints from velocity-strengthening to velocity-weakening behaviors. (3) The strain energy accumulated during the shear process of the high-order roughness joint (JRC = 18.96) is 1.8 times that of the low-order roughness joint (JRC = 0.42), and the energy released during the instability stage is also significantly higher in the high-order roughness joint, indicating that rapid energy dissipation serves as a critical driving force for joint instability. (4) The AE characteristic b-value is strongly correlated with velocity-dependent parameters a－b1, indicating that the joint has entered a critical instability state when b＜1 and a－b1＜0. This work establishes an innovative dual-parameter framework for assessing the shear instability of rock joints and proposes a coupled destabilization criterion based on critical decreases in the acoustic emission b-value and the velocity-weakening effect. It elucidates the instability mechanisms of rock joints under complex conditions and potentially provides a theoretical foundation and quantitative criteria for the stability assessment of rock masses in deep underground engineering.
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2025, Vol. 44 
