Rate-dependent shear behavior of rough joints based on acoustic emission

Understanding the rate-dependent shear behavior of rough joints is crucial. This study explores the rate-dependent shear behavior of rough joints through direct shear tests conducted under constant normal stiffness (CNS) boundary conditions, with the shear failure process monitored using acoustic emission (AE) technology. As the shear rate increases, both the peak and ultimate shear stresses of rough joints exhibit a decrease, highlighting a pronounced rate-dependent behavior. Asperity degradation under different shear rates is effectively characterized by normalized AE counts, exhibiting a three-stage S-shaped trend: Stage I (quiescent), Stage II (growth), and Stage III (stable). The simultaneous occurrence of the lowest AE b -value and the highest AE amplitude closely aligns with the moment of peak shear stress. This synchronization suggests that AE events of significant energy are predominantly clustered around the peak shear stress, which critically influences the overall progression of failure. Three failure modes of asperities were categorized, including the biting-off failure mode (BFM), the climbing-sliding failure mode (CFM), and the hybrid biting-off and climbing-sliding failure mode (HFM). Analysis of the multifractal spectra reveals that both the multifractal spectrum width (Δ α ) and the fractal dimension variability (Δ f ) diminish as the shear rate increases, suggesting that the complexity of the failure modes is inversely related to the shear rate. With increasing shear rates, the dominant failure mode evolves from BFM to CFM. The research findings facilitate a comprehensive understanding of the rate-dependent shear behavior of rough joints, providing valuable guidance for rational support in underground engineering.