Influence of joint morphology evolution on shear damage behaviors

Understanding the evolution of shear-induced surface damage is critical for estimating the shear characteristics of rough rock joints. This study aims to bridge the gap between the evolution of joint morphology and shear damage behaviors, and to develop a physics-based shear damage model capable of capturing the complete shear stress-shear displacement ( τ - u ) relationships. In this study, deformation and damage phenomena are analyzed through direct shear tests on specimens with various joint morphologies. Asperity-based morphological analysis confirms that both shear displacement and asperity deformation dominate the shear characteristics of joints. A probability distribution parameter for the apparent dip angles( θ ⁎ ) of asperities along the shear direction is introduced to quantitatively characterize shear-related joint morphology. Joint roughness evolution results indicate that damage is mostly induced by high apparent dip angles, demonstrating that roughness reduction - characterized by diminishing dip angle probabilities - directly influences joint shear properties. A threshold apparent dip angle ( θ cr ⁎ ) is proposed to quantify the spatial distribution of shear damage, revealing that damage concentrates on asperities exceeding θ cr ⁎ . The parameter θ max ⁎ - θ cr ⁎ (where θ max ⁎ denotes the maximum apparent dip angle) positively correlates with the joint roughness, directly reflecting the range of shear failure zones on the joint surfaces. A shear damage model that distinguishes between progressive degradation (PD) and constant residual (CR) patterns of post-peak shear behavior is developed, which accurately captures the shear stress-shear displacement relationships of rough joints. This work provides a damage-based framework for predicting progressive failure in rough joints, directly enhancing shear behaviors assessment for rock mass engineering.