Influence of roughness on the mechanical response of rock-like specimens with nonpersistent joints under uniaxial compression based on joint deformation analysis

Joint deformation is a key factor controlling the mechanical behavior of discontinuous rock strata under changing stress conditions, including dominating the elastic deformation in near-surface excavations and serving as a major component of settlement under higher stress. This study, focusing on joint deformation behavior, investigates the effect of joint roughness on the peak stress and failure modes of specimens under uniaxial compression. Rock-like specimens with two layers of parallel, nonpersistent joints, one rough, were fabricated using 3D printing technology. Digital image correlation was used to capture real-time surface displacement fields, and a joint deformation analysis method was developed. The results show that joints exhibit staged, non-uniform closure and slip behavior, influenced by joint roughness, distribution of primary and secondary joints, and layered arrangement. Rough joints accelerate closure but hinder slip coordination, resulting in a three-stage loading process. In stage I, primary closure and layer-coordinated slip occur, accompanied by crack initiation, joint coalescence, and steady stress growth. Stage II involves secondary closure and overall coordinated slip, leading to localized failure and stress stabilization. Stage III is characterized by complete closure, uncoordinated slip, intensified crack propagation, and specimen failure, accompanied by stress hardening. The study reveals that joint deformation serves as a bridge linking roughness and peak strength. The average joint closure level and slip coordination are linearly negatively correlated with roughness but nonlinearly positively correlated with peak strength. Roughness restricts slip coordination, limiting crack propagation and delaying failure, which slows stress growth. Redistribution of joint aperture during slip reduces joint closure, weakens wall contact, and diminishes stress hardening.