Macroscopic and Microscopic Analysis of Shear Creep–Impact Damage Evolution in Anchored Jointed Rock Masses under Constant Normal Stiffness Boundary Conditions

Abstract To investigate the mechanical behavior of deep anchored jointed rock masses (AJRMs) under long-term shear loading and impact disturbances with constant normal stiffness (CNS) boundary conditions, shear creep-impact tests were conducted. Specimens with three joint roughness coefficients (JRC) were tested under various shear creep stress levels and five levels of impact energy. The acoustic emission (AE) system and industrial CT were employed to reveal the internal structural damage degree and spatial evolution characteristics at the micro-scale. This study systematically analyzes the creep deformation behavior, creep rate characteristics, long-term strength, and parameter sensitivity. A dual-dimensional quantitative evaluation method based on a "mass-area" concept was established to quantitatively characterize the damage evolution of AJRMs, clarifying the cumulative damage mechanism during the shear creep-impact process. The results indicate that the shear strain evolution caused by two impacts exhibited opposite trends in specimens J₁ and J₃. Specimen J₂ displays a distinct critical damage state, with a "shear stress-impact energy" threshold at and . When , both and decrease with increasing JRC. However, at , the specimens with higher JRC present the greatest values of and . CT scan results revealed that no large-scale disintegration occurred under impact disturbance; damage was primarily concentrated in the local area surrounding the anchor rod. In the final stage, AE signals exhibit a characteristic "AE critical quiet period," which closely corresponds to the macroscopic accelerated failure process. This phenomenon can be considered a precursor to structural failure and has significant implications for early warning of instability in AJRMs.