Damage-fracture evolution mechanism of rock bridge structures in flawed sandstone under cyclic disturbance: Insights from DIC-AE

Abstract

In deep mining engineering, the geological-mining interaction (repeated disturbance from mining activities leading to stress field reconstruction) results in significant roof instability and failure. This study uses combined Acoustic Emission (AE) and Digital Image Correlation (DIC) techniques to monitor and conduct cyclic loading tests on double-fractured sandstone specimens with different rock bridge angles. The study systematically analyzes the impact of rock bridge angle on the dynamic response and damage-fracture mechanisms of sandstone under cyclic loading. The results show that cyclic loading hardens sandstone, but the weakening effect of initial defects is more dominant. The 60° rock bridge angle specimen exhibits the lowest D_ed, with most of the energy stored elastically. Furthermore, the evolution of AE parameters characterizes the progressive damage under cyclic loading. For the 60° sample, the rapid crack propagation results in AE energy concentrating at the peak release stage, consistent with the macroscopic energy release characteristics. The RA-AF plot indicates that microscopic damage is primarily driven by the propagation of tensile cracks, with their proportion first increasing and then decreasing as the rock bridge angle changes. Based on DIC displacement fields, two types of single-mode cracks and six types of mixed-mode cracks were identified. The evolution of macroscopic crack types is associated with the trend of tensile cracks in the RA-AF plot, with the proportion of tensile cracks being highest in the 60° rock bridge specimen. Finally, through analyzing the RA-AF values and the surface strain field characteristics captured via DIC at distinct loading stages, the disaster-causing mechanisms induced by varied rock bridge angles under cyclic loading were elucidated. Based on these findings, a dual-control theory of rock damage evolution under cyclic loading, comprising an energy dissipation-driven mechanism (the competition between tensile and shear energy efficiencies) and a spatial configuration-regulated mechanism (rock bridge angles governing crack propagation directions), was proposed. This theoretical framework provides a robust foundation and quantitative criteria for evaluating surrounding rock stability and preemptively mitigating hazards under high-intensity disturbance conditions in practical engineering contexts.