Damage mechanism and AE characteristics of water-rich sandstone under chemical corrosion and mechanical coupling

This study addresses the deterioration of the tunnel surrounding rock caused by groundwater chemical corrosion. Uniaxial compression tests were performed on sandstone after immersion in solutions of varying pH. Real-time acoustic emission (AE) monitoring was used to study the damage mechanisms and instability precursors under coupled chemical-stress effects. Across the full pH spectrum, a non-monotonic deterioration pattern in mechanical properties was discovered. A nonlinear change in porosity was also observed, where it first decreased and then increased with rising pH. These findings clarify the distinct mechanisms: acidic dissolution-plugging versus alkaline structural corrosion. A segmented damage constitutive model was developed, incorporating initial chemical damage and the compaction stage. This model improves theoretical calculation accuracy. Based on rise time/amplitude–average frequency analysis and Critical Slowing Down theory, chemical corrosion was found to significantly increase the proportion of shear fracture signals to 91.6%. The instability warning window was quantitatively shown to vary with pH, with the longest warning time occurring under in situ solution conditions (pH = 7.68). At both the macroscopic and microscopic scales, the dominant mechanism was elucidated: chemical corrosion promotes shear failure by dissolving cement and weakening cohesion. The research provides an important theoretical basis for assessing the long-term stability and early warning of disasters in engineering rock masses within complex chemical environments.