Meso-damage characterization of chemically corroded rocks under unloading confinement conditions

Characterizing meso-damage and understanding its correlation with macroscopic mechanical responses of rocks under coupled chemical-mechanical (C-M) conditions are crucial for the stability analysis and safety design of underground constructions in chemically corrosive environments. This research proposes a model to quantify coupled C-M meso-damage of rocks, utilizing geochemical surface reaction theory, statistical mechanics, thermodynamic principles, and novel principals proposed in this study, termed Random Energy Release Rate (RERR) and Effective Chemical Damage (ECD). To achieve this goal, a multiscale experimental investigation, including Nuclear Magnetic Resonance (NMR), X-ray diffraction (XRD), Scanning electron microscopy (SEM), pH and ion chromatography analysis, triaxial compression and unloading confinement tests, is employed to examine meso-damage evolution and its linkage with the macro-mechanical responses of limestone under coupled C-M conditions. Based on the experimental investigations, the ECD model is introduced to differentiate chemical damage into effective and apparent categories. Then RERR is proposed to characterize the heterogeneity of damage. Utilizing ECD, along with RERR, the coupled C-M meso-damage model is finally proposed and validated with experimental data. Results show that the evolution of coupled C-M damage follows an S-shaped curve with four stages; Confining pressure limits ECD and C-M damage development, while ECD accelerates C-M damage; As dual-pore geo-media, RERR predominantly originate from the crack-like pores, and ECD is closely tied to crack-like pore closure and rock skeleton flexibility.