Deterioration mechanisms of pre-holed sandstone under freeze–thaw cycling in a tailings-water environment: Microstructural evolution, energy response, and failure behavior

Sandstone surrounding tailings facilities in cold regions may be subjected simultaneously to freeze–thaw cycling and chemically active seepage water. This study investigated the deterioration of pre-holed sandstone continuously immersed in field-collected tailings water under 0-90 freeze–thaw cycles using hydrochemical analysis, nuclear magnetic resonance, scanning electron microscopy, digital image correlation, and uniaxial compression tests. freeze–thaw exposure produced pronounced hydrochemical evolution, with Ca²⁺, Mg²⁺, and K⁺ concentrations increasing by 94.04%, 80.10%, and 65.07%, respectively, while Na⁺ decreased by 87.82%. NMR-derived porosity increased from 7.25% to approximately 10.36-10.61%, accompanied by redistribution toward longer T2 relaxation domains and progressive microcrack development observed by SEM. After 90 cycles, peak compressive stress and elastic modulus decreased by 19.95% and 32.34%, respectively. DIC and energy analyses further showed earlier damage development, enhanced strain localization around the circular defect, and increased energy dissipation with freeze–thaw deterioration. The observed hydrochemical changes indicate possible water-rock interactions but do not uniquely identify specific geochemical pathways. These results provide experimental insight into the deterioration of defective sandstone under saturated tailings–water–assisted freeze–thaw conditions.