Coupled hydrochemical and freeze-thaw deterioration of confined red-bed mudstone with respect to disintegration behavior and post-disintegration hydraulic properties

Red-bed mudstone exhibits significant susceptibility to both disintegration and degradation when exposed to cold environments characterized by active hydrochemical conditions. Nevertheless, the synergistic disintegration mechanisms arising from freeze-thaw cycles coupled with hydrochemical erosion remain insufficiently characterized, particularly under confined conditions designed to replicate in situ stress states. In this study, an extensive experimental investigation was conducted to elucidate the disintegration behavior and post-disintegration hydraulic properties of confined red-bed mudstone subjected to the coupled effects of hydrochemical erosion and freeze-thaw cycling. The disintegration process of laterally confined specimens was monitored in real time via continuous photographic documentation and high-precision gravimetric recording to quantify the kinetic parameters of disintegration. Experimental results demonstrate that the disintegration rate increases systematically with the cumulative number of freeze-thaw cycles and exhibits an asymmetric U-shaped dependence on solution pH, wherein the maximum kinetic reactivity is consistently achieved under both strongly acidic and strongly alkaline conditions. The temporal evolution of confined disintegration is confirmed to proceed through four sequential stages and three distinct final morphological modes have been identified. Furthermore, the hydraulic conductivity and swelling ratio of the reconstituted specimens exhibit progressive increases, which are strongly positively correlated with the preconditioning treatment intensity characterized by the disintegration rate constant.