Interactions among cracking, pore structure, and hydrothermal responses in soils under wetting-drying-freeze-thaw cycles

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Understanding the interactions between surface cracking and internal hydrothermal processes is essential for predicting water and heat transport and deformation in soils under wetting-drying-freeze-thaw (W-D-F-T) cycles. However, data and quantitative parameterizations linking pore structure evolution and cracking to hydrothermal responses remain limited. This study monitored surface crack patterns, internal hydrothermal dynamics, and pore structure distributions under W-D-F-T cycles through laboratory soil column tests. Empirical parameterizations and term-exclusion analyses were developed for two key indices, namely the freezing front propagation velocity ( v T ) and infiltration-affected depth ( d i ). Results show that the soil column develops a distinct three-layered structure characterized by surface shrinkage, upper-layer expansion, and lower-layer stability, with successive cycles further intensifying this stratification within the frost depth. Crack propagation is controlled by the combined presence of high soil shrinkage potential, sufficient evaporable water, and limited water supply. Under these conditions, drying-induced cracking can offset frost-heave-induced closure even at sub-zero temperatures. The parameterizations of v T and d i show that cracks dominate hydrothermal responses by providing preferential pathways for heat transfer, infiltration, and vapor exchange. In contrast, pore structure plays a secondary modulating role by altering matrix thermal conductivity and water retention behavior. The freezing-stage parameterization also remains accurate for thawing stages when the crack ratio does not exceed about 1.16 times the maximum value in the calibration dataset. These findings provide benchmark data and empirical relationships for predicting and calibrating hydrothermal responses in cracked soils under W-D-F-T cycles.