Origin, General Definition, and Implications of Cryosuction in Frozen Soil

Unfrozen water in frozen soils can migrate from warmer to colder regions driven by a force commonly referred to as cryosuction. Existing explanations of cryosuction based on capillary or premelting theories generally assume a spatially uniform negative pore-water pressure within the unfrozen water film. This assumption contradicts experimental observations of increased viscosity and density in adsorptive unfrozen water. Phase equilibrium at the ice–unfrozen water interface is considered in this study to reveal the thermodynamic origin of cryosuction by incorporating a spatially varying water pressure distribution including positive water pressure due to adsorption. Cryosuction is formulated as the net pressure difference attributable to both capillary and adsorptive unfrozen water through a unified formulation that remains consistent with the intrinsic spatial variability of adsorptive water properties. The formulation is validated using macroscopic soil column experiments and microscopic film-flow experiments. Quantitative comparisons with other potential fluid migration mechanisms in frozen soil demonstrate that cryosuction is the dominant driving force governing unfrozen water migration in Arctic permafrost environments. The formulation advances conceptual and quantitative understanding of cryosuction and provides a unified framework for predicting frost-heave phenomena in frozen soil systems.