Moisture migration during freeze and thaw of unsaturated soils: Modeling and large scale experiments

A coupled heat flow and moisture flow model (FROSTB) was used to simulate large-scale freeze-thaw experiments to assess its ability to predict soil moisture conditions. The experimental data consist of temperature and soil moisture profiles measured during freeze-thaw cycles in a 1-m layer of frost-susceptible silty sand over roughly 2 m of gravelly sand. Two experimental conditions were modeled: (1) where the soil was fairly wet and the water table was shallow (1 m below surface), and (2) where the soil moisture was lower than specific retention and the water table was deep. Overall, the model predicts the frost penetration and heave quite well; however, it tends to overpredict ice formation. The additional ice in the modeled frozen soil then causes a slower thaw. Matching the (total) moisture contents in the drier soils results in underpredicting the heave. The discrepancies stem from the model representation of the physical processes involved in freezing (and frost heave) of unsaturated soil. We propose improvements through using a ''pseudo'' three-phase flow potential and calculating volumetric segregated ice content starting at 90% of saturation. The effects of changing the constants related to hydrologic properties are also discussed.