A New Model for Predicting Hydraulic Conductivity of Soil during Freeze-thaw Processes that Accounts for Both Capillary and Adsorption Forces

Understanding the change of soil hydraulic conductivity with temperature is a key to predicting the groundwater flow and solute transport in permafrost and seasonally frozen area. The most commonly used models for hydraulic conductivity during freeze-thaw cycles only consider the flow of capillary water in the soil and neglect water flowing along thin films around the particle surface. This paper proposed a new hydraulic conductivity model of frozen soil via Clausius-Clapeyron equation based on an unsaturated soil hydraulic conductivity model over the entire moisture range using analogy between freeze-thaw and dry-wet process in soils. The new model used a simple single equation to describe the conductivity behaviors resulting from both capillary and adsorption forces, thus accounting for effect of both capillary water and thin liquid film around soil. By comparing with other existing models, the results demonstrated that the new model is applicable to various types of soils and the predicted hydraulic conductivity is in the highest agreement with the observed data. Finally, our new model was validated with a thermal-hydrological benchmark problem and a laboratory experiment result, and the benchmark results indicated that the advective heat transfer was more significant and the phase change completed earlier when considering both capillary and adsorption forces than that only considering capillary forces. Further, the coupled flow-heat model with the FXW-frozen-M2 replicate well the results from a laboratory column experiment.