Prediction of Soil Freezing Curve from Adsorption-Induced and Capillarity-Induced Water Pressure

Abstract

The soil freezing curve (SFC) is the constitutive relationship between the unfrozen liquid water content of soil and temperature in subzero (<0°C) environments. The water-to-ice phase transition is governed by the pressure and temperature conditions. Most existing models for predicting the SFC are built around the Clapeyron equation and do not correctly account for the intermolecular water pressure induced by adsorption, leading to overestimation of unfrozen water content for various soil types. A novel approach based on soil sorptive potential theory is proposed to predict the SFC from the soil water isotherm. The method directly considers the intermolecular water pressure of soil water induced by adsorption and capillarity and the fundamental pressure-temperature phase diagram to predict the freezing point of pore water. Experimental measurements independently obtained from the literature demonstrate that the proposed method can accurately predict the SFC for fine-grained soils. The proposed approach outperforms the Clapeyron equation-based methods, highlighting the importance of properly accounting for the intermolecular water pressure, especially the adsorption-induced positive water pressure, in the freezing point depression of soil water. The method also reconciles observations that the SFC depends on initial water content for soils with high clay content.