Improved soil freezing characteristic curve based on thermodynamics considering unequal particle contact

The soil particle contact pattern plays a crucial role in predicting the soil freezing characteristic curve (SFCC) from the soil water characteristic curve (SWCC). SFCC affects soil water migration and heat transfer. A novel soil freezing characteristic curve considering soil particle contact pattern based on thermodynamics is proposed. To quantify contact pattern, unequal particle contact structure is used considering particle size effects and void ratio. It is verified by the measured soil, including silt, clay, sand, silty clay, and lean clay. The results show that the established theoretical model has applicability and accuracy (RMSE ≈ 0.0316). Capillarity and adsorption jointly control SFCC. Pore water phase transition stages can be divided by capillary and adsorbed water changes. Higher initial water content leads to higher unfrozen capillary water content. When the particles size difference is smaller, the void ratio is larger, the fine content is higher, and soil particle contact pattern is closer to solid-liquid-solid. It causes the capillary water content under the same negative temperature is lower, and decreasing rate with temperature becomes faster. The proposed model can be easily used into the frost heave and thawing areas to provide a reference for heat and water transfers behavior in cold regions.