A coupled hydraulic-thermal-mechanical model incorporating particle size effects for water, heat and stress in saturated freezing soil

Accurate prediction of frost heave in saturated freezing soil is of significant importance critical for engineering practices in cold regions. Based on the principles of thermodynamics and continuum mechanics, this study presents a fully coupled hydraulic-thermal-mechanical (HTM) model for saturated freezing soil that explicitly incorporates the influence of particle size effects. The model integrates the particle size effect into key parameters governing the phase transition temperature, unfrozen water content, and hydraulic conductivity. It comprehensively describes the coupled processes of heat transfer, moisture migration, phase change, soil deformation, and ice lens initiation. The void ratio is adopted as a unifying variable that connects the processes of water-heat transfer and stress-deformation with the formation of ice lens. Based on the Clapeyron equation, the pressure relationship between coexisting ice and water phases under equilibrium conditions is described. The proposed model is validated against experimental data from a unidirectional freezing test conducted in our laboratory. The simulated results for temperature evolution, water content distribution, ice lens formation, and frost heave development show good agreement with the measurements. Incorporating the particle size effect significantly improves model accuracy, reducing the total error for simulated water content from 7.11% to 5.56% and for frost heave from 25.38% to 14.02%.