THM Model of Saturated Partially Frozen Soils: From Pore- Scale Ice Morphology to Macroscopic Behaviors

The application of energy geotechnology and artificial ground freezing technique always encounters the frozen soil layer in the subsurface. In cold regions, accelerated climate change induces freeze-thaw cycles on earthen structures. It is essential to develop a constitutive model for thermo-hydro-mechanical (THM) behaviors of frozen soils to assess the stability and serviceability of geotechnical infrastructure in the frozen ground. This study developed a constitutive model to investigate the pore-scale granular interaction between soil grains and ice crystals in saturated partially frozen soils. The microscopic temperature-dependent distribution of the ice phase in the soil pore spaces was anticipated as pore-filling and load-bearing particles. It was found that not all the ice crystals were being loaded in the soil skeleton. This microscopic morphological distribution of the ice phase was found to be associated with the soil stress states, indicating the dependency of THM behaviors of frozen soils on stress state and temperature. The model was validated by existing experimental results and showed considerable accuracy in the prediction of undrained shearing behaviors of frozen soils under various temperature and confining conditions. It also revealed the process of the ice invasion in the pore spaces, affecting the stress state and yield surface. Furthermore, the model might also explain the soil degradation due to freeze-thaw cycles by considering the variation in the effective granular void ratio, as reflected by the soil freezing characteristic curves. This study provides insight into the pore-scale mechanistic soil-water-ice interactions for frozen soils. The proposed model is compatible with the critical state framework and could be applied to geomaterials' characterization in cold regions.