Moisture migration in frozen silt under different moisture content and negative temperature gradient

To investigate the effects of initial moisture content and negative temperature gradient on water migration during the freezing process of silt, five numerical experiments under undrained conditions were conducted using the simulation software COMSOL Multiphysics 6.0. The study focused on analyzing the dynamic response of freezing depth development, temperature field evolution, unfrozen water distribution, water migration flux, and frost heave deformation throughout the freezing process. This analysis revealed the combined influence of the two factors on the water migration mechanism. The results show that the freezing process of silt exhibits distinct stages, characterized by a rapid initial increase in freezing depth followed by a gradual stabilization. The negative temperature gradient plays a significant regulatory role in the freezing process. Increasing the negative temperature gradient notably accelerates the advancement of the freezing front and leads to a substantial increase in the final stabilized maximum freezing depth. When the negative temperature gradient rises from 12.5 ℃·m^-1 to 22.5 ℃·m^-1, the maximum freezing depth increases by approximately 63%. The vertical distribution of moisture content changes significantly before and after freezing. Higher initial moisture content and a steeper negative temperature gradient induce more pronounced water migration in the unfrozen zone, with the peak moisture content shifting downward as the negative temperature gradient increases. In the early freezing stage, continuous water supply from the underlying unfrozen zone to the freezing front is the primary cause of rapid frost heave. As freezing progresses, the water migration flux gradually weakens due to the stabilization of the temperature field and the reduction in unfrozen water content. Consequently, the rate of frost heave development decreases, eventually reaching a relatively stable magnitude. Based on the moisture migration characteristics of frozen silt identified in this study and considering the potential limitations of current drainage measures on the Gongyu Expressway, the importance of blocking upward water migration within the subgrade for deformation control is further emphasized.