Prediction of Cryo-SWCC during Freezing Based on Pore-Size Distribution

The freezing process in soils is generally recognized as a coupled problem of heat and moisture transfer. Especially in the process of transfer, it is essential to understand the status of unfrozen water. In this paper, the freezing process in unsaturated soils has been studied with the hypothesis that initially unsaturated soil maintains the apparent unsaturated condition during freezing. Accordingly, the concept of the soil-water characteristic curve (SWCC) of unfrozen soil could be also applied to soil in the freezing stage. Therefore, a methodology for estimating a correlation between the suction and the amount of unfrozen water content, named cryo-SWCC, which considers the volume change of soil pores owing to ice formation, is proposed with the assumption that any deformation in unsaturated frozen soils owing to freezing can be negligible. On the basis of a relationship between a statistical pore-size distribution and the SWCC represented by the Mualem model, the variation of characteristic parameters $a$ and $n$ in the cryo-SWCC with respect to ice content is evaluated based on an incremental formulation using optimized average unsaturated soil data values. According to the analysis results, the predicted parameters $a$ and $n$ tend to decrease as ice content increases, and the status of unfrozen water during freezing moves across each cryo-SWCC during freezing, which indicates the proposed method is able to describe variations of the pore system, matric suction, and freezing temperature depression induced by ice formation during freezing.