Freezing characteristic curves and water retention characteristics of soils

The soil-water characteristic curve (SWCC) is an important constitutive model for unsaturated soils. It represents the water retention capacity of soils, which defines the relationship between pore water potential and water content and can be capable to describe the transport phenomena and the mechanical behavior of unsaturated soils. The soil freezing characteristic (SFC) expresses the relationship between the quantity and the energy status of liquid water in frozen soils, which also represents the water retention behavior. The soil-water characteristic curves over the full water content range of silt and clay are obtained by using the pressure plate extractor and vapor equilibrium method. The soil freezing characteristic curves are obtained by the temperature control bath combining with the low-field nuclear magnetic resonance (NMR) system. Based on the similarity between the freezing/thawing and drying/wetting behavior, the corresponding energy status of pore water at the specified water content is inferred from soil temperature measurements with the Clapeyron equation. The relationship between pore water potential and water content obtained by the freezing method is compared with the measured SWCC, showing that the pore water potentials are different due to the existence of air and ice at the other side of the water film (different soil-water interactions). Based on the concept of surface chemistry, a relationship between the intermolecular force and the water film thickness is developed, which can be capable to describe the water retention behavior under adsorption condition.