Soil Freezing and Soil Water Characteristic Curves

Abstract An earlier paper suggested that the soil water characteristic (SWC) of soil should have an analogue to be called the soil freezing characteristic (SFC) that could be obtained by freezing saturated soil in an apparatus functionally related to the pressure plate apparatus. The analogy for granular soil, free of colloids, is on a different basis (capillary effects) than for soil that is wholly colloidal (absorption effects). Different rules are needed to demonstrate the analogies for the respective types. Apparatus was devised to permit SFC and SWC data to be obtained, in turn, with each material placed in the apparatus. Two silt fractions, a sodium‐montmorillonite paste, and a whole soil were used. The results confirm the expected analogies and indicate that in these experiments, the ratio of the specific surface energy of an airwater interface at 20C to that of an ice‐water interface near 0C was as 72.7:33.1. The results demonstrate significant mobility for unfrozen water at temperatures as low as −0.15C even in clean silt fractions. It is concluded that the inherent instability of some of the residual water in soils during drying does not significantly affect the SWC in the range 0 to 4 bars of matric suction.