Hydromechanical Processes in Freezing Soils

The study of freezing in soils has benefited immensely from analogies with physical processes that take place within the unsaturated zone. The surface energies and wetting interactions that produce differences in pressure between the pore-filling phases cause a qualitatively similar saturation dependence on geometrical characteristics, such as the pore size distribution. The ability of solid ice surfaces to support shear tractions contrasts with the fluidity of air, however, and the limited need for transport on solidification is notably different from the wholesale displacement of gas and liquid volumes that is necessary to change saturation levels in the vadose zone. This brief review outlines the main points of common ground and some of the essential differences that separate partially frozen and unsaturated soils. Particular attention is paid to an illustration of the ice and liquid saturation behavior in a two-dimensional model porous medium, both in a pure water system and with solutes present at a specified (bulk) concentration relative to the total mass of pore constituents. A derivation is developed for the net thermomolecular force exerted by sediment particles on an ice lens, and the model soil parameters are used to examine how the colligative effects of impurities modify the loads that can be supported in this way. The focus of this study is on describing and quantifying the physical interactions that underlie the vast range of hydro-mechanical processes in freezing soils.