Moisture movement in soils under temperature gradients with the cold‐side temperature below freezing

Moisture movement to a freezing front in an unsaturated porous medium of Fairbanks silt was measured by γ‐ray attenuation. It was shown that the presence of an ice phase greatly enhances the amount of moisture transfer under temperature gradients. The chemical potential of soil water in the frozen soil as a function of temperature is calculated. The chemical potential of unfrozen absorbed water in frozen soils, if in equilibrium with ice, is independent of total water content (unfrozen water plus ice). Consequently, no equilibrium moisture content distribution is reached, and water content in the frozen soil changes continuously. Moisture flow in the frozen soil takes place under temperature gradients through the films of unfrozen water. Since the thickness of the unfrozen films decreases with temperature, the rate of water transport also decreases rapidly with decreasing temperature below 0°C. (Key words: Frost; soil moisture.)