Freezing processes in saturated soils

When a soil saturated with water is subject to freezing, a volume expansion can generally be observed. The increase in volume is due not only to the different densities of water and ice, but mainly to a water migration process that is transported from the base of the soil up to an intermediate region where the change of phase occurs. It is generally accepted that a transition region, called frozen fringe, where ice and water coexist in the porous space, separates the unfrozen from the frozen part of the soil. Immediately over the frozen fringe a pure segregated layer of ice (ice lens) can form. If the freezing process is too fast or the weight acting on the soil (overburden pressure) is relevant, the porous matrix does not separate and the shifting of the frozen fringe towards the base of the soil (frost penetration) is observed. Many mathematical models have been proposed for the frost heave process. The main features of the one-dimensional model we are considering are summarized in Sec. 1. In Ref. 9 the case of assignment of the boundary thermal fluxes (at the base and on top of the soil) is studied. In practical cases, sometime the boundary temperatures, instead of the thermal fluxes, can be registered or imposed: in this paper we will investigate the model in such case. The main purpose is to detect which are the boundary values for temperature that determine the process of lens formation or frost penetration, once the properties of the soil are known.