Mechanisms of ice lens formation in freezing soils.

Frost heave is a process in which the ground swells upon freezing. This phenomenon plays a central role in the formation of unique geological features in permafrost areas. Frost heave also causes annual damage to roads and buildings in northern climates. During the freezing process regions of nearly pure ice (ice lenses) form in the soil. Similar phenomena occur during the freezing of tissue, food products, and many other materials. In the last several years, the first experiments capable of viewing the formation of ice lenses in a well-characterized model soil consisting of glass beads in water have been performed. These experiments have yielded insight into the basic mechanisms behind frost heave. Recently we have developed mathematical models of these experiments. Our models indicate that ice lenses can form via three distinct mechanisms: nucleation of ice beyond a compacted layer of particles, periodic rejection and engulfment of particles by the ice front, and (in highly colloidal soils) morphological instability of the solidification front. The interplay between these mechanisms could explain some of the great variation in ice lens structure and orientation seen in real soils.