Chemical factors in soil freezing and frost heave

Abstract

Chemical factors that are essential in frost heaving of soils are examined through consideration of the process of ice formation in soils and the role of temperature gradients in generating water potential gradients in freezing soils. Unfrozen films are maintained around soil particles in frozen soils. The osmotic potentials at the ice–water interface of the unfrozen films and in the frozen fringe, the thin zone between the frozen and unfrozen soil, generated by dissolved salts and exchangeable cations that satisfy soil particle surface charge, are controlled by the local temperature. The coldest location and the most negative osmotic potentials at the ice–water interface are located immediately below the base of the ice lens, in the unfrozen films that separate the underlying soil particles from the ice lens. An osmotic potential gradient is generated because the osmotic potential at the water–ice interface in the frozen fringe becomes less negative with increasing temperature and distance from the ice lens. As water freezes onto the ice lens, re-supply of water to the unfrozen film along the osmotic potential gradient is the temperature-gradient-induced mechanism that generates the force that lifts the overlying frozen soil. Models that recognize this driving mechanism should improve predictions of soil freezing and frost heave, analysis of contaminant transport in freezing and frozen soils, and other aspects of the soil-freezing and frost-heave processes.