THE MECHANISM OF FROST HEAVING IN SOILS

The "mechanism of frost heaving" involves the interaction of the three frost action factors: a water supply, a frost- susceptible soil, and below-freezing temperatures. The propagation of ice between soil particles depends on pore size, that is, the smaller the pores and channels between pores, the lower the temperature necessary before the ice front can advance. This provides a means for supercooling the pore water beneath an actively growing ice lens. The subsequent release of energy in such systems is utilized to create a moisture suction gradient which induces a moisture flow to the ice front and also to develop a positive pressure to raise the overburden and provide a space for the ice lens. Consistent with the theory, it can be shown that compact clay soils, which have the greatest resistance to ice propagation, can develop the largest moisture suction and heaving pressure in a closed system and coarse-grained soils, the lowest. In the over-all phenomenon of frost heaving the most difficult combination of related processes to treat, even on a semi-quantitative basis, is the heat and moisture flow. This difficulty arises not only from the complexity of the mathematics but also from the lack of experimental measurements of heave rates, heat flow, moisture flow, temperature distributions, and moisture tensions while ice lensing is in progress. In the absence of such information the quantitative treatment of the combined heat and moisture flow appears impossible.