A Review of the Thermodynamics of Frost Heave
Thermodynamic equilibrium requires a balance of thermal, mechanical, and chemical forces. The general equation for mechanical equilibrium between two phases describes capillary effects in porous materials, important in both unsaturated water flow and in understanding ice/water interfaces in freezing...
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| Format: | Text |
| Language: | English |
| Published: |
2000
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| Online Access: | http://www.dtic.mil/docs/citations/ADA381842 http://oai.dtic.mil/oai/oai?&verb=getRecord&metadataPrefix=html&identifier=ADA381842 |
| Summary: | Thermodynamic equilibrium requires a balance of thermal, mechanical, and chemical forces. The general equation for mechanical equilibrium between two phases describes capillary effects in porous materials, important in both unsaturated water flow and in understanding ice/water interfaces in freezing soil. The Gibbs-Duhem equation, which relates changes in chemical potential of a substance to changes in temperature, pressure, and presence of other chemicals, is of critical importance in understanding the flow of water in freezing soils. Osmotic pressure, related to the chemical potential of the substance, is useful in formulating expressions for total soil water pressure because soil water contains solutes, and the influence of soil particle surfaces can be "approximated" as solutes. It is the gradient in the total soil water pressure that drives flow to the freezing front in soils. The generalized Clapeyron equation is utilized by the thermodynamically based models of Miller (1978) and Gilpin (1980). In these models Fourier's Law and Darcy's Law describe heat and mass transfer in the frozen fringe, respectively, and mass flow and heat flow are coupled by one equation that describes heat transfer in the frozen soil. Ice lenses start to grow when the effective stress in the frozen fringe becomes zero (Miller 1978, Gilpin 1980). Once an ice lens is established, liquid water is removed from the adjacent pores because of phase change, and water flows up through the soil to replenish the liquid water. If the rate of water loss caused by phase change is matched by the rate of water flow to replenish the liquid water, the ice lens will continue to grow in thickness. If the hydraulic conductivity of the soil limits the rate of water replenishment to the ice lens for the given rate of heat loss, soil water will freeze at increasing depths with associated changes in the depth and thickness of the frozen fringe. |
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