Evaluation of hydraulic properties of a frozen soil based on observed unfrozen water contents at the freezing front

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  • 凍結面近傍の不凍水量変化に基づく凍土の水分特性曲線と不飽和透水係数の検討
  • トウケツメン キンボウ ノ フトウスイリョウ ヘンカ ニ モトズク トウド ノ スイブン トクセイ キョクセン ト フホウワ トウスイ ケイスウ ノ ケントウ

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Abstract

We evaluated hydraulic properties of a frozen soil based on the observed temperature, water content, and pressure head near the freezing front in a one-dimensional freezing column experiment for an unsaturated silty loam soil. Amount of unfrozen water near the freezing front was more than equilibrium amount of water according to the retention curve at the equivalent pressure head because freezing was a slow process. We proposed a modified-θ model to describe nonequilibrium amount of unfrozen wa-ter in the retention curve. Coupled heat and water flow equations were simulated with a modified-θ model as well as two other existing hydraulic property models: the clas-sical Harlan model, and the modified-K model. The Har-lan model overestimated water flow from the unfrozen re-gion to the frozen region. Although the modified-K model well simulated water flow in a frozen soil, calculated pres-sure heads and liquid water content showed unrealistic changes at the freezing front due to the extremely large decrease in the hydraulic conductivity. The modified-θ model agreed well with observed liquid water contents and pressure heads in a frozen soil. The unsaturated hy-draulic conductivity of a frozen soil based on the modified-θ model would be more physically feasible than other two hydraulic property models.

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