Development Of Separated Ice Model Coupled Heat And Moisture Transfer In Freezing Soils

There are so many hazards associated with excessive frost heave in cold regions and engineerings using artificial freezing method. Study on the mechanism of frost heave in freezing soils has been put great effort on, lots of frost heave models have been proposed by researchers, however, some different opinions still exists. Separated ice model represents characteristics of segregation ice, but some shortcoming exists, such as rigid soil porosity, ignorance of overburden pressure, critical separation pressure using empirical value. Based on the separated ice model, considering overburden pressure, deformation of soil porosity and critical separation pressure, we formulated governing equations coupled heat and moisture transfer and built up frost heave model which could explain the evolving rules of segregation ice during soil freezing. Frost shrink phenomenon was obtained during the initial period of soil freezing by numerical calculation. Finally, the evolving rules of segregation ice in different overburden pressure were studied by tests and calculations.Heat transfer differential equation was deduced based on the law of Conservation of Energy and Fourier Law; setting equivalent water pressure as driving force of water migration, moisture transfer differential equation was deduced based on the law of Conservation of Mass and Darcy Law. Soil particles and ice phase were supposed as rigid medium, soil skeleton was thought as elastomer, considering the influence of overburden pressure and deformation of soil porosity, governing equations coupled heat and moisture transfer in soil freezing were formulated. Formation standard of segregating ice was improved by using moisturefilm pressure in ice-water interface as the collapsing force, which means the segregation ice would be born when the collapsing force overcome the overburden pressure and tensile strength of soil. Separated ice model coupled heat and moisture transfer was developed by combining the governing equations and improved formation standard of segregating ice.This paper carried out split tests on high-temperature frozen soils in the temperature range of frozen fringe, obtained tensile strength of high-temperature frozen soils which varied from 0 to -2.0℃, supplied important parameters for numerical calculations.This paper discretized governing equations and definite conditions using finite volume method, calculated with Matlab and conducted comparison of calculated and experimental results, which confirmed the model feasible. Frost shrink was obtained during the initial period of soil freezing by numerical calculation which agreed well with experimental results. Frost heave model using rigid porosity assumption can not obtain frost shrink by the way of numerical calculation, because it assumes that soil porosity does not change any more during the whole process of soil freezing, only segregation ice is calculated in the formation of frost heave. Therefore, calculated frost heave using rigid porosity assumption can not be less than zero.Frost heave tests were carried out using saturated granular soils, the results showed that water uptake and frost heave diminished with the increasing of overburden pressure, and the mechanism of tests phenomenon was explained. Based on resistance variation of soils in the process of soil freezing, a new device of measuring frost depth was proposed. Frost depth results using new device agreed well with the thermal couple results. The evolving rules of segregation ice were studied by using visual equipments and binarization processing of images in frost heave tests. The average segregation rate of saturated silty clay and yellow clay were acquired, and fitting functions of average segregation rate with overburden pressure were obtained.The evolution rules of segregation ice were calculated by using frost heave model proposed in this paper, the results agreed well with experimental results. The calculated results showed that segregation ice thickness decreased exponentially with the increase of overburden in the process of soil freezing.This paper has 110 Figures, 21 Tables and 138 References.