Abstract
It is very important to elucidate the mechanism or mysteries in soil freezing and thawing processes, such as the actual situation of freezing or thawing fringe, the effect of initial water content on the maximum frozen depth, the role of each terms of heat balance under different conditions or different periods etc., for the correct understanding and prediction of freezing and thawing phenomena, the prevention of freeze injury, the use of freezing method, and the explication and control of mass transfer in soils as an environmental problem. However it is difficult to be practiced only by measurement method. Herein a numerical experiment method was made by the coupled heat and water transfer model to simulate both the freezing and thawing processes of soil under in situ boundary conditions for a long period and large scale. The dealing method of the ice formation and ice thawing plays a very important role in the simulation, because it affects the convergence and precision principally. Therefore a new method following the mechanism closely (without using any unreasonable or unrealistic assumption) was presented here, which made us possible to simulate especially the thawing process as well as the freezing process more sensitively and reasonably than any previous approach. The frozen or thawed depth was determined due to the definition of frozen soil but not the 0℃ line. All the numerical experiment results of freezing and thawing penetration, frost heave, temperature, liquid water content, ice content and soil particle content profiles at different time responded the mechanism of freezing and thawing processes of soil very well.
