Account for the Process of Underground Condensation in Modeling Heat and Moisture Exchange in Frozen Soils

A mathematical model of heat and moisture transfer with account for condensation and evaporation of underground moisture during seasonal thawing of permafrost is considered. The motion of moisture can be described with the aid of transfer equations in its moisture content-governing or potential forms in saturated and nonsaturated soils. Based on experimental and full-scale data, verification of the parameters of underground condensation and evaporation of the pore moisture has been made. Numerical realization of the set nonlinear problem of heat and moisture transfer is made by the finite-difference method with the use of the Newton method. The adequacy of the proposed model of seasonal thawing of perennially frozen soils is shown. As a result of numerical experiment under the conditions of Central Yakutia, it has been established that with account for the condensation of underground moisture the overall moisture content of the soil increases. In the spring–summer period, an intense process of evaporation of the underground moisture and lowering of the temperature are observed, while in the summer–autumn period, an increase in the heat content of the soil is observed with increase in the quantity of condensate fallout. At the end of the summer season, in September and at the beginning of October, the choking of the moist thawed layer occurs. The proposed mathematical model with account for the process of underground condensation more adequately reflects the process of freezing of the zone of "choking." These results are indicative of the adequacy of the improved model and of the possibilities of using it for predictions.