PSI - Issue 17

O. Plekhov et al. / Procedia Structural Integrity 17 (2019) 602–609 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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for the presence of water bearing horizons in the vicinity of hydro-observation well GN2.

Table 1. Physical and mechanical parameters of the soil in the area of water feeding of the hydro-observation well GN2. Physical quantity value Water density, kg/m 3 1000 Ice density, kg/m 3 900 Density of dry skeleton, kg/m 3 2590 Porosity 0.69 Heat capacity of water, J/(kg*K) 4191 Heat capacity of ice, J/(kg*K) 2000 Heat capacity of skeleton, J/(kg*K) 770 Thermal conductivity of water, W/(m*K) 0.591 Thermal conductivity of ice, W/(m*K) 2.39 Thermal conductivity of dry skeleton, W/(m*K) 2.9 Latent heat, J/kg 332430 Phase transition temperature, K 271.03 Initial temperature, K 279.45 Initial moisture content 0.27 Initial ice content 0 Air density, kg/m 3 1.369 Thermal conductivity of air, W/(m*K) 2.28e-2 Heat capacity of air, J(kg*K) 1009 a 0 18 T  , K 2

To analyze the specific features of each of the models considered, we successively solved three problems, in which the cryogenic migration produced different effects on the peculiarities of the process. The first problem concerned the propagation of the phase transition front from a single freeze pipe. In the case of propagation of a single-phase transition front in an infinite medium, the main parameter to be determined is the front velocity. In the second problem, we considered the process of coalescence of two freezing zones. In this case, the processes of cryogenic migration had a significant effect on the distribution of ice content in the closure region and thus, on the strength of the AGF system. In the last problem, we investigated the growth of a closed ice wall and, the resulting drop of moisture in the internal zone. Figure 2 compares the data obtained by the above two models after ten days of operation of the freeze column. The solution for standard two-phase model (used in Comsol) is added to the figure for comparison.

Fig. 2. Distribution of ice content along the radial line (the red curve is calculated by model 2, the blue curve - by model 1, the purple curve corresponds to the base Comsol model).

All the models predicted approximately the same radius of the frozen zone in the soil. However, the structure of the zone of water and ice coexistence and that of the frozen zone differs significantly. The cryogenic flow leads to an increase in the fraction of ice and should be taken into account in estimating the stress-strain state and strength of the AGF system. The cryogenic migration of moisture can produce a fairly strong effect on the process of coalescence of frozen