ИСТИНА

The phase composition of saline frozen soils is a standard parameter for foundation design in Russia (Soil bases and foundations on permafrost soils, Appendix B, 2012). Saline frozen soils have lower deformation and strength properties, lower freezing temperatures and high unfrozen water content. The objective of the study is accurate identification of phase composition using field and laboratory data of frozen soils that is improving a design. The phase composition of frozen soils was investigated using thermodynamic modeling method on the basis of the Pitzer model. Algorithm of phase composition calculation is as follows: freezing temperature (FT, °C) and unfrozen water content (UWC, %) using software «FREEZBRINE»; FT and UWC including soils water content; FT and UWC including solid soil particles influence; heat capacity of soil (J/kg*°C). Input data are: soil and water chemical composition; water content (%), plastic limit (%), plasticity index of soils (%); soil density (g/cm3), dry soil density (g/cm3), solid particles density (g/cm3). Output data are freezing temperature of soils and solutions, unfrozen water content. Nearly 80 soil samples (sands, sandy loams, loams, and clays) from onshore and offshore at Yamal and Gydan peninsulas were analyzed. The freezing temperatures of sands ranges from -3,32 to -0,37°C; of loams from -10,32 to - 0,27°C. The possible cause is an increased salinization (up to 7 %) of several samples offshore and onshore. This potential salinization anisotropy must be taken into account in foundation design. Standard deviation of the some measured and calculated freezing temperature is 0,2°C for sands and 0,7°C for loam. The calculated values of FT are higher than measured. This may be caused by the presence of organic matter in the soil. The results are using for geotechnical and thermal models. For example, to calculate the soil thawing under the foundation or to predict the change of soil 137 temperature. Also, unfrozen water content is a necessary parameter for soils heat capacity calculation that is potentially interesting for the design of thermosyphons.