EXPERIMENTAL STUDY OF MIGRATION OF IONS OF DISSOLVED SALT NaCl DURING VERTICAL FREEZING OF THE GROUND

Abstract

The work is devoted to the laboratory investigation of the causes of cryopeg formation – objects of cryolitosones of natural or man-made character, which are lenses of supercooled pore solution in the environment of frozen fluid stop. In particular, processes promoting cryogenic concentration of salts, as well as peculiarities of laboratory experiment are considered. The paper describes the experimental installation and procedure of experiment on controlling freezing–thawing of soil in closed volume – vertical heat-insulated cylinder, in which heat transfer was carried out through end sides according to preset algorithm. The experiment repeated the situation typical for the autumn-spring period: the daily freezing and thawing of wet soil contaminated with easily soluble salts. Four series of experiments were carried out with different number of repeated cycles of freezing front and thawing front motion in soil saturated with concentrated salt solution NaCl directed from top to bottom at a distance of 70-80% from cylinder height. At the same time, the lower area was always supported in the thawed form. The paper considers the phenomena and introduces the probable explanation for processes accompanying soil freezing and thawing, such as decrease of freezing start temperature in vertical section, formation of thermal barrier in direction of freezing front movement in low-temperature area, redistribution of salt ions along vertical section, dependence of concentration gradient on number of freezing – thawing cycles, deviation of melting temperature value in comparison with freezing start temperature. Numerical values of moisture redistribution and solution concentration in soil after each series of experiments were obtained. Methods of modernization of experimental installation and carrying out the experiment are proposed.

Keywords

• cryopegs
• freezing front
• salt concentrating
• phase transition
• freezing beginning temperature