Release:
2018, Vol. 4. №4About the authors:
Boris V. Grigoriev, Cand. Sci. (Tech.), Associate Professor, Department of Applied and Technical Physics, Institute of Physics and Technology, University of Tyumen; b.v.grigorev@utmn.ruAbstract:
Industrial development of cryolithic zone is often followed by thermal regime change and surface layer’s ion balance disruption. Accumulation of thermal energy and highly soluble salts in the ground’s surface layer leads to an increase of thawing depth and ground salinization on significant depths. Similar phenomena can also happen outside of the seasonal thawing depth range. After pore solutions spend years migrating and concentrating in the permafrost, cryopegs are formed inside the underlying rock formations. Cryopegs are lenses of thawed highly-mineralized pore solutions surrounded by frozen ground.
Cryopegs are widely distributed throughout the permafrost. They decrease the load bearing capacity of formation grounds and cause corrosion of concrete and metallic constructions. Currently cryopegs are underexplored in Russia and the rest of the world, therefore, detailed investigation of this cryologic object is required, in particular, in laboratory conditions.
This article studies the migration of salt ions in the pore water during the motion of the freezing front. In order to investigate the subject, the authors developed an experimental unit and created a measuring unit where studied moist grounds are inserted. Temperature can be set on the opposite sides of the experimental unit. Controlling the extent and speed of temperature change provides a means to regulate freezing front movement (directed from top to bottom). After a number of freezing-thawing cycles salt compositions and concentrations are checked and measured in four intervals of sampling.
Two series of experiments yielded an unexpected result: a significant increase in salt concentration (24% and 29%) in the freezing front movement starting area. It can be explained as a result of a concentrated solution mass-transfer to the crystallization centers due to osmotic powers, which is a viable explanation as clayey, pulverulent grounds were used in the study. These grounds have a large active surface area and a high unfrozen water content.
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