Features of the study of the unfrozen water content in permafrost soils under oil-salt contamination

The aim of the study was to investigate the effect of oil-salt pollution on moisture due to unfrozen water in clay and to identify methodological peculiarities when working with soils containing oil. The object of the study was a model clay soil, and tests were conducted on model samples. The research was conducted for "clean," saline, and oil-contaminated soils, as well as soils with oil-salt pollution. The authors pay special attention to aspects such as the preparation of soil pastes, as laboratory modeling of such a complex system as "soil-water-ice-salt-oil" is associated with a number of methodological peculiarities. The authors also highlight the requirements and methods traditionally used in conducting engineering and geological surveys in accordance with regulatory documentation. The tests were carried out using standard contact and cryoscopic methods. For comparison, tests were conducted using nuclear magnetic resonance (NMR) method. The moisture due to unfrozen water in a wide temperature range for soils with oil-salt pollution was investigated for the first time. When examining this characteristic, not only was the dependence of unfrozen water content on temperature obtained, but the limitations of standard methods for determining moisture due to unfrozen water were also identified. It was established that the contact method for determining moisture due to unfrozen water cannot be applied when investigating unsalinated and saline soils containing oil. To obtain correct results, methods should be used that do not change the ratio of oil, water (or solution), and ice. The results of the cryoscopic and NMR methods showed that the effect of oil-salt pollution on the content of unfrozen water is identical to the effect of salinity, with a discrepancy of less than 8%.