Study on the Effect of Temperature on the Soil-Water Characteristics of Sodium Sulfate-Bearing Loess

Sulfate saline soils widely exist in Northwest China. During the alternation of seasons, water and salinity will produce phase changes, which will cause changes in the matric suction of saline soils. Therefore, taking sodium sulfate loess as the research object, freeze-thaw experiments with different salinity and compaction degrees were designed. The results show that the change of sodium sulfate content and dry density has limited influence on the curve shape of soil temperature and unfrozen water content; The frozen water content decreased significantly with the decrease of temperature, and there was a hysteresis effect of the unfrozen water content in the process of alternate freezing and thawing. In the process of temperature decrease, under the same salt content, the initial value of matric suction increases with the increase of dry density; when the dry density is the same, the initial value of matric suction increases with the increase of salt content; in soil Before freezing, the matric suction of soil samples increases linearly with decreasing temperature. The soil will undergo a phase transition due to the presence of sodium sulfate. The primary phase transition only obviously exists in the soil sample with a salt content of 4% at about 12 ℃. At this time, the matric suction of the soil sample has a sudden change of about 100 kPa; the secondary phase transition The transformation occurred in all the test soil samples at negative temperature, and the soil with higher salinity had a smaller increment of matric suction during the secondary phase transformation process. The research in this paper can provide an important reference for the study of water-salt phase transition and water migration dynamics of sodium sulfate saline soil.