关键词: 冻土, 未冻水含量, 比表面积, 冻结温度, 核磁共振

Abstract: The soil-freezing characteristic curve (SFCC) is significantly affected by the specific surface area of soil particles. The existing studies about the relationship between the SFCC and the specific surface area so far have mainly taken natural soils as research objects, which cannot avoid the interference of other factors such as dry density and total water content, and the test data obtained are discrete. In the present study, Qinghai-Tibet silty clay and bentonite are mixed in different proportions to prepare artificial soils with various specific surface areas. The temperature-controlled nuclear magnetic resonance (NMR) test and the freezing temperature test are conducted on these artificial mixtures. The test results indicate that: (1) In comparison with the classical three-stage SFCC, the SFCC of the mixtures consists of four stages, i.e., the super-cooling stage, the rapid-drop stage, the slow-drop stage, and the stable stage. As the specific surface area increases, the changing range of the unfrozen water content (wu) in the rapid-drop stage narrows, correspondingly the changing rate of wu in the slow-drop stage and wu in the stable stage both increase. (2) As for the temperature-time relationship curve obtained from the freezing temperature test, the duration of its isothermal stage decreases with the rise of specific surface area, while its corresponding freezing temperature decreases. (3) According to the evolution of transverse relaxation time distribution curve with temperature, it is found that the mixture with a larger specific surface area has a higher content of bound water. Bound water is strongly constrained around soil particles and exhibits lower freezing temperature, making the mixture with the larger specific surface area more difficult frozen, which is the rudimentary reason that the specific surface area influences the SFCC.

Key words: frozen soil, unfrozen water content, specific surface area, freezing temperature, NMR