The soil freezing-thawing characteristic curve (FTCC) can reflect the physical and mechanical properties of soil–water system during freezing-thawing (FT) process, which is of guiding significance to the study of soil moisture, heat and matter transport in cold regions. In this study, firstly, according to the evolution law of freezing-thawing hysteresis with freezing-thawing process, revealing the hysteresis mechanisms at different stages based on ice-water transformation theory. The freezing-thawing hysteresis can be divided into four stages as temperature decreasing. The hysteresis of the first three stages are due to nucleation and electrolyte effects, capillarity and pore clogging effects, structural damage effect, respectively; and the last stage is extremely weak and can be ignored. Secondly, evaluating freezing-thawing curves of soil–water system with three pore structures (cylindrical, spherical, and sphere-cylinder binary pore) based on the thermodynamic theory, quantitatively. The upper and lower boundaries of the freezing/thawing characteristic curve with natural pores are those with idealized cylindrical and spherical pores, respectively. Finally, the evaluation index (i.e., hysteresis degree) was introduced to quantitatively describe the variation of unfrozen water hysteresis degree with freezing-thawing process. The relationship between the unfrozen water hysteresis degree and temperature can be divided into four stages. The maximum hysteresis degree was found in the second stage, indicating that hysteresis was most significant in the second stage, followed by the first, third, and fourth stages. Our results provide theoretical support for studying hydrothermal characteristics and water, heat, and solute transport of geotechnical materials in seasonally frozen regions.

中文翻译：

---

基于土壤微观结构的土-水系统冻融滞后机制


土壤冻融特性曲线 （FTCC） 可以反映冻融 （FT） 过程中土壤-水系统的物理力学特性，对寒冷地区土壤水分、热量和物质传递的研究具有指导意义。本研究首先，根据冻融磁滞随冻融过程的演化规律，基于冰水转化理论揭示了不同阶段的磁滞机理。随着温度的降低，冻融滞后可分为四个阶段。前三个阶段的滞后分别是由于成核和电解质效应、毛细管和孔隙堵塞效应、结构损伤效应;而最后一个阶段非常弱，可以忽略不计。其次，基于热力学理论定量评价具有三种孔结构（圆柱形、球形和球圆柱形二元孔）的土-水系统冻融曲线。具有天然孔隙的冻融特性曲线的上边界和下边界分别是具有理想化的圆柱形孔隙和球形孔隙的曲线。最后，引入评价指标（即滞后度），定量描述未冻结水滞后度随冻融过程的变化。未冻结水滞后度与温度的关系可分为四个阶段。滞后度在第二阶段发现最大，表明滞后在第二阶段最显著，其次是第一、第三和第四阶段。 研究结果为季节性冰冻区岩土材料的热液特性和水、热、溶质输运提供了理论支持。