基于孔隙结构的土体未冻水含量滞回效应研究

冻结特征曲线（SFCC）是描述负温与土体内部未冻水含量之间的关系曲线，是非饱和冻土研究的重要基础。冻融循环是冻土研究的关键因素。以粉土和黏土为试验对象，采用低场核磁共振（NMR）技术，测得了土体在冻融循环作用下的冻结特征曲线和孔隙结构分布图，研究土体在冻融循环作用下冻结特征曲线的变化。试验结果表明：随着循环次数的增加，土体孔隙分布发生了变化，进而导致冻结特征曲线滞回圈和特征温度点的变化，冻结特征曲线变化的本质是孔隙结构的变化；从微观结构出发得到了基于孔隙结构的SFCC表达式，指出融化过程的冻结特征曲线是主冻结特征曲线；结合试验数据的对比分析，模型有效展示了多次冻融循环下土体冻结特征曲线的滞回效应，适用于多次循环下的非饱和冻土。

Hysteresis Effect of Unfrozen Water Content in Soil Based on Pore Structure

Soil-freezing characteristic curves (SFCC) are used for describing the relationship between negative temperature and the unfrozen water content. The SFCC and freezing-thawing cycle are essential factors in investigating unsaturated frozen soil. In this study, the tested soil materials were silt and clay, and the freezing-thawing cycle was determined using the low-field nuclear magnetic resonance technique, which can be used to plot the SFCC and examine the pore structure distribution of the soil. The results show that the pore distribution of soil changes with the increase in cycle time. The pore distribution of soil influences the hysteresis of SFCC and the change point of the characteristic temperature. Therefore, the change in the SFCC indicates variation in the pore structure. Based on the microstructure, the SFCC expression based on the pore structure was obtained. The SFCC of the melting process is the main freezing characteristic curve. Combined with a comparative analysis of experimental data, the proposed model conclusively shows the hysteretic effect of multiple freezing-thawing cycles. The model is suitable for analyzing unsaturated frozen soils under multiple cycles.