In this study, a series of one-dimensional freezing deformation tests were conducted within a closed system to evaluate the influence of fines content and initial water content on the frost susceptibility of soils. Also, the pulsed nuclear magnetic resonance (P-NMR) method was adopted to investigate the pore water distribution and deformation mechanism of freezing soils. Results show that as soil temperature decreases, pore water freezes in two stages: the capillary (or free) water freezes first, followed by certain amounts of adsorbed water turned into pore ice. Soil specimens with higher fines content usually have higher unfrozen water content due to the more abundant adsorbed water from fine particles. The initial water content influences the soil-freezing characteristic curve significantly when the fines content is relatively high (e.g., FC = 50%), while this influence becomes negligible with lower fines content. In addition, the freezing deformation properties of soil within a closed system are affected by the initial water content. A higher degree of saturation (e.g., S_r > 0.5) results in frost heave, and a lower degree of saturation (e.g., S_r < 0.4) results in frost shrinkage. In fact, there is a critical degree of saturation (between 0.4 and 0.5) that separates soil's properties of frost heave and frost shrinkage. Frost heave or frost shrinkage of soil depends on which of the two, freezing of pore water or thinning of adsorbed water (i.e., dehydration), is predominant.

本研究在封闭系统内进行了一系列一维冻结变形试验，以评估细粒含量和初始含水量对土壤霜冻敏感性的影响。此外，采用脉冲核磁共振（P-NMR）方法研究冻土的孔隙水分布和变形机制。结果表明，随着土壤温度的降低，孔隙水分两个阶段结冰：毛细水（或游离水）首先结冰，随后一定量的吸附水变成孔隙冰。细粒含量较高的土壤样品通常具有较高的未冻水含量，这是因为细粒中吸附的水较多。当细粉含量相对较高时（例如，FC = 50%），而这种影响在细粉含量较低时可以忽略不计。此外，封闭系统内土壤的冻结变形特性受初始含水量的影响。更高的饱和度（例如，S _r  > 0.5) 导致冻胀，较低的饱和度(例如，S _r  < 0.4) 导致冻缩。事实上，有一个临界饱和度（在 0.4 和 0.5 之间）将土壤的冻胀和冻缩特性区分开来。土壤的冻胀或冻缩取决于两者中的哪一个，孔隙水的冻结或吸附水的变薄（即脱水）占主导地位。