Soil pore size distribution (PSD) is typically used to predict the soil freezing characteristic curve and estimate the hydrological and mechanical properties during freeze–thaw cycles. However, direct measurements of frozen soil PSD remain a great challenge. This study proposed a method to determine the PSD of frozen soils based on nuclear magnetic resonance (NMR) relaxometry. Tests were performed on a saturated chloride silt soil at different salt contents (0.3, 1.0, 2.0, and 3.0%) and temperatures (between –30 and 0 °C) during a freeze–thaw cycle. The NMR‐detected PSD (only accounting for pores occupied by unfrozen water) varied with soil temperature, salt content, and freeze–thaw cycle. The sequence of the water–ice phase change and hysteresis were also identified in a freeze–thaw cycle. A regression analysis was performed on the cumulative NMR‐detected PSD via a variant van Genuchten model. The critical freezing pore radius and the thickness of unfrozen water film were computed and used to transform NMR‐detected PSD into the actual PSD of frozen soils on the basis of a pore radius transformation equation established in this paper. Notably, the actual PSD accounted for pores occupied by ice and unfrozen water. The actual PSD indicated that the water–ice phase change was more pronounced in macro‐ and mesopores, especially at lower temperatures and salt content. A comparison between the calculated average pore size and those presented in other studies showed that the proposed technique is a valuable alternative for the prediction of actual frozen soil PSD.

中文翻译：

---

通过核磁共振弛豫法表征冻融过程中氯化物淤泥土壤的孔径分布

土壤孔径分布（PSD）通常用于预测土壤的冻结特性曲线，并估算冻融循环中的水文和力学特性。但是，直接测量冷冻土壤的PSD仍然是一个巨大的挑战。这项研究提出了一种基于核磁共振（NMR）弛豫法确定冻土PSD的方法。在冻融循环中，在不同盐含量（0.3、1.0、2.0和3.0％）和温度（–30至0°C之间）的饱和氯化物淤泥土壤上进行了测试。NMR检测的PSD（仅考虑未冻结水占据的孔隙）随土壤温度，盐分含量和冻融循环而变化。在冰冻融化循环中还确定了水冰相变和滞后的顺序。通过变型van Genuchten模型对累积NMR检测的PSD进行了回归分析。根据本文建立的孔半径转换方程，计算了临界冻结孔半径和未冻结水膜的厚度，并将其用于将NMR检测的PSD转换为冻结土壤的实际PSD。值得注意的是，实际的PSD解释了被冰和未冻结的水占据的孔隙。实际的PSD表明，大孔和中孔的水冰相变更为明显，特别是在较低温度和较低盐含量下。将计算出的平均孔径与其他研究中给出的平均孔径进行比较表明，所提出的技术是预测实际冻土PSD的有价值的替代方法。根据本文建立的孔半径转换方程，计算了临界冻结孔半径和未冻结水膜的厚度，并将其用于将NMR检测的PSD转换为冻结土壤的实际PSD。值得注意的是，实际的PSD解释了被冰和未冻结的水占据的孔隙。实际的PSD表明，大孔和中孔的水冰相变更为明显，特别是在较低温度和较低盐含量下。将计算出的平均孔径与其他研究中给出的平均孔径进行比较表明，所提出的技术是预测实际冻土PSD的有价值的替代方法。根据本文建立的孔半径转换方程，计算了临界冻结孔半径和未冻结水膜的厚度，并将其用于将NMR检测的PSD转换为冻结土壤的实际PSD。值得注意的是，实际的PSD解释了被冰和未冻结的水占据的孔隙。实际的PSD表明，大孔和中孔的水冰相变更为明显，特别是在较低温度和较低盐含量下。将计算出的平均孔径与其他研究中给出的平均孔径进行比较表明，所提出的技术是预测实际冻土PSD的有价值的替代方法。