Abstract The unfrozen water content has a significant impact on the mechanical and thermal properties of saline soils during freezing, and their electrical properties measured by electromagnetic sensors can be a promising proxy of the unfrozen water content. This paper investigated the electrical properties and their relationship with the unfrozen water content of saline lean clay. Specimens with increasing concentration of sodium chloride were prepared for assessing their initial freezing points and unfrozen water content by the cooling test and the nuclear magnetic resonance relaxometry, respectively. In addition, the apparent dielectric permittivity and bulk electrical conductivity were measured by sensors based on frequency-domain reflectometry in the electrical property test. A significant variation was observed in both the apparent dielectric permittivity and bulk electrical conductivity of saline lean clay near the initial freezing point. They generally decreased linearly with decreasing temperatures above their initial freezing points and then dropped according to a power curve with temperatures below their initial freezing points. The bulk electrical conductivity of saline lean clay depended on salt concentration and ion conductive pathway, with the latter being dominant at temperatures below its initial freezing point. A new empirical equation was proposed for estimating unfrozen water content based on the apparent dielectric permittivity and initial salt concentration, and independent data validated its applicability of similar soils at relatively low salt concentrations. The proposed equation could be useful for the evaluation of the unfrozen water content of saline lean clay via the apparent dielectric permittivity and initial salt concentration.

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冻盐粘土的电学性质及其与未冻含水量的关系

摘要 未冻水含量对冻结过程中盐渍土的力学和热学性质有显着影响，通过电磁传感器测量的其电学性质可以作为未冻水含量的有希望的代表。本文研究了贫盐粘土的电学性质及其与未冻水含量的关系。制备氯化钠浓度增加的样品，分别通过冷却试验和核磁共振弛豫测定法评估其初始冰点和未冷冻水含量。此外，在电性能测试中，表观介电常数和体电导率由基于频域反射计的传感器测量。在初始凝固点附近观察到贫盐粘土的表观介电常数和体积电导率的显着变化。它们通常随着高于其初始冰点的温度降低而线性下降，然后根据温度低于其初始冰点的功率曲线下降。贫盐粘土的整体电导率取决于盐浓度和离子传导途径，后者在低于其初始冰点的温度下占主导地位。基于表观介电常数和初始盐浓度，提出了一个新的经验方程来估计未冻结水含量，独立数据验证了其在相对低盐浓度下类似土壤的适用性。