未冻水含量改变直接影响冻土的热力学及变形特性,也是水热数值计算的关键条件。为了探究未冻水含量变化规律,首先采用等效粒径表征土颗粒粒径分布,将土体简化成等效粒径球状堆积体系。其次考虑简单立方堆积和立方最密堆积平均的堆积方式,基于多孔介质预融理论,提出土中未冻水含量的计算方法,并通过试验数据验证其合理性。最后分析了杂质密度以及有效粒径大小对水膜厚度以及未冻水含量的影响。研究结果表明：土颗粒表面电荷密度引发的自由能对水膜厚度的改变极易受杂质浓度的影响,随着浓度增大,土颗粒表面电荷对水膜的影响越来越小。土中液态水含量主要由土颗粒表面水膜厚度变化来决定,当等效颗粒减小时,通过间隙水求解的未冻水体积比例逐渐增大,并且在较低浓度时发挥更大作用。对于较大颗粒土,未冻水含量模型预测效果好。当粉质黏土、黄土、砂土等效粒径分别缩小0.28、0.3、0.36倍时,未冻水体积含量计算结果与试验值吻合较好。

The variation of unfrozen water content directly influences the thermodynamics and deformation properties of frozen soils, and it is also the key condition for water-heat coupled simulations. In order to study this variation, the distribution of soil particle size was used to an equivalent particle size, and soil was simplified to the equivalent particle size spherical packing system. Based on the premelting theory in porous medium, the calculation method of unfrozen water content in soil was put forward with the considered average packing system of simple cubic packing and cubic close packing, and the accuracy was verified by the experimental data. Moreover, the effect of impurity density and the equivalent particle size on water film thickness and unfrozen water content was analyzed. The results show that the thickness of water film calculated using the surface charge density of soil particles was easily affected by impurity concentration, and the effect of surface charge density on water film was progressively reduced as the impurity concentration increased. The liquid water fraction was mainly determined by the variation of water film thickness on the surface of soil particles, and the contribution of interstitial water to the total liquid fraction increased as the equivalent particle size decreased, especially at low impurity concentrations. Moreover, the model of unfrozen water content produced better predictions in larger particle soils. The calculated values of volumetric unfrozen water were close to the experimental values when the equivalent particle sizes of silty clay, loess, and sand were reduced by 0.28, 0.3, and 0.36, respectively.