Abstract:

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.

Key words: premelting, unfrozen water content, equivalent particle size, impurity density, surface charge density