Heat, water and solute transfer in saline loess under uniaxial freezing condition

Salt weathering of loess slopes in the seasonally frozen region is closely related to water and salt migration induced by temperature gradient. This paper carried out uniaxial freezing tests on sodium sulfate saline loess with three temperature gradients considered. Visible cracks are developed in the frozen domain during testing while little change noted in lower unfrozen part. The lower the cold-end temperature, or the higher the temperature gradient, the less developed cracks emerge. At higher temperature gradients, the freezing front descends more rapidly, corresponding to higher freezing rates and larger maximum frozen depths. Synchronous variations were found in water and salinity profiles, with peak values near the frozen fringe. An improved Harlan model was then established for heat-water transfer in freezing soils, incorporating an impedance factor. Considering the convection and diffusion of solute, the models for salinity field were proposed based on Darcy's and Fick's law. Numerical simulations were carried out on the coupled heat-water-solute transfer in freezing saline loess columns. Comparisons of calculated and measured data prove the rationality of the models. Finally, dynamic changes of unfrozen water content and the influence of freezing point on thermal regime, water and salinity profiles were discussed.