Water and Salt Migration with Phase Change in Saline Soil during Freezing and Thawing Processes
Water and salt transfer coupled with phase change may cause serious damage to engineering structures in saline soil regions. In this study, the migration of water and salt in silty clay collected from the Qinghai‐Tibet Plateau is explored experimentally and numerically during freezing and thawing processes. The results revealed that there are significant differences in the variations of liquid water content and solution concentration for different initial salt contents, due to salt crystallization and dissolution. The temperature‐induced water migration is determined by the soil properties, which can be well explained by the thermodynamics of mass transfer. The amount of salt migrated upward during cooling is slightly larger than that transported downward in the warming period, implying that salt may be accumulated in the surface soil after a large number of circulations and finally result in soil salinization.
Heat, water and solute transfer in saline loess under uniaxial freezing condition
Abstract 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.
Adrenocorticotropin insensitivity syndromes.
I. Introduction II. Familial Glucocorticoid Deficiency A. Clinical presentation B. Investigation C. Treatment D. Pathogenesis III. Triple A Syndrome A. Clinical features B. Treatment C. Pathogenesis D. Mapping of triple A syndrome gene E. Candidate genes IV. Acquired ACTH Resistance V. Conclusions