Heat, water and vapor coupled migration in loess under uniaxial freezing condition

Abstract

Water vapor migration induces frost damage to airport runways and highways in loess areas. In this study, the freezing point, soil-freezing characteristic curve (SFCC) and soil-water characteristic curve (SWCC) of Xining loess were measured. While the temperature and water profiles of loess columns under three temperature gradients were obtained by uniaxial freezing tests. Results show that the freezing point of loess is positively correlated with water content in the range of 2.6%–34%, which was well fitted by the Boltzmann function. Unfrozen water content declines more pronounced with temperature at higher water contents and power functions were fitted for SFCC. At higher water contents or lower cold-end temperatures, water migration in soil column is more significant. The above functions were introduced to the non-isothermal heat-water-vapor coupled migration model and numerically implemented in COMSOL Multiphysics. It was verified by comparing with uniaxial freezing test data. Under a given temperature gradient, the lower the freezing point, the smaller the frozen depth, the more insignificant the liquid water migration, and the lower volume fraction of ice. Vapor migration is less affected by freezing point but by vapor density and flux.