Abstract: Temperature gradient, moisture gradient and pressure gradient significantly affect hydrothermal migration in unsaturated soils. The unsaturated loess sample under 0.10 MPa of high-temperature water vapor is tested to study the hydrothermal migration under the gradients of steam pressure, temperature and moisture. The results show that the high rate of temperature rise, and water vapor humidification observed within the range of water vapor migration and the steam humidification are mainly driven by steam heat transfer and pressure gradient. In the region beyond water vapor migration, the heat conduction caused by temperature gradient and water migration driven by moisture gradient coupled with temperature gradient are the main factors. Under the influence of soil particle obstruction and steam pressure dissipation, the rate of soil heating, humidification and temperature diffusion decrease with the increase of radial distance, and the rate of humidification is less than temperature diffusion. The maximum moisture content of water vapor humidified soil is close to the optimal moisture content, and the humidifying effect is good, which can effectively improve the compaction performance of soil within a certain range. Based on the boundary conditions of the model test, a set of algebraic explicit special solutions to the two-dimensional heat-wet migration equation in a moist porous medium is determined. The measured and calculated values of temperature and water content are compared and analyzed at 20 cm measurement points. The results can provide theoretical support for the research on the transmission of water-vapor-thermal in unsaturated loess and the new technology of water vapor humidification.

Key words: unsaturated loess, moisture-heat coupling migration, humidification, model test, analytical solution