Abstract: In the natural state, the moisture content of the soil in the unsaturated loess ground is low, resulting in the poor compaction effect of the loess ground by the heavy ramming method, which cannot meet the requirements of ground bearing capacity. Thereby, how to humidify the loess ground has become the focus of the research. In order to study the humidification effect of unsaturated loess under the action of water vapor, the water vapor humidification model experiment was carried out with the unsaturated loess as the research object, and the variation of water vapor diffusion rate, temperature and gas transport with time under different water vapor pressure gradients, the number of flower tube openings and the spacing of open holes were analyzed. The results show that the humidification of water vapor is a dynamic change process in which the moisture content gradient, pressure gradient and temperature gradient are coupled and interact with each other, of which the temperature gradient is the main factor affecting the transport of water vapor. After the water vapor is introduced into the soil, the volumetric moisture content, air pressure and temperature at each measurement point with the passage of ventilation time, all show two stages of rapid rise-gradual stabilization. In the test, Increasing water vapor pressure results in significant changes in the degree and range of humidification, and raising the number of open pores, the uniformity of soil humidification increased. Reducing the spacing between the opening pores and the degree of humidification does not change much. The research results can provide certain experience for the engineering of water vapor humidification of unsaturated loess foundations.

Key words: unsaturated loess, water vapor diffusion, temperature changes, changes in barometric pressure, water content