Water Vapor Migration and Phase Change Mechanism of Unsaturated Cohesive Soil Subgrade

In areas with sparse rainfall and deep groundwater, the internal water transport in unsaturated embankments is mainly dominated by water vapor transport. The phase change during the transport process will cause the transformation of energy within the soil, resulting in road deformation and subgrade strength attenuation. Small-scale model tests were conducted to investigate the mechanism of water vapor transport and phase change in unsaturated embankments. The results indicate that the main factors affecting the water vapor transportation of the subgrade include: moisture gradient, initial moisture content, test time, and environmental temperature. The proportion of gaseous water transport in total water transport increases with the increase of experimental time. The freezing condition is crucial and will cause a significant increase of water content in shallow soil of the subgrade, while the magnitude of the freezing temperature has little effect on the increase of water content in shallow soil. Under the same temperature gradient, at low initial moisture content, the transport of gaseous water in the soil is dominant. On the contrary, at high initial moisture content, the transport of liquid water is dominant. When the initial moisture content is greater than a certain value, under the action of gravity potential, the soil sample will experience downward water transport under no temperature gradient. Due to environmental temperature, the driving force of gaseous water transport is significantly greater than that of liquid water transport. © 2023 Chinese Society of Civil Engineering. All rights reserved.