Water-vapor-heat behavior in a freezing unsaturated coarse-grained soil with a closed top

A series of one-side freezing experiments with closed tops were performed to illustrate moisture migration and frost heave mechanisms of the coarse-grained soil for high speed railway subgrades in cold regions, as well as silty clay and standard sand as controls. The experimental results show that the pot effect can be formed in the soils with different unsaturated porosities when their tops are closed. The vapor migration and frost heave of unsaturated soils become more significant under larger temperature gradient. Water supply can not determine the formation of the pot effect, and only influence its intensity. Vapor migration is prominent when the initial water contents of soils are low (e.g. saturation of 30%), however, the water migration is dominant when the initial moistures of soils are high (e.g. saturation of 70%). It is also found that the initial water contents of the soils only influence the in-situ frost heave amounts; however, the total frost heave amounts are related to the combined actions of soil frost susceptibility and water migration, etc.