Effect of different freezing modes on the water-heat-vapor behavior in unsaturated coarse-grained filling exposed to freezing and thawing

Abstract

A series of experiments are carried out for different freezing modes during freezing and thawing to study the water-heat-vapor behavior in the coarse-grained soil (CGS) of high-speed railway (HSR) subgrade in cold regions with an open water supply. The final negative temperature of the freezing mode is kept the same. The total freezing time is 72 h. Three different modes, namely a constant temperature freezing mode, a three-step freezing mode, and a six-step freezing mode, are used. Fluorescein is used as the tracer for the rising height and variation of the liquid water in the external water supply. The external water migrates to the inside of the soil sample when it freezes, and the internal water of the soil sample migrates to the outside when it thaws. The number of steps for the different freezing modes is the key factor affecting the water intake. The amount of water intake affects frost penetration during freezing and thawing. There may be a suitable temperature gradient range for liquid water and vapor coupling migration. In all freezing modes, ice layers appear on the top of the top bath pedestal at the end of freezing. More freezing steps lead to a more uniform water content distribution. Moisture migration in HSR subgrade mainly occurs by vapor migration during long cold winters and winters with slow temperature drops.