A study of freezing process in variably-saturated sandy-loam soil under different water table depths:Experiment and simulation

Two soil column freezing experiments were conducted to understand the effect of water table depths on the transport of water, heat, and salt in soil columns. Column A was 60 cm soil in height but without water recharge, while column B involved a stable water table at 60 cm depth from the soil surface. While the soil was freezing, water content and temperature were measured. Results show that water and salt move upwards during the freezing process, and accumulate at the freezing front when there is a shallow water table. The movement of water and salt brings heat to the frozen soil. Such a redistribution of heat in the soil column can slow the progress of a freezing front. The HYDRUS-1D freezing and thawing module was used to simulate water movement and heat transfer during freezing at different water table depths (0.5 m, 1.0 m, 1.5 m, 2.0 m, and 2.5 m). Results show that the shallower the water table, the smaller the cumulative recharge, that is, a shallow water table supplies water more intensely and seems to stop the progress of the freezing front; a deeper water table has difficulty in recharging the upper layers.