Abstract: Saline soil, common in the western China, poses a significant threat to road engineering due to its salt swelling characteristics. Therefore, studying the water-salt migration patterns within saline soil subgrades and developing methods to interrupt this migration are crucial for road safety prevention and control. Based on the utilization of excavated waste soil, a new type of foamed lightweight soil based on saline soil is proposed as a subgrade separation fault in saline soil areas. Using self-developed equipment, we tested internal temperature changes, vertical displacements, and water and salt distribution after freeze-thaw cycles. The objective was to evaluate its salt insulation and swelling suppression capabilities and to explore the microstructure-based mechanisms underlying salt inhibition. Results indicate that under a temperature gradient, water and salt in the saline soil sample migrate upward, accumulating mainly in the middle and upper sections. Notably, the novel foamed lightweight soil separation fault effectively blocks water and salt migration, significantly suppressing salt swelling. Interestingly, a higher soil salt content results in a more pronounced anti-swelling effect. The porous structure of the foamed lightweight soil can not only store salt effectively, but also block salt migration, allowing salt crystallization within the soil, thereby reducing salt swelling damage.

Key words: saline soil, water-salt migration, separation faults, freeze-thaw cycles, foamed lightweight soil