Experimental study of polyurethane cement composite-reinforced soft soil in the thawed layer in permafrost regions

Permafrost degradation induces a large number of thawed layers that have high water content, low bearing capacity, and high compressibility, which threaten the stability of infrastructure in permafrost regions. How to reinforce the soft layers of thawed permafrost is very essential for maintaining and repairing such infrastructure. This study investigates the reinforcement effect and mechanism of a polyurethane cement composite (PUC) on the soft soil in the thawed layer (SSTL) of permafrost through mechanical and microscopic tests. The experimental results indicate that the unconfined compressive strength (UCS) of the SSLT initially increases and then decreases with increasing hydrophilic polyurethane (WPU) content, while it increases with higher polymer cement content (PMC). The UCS of the SSLT reinforced with 10% WPU increases by 41.96% and 18.75% in the early and late stages, respectively, compared to a SSLT sample without added WPU at a moisture content of 40%, while the cohesion of the SSLT increases by 7.74%, and the internal friction angle increases by 29.48%. A microscopic analysis reveals that the PUC significantly enhances the microstructure of the SSLT through intricate physical and chemical reactions. PUC-reinforced SSLT provides a new way to address the settlement and deformation that adversely affect subgrade in permafrost regions.