Stabilized effects of L-S cement-mixed batter pile composite foundation for existed warm frozen soil subgrade

In permafrost regions with warm frozen soil, subgrade thaw-collapse phenomenon commonly occurs, facing thaw collapse problems of the existed frozen soil subgrade, thus it is difficult to use traditional methods such as active cooling and passive protection technology to stabilize the existed warm frozen soil subgrade. This study derives a novel stabilizer method, a long-short (L-S) cement-mixed batter pile composite foundation to stabilize the existed warm frozen soil subgrade. To solve the thaw-collapse problems in warm frozen soil subgrade, high water content and large compressibility characteristics were compared between soft soil and warm frozen soils. Theoretical analysis of heat conduction and numerical simulation of finite element model were used to study the freeze-thaw process and evaluate the stabilized effects of the L-S cement-mixed batter piles on the warm frozen soil foundation of the Qinghai-Tibet Highway. Furthermore, the thaw process and mechanical properties of foundation and piles were analyzed by introducing the hydration heat factor in the thermodynamic control equation. The results indicate that the thawing displacement of the existed warm frozen soil subgrade was reduced owing to the “support” and “grasp” effects of the L-S cement-mixed batter piles on the surrounding soil. The composite ground formed by strengthening the warm frozen ground with batter piles could considerably improve the bearing capacity of the existed warm frozen ground, effectively restrain the deformation of the upper embankment, and improve the strength of the ground. The analysis can provide method for the construction design of cement mixing batter pile foundation in cold regions.