Experimental investigation and prediction model of permeability in solidified coarse-grained soil under freeze-thaw cycles in water-rich environments

In freeze–thaw and water-rich environments, high-speed railway subgrade systems experience significant changes in their moisture field due to the combined effects of temperature and pore pressure gradients. This poses a serious challenge to the long-term safety of high-speed railways. To address this issue, the permeability of high-speed railway subgrade fill materials before and after modification was tested using a self-developed infiltration instrument. Modifications included increasing the fine particle content and adding self-developed solidifying additives. Based on experimental results and discussions on the solidification mechanism of the fill, a model for predicting the permeability coefficient of the fill was proposed and analyzed. Results show that the self-developed additive is an efficient material for reducing permeability, with effects reaching up to the order of 107. The additive also demonstrates excellent resistance to freeze–thaw environments. Mineral-based cementitious materials have a greater impact on permeability coefficient than cement-based materials. The permeability coefficient prediction model was validated, showing a 92.3% consistency level with laboratory test results. Parameter analysis revealed that the model's parameters effectively characterize the pore structure, fluid environmental temperature, pore pressure, and other characteristics of porous media. The findings have important implications for stable control and moisture field guarantee in high-speed railway subgrades under freeze–thaw and water-rich conditions.