Feasibility Experiment and Simulation on Controlling the “Pot Cover Effect” of Subgrade in Seasonally Frozen Regions by Capillary Barrier Layer

The pot cover effect can increase the moisture content in shallow soil, which reduces subgrade strength and may lead to engineering issues, such as pavement cracks and deformation. Therefore, studying the prevention measures for the subgrade pot cover effect is essential. This paper proposes preventive measures, inspired by capillary barrier layers used in landfills, that involve installing such layers to mitigate the subgrade pot cover effect. First, a self‐designed test device was used to compare the hydrothermal changes in conventional fill subgrade and subgrade with gravel and sand capillary barrier layer in a seasonal frozen soil environment. Second, a water–vapor–heat coupling model was developed to simulate the quantitative changes in water migration induced by the capillary barrier layer during the experiment. Finally, the long‐term effect of using a capillary barrier layer to mitigate the pot cover effect on a loess subgrade in northwest China was simulated. The results show that at a depth of 2.5 cm, the liquid water content without a capillary barrier increases with the number of freeze–thaw cycles, reaching a maximum increase of 5.9%. In contrast, the maximum increase in liquid water content at the same depth in the soil layer with a capillary barrier is only 0.9%; the water vapor flux of the subgrade with a capillary barrier layer is 1/10 of that of the subgrade without a capillary barrier layer. The proposed capillary barrier layer method offers theoretical insights for mitigating the pot cover effect and guiding future subgrade designs.