A Novel Double-layer System for Infiltration Control and Improvement in the Stability of Expansive Soil Slopes

In this study, a novel cover system composed of an overlying fine soil layer and an underlying coarse soil layer was used to control water content variation in expansive soil slopes. The capillary barrier generated by the permeability difference between fine and coarse soil prevented rainfall infiltration into the coarse soil layer. The coarse soil layer facilitated water drainage along the slope upon rainfall entry. First, model experiments were carried out to select the particle composition of the coarse soil layer. Then, five rainfall experiments were designed to study the infiltration control and drainage effect of the cover system. The experimental results showed that the capillary barrier inhibited the rainwater from infiltrating downward, and the capillary barrier effect was related to the initial water content of coarse soil. Approximately 69.6–88.9% of rainwater was drained along the slope, but there was no leakage at the bottom of the slope soil under the protection of the cover system. While a single coarse soil layer could provide a certain drainage capacity, but the rainwater was still drained from the bottom of the slope. The cover system effectively controlled the water content variation in the slope soil.