Numerical Investigation on the Influence of XC‐CBS Cover Structure on Seepage Performance of Expansive Soil Slopes Under Sustained Heavy Rainfall

ABSTRACT

Expansive soil slopes in humid and rainy regions are particularly susceptible to shallow instability failures during prolonged heavy rainfall. Continuous infiltration of rainwater leads to a rapid increase in soil moisture content and a significant reduction in shear strength, which in turn precipitates frequent landslides and collapses, posing a threat to the stability of transportation infrastructure. To tackle this critical engineering problem, this study takes the expansive soil in Ningming, Guangxi as the research object, and conducts numerical simulations of GeoStudio. It systematically examines how various structural parameters of the fine‐coarse double‐layer capillary barrier system (XC‐CBS, where XC stands for Xi‐Cu in Chinese pinyin meaning fine‐coarse), including layer thickness, slope ratio, and slope height, influence the seepage behavior of expansive soil slopes. The results indicate that the thickness of the XC‐CBS cover structure primarily governs the infiltration regulation effect. A combined structure featuring a 20–30 cm fine‐grained soil layer and a 20 cm coarse‐grained soil layer demonstrates optimal performance, delaying the saturation of the highly weathered soil interface by 23%–25% and maintaining peak pore‐water pressure below the critical stability threshold. The slope ratio of 1:1.5 maximizes lateral drainage efficiency and significantly minimizes pore‐water pressure accumulation. Conversely, a steeper slope height increases deep pore‐water pressure and impairs lateral drainage, necessitating enhanced drainage facilities at the slope toe. This research elucidates the synergistic mechanisms of seepage blockage and rapid lateral drainage within the double‐layer XC‐CBS. The findings provide a quantitative foundation for the anti‐seepage design of expansive soil slopes in humid and rainy regions, and effectively contribute to mitigating the risks of rainfall‐induced slope instability.