This study employs the FLAC3D numerical simulation software to systematically analyze the stability of multitier embankment slopes in the G4 Beijing–Hong Kong–Macau Expressway expansion project, under various rainfall conditions in Hunan Province. The research innovatively compares slope designs before and after the highway expansion, as well as the response characteristics of single‐tier versus multitier slope structures under five distinct rainfall scenarios. The results demonstrate that the new slope design significantly enhances slope stability, with a 23% higher factor of safety (FoS) compared to the old design under dry conditions. Even after 72 h of extreme rainfall, the new design maintains a 15% safety advantage. The multitier slope structure, by truncating potential sliding surfaces via platforms, effectively alters the rainwater infiltration path, increasing the width of the critical unsaturated zone by 3–4 m. After prolonged rainfall, peak pore‐water pressure is 29.5% lower than that of the single‐tier slope. A detailed analysis of saturation, pore‐water pressure, and shear strain distributions reveals the mechanisms by which rainfall infiltration influences slope stability. The findings provide not only direct technical support for the G4 Expressway expansion but also scientific guidance and design references for highway construction in similar climatic and geological conditions.
Li et al. (Thu,) studied this question.