Deformation mechanism and design method of embankment supported by composite foundation in soft soil regions

To clarify the settlement mechanisms of rigid-pile composite ground supporting embankments in soft soil regions during both construction and long-term service, and to propose an optimal pile arrangement strategy for effectively controlling pavement settlement, this study is based on an actual embankment construction project at the Xinxing Interchange section. A three-dimensional finite element model reflecting the entire process of embankment construction and consolidation is established according to the soil conditions along this section. The model is used to investigate the overall deformation patterns and settlement mechanisms under different pile arrangement methods. A comprehensive comparison of safety, settlement control effectiveness, and economic efficiency among these methods is conducted, leading to the selection of the most suitable design for the section. Furthermore, the long-term deformation and service performance of the embankment are evaluated using field monitoring data collected over the project's service life. The results indicate that compared to the conventional uniform pile layout, increasing the pile density beneath the embankment shoulder effectively limits surface settlement caused by shear stress. As the pile spacing beneath the shoulder decreases, the surface settlement pattern transitions from a depression-type settlement to a typical settlement mode. For the non-uniform pile arrangement, the ratio of pile spacing between the shoulder and centerline (s₁/s₂) should satisfy 1 < s₁/s₂≤1.4; otherwise, the composite ground may experience localized excessive settlement due to insufficient vertical bearing capacity. Additionally, pile densification in the shoulder area facilitates the transfer of the embankment load to deeper soil layers, thereby reducing the risk of shallow foundation failure.