Load Transfer and Performance Evaluation of the Composite Foundation Reinforced by Penetrated PCCSs and Partially Penetrated DCM Columns under Embankment Loads

The geosynthetic-reinforced and pile-supported (GRPS) embankment is a cost-effective and efficient method for addressing soft soil conditions. A noteworthy addition to this approach is the introduction of a precast concrete pile reinforced with cement-treated soil (PCCS), a novel composite pile formed by inserting a precast concrete (PC) pile into a deep cement mixing (DCM) column. This research aimed to delve into the bearing mechanism and deformation characteristics of a multielement composite foundation featuring PCCSs (long piles) and partially penetrated DCM columns (short columns) under embankment loads. Furthermore, the study performed a comparative analysis, juxtaposing calculated stress reduction values obtained from eight existing analytical methods with both field data and numerical results. The findings underscore the efficacy of the long-short pile composite foundation in effectively controlling settlements under embankment loads. Specifically, the maximum settlements recorded for the PCCS, the DCM column, and the surrounding soil within the piled-supported embankment system were 11.6, 19.0, and 54.0 mm, respectively. Under undrained end-of-construction conditions, the stable stress ratios of the PCCS–soil and the DCM column–soil were 10.7 and 4.5, respectively. As the loads transition from the surrounding soil to the piles, a major arch and a minor arch gradually form between the adjacent PCCSs and PCCS–DCM columns within the embankment filling. The outcomes of this investigation indicate that incorporating PCCSs and DCM columns as composite piles in GRPS embankments significantly enhances bearing capacity and curtails deformation under embankment loads.