Analytical Solution for the Settlement Calculation of a PCCS Composite Foundation under Embankment Loads

Precast concrete pile reinforced by cemented soil (PCCS) is a novel composite pile widely used for soft soil improvement, particularly in supporting embankments. This technique involves installing a PC pile (inner core) at the center of a deep mixing (DM) column (outer core), effectively combining the advantages of both technologies. However, there remains a lack of feasible methods for calculating the settlement of the PCCS with long-core-supported embankment, especially in deep soft soils. This study develops an analytical model designed to calculate the settlement of the PCCS with a long-core composite foundation under embankment loads. The proposed analytical model simplifies the embankment load to a uniformly distributed load acting on a composite foundation and then analyzes a pile body and underlying soft soil unit within the influence range of a single pile. The model then divides the unit into three regions—composite section, noncomposite section, and firm soil layer—and calculates the total settlement separately for each region. The models specifically treat the inner-core, outer-core, and the surrounding soil as isotropic linear elastic materials. By employing the Coulomb friction model, the distribution of lateral friction resistance between the inner and outer core, as well as the pile–soil interface, is analyzed, with the cemented soil and the surrounding soil in the composite section considered composite materials. The effectiveness of the analytical model is validated through comparison, with results from numerical analysis with the discrepancy being within 13%. Based on the analytical model, a sensitivity analysis explores the impacts of the key parameters of the DM column on the settlement of the PCCS with a long-core-supported embankment. The findings can be used for engineering design and optimization of this type of embankment.