On-site recycling of construction surplus soil in winged composite piles for enhanced uplift resistance

This study proposes a winged composite pile system that simultaneously achieves high uplift resistance and maximizes on-site recycling of construction surplus soil, thereby contributing to waste reduction and circular economy principles in geotechnical engineering. In Japan, although construction waste attains a recycling rate of 97.2%, the effective utilization rate of surplus soil is only 79.8% and on-site reuse remains at 54.3%, resulting in significant unnecessary off-site disposal and environmental impact. The developed system consists of a winged steel pipe pile centrally installed within permanent steel casing, with the annular space backfilled using excavated surplus soil to create a structurally integrated composite pile. A comprehensive three-dimensional elasto-plastic finite element analysis employing the Mohr-Coulomb model was conducted through 224 parametric cases by varying shaft diameter (0.2–0.6 m), expanded wing diameter (0.3–2.0 m), and pile length (10–20 m). Results revealed (1) optimal wing diameters of 1.6–1.7 m for 10 m piles and 1.9–2.0 m for 15–20 m piles, (2) negligible influence of shaft diameter on uplift resistance (<10% variation), permitting substantial steel reduction and greater soil incorporation, (3) uplift resistance scaling proportionally with pile length at equivalent displacement, and (4) failure mechanism dominated by localized shear zones above the wings. These findings enable the design of foundation systems that provide excellent structural performance while achieving near-complete on-site reutilization of surplus soil, offering a practical and scalable solution for minimizing construction-derived soil waste and advancing cleaner waste management systems in civil and geotechnical engineering practice.