Sustainable fill solutions: recycling EPS waste in shredded EPS-clayed soil composites for improved mechanical and compaction behaviour

The disposal and recycling of expanded polystyrene (EPS) waste pose significant challenges. Although previous research has explored the engineering characteristics of coarse-grained soils mixed with EPS waste for lightweight fill materials, limited attention has been given to fine-grained clayey soils. This study investigates the compaction, strength, and deformation behavior of three types of clayey soils with varying plasticity, mixed with 0.5% to 3.0% shredded EPS content. Experimental results indicate that the addition of shredded EPS to all three clayey soils significantly reduced the maximum dry density (MDD), making them suitable for lightweight fill applications. Direct shear tests revealed a decrease in cohesion and an increase in the angle of internal friction as the shredded EPS content increased. The unconfined compressive strength (UCS) initially increased with EPS content, then decreased after reaching an optimal EPS proportion. The addition of shredded EPS also enhanced the workability of the clayey soils, as evidenced by a reduction in their plasticity indices. Based on these findings, a framework is proposed to determine the optimum shredded EPS content, which provides the best balance between strength and reduced unit weight for different clayey soils. This research highlights the potential of EPS waste as a sustainable additive for improving the properties of clayey soils, making them more efficient and eco-friendly for construction purposes, particularly in transportation geotechnics for road embankments and subgrade stabilization.