Abstract
Despite extensive studies on EPS cushions or lightweight backfill separately for reducing lateral earth pressure on retaining walls, limited research has addressed the combined application of both techniques in a single wall system. The interaction mechanisms and potential combination between an EPS cushion and EPS bead lightweight fill remain largely unexplored, particularly for high-plasticity clay backfills under varying surcharge loads. This study therefore investigates the lateral earth pressure distribution and load reduction performance of retaining walls incorporating both an EPS cushion layer and EPS bead lightweight fill. Laboratory model tests were conducted using a custom-built apparatus with clayey soil collected from a gravity retaining wall site in Guangzhou. Four cushion thicknesses (0–6 cm), three foam contents (0.1%–0.3%), and four surcharge load stages were examined. Two indices, load reduction value and load reduction rate, were introduced to quantify pressure relief efficiency. The results show that increasing cushion thickness from 2 cm to 6 cm raises the reduction rate from 12% to 55%, while adding 0.2% foam roughly doubles the reduction value compared to 0.1% foam. The integrated system shows enhanced performance compared with either technique applied alone: the optimal combination (4 cm cushion with 0.2% foam) reduces base lateral pressure by 50%–60% under the highest load, outperforming either technique alone. A load-dependent dominance shift is observed: foam governs under low loads, while cushion thickness dominates under high loads. Diminishing returns occur beyond 4 cm cushion thickness and 0.2% foam content. These findings fill the research gap by demonstrating the enhanced performance of the integrated system and providing optimal design ranges for cost-effective pressure reduction.