Abstract: Expansive soils, known for their considerable swelling pressure upon wetting, have been identified as potential instigators of instabilities in retaining walls. The incorporation of expanded polystyrene geofoam (EPS) inclusions between the retaining wall and the backfilled expansive soil has been found to considerably mitigate the lateral pressure on the wall, which results from the water absorption and expansion of the expansive soil. This substantial reduction is due to the impressive compressibility of the EPS inclusion. To explore the implications of the EPS inclusion on the lateral pressure distribution on retaining walls, and to analyze the factors influencing this pressure, a comprehensive model test and a corresponding lateral pressure theoretical analysis were performed. The results show that (1) the total lateral pressure acting on the retaining wall was reduced by about 50% by the EPS inclusion with a density of 12 kg/m³ when the expansive soil is saturated in the model test; (2) in the absence of the EPS inclusion, the lateral pressure distribution acting on the retaining wall escalated along its depth, whereas with the EPS inclusion, it remained largely uniform throughout the wall’s depth; and (3) the lateral pressure reduction due to the EPS inclusion was enhanced with increasing thickness and decreasing density of the EPS inclusion.

Key words: retaining wall, expansive soils, expanded polystyrene geofoam, model test, lateral pressure