Reduction of lateral pressures on retaining walls using geofoam inclusion

Expanded polystyrene geofoam has long been used as a compressible lightweight alternative for soil backfills to reduce lateral pressure behind retaining walls. Uncertainty in material properties and lack of design parameters are the main constraints to using local geofoam products. In this study, the main goal was to characterise geofoam properties and to calibrate a standard numerical model to capture the behaviour of rigid and flexible walls with geofoam inclusions. A laboratory-testing programme was conducted to measure the shear strength and interface properties between geofoam-geofoam, geofoam-soil, and geofoam-concrete. These measurements were then used to calibrate the numerical model in which geofoam was represented using a hardening soil constitutive model. For both wall types, outcomes were verified against results from the literature. From the main outcomes, a geofoam inclusion thickness-to-wall-height ratio (t/h) of 0.085 was sufficient to change the behaviour of the backfill soil behind rigid walls from at-rest to active conditions. In addition, an inclusion with t/h ratio of 0.065 reduced the lateral pressure behind flexible walls by 28%, and represents a borderline criterion between reduced pressure and zero pressure results.