Soaked behaviour of EPS geofoam in geotechnical applications

Expanded Polystyrene (EPS) geofoam isa thermoplastic material (of synthetic origin) used increasingly as an ultra-lightweight fill in geotechnical applications.Its use extends from replacing the low load bearing, highly compressible subgrade soil in road pavements to as a backfill body in the construction of retaining walls and embankments. In these and other sub-surface construction, the material is subjected to varying moisture conditions. It has been observed in field studies that as much as 9% moisture pickup by volume occurred in blocks lying permanently under the ground level for 9 years. Moisture impinges on geotechnical design in that it not only increases the unit weight of the EPC geofoam, but may significantly affect the mechanical properties as well. As little by way of experimental evidence is available to form appropriate conclusions, the authors have undertaken a study to investigate moisture effects on the mechanical behaviour of EPS. In the study, EPS samples were prepared and carefully soaked in distilled water for various lengths of time ranging from two weeks to one year. At appropriate points in time, batches of thirty soaked samples were withdrawn and subjected to uniaxial and triaxial compression tests to assess the mechanical behaviour. Preliminary findings show that the volumetric moisture content (VMC) increases with the duration of soaking. It appears that moisture has little effect on the material elastic stiffness or its yield stress, but causes an increase in the plastic modulus.