Behavior of EPS geofoam in true triaxial compression tests

This paper investigates the behavior of EPS geofoam in a true triaxial apparatus using 70 mm×70 mm×140 mm prismatic brick-shaped specimens. The specimens are subjected to different stress paths in the deviator (π) plane by means of stress-controlled loading, in which the axial stress is imposed at a rate of 75 kPa/min in the major principal direction. Stress-strain characteristics and volume change behavior have been recorded, and the yield surface has been deduced from the experimental data. The following observations have also been made for the geofoam: (a) it is an elastoplastic hardening material with plastic contractive volume change under compressive loading, (b) it softens stiffness-wise under confining stress, (c) the onset of contractive volume change corresponds quite well to the proportional limit, and (d) yielding is a slightly decreasing function of the intermediate principal stress. The study found that yielding can be represented reasonably well by a Drucker-Prager yield surface.