Design parameters for EPS geofoam

Over the past 30 years, design with geofoam has been based on either factored strength or limit strain approaches. Geofoam parameters for design have been derived from unconfined compression testing of small laboratory samples. Closer examination of performance observations indicate extrapolation of small sample laboratory results can lead to misleading interpretation of field results. The potential for creep deformations is exaggerated and design modulus values are underestimated when based on small sample laboratory tests. Possible reasons for these shortcomings, in reference to field observations, are examined on the basis of creep tests on small samples, uniaxial loading of large samples, compression tests using tactile pressure sensors and review of enlarged images of geofoam surfaces. Creep deformations in geofoams under uniaxial loading remain mainly in primary stages where strain rates continually decrease. Modulus values for design that are derived from small sample laboratory tests are about half of the values that were estimated from field observations. Accordingly, the suggestion is made to increase small sample based modulus values from laboratory tests for design applications.