On the role of geofoam density on the interface shear behavior of composite geosystems

Abstract

Expanded polystyrene (EPS) geofoam has been increasingly used in geotechnical engineering applications to replace conventional backfill material or to reduce earth pressure on retaining and buried structures. In most of these applications, geofoam blocks are installed in direct contact with different construction material (soil, concrete, steel, wood, etc.). This results in a composite system that is subjected to loading in both the normal and shear directions. Therefore, successful analysis and design of these composite structures require a detailed knowledge of interface strength characteristics of geofoam under a combination of normal and shear stresses. In the current research, an attempt has been made to study the interface shear characteristics of geofoam with selected materials, including concrete, wood and steel. Three different geofoam densities namely, 15, 22 and 39 kg/m3 were used in this study. A series of direct shear tests (DST) was conducted with a shear box of dimension 100 mm × 100 mm × 50 mm under three different normal stresses 18, 36 and 54 kPa. Test results revealed that geofoam density and applied normal stress have significant effects on the vertical compression and interface strength properties (i.e. adhesion and friction angle) of the investigated geosystem. Surface roughness was found to play a significant role in the shear resistance at the contact. Geofoam–concrete interface showed maximum strength as compared to wood and steel materials. Care should be exercised when placing geofoam against steel or wood surfaces as the mobilized friction angle is generally small and sliding may develop depending on the applied normal stress level.