NA-00  Direct Shear Test on EPS Samples

EPS Geofoam is a very low density solid that can be used as soil substitute in many geotechnical applications. To prove the suitability of EPS Geofoam as soil substitute, many tests that are performed on soils are also performed on EPS blocks. The weakest plane of failure within a geofoam fill under load at the interface between geofoam blocks and between geofoam blocks and interfacing materials. The interface friction resistance is an important engineering property required to perform analysis and design. The interface friction factor between geofoam to geofoam had been determined by many researchers through different testing methods in the past years. This report summarizes the work done on EPS geofoam to determine the effects of density and the normal load on the interface properties. Direct shear tests were performed on EPS blocks from four different manufactures with nominal densities ranging from 12 to 20 kg/m3. For each density tests were performed with normal loads 10, 12, 20, 26, 30, and 52 kPa. The test results show that the peak friction factor is not effected by the applied normal stress whereas the residual friction factor slightly drops with the increasing normal stress. Both residual and peak friction factors are found to be different for EPS blocks from different manufacturers. The results based on the testing of EPS blocks from four different manufacturers show that in general the peak friction factor is between 0.97 and 1.16 and the residual friction factor is between 0.82 and 0.61.

Test is carried out in the same manner as in the case of dry-interface condition with water in between geofoam blocks. The effect of displacement rate on the residual friction factor is also investigated.

Test was carried out on 4-inch x 4-inch direct shear testing machine. The geofoam sample was sheared in a displacement-controlled mode with a given normal load and once the peak stage passed and the shearing was in residual stage the shearing was continued with a constant load. The constant load was increased from 0 kPa to the residual stress in steps. At each step the creep shear variation with time is investigated.

Test carried out on 4inch x 4inch block geofoam samples from four different manufacturers. In each case samples were sheared with different normal loads ranging from 20 kPa to 50 kPa. The data is available and interpretation of results is in progress.