Effect of Geofoam on Vertical Stress Distribution on Buried Structures Subjected to Static and Cyclic Footing Loads

Abstract

Buried structures, such as pipes and culverts, are extensively used for transportation applications. The existence of these structures within the soil mass causes a redistribution of stresses. The stiffness of the buried structure relative to the surrounding soil affects the magnitude and distribution of vertical stresses. Higher stresses on a buried structure may cause excessive deformations and even failure of the buried structure. Expanded polystyrene (EPS) geofoam, a lightweight material, has been increasingly used above buried structures as a compressible inclusion to reduce vertical stresses acting on the buried structures. This experimental study investigated the effects of EPS geofoam, including geofoam stiffness and thickness, on the distribution of vertical stresses above a rectangular concrete culvert under static and cyclic footing loads. Reduced-scale models were constructed in a test box under a plane-strain condition. This study adopted the induced trench installation (ITI) method to place the concrete culvert overlaid with an EPS geofoam. The backfill material was a dry, poorly graded Kansas River sand. The footing load was applied parallell to the culvert axis. Earth pressure cells were used to monitor the vertical stress distributions above the geofoam and surrounding soil. The experimental results show that the EPS geofoam reduced the vertical stresses on the buried structure due to the mobilization of soil arching. The lower stiffness and thin geofoam had more effect on the vertical stress reduction. Cyclic loading minimized the soil arching effect induced by the compressible geofoam. This paper also examines the test results with available analytical solutions. The effects of soil arching and the induced vertical stress above the rigid structure under static footing load were considered separately. The analytical solutions were found to match well with the experimental results.