Geofoam and the “Imperfect Ditch” method can be used effectively on embankment projects to reduce pressures on underground structures when sufficient fill height is available to create an arching effect. When the fill height is too shallow the arching effect cannot be created. However, the pressure acting on the underground structure can still be reduced by making use of the very small unit weight of lightweight geofoam material. In this study, stresses acting on a three-sided culvert were reduced using lightweight geofoam. Initially, the culvert had been designed to carry a 6-foot loading. During construction it was discovered that the culvert must support a 9-foot embankment loading. In an attempt to maintain the original design pressure and accommodate the increased height of backfill, the contractor proposed substituting 2 feet of the fill soil with 2 feet of ultra-light weight geofoam. To check the proposed solution, stress cells were installed on the three-sided culvert to measure actual in situ pressures. Using measured pressures acting on the culvert, a numerical model (by using FLAC 4.0) was “calibrated” to back calculate pressure for the original design situation involving the fill height of 6 feet. Using the “calibrated” properties of the fill materials, pressures were calculated for fill heights with and without geofoam. Pressures obtained from the calibrated model involving 7 feet of fill and a 2-foot layer of geofoam are compared to the pressures obtained for the 6 feet of fill.

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The contents of this report reflect the views of the authors, who are responsible for the facts and accuracy of the data presented herein. The contents do not necessarily reflect the official views or policies of the University of Kentucky, the Kentucky Transportation Cabinet, nor the Federal Highway Administration. This report does not constitute a standard, specification, or regulation.