The natural engineering tendency when posed with a loading problem is to find a way to support it. We have learned, however, an equally good question to ask is - can the load be reduced? This applies to both seismic analyses and static analyses.
The James Road project in Weybridge, VT is an excellent example. The solution was the first known use of Geofoam as a full-scale slope stabilization repair for a roadway in Vermont. Previous Geofoam uses in Vermont included a pilot study application behind a VTrans bridge abutment, lightweight fill under building slabs, and as a roadway fill material to prevent frost heaving of frost-susceptible soils.
James Road was built many years ago into an existing slope on native clay soils. Later, in the 1970s, the elevation of the road was changed and up to 10 feet of fill was added. The weight of the fill over the years caused sliding and movement, followed by ongoing periodic placement of additional pavement to maintain the roadway grade. Over the years, up to six feet of pavement accumulated.
GeoDesign, Inc. teamed up with Phelps Engineering, Inc. to develop a solution to the on-going movement and unusually high required maintenance. After the evaluation of the problem, GeoDesign recommended unloading the roadway by replacing eight feet of the roadway fill with lightweight Geofoam. Geofoam is a trade name for an expanded polystyrene (EPS) material that is manufactured in large lightweight structural blocks. The blocks vary in size and can be manufactured with different material properties.
By utilizing lightweight Geofoam blocks, the load on this slope was significantly reduced resulting in much lower repair and maintenance costs for this roadway. We used Geofoam that weighed 1.8 pounds per cubic foot. Compare this to typical roadway backfill at 120 pounds per cubic foot and the Geofoam presents a sizeable reduction in load applied to the slope (i.e., a little more than a 118 pounds per cubic foot reduction in load).
The design and construction consisted of excavating the full depth of the roadway repair followed by placement of granular bedding, drainage layers, and Geofoam blocks. We drained the Geofoam by gravity using a buried PVC pipe to a down-slope sump pit.
Construction began on October 12, 2011 and the project was substantially completed on November 23, 2011, one week ahead of schedule.
During the project design phase, Tropical Storm Irene damaged numerous other Vermont roads, which limited the availability of potential contractors and competitive pricing. To minimize such cost impacts, contractors were notified of the project before advertising for bids to both stimulate interest in bidding and allow time to gain familiarity with Geofoam. To allow the road to be rebuilt before winter, geotechnical evaluation of the site, evaluation of alternatives, repair design, and bid documents were completed within three months.
This example shows how load reduction provides a cost effective solution to a load bearing problem.