State Route 520, Washington

Steve Nelson, Western Insulfoam, Kent, WA

EPS geofoam fill between highway retaining wall and building wall.

The new SR 520 bike path at retaining wall #5 is supported by 500 cubic yards of Type VIII EPS geofoam. The geofoam blocks (32"x24"x96") were used as lightweight backfill behind the retaining wall, in place of traditional soil backfill. Insulfoam and Max J. Kunny worked with Robert Fawcett of Sverdrop Jacobson to engineer the design of EPS geofoam and precast concrete retaining wall panels in a very tight construction space. There is only 12 feet between the retaining wall and the back wall of a structural building. By using EPS geofoam, the contractor eliminated the possibility of settlement under the new backfill wall and to the adjacent structure. This unique design proved to be a cost savings measure and kept the project ahead of schedule.

Left: EPS geofoam adjacent to retaining wall. Foundation for facade visible to right of geofoam. Right: Facade supports resting on geofoam.