The SR 520 Floating Bridge in Seattle, Washington, won the American Council of Engineering Companies’ (ACEC) “Grand Conceptor” award, marking it as the year’s most impressive engineering project in the United States. GeoEngineers played a critical role on the Kiewit/General/Manson Joint Venture construction team, providing geotechnical consulting, design and construction support.
Stretching 1.5 miles across Lake Washington, the SR 520 bridge is the longest floating bridge in the world. Engineering firm HDR designed the bridge, and cooperated with more than 100 sub-consultants to complete the project.
The GeoEngineers team provided geotechnical designs and consulting for the three large piers supporting the east bridge landing, along with groundwater investigation, dewatering plans for the cofferdams used during construction of the piers, and recommendations for retaining walls throughout the site. GeoEngineers also consulted on the design and engineering for the casting of gravity anchors used to stabilize critical portions of the bridge’s floating expanse.
Notably, the GeoEngineers team recommended a change from using drilled shafts to support the east approach to using shallow foundations—a move that saved the client approximately $20 million. The team used a combination of field explorations and sophisticated 3D numerical modeling to evaluate the proposed shallow footings and determine their performance under a variety of load conditions.
