Subscribe / Renew
January 22, 2013
Project: State Route 99: South Holgate Street to South King Street viaduct replacement
Client: Washington State Department of Transportation
The Alaskan Way Viaduct on state Route 99 in Seattle is in the process of being transformed from an elevated highway into a tunnel, a massive construction project.
Because SR 99 is a heavily traveled north-south artery through the city, temporary closures for construction needed to be kept to a minimum. To maintain mobility for the public, a bypass roadway needed to be constructed to connect the new SR 99 bridges to the remaining viaduct structure along the waterfront.
Parsons Brinckerhoff was the prime consultant for both the final design and design support services of this project, but they faced a constrained construction staging area and multiple existing utilities that had to be avoided. Their solution was to use materials that could be prefabricated and assembled quickly and easily instead of cast-in-place elements that might prolong construction.
The firm also used lightweight expanded polystyrene fill rather than conventional gravel fill for the SR 99 approaches to the new bridges. Geotechnical studies predicted that standard fill material would cause several inches of settlement of the existing viaduct, which was totally unacceptable.
The design-build team overcame a myriad of complex issues, satisfied the competing needs and concerns of multiple stakeholders, and delivered a product that exceeded client expectations. These steps included building a tail track for BNSF Railway, using the expanded polystyrene fill for the SR 99 approaches, sequencing construction to satisfy the city and Port of Seattle’s concerns for mobility and safety, and constructing a temporary bridge in a way that minimized road closures.
The team’s efforts contributed to the contractor’s ability to deliver the project 14 months early, and reduced WSDOT’s program costs by more than $100 million.
Perhaps most importantly, Parsons Brinckerhoff and its design-build team prevented disruption and delays for the Seattle Seahawks, Sounders and Mariners, which play at nearby stadiums.
comments powered by Disqus