Alaskan Way Viaduct and Seawall Replacement

SR 99 Alaskan Way Viaduct and Seawall Replacement | Seattle, WA, US
SR 99 Alaskan Way Viaduct and Seawall Replacement | Seattle, WA, US
Washington State Department of Transportation
Seattle, Washington, USA

The Alaskan Way Viaduct along SR 99 is a critical link in the Washington State transportation system. Potential plans call for replacement of the viaduct, which was significantly damaged in the 2001 Nisqually earthquake. We have been involved in numerous aspects of this major infrastructure project.

We provided acquisition and relocation services for construction of the SR 99 tunnel. Our role included impact assessment, securing rights-of-entry for geotechnical and environmental testing, negotiating purchase and sale agreements, coordinating with surveyors and appraisers, assisting attorneys with possession and use agreements, and relocating displaced residential and commercial owners and tenants. We were successful in moving negotiations forward years in advance of condemnation authority.

As part of a Project Management Assistant Consultant team, we provided design and construction phase services. Activities included technical and management staff support, independent oversight and review of preliminary design, and constructability and contract methods packaging guidance and support. Under separate contracts, we also developed a stormwater management approach and prepared preliminary and final designs for the replacement and relocation of a combined sewer system.

Replacing the structure with a cut and cover tunnel will displace numerous utilities, including the combined sewer system and outfalls in Seattle's Central Business District. We prepared conceptual design drawings, design studies, and a Basis of Design Report for approximately 4,000 feet of 72-inch-diameter gravity combined sewer (Alaskan Way Interceptor), 2,200 feet of 84-inch-diameter combined sewer (offline storage), 3,000 feet of 12 to 36-inch-diameter combined sewers, four CSO outfalls, odor control facilities, four CSO diversion structures, and two hydraulic control structures. The Interceptor would provide SPU with the flexibility to support a future CSO control project to reduce CSOs to one per year per outfall.

Most recently, we employed our Cost Risk Assessment and Value Engineering (CRAVE™) process to identify major cost and schedule risk factors. Our analysis led to a revised alignment and avoided identified risks quantified at over $50 million. This is a continual process that will take place throughout the project lifecycle to ensure proper risk monitoring and control, and to keep the risk-based estimate current.