WSDOT Alaskan Way Tunnel Design Build, S.R. 99 Deep Bored Tunnel
Award of Merit
Owner Washington Dept. of Transportation
Engineer-of-Record, Lead Tunnel Designer, Civil, Structural And MEP Engineer HNTB Corp.
Contractor Seattle Tunnel Partners—Dragados USA and Tutor Perini Inc., Joint Venture
General Engineering Consultant WSP USA
Project Management Assistant Consultant Mott MacDonald
Subcontractors Desert Mechanical; Fisk Electric Co.; SICE; Hitachi Zosen
Replacing Seattle’s aging Alaskan Way Viaduct required a bored tunnel solution, forming a nearly two-mile section of State Route 99 underneath the city’s downtown. Seattle Tunnel Partners, a joint venture led by Dragados of Spain, worked in partnership with U.S.-based Tutor Perini Inc. and key subcontractors from Japan and France to create the largest soft-ground bored tunnel in the U.S. with a 57.5-ft excavated tunnel diameter.
The $1.3-billion project, part of a larger $3.3-billion program, represents one of the largest infrastructure projects in the country and challenged the team to mine under 157 buildings with Bertha, at the time the world’s largest-diameter earth pressure balance tunnel-boring machine. Now open, the stacked roadways carry two lanes on each level and include fire detection and suppression, a ventilation system, security operations and an intelligent transportation system designed to react to conditions in the tunnel.