A huge project under construction in Seattle, Wash., involves replacing a viaduct with a bored tunnel underneath the city. In fact, the Alaskan Way Viaduct Program includes more than 20 projects that will work together to replace the viaduct and reshape the State Route 99 corridor.
According to KaDeena Yerkan, manager of communications and public involvement of the Viaduct Program, construction on the first project began in 2008, and involved crews stabilizing four viaduct columns that had settled following the 2001 Nisqually Earthquake.
“Since then, more than a dozen projects have been completed, with several more in progress or set to break ground soon,” Yerkan said. “The centerpiece of the program — the SR 99 tunnel — will open to drivers in late 2015.”
The project Web-site states that the Alaskan Way Viaduct plays a major role in sustaining the economy and maintaining citizens’ ability to travel to and through Seattle.
“However, the viaduct is at risk of failure from earthquakes, with unacceptable risk to lives as well as property,” the site states. “ The structure must be replaced. The SR 99 tunnel will move the state highway underground, reconnect the street grid at the ends of the tunnel, and remove the viaduct along Seattle’s downtown waterfront. It will maintain a vital route for people and goods through downtown, while opening up more than nine acres of public space for a world-class waterfront.”
The viaduct replacement projects are estimated to cost $3.1 billion. A total of $2.8 billion has been committed from the state gas tax, federal sources and tolls on users. In addition, the Port of Seattle also committed $300 million to the replacement program.
“Seattle Tunnel Partners is the design-build contractor for the SR 99 tunnel,” Yerkan said. “Design-build combines project design and construction in a single contract. Key members of Seattle Tunnel Partners, a joint venture of Dragados USA and Tutor Perini Corp., delivered the comparable 49.5-ft-diameter Madrid M-30 highway tunnel in Spain. The team includes local firms Frank Coluccio Construction and HNTB Corp. Hitachi Zosen Corp. is designing and building the tunnel boring machine.”
The Washington State Department of Transportation’s work to replace the viaduct includes a 2-mi.-long (3.2 km) tunnel beneath downtown Seattle, a mile-long (1.6 km) stretch of new highway that connects to the south entrance of the tunnel near Seattle’s stadiums, a new overpass at the south end of downtown that allows traffic to bypass train blockages near Seattle’s busiest port terminal, demolition of the viaduct’s downtown waterfront section in 2016, and a new Alaskan Way surface street along the waterfront that connects SR 99 to downtown.
In addition, as part of the Alaskan Way Viaduct Replacement Program, King County, the City of Seattle and the Port of Seattle are planning street, transit, seawall and waterfront improvements.
Yerkan noted that crews will use the world’s largest-diameter tunnel boring machine to build the SR 99 tunnel. Currently being manufactured in Japan, the machine will arrive in Seattle early next year. The 57.5-ft-(17.5 m) diameter, 326-ft-long (99 m) machine is the size of some of Washington State Ferries’ largest vessels, and weighs nearly 7,000 tons (6,350 t).
According to the Web-site, Seattle Tunnel Partners selected Hitachi Zosen Corporation to supply the machine that will construct the tunnel. Hitachi Zosen is responsible for designing, manufacturing, assembling, testing and commissioning the machine, as well as training Seattle Tunnel Partners’ personnel.
Located in Osaka, Japan, Hitachi Zosen has successfully built a number of large-diameter tunnels including the Tokyo Metropolitan Expressway (45 ft. [13.7 m]in diameter) and the Tokyo Bay Highway Tunnel (47 ft. [14. 3] in diameter). They supplied the tunnel boring machines for Sound Transit’s Link Light Rail Capitol Hill Station to Pine Street segment. Hitachi Zosen has manufactured more than 1,300 tunnel boring machines (TBM).
A TBM is a cylindrical machine with a cutter head at the front. It contains a system to mine the soil and transport it out of the tunnel. As the soil is removed, pre-cast concrete segments are placed to form the tunnel structural liner.
The SR 99 tunnel will be 1.7 mi. long. Over the course of tunneling, crews will remove more than 850,000 cu. yds. (649,871 cu m) of soil.
In September, crews completed the viaduct’s south-end replacement a full year ahead of schedule and on budget. The SR 99 tunnel project broke ground in the fall of 2011 and is on schedule and budget.
“State Route 99 is a vital north-south corridor located near two major stadiums and the Port of Seattle’s busiest freight terminal,” Yerkan said. “Maintaining traffic and minimizing construction impacts while building a project of this size requires sound planning and strong coordination with our partner agencies and stakeholders.”
Crews are currently working to dig the launch pit for the tunnel boring machine. Located to the west of Seattle’s stadiums, it will reportedly be slightly longer than a football field and about 80 ft. (24 m) deep when completed early next year.
Major subcontractors include HNTB, Bellevue, Wash., for design; Frank Coluccio Construction Company, Seattle, for utility relocation; J.H. Kelly, Longview, Wash., for mechanical and electrical; Malcolm Drilling, Kent, Wash., for secant piles and jet grouting; Harris Rebar, Lake Stevens, Wash., for furnishing and installing reinforcing steel; J. Harper Contractors, Maple Valley, Wash., for demolition; Ballard Diving & Salvage, Seattle, for hyperbaric services; and Barnhart Crane, Portland, Ore., for tunnel boring machine assembly.
Major equipment used on the job includes an American HC230 230-ton (208.6 t) crawler crane, a Grove RT9100 100-ton (90.7 t) rough terrain crane, a P & H CN-150 50-ton (45 t) crane, a Bauer BG 40 rotary drilling rig, a Bauer BG 50 rotary drilling rig, a Caterpillar 330CL excavator, a Caterpillar 345CL excavator, a Caterpillar 365BL excavator, a Caterpillar 385BL excavator, a Komatsu PC750LC-6 excavator, a Komatsu PC1100LC-6 excavator, a Volvo A40 articulated rock truck, a Caterpillar 140H VHP motor grader, a Caterpillar D7 dozer, a Caterpillar 973C track loader and a Caterpillar 980H rubber-tired loader.
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