Work on the new tunnel under Seattle’s waterfront is on hold while Seattle Tunnel Partners repair damage to “Bertha,” the world’s largest-diameter tunneling machine named after Bertha Knight Landes, the first woman elected mayor of a major American city (Seattle) in 1926.
The tunnel is part of a large $3.1 billion project to replace the Alaskan Way Viaduct, the portion of State Route 99 that travels through downtown Seattle. SR 99 is one of two major north-south traffic corridors through the Emerald City, carrying 90,000 vehicles per day, according to a 2015 study. “That number has dropped from 120,000 per day during the recession,” said Laura Newborn, media relations manager with Washington State Department of Transportation, who said it’s down because the number of bus riders is up.
The Alaskan Way
The Alaskan Way Viaduct Replacement Program is headed by the Washington State Department of Transportation in partnership with the Federal Highway Administration, King County, the City of Seattle and the Port of Seattle. Funding comes from state, federal and local sources, as well as the Port of Seattle and future tolls.
The program is made up of 30 projects, with each jurisdiction responsible for management of its own projects, environmental work, design and construction. Two contracting methods are being utilized on the various projects to replace the viaduct: design-build and design-bid-build.
Construction on the first project started in 2007, when crews stabilized four viaduct columns that settled as a result of an earthquake. Since then, 21 projects that are led or funded by the state have been completed, with several more in progress or set to break ground soon. The SR 99 tunnel is the largest project in the program.
The Viaduct is a two-mile-long elevated double-deck road built in the 1950s. Damaged during the 2001 Nisqually 6.8 magnitude earthquake, it was stabilized and repaired by WSDOT, which imposed roadway restrictions for large vehicles.
Simultaneously, WSDOT began considering alternative plans to replace the aging and vulnerable structure and implements quarterly inspections. For a decade, state and local agencies studied more than 90 plans.
While the discussion continued, crews began to replace the Viaduct’s south end with surface road that features wider lanes and shoulders and an earthquake-resistant design in 2007. Foundations for the roadway are buried up to 260 ft. (79.25 m) deep — nearly half as tall as the nearby Space Needle — to reach beyond unstable soils and into sturdy ground.
Crews demolished the southern mile of the Viaduct in 2011 and replaced it with roadway. Completed on budget and one year ahead of schedule, this new section of SR 99 connects to the remaining Viaduct along the waterfront to keep traffic moving during construction.
“The Viaduct is two-plus miles; all of it was torn down but one mile and new roads were built.” While much of the double-deck bridge has been replaced with road, ultimately, the Viaduct will be replaced by the tunnel. The remaining portion of the Viaduct will be demolished after the SR 99 tunnel opens to traffic. “It’s at the end of its lifespan,” Newborn observes. “It’s seismically vulnerable and needs replacing,” said Newborn.
A temporary bypass structure connects the south end replacement to the Viaduct, enabling SR 99 to remain open during tunnel construction. That became a critical component of the decision making.
Can You Dig It?
By 2009, a plan involving a bored tunnel became the leading proposition to replace the Viaduct, in part because it was the only alternative that would allow SR 99 to remain open during construction. “There is the least impact to traffic by boring,” Newborn said. “Other than some temporary closures, traffic is undisturbed.”
Construction on the tunnel project began in 2011 after a detailed environmental study and approval from the Federal Highway Administration. The SR 99 Tunnel Project is estimated to cost $2 billion.
“The $2 billion includes other parts of the tunnel project that aren’t part of the contract,” said Newborn. A contract for $1.35 billion with Seattle Tunnel Partners includes design and build of the tunnel, boring the tunnel, building the double-deck highway inside the tunnel, building ramps for entrances and exits at the south and north portals and operations buildings on both ends that will house lighting, ventilation and other necessary systems. “Connections to the roads are a separate contract.”
The tunnel will connect with a mile-long stretch of new highway near Seattle’s stadiums at the south end of the tunnel and Aurora Avenue North at the north end. WSDOT maintains a role as the project’s “owner” and will verify the quality of STP’s work and ensure compliance with the contract.
Meet Bertha
In order to tunnel a two-mile stretch under Seattle’s busy streets, a massive boring machine was required. Manufactured in Japan by Hitachi Zosen Corp., a firm that has built more than 1,300 tunneling machines, Bertha is the world’s largest-diameter tunneling machine at 57.5 ft. (17.5 m) Hitachi was selected as the SR 99 tunneling machine manufacturer ahead of three other American and international firms based on technical requirements, support capabilities, price and schedule.
Bertha was specifically designed for the ground conditions beneath Seattle’s waterfront. “This area was built on tidal fill,” Newborn said. “There are different geological kinds of soil: glacial till (undisturbed soil), fill dirt, boulders and sand. The drill is designed to handle it.” There were no surprises, she added, due to extensive testing, boring and research.
In 2013, Bertha was shipped to Seattle, where she was reassembled in an 80-ft. (24.4 m)-deep pit located west of the city’s stadiums. After a series of tests, she began boring on July 30 that year.
The tunnel route begins on Alaskan Way South south of South King Street, moving toward First Avenue near Yesler Way before turning north near Stewart Street and ending at Sixth Avenue North and Thomas Street.
With an inside diameter of 52 ft. (15.8 m), the tunnel is big enough to support a double-deck road inside. The bored portion of the tunnel will be 1.7 mi. (2.7 km) long. There is cut-and-cover tunnel construction on both ends, bringing the total length of the SR 99 tunnel to two miles.
When completed, the tunnel will have two 11-ft. (3.3 m) travel lanes with an 8-ft. (2.4 m) safety shoulder and a 2-ft. (.6 m) shoulder in each direction to ensure there’s enough space for all vehicles and legal-size trucks.
The machine’s cutterhead will chip away the ground as it rotates and then carry excavated soil back through the machine using a spiral screw conveyor. The machine will dig an average of 35 ft. (10.7 m) per day. Bertha will advance 6 ft. (1.8 m) at a time, shoving off the rim of each ring, until the next ring is installed.?
Approximately 850,000 cu. yd. (649,871 cu m) of soil will be removed during the project. A conveyor belt that will eventually reach 9,000 ft. (2,743 m) in length will move excavated soil from the front of the machine out of the tunnel to barges waiting at nearby Terminal 46. Clean tunnel spoils will be barged to CalPortland’s Mats reclamation facility at Port Ludlow, where they will help fill a gravel quarry, Newborn reports.
The tunneling machine uses a laser as a reference as it moves forward through the earth. Projected from a fixed point behind the machine, the laser is received by a guidance system at the front of the machine that is precisely calibrated to the tunnel’s predetermined path. The guidance system is referenced by the machine’s operator to ensure the machine remains on course. The operator steers the machine by making slight adjustments with each push forward.
Next, 10 precast 6.5-ft. (2 m)-long concrete liner segments weighing 3,800 lbs. (1,724 kg) (slightly less for the keystone segment) form a “ring” that is placed in the excavated tunnel behind the front end of the machine. Newborn estimates that nearly 14,500 are required to complete the tunnel. “One hundred fifty-eight rings have been installed so far.”
“It’s challenging,” Newborn said of the work. Because of the proximity to Puget Sound, “dewatering is a requirement.” So is hundreds checking for ground movements as small as a fraction of an inch throughout the downtown construction area with the aid of monitoring devices.
Another challenge arose in December 2013: roughly 1,000 ft. into the tunnel drive, increased temperatures were recorded in the tunneling machine. Work stopped to allow for cleaning, replacing cutting tools on the machine’s cutterhead and re-starting the machine. However, the overheating persisted. An investigation into the cause revealed damage to the machine’s seal system and contamination within the main bearing.
To access the machine for repair, STP built an 80-ft. (24.4 m) wide, 120-ft.(36.6 m) -deep access pit in front of the machine, which is located about 60 ft. (18 m) below the surface in a fenced off construction zone. Once the pit was complete, the machine tunneled forward into it. Hitachi Zosen hired Mammoet to build a super crane to lift the front end of the machine—the cutterhead and drive unit—out of the ground for repair. On March 30, 2015, STP safely placed the front end of the tunneling machine and three other pieces on the repair platform located just south of the access pit.
Four major repairs and enhancements were planned:
• Replacing the damaged seal system with a more robust system
• Replacing the main bearing
• Installing enhanced monitoring systems
• Adding steel to strengthen the machine and accommodate the new seal system
The machine was fully disassembled by May of 2015. Seattle Tunnel Partners reported to WSDOT that damage to the machine was more extensive than anticipated.
Although, per contract, it is STP’s responsibility to repair the damaged machine, Newborn said, “The contractor is asking for a change order to pay for repairs.” STP requested $125 million in additional compensation, but WSDOT denied the request after determining it had no contractual merit. The contract includes specific and lengthy measures for resolving disputes. WSDOT continues to believe the state or taxpayers will not be responsible for costs associated with tunneling machine repairs.
Business as Usual
Meanwhile, other work continues, such as building the cut-and-cover sections of the tunnel, building the operations buildings on both sides of the tunnel and construction of a portion of the double-deck road inside the tunnel.
WSDOT reports that the north portal is taking shape near the Space Needle, including construction of the pit where the tunneling machine will emerge at the end of the job. Crews are also building the cut-and-cover tunnel that will connect the bored section of the tunnel to SR 99/Aurora Avenue North.
Crews at the south portal are continuing to work on the south portal operations building. Work is also focused on the south cut-and-cover tunnel that will connect the new south-end SR 99 roadway with the bored section of the tunnel.
“They’re still making the concrete segments in Puyallup that form the tunnel,” Newborn added. At its peak, the viaduct program will sustain more than 3,900 jobs
For the most part, SR 99 remains open during construction, except for inspection, maintenance and when the tunneling machine tunnels beneath the Viaduct, thanks in part to a construction bypass roadway that connects SR 99 to the Viaduct along the waterfront.
On budget, the project is “about two years behind schedule,” Newborn said, explaining that “STP controls the schedule.” Hoping it will be open to traffic in March 2018, she said, “The big test is when they put the borer in the ground and see how it functions. Nobody wants to see a delay.”
Light at the End
of the Tunnel
When completed, the tunnel will change the way traffic uses SR 99 in Seattle. Drivers approaching the tunnel from either direction will face a choice depending on their destination: use the tunnel to bypass downtown or exit to city streets and head into downtown. At the tunnel’s north end, downtown access will be similar to today, with on- and off-ramps near Seattle Center. From the south, new on- and off-ramps will connect SR 99 to downtown via the new waterfront street. A new overpass at the south end of downtown allows traffic to bypass train blockages near Seattle’s busiest port terminal.
Once the tunnel is operational, crews will demolish the Viaduct’s downtown waterfront section in preparation for street, transit and waterfront improvements planned by King County, City of Seattle and the Port of Seattle as part of the Alaskan Way Viaduct Replacement Program.
After the tunnel is open, WSDOT will permanently close the Battery Street Tunnel. WSDOT will then assist the city of Seattle in building a new Alaskan Way along the waterfront to connect SR 99 to downtown. “A new Alaskan Way will be built by city of Seattle,” Newborn said, “although WSDOT will be involved in the design, scope and financing.”
WSDOT’s vision is to create a “world-class waterfront on par with Sydney,” she continued. The tunnel and the new Alaskan Way are intended to be the cornerstone of the new waterfront.
But not everyone is pleased about it. Seattle environmentalists oppose the $2 billion project, noting that public transit, which carries more than 24,000 riders a week on the old Viaduct, will be inconvenienced by having to navigate surface streets into downtown next year.
WSDOT is working with businesses, residents and visitors to Pioneer Square to minimize inconvenience. A parking mitigation program features strategies to offset the impact of construction in the waterfront neighborhoods.
As for Bertha, once her work on the tunnel is done, STP will most likely dismantle her, possibly reusing or salvaging some of her parts for other projects.
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