Bertha, the 57.5-ft diameter TBM building the SR 99 tunnel in Seattle, emerged into the reception pit on shortly before noon local time on Tuesday, completing its almost 2 miles of tunneling. The completion of tunnel boring operations ends one of the most high-profile tunneling projects undertaken in the United States.
Tunneling on the project, using the largest TBM in the world at the time it was built, began mining in July 2013 with an estimated completion date of late 2015. After mining about 10 percent of the tunnel, however, the TBM was halted in December 2013, about 60 ft underground. Seattle Tunnel Partners, the joint venture contractor building the project for the Washington State Department of Transportation, built an access pit to repair the machine in place, before relaunching the machine in earnest in early 2016.
Construction of the access pit and repair of the TBM led to a two-year delay in the project, but once repaired the machine made good progress and reached the end point in advance of the revised scheduled.
Completion of the tunnel, estimated in early 2019, will allow for the removal of the Alaskan Way Viaduct, which was damaged in the 2001 Nisqually earthquake.
The following is a press released issued on April 4 by WsDOT:
Bertha breaks through: SR 99 tunneling machine emerges near Seattle Center
Work continues inside the tunnel as crews work toward early 2019 opening
SEATTLE – A year ago, SR 99 tunnel crews were about to face their biggest challenge: a trip beneath the Alaskan Way Viaduct they were working to replace. Today, with the viaduct and more than 9,270 feet of new tunnel safely behind them, there was nothing left to face but daylight as the SR 99 tunneling machine chewed its way into a pit near Seattle Center.
Bertha’s 1.7-mile drive beneath Seattle came to a successful end Tuesday afternoon, 64 years to the day since the viaduct first opened to traffic. Led by the Washington State Department of Transportation, and designed and built by contractor Seattle Tunnel Partners, the tunnel project will move a two-mile section of SR 99 underground when it wraps up in early 2019. Crews will then demolish the viaduct, clearing the way for the city’s new waterfront.
“This is a historic moment in our state’s transportation history,” Gov. Jay Inslee said. “Innovation and perseverance are the engines that keep Washington in the forefront. There is still more work ahead but this moment is one worth celebrating.”
Crews will spend the next several days removing steel support braces that stand between Bertha and the interior of the 90-foot-deep disassembly pit. When the braces are gone, crews will drive the machine into its final position and begin cutting it into pieces for removal. As owner of the machine, the contractor will determine which pieces could be salvaged for use on other projects or recycled.
“We were always confident that we would successfully complete the tunnel drive,” Seattle Tunnel Partners Project Manager Chris Dixon said. “The dedication and commitment of everyone on the Seattle Tunnel Partners team has been exceptional, and we wouldn’t be at this milestone without the hard work of our crews. We look forward to continuing this outstanding progress through project completion.”
STP still has significant work to complete before the tunnel opens. Crews must finish building the double-deck highway within the circular walls that were built by crews inside the tunneling machine. Mechanical and electrical systems, plumbing and safety features also must be installed.
Even as crews are installing these systems, crews will begin the extensive task of testing and commissioning the tunnel to ensure it’s ready for traffic. Inspectors will individually test more than 8,500 separate components before testing each of the tunnel’s various systems as a whole.
“This truly is a remarkable feat of engineering,” Transportation Secretary Roger Millar said. “There’s still work to be done, but the individuals working on this job should be proud of this accomplishment.”
Over the next several years, the City of Seattle’s Waterfront Seattle project will build new public space and a surface boulevard in the place of the double-deck viaduct, which is scheduled for demolition in 2019.
“Today is a major construction milestone in our plan to reclaim Seattle’s waterfront,” Seattle Mayor Ed Murray said. “We are one step closer to taking down the viaduct to make way for a reimagined waterfront and surrounding downtown neighborhood. We will build a waterfront for pedestrians, transit and sensible car trips without a freeway wall casting a shadow over our vision of a well-connected 21st century city.”
King County Metro will continue to rely on SR 99 to route buses to Seattle after the tunnel opens, said King County Executive Dow Constantine.
“The new tunnel will provide fast, reliable travel for transit and freight past downtown traffic, and reunite the city with its waterfront,” said Constantine. “The breakthrough highlights what we can accomplish when we think big, act boldly, and embrace the ‘can-do’ tradition of our region.”
Port of Seattle Commission Commissioner Courtney Gregoire said the tunnel will work with the new waterfront surface street to accommodate freight traffic.
“This Alaskan Way route is essential to a strong port and linking our industrial lands between SODO and Ballard,” Gregoire said. “Strong, vibrant transportation connections are essential to keep our economy growing and creating middle-class jobs.”
Background on tunneling machine repairs
Manufactured in Japan by Hitachi Zosen Corp., Bertha arrived in Seattle in April 2013. The machine was launched from a pit near the stadiums in July of that year. In December 2013, STP stopped mining after measuring increased temperatures in the machine.
After an investigation, STP discovered damage to the machine’s main bearing. Crews completed repairs and resumed mining in December 2015. The cause of damage to the tunneling machine is in dispute and is currently in litigation. Neither WSDOT nor STP is able to comment further on ongoing legal issues.