After 10 days of around-the-clock tunneling, the SR 99 TBM’s biggest hurdle has been cleared. That hurdle – the Alaskan Way Viaduct it was built to replace – reopened for the Monday morning commute, bringing an early end to the much-anticipated closure of the highway.
Structural engineers with the Washington State Department of Transportation completed a thorough inspection of the viaduct on Sunday. Their inspection confirmed what a team of engineers observed throughout the past 10 days of tunneling: continued stability of the ground and the viaduct.
Contractor Seattle Tunnel Partners estimated that tunneling beneath the viaduct would take approximately two weeks. With the ground holding steady, and the most challenging part of the machine’s drive beneath the viaduct complete, WSDOT made the call to reopen both directions of State Route 99 through downtown.
“Closing a major highway is never easy, and the public deserves a big thank you for their patience and flexibility while this crucial work took place,” said Gov. Jay Inslee. “I would like to thank the WSDOT and STP project teams and construction crews on a job well done. To finish this piece of the project almost a week early is commendable. The planning and flexibility of commuters, along with strong coordination between WSDOT and partner agencies, ensured commuters had access to real-time information that helped them plan ahead.”
WSDOT temporarily closed SR 99 through Seattle so crews could more closely monitor the structure as the machine passed beneath. The tunnel team originally planned to keep the highway closed until after the machine had completely cleared the viaduct, but the success of the tunneling operation and the continued stability of the ground led to discussions of an early opening as work progressed.
By Friday, the machine had successfully tunneled through complex soils only 15 ft below the viaduct’s foundation – the closest the machine will come to any structure at any point in its drive beneath Seattle. On Sunday, STP completed installation of the rings beneath this critical location, clearing the way for the final inspection and the early opening of the highway. WSDOT’s 24-hour command center will remain open until the machine has successfully tunneled 385 ft, the distance at which it will be completely clear of the viaduct.
WSDOT worked closely with Seattle Department of Transportation, Seattle Police Department, King County Metro, King County Water Taxi, Sound Transit, Community Transit and the Port of Seattle to keep traffic moving and provide travel options for drivers during the closure.
“Removing traffic from the viaduct was critical to the success of this work, but we don’t want the closure to last a moment longer than it needs to,” said Acting Transportation Secretary Roger Millar. “I want to thank the WSDOT and STP project teams as well as our local partners for successfully managing the closure of a major highway in our system. And, a special thank you to the community for their patience. I hope commuters saw the value of having several transportation choices, and consider using alternatives to driving alone more regularly going forward.”
Millar said the success of STP’s drive beneath the viaduct will help build momentum for the remainder of the tunnel drive.
“The end of this closure marks a new beginning for the SR 99 Tunnel Project,” he said. “Much work remains, but we are encouraged by the contractor’s performance during this phase of the project. Our shared focus now, as it has been, is on delivering this tunnel to Washington taxpayers.”