Mining Resumes on SR 99 Tunnel
The State Route 99 tunneling machine entered its next phase of testing Dec. 22 as it moved forward, installing a tunnel ring at the bottom of the 120-ft deep repair pit. Seattle Tunnel Partners (STP), the Washington State Department of Transportation’s design-build contractor for the tunnel project, plans to tunnel a short distance further in the access pit tunnel before giving crews a break for the holidays.
“Testing the machine in the conditions it will face during the rest of the tunnel drive is a critical part of our work to resume full-production mining,” said Chris Dixon, STP project manager. “The next several hundred feet of excavation will give us the information we need to make final adjustments
In this Dec. 15, 2015 photo, a crew member working for Seattle Tunnel Partners watches a crane lift other crew members out of the pit that STP used to access and repair Bertha, the SR 99 tunneling machine. Crews are filling in the pit as they prepare to resume tunneling, which began Dec. 22.
before we tunnel beneath the viaduct and downtown.”
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After the new year, STP plans to mine out of the access pit toward a planned maintenance stop 450 ft to the north. Along the way crews will mine slowly while installing tunnel rings and continuing to run tests. When the machine reaches the maintenance stop – essentially an underground block of concrete just south of Colman Dock – crews will perform maintenance and make final adjustments before diving beneath the viaduct.
Tunneling under the viaduct will require a full closure of SR 99 through downtown for approximately two weeks. The contractor’s latest projections show that the closure will occur in March, but the actual closure date will depend on Bertha’s progress and the state cannot verify the contractor’s schedule.
STP and Bertha’s manufacturer, Hitachi Zosen, are responsible for the repair effort, including the schedule. While the machine was under repair, STP continued essential work at the future tunnel portals, including construction of ramp and highway connections, and the buildings that will house tunnel operations.
STP crews halted tunneling in December 2013 after the machine overheated. After an investigation, they discovered damage to the seal system and determined it needed to be replaced along with the main bearing. The cause of the damage has not been determined. Responsibility for costs associated with the delay will be determined through the process outlined in the tunnel contract.
Click here to see a new time-lapse video showing STP’s work to backfill the access pit. Click here for more information about the SR 99 Tunnel Project, part of the Alaskan Way Viaduct Replacement Program.
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