SR 99 TBM to Resume Digging in March 2015


TBM mining on the SR 99 tunnel is expected to resume in March 2015.

Seattle Tunnel Partners, the design-build contractor for the SR 99 tunnel project in Seattle, on April 21 released a new schedule that shows the tunneling machine will resume digging by the end of March 2015, according the Washington State Department of Transportation (WsDOT) website.

Construction will begin in late May on the pit STP will use to access and repair damage to the machine, which stopped tunneling in December. Building the pit is the first of several steps STP has laid out to resume tunneling:

  • Late May: Begin building the access pit’s underground walls.
  • Late July through September: Excavate the pit.
  • October: Remove the machine’s cutterhead and begin repairing damage to the seal system and main bearing.
  • February 2015: Test machine to ensure it is ready to tunnel beneath downtown.
  • Late March 2015: Resume tunneling.

These construction activities will be addressed in accordance with the SR 99 tunnel contract. The updated construction timeline delays tunnel boring by up to 16 months, but STP hopes to recover as much as four months of schedule to meet the November 2016 tunnel opening date established in the 2010 request for proposals. STP had proposed opening the tunnel in late 2015, 11 months earlier than WsDOT’s our original requirement.

STP informed WsDOT that crews will replace the machine’s main bearing and install a more robust seal system, which could include strengthening the seals, installing redundant systems, and adding monitoring equipment. Additional details will be included in a plan to be submitted for review by June 16.

The repair schedule will include additional time to accommodate potential improvements to the machine that STP or the machine’s manufacturer, Hitachi Zosen Corp., might choose to make after the cutterhead is removed and crews are able to perform a full inspection. WsDOT will work with its strategic technical advisory team, made up of international and national tunneling experts, as well as consultants, to review the plan.

Despite the delay in tunneling, more than $750 million worth of work at the tunnel portals and elsewhere along the SR 99 corridor is not affected and continues full speed ahead.

West of Seattle’s stadiums, crews are building the future connection between the tunnel and the new section of SR 99 that was completed in 2012 after the viaduct’s southern mile was demolished. Crews are also making progress on the south portal operations building, which will house lighting, ventilation, emergency systems and other vital components needed to operate the tunnel.

Meanwhile, at the tunnel’s future north portal, crews are building the connection between the tunnel and Aurora Avenue North, the north portal operations building and the 80-ft deep pit where the tunneling machine will emerge at the end of its journey beneath downtown. Work is also ongoing in Frederickson, Wash., where crews have manufactured 72 percent of the concrete segments that are pieced together to form the tunnel’s exterior walls.

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