SR 99 tunneling machine to resume digging in March 2015

Posted on Apr 21 2014 12:11 PM

See video of Monday's press conference

Today, Seattle Tunnel Partners, our design-build contractor for the tunnel project, released a new schedule that shows the SR 99 tunneling machine will resume digging by the end of March 2015.

Construction will begin late next month on the pit STP will use to access and repair damage to the machine, which stopped tunneling in December. Building the pit (pdf 715 kb) 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 five months of schedule to meet the November 2016 tunnel opening date we established in our 2010 request for proposals. STP had proposed opening the tunnel in late 2015, 11 months earlier than our original requirement.

STP has informed us 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 to us 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. We will work with our strategic technical advisory team, made up of international and national tunneling experts, as well as consultants, to review the plan.

More than $750 million in continuing work
We’re disappointed by this delay, but believe the schedule is moving in the right direction. We’re also focused on the bigger picture, which includes more than $750 million worth of work at the tunnel portals and elsewhere along the SR 99 corridor. That construction is not affected by the tunneling stoppage 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-foot-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.  

Before and after images of our progress are available on Flickr, along with regularly updated photos of construction. 


Previous updates 

April 3, 2014 update - Setting the stage for Bertha's repairs

March 13, 2014 update - Seattle Tunnel Partners submits repair plan, archaeological surveys underway

Feb. 28, 2014 update - A week in review: Bertha repair plan, ERP’s 2014 report and a viaduct weekend closure reminder

Feb. 27, 2014 update - How is an early or late tunnel opening addressed in the design-build contract?

Feb. 25, 2014 update - Ground settlement near the viaduct is safe, expected

Click here to see a full archive of progress updates