The state Route 99 tunneling machine will resume digging by the end of March 2015, according to a schedule released today, April 21, by the project’s design-build contractor, Seattle Tunnel Partners.

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 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 the 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. While this timeline delays tunnel boring by up to 16 months, STP hopes to recover as much as four months of schedule to meet WSDOT’s original tunnel opening date of November 2016. STP had proposed opening the tunnel in late 2015.

“Resuming tunneling will take longer than any of us would have liked, but making these repairs is a significant engineering challenge that must be done safely,” said Chris Dixon, Seattle Tunnel Partners project manager. “We are committed to this project, and to taking the necessary steps to recover time and open the tunnel to drivers by WSDOT’s original target date.”

STP has 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 to WSDOT 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.

“We are disappointed by this delay, but we believe the new schedule is moving in the right direction,” said Todd Trepanier, WSDOT’s Alaskan Way Viaduct program administrator. “We’ll continue to work with STP in their efforts to resume tunneling. We’re also focused on the rest of the program, 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.