Seattle Tunnel Partners (STP), the design-build contractor for the Alaskan Way Viaduct replacement tunnel in Seattle, announced on April 21 it will replace the bearing on the State Route 99 tunneling boring machine (TBM) and expects the machine to start tunneling again in March 2015.
Construction began 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. From July through September, STP will excavate the pit, and in October the machine’s cutterhead will be removed and repairs to the seal system and main bearing will begin. In February 2015, the TBM will be tested before it resumes tunneling in March.
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.
“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, STP project manager.
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.”