Bertha damage halts excavation for 12 months 22 Apr 2014
- TBM Bertha will not resume excavation of the Alaskan Way viaduct replacement tunnel for nearly a year while the damaged main bearing is replaced and a new “more robust” seal assembly system is installed.
- According to a revised works schedule released yesterday (April 21, 2014) by the design build contractor - Seattle Tunnel Partners (STP) - the world record 17.48m diameter Hitachi Zosen EPBM will resume tunneling at the end of March 2015.
Explaining the Bertha recovery strategy
- Excavation of the shaft that STP will use to access the cutterhead from in front of and above the machine will begin at the end of next month (May 2014). TBM Bertha stopped tunneling in December last year after experiencing higher than usual temperature readings at the cutterhead. Initially the cause was thought to be a buried steel well casing, but in February this year, after the mangled pipe was cleared from the cutterhead following a number of interventions under hyperbaric conditions, failure of the seals protecting the main bearing was cited as the likely cause.
- The revised recovery schedule drawn up by WSDOT’s tunnel contractor comprises: construction of the access shaft underground walls (late May); shaft excavation (July-September); removal of Bertha’s cutterhead and the start of repairs to the damaged seal system and main bearing (November 2014-February 2015); testing the machine to ensure it is ready to tunnel beneath Downtown Seattle (February 2015); leading to a resumption of mechanized tunneling in late March 2015.
- A spokesman for the project owner, WSDOT, said: “These construction activities will be addressed in accordance with the SR99 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 our original tunnel opening date of November 2016.”
TBM Bertha’s seal system has failed
- STP, the joint venture partnership of Dragados and Tutor Perini, won the tunnel excavation contract partly as a result of gaining added value to its bid by promising to deliver the tunnel by 31 December 2015, although incentives to a maximum value of US$25 million are still payable for contract completion before the November 13, 2016 date. If this date is missed the contractor faces financial penalties of up to $100,000 per day.
- “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.” (November 2016)
- 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.
TBM Bertha has moved 2ft since December 6, 2014
- The repair schedule will include additional time to accommodate potential improvements to the machine that STP or the machine’s manufacturer, Hitachi Zosen, 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 (STAT), 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 Alaskan Way Viaduct Program Administrator. “We will 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 US$750 million worth of work at the tunnel portals and elsewhere along the SR99 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 SR99 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, Washington, where crews have manufactured 72 percent of the concrete segments needed to complete the tunnel lining.
WSDOT questions contractor TBM decisions - TunnelTalk, March 2014
STP-WSDOT clashes threaten Seattle project - TunnelTalk, March 2014
TBM Bertha suffers main bearing seal failure - TunnelTalk, February 2014
Addressing Bertha's bearing seal issues - TunnelTalk, February 2014
Mighty TBM procurement for Seattle - TunnelTalk, July 2011
Hyperbaric inspections begin in Seattle - TunnelTalk, January 2014
Investigating the Seattle meg-TBM stoppage - TunnelTalk, January 2014
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