Bertha bearing to get 86-tonne reinforcement
25 June 2014
Peter Kenyon, TunnelTalk
- Seattle Tunnel Partners (STP), the contractor joint venture team of Dragados USA and Tutor Perini, announces details of its repair strategy for the world record 17.48m diameter Hitachi Zosen TBM.
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Bearing block undergoing modification in Japan
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New outer seal ring fabrication (June 9, 2014)
- Under what Project Manager Chris Dixon called an “aggressive schedule”, replacement of the main bearing, repairs to the ruptured sealing system that should have protected the bearing from dirt and grit, and installation of 86 tonne of extra steel ribs and blocks to make the machine more rigid, will take until January next year (2015) to complete.
- The latest schedule has been submitted to project owner WSDOT following a series of meetings between the contractor team that is excavating the 2.7km SR99 Alaskan Way Viaduct Replacement Tunnel, and the Japanese manufacturer of the machine that has not moved since December 2013.
- Dixon told a press conference that he and executives from Tutor Perini and Dragados flew to Japan for a “critical meeting” on June 4 to discuss Bertha’s repair plan with Hitachi Zosen.
- “We got a commitment to meet the schedule, which is an aggressive one, and the other thing we've impressed upon them is that whatever repairs they carry out to fix the seal problem, we expect them to go above and beyond that, so that we have a machine that we are 100% confident can tunnel the remaining 8,000 ft under the city of Seattle, without any further incident.”
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1. Grout injection
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2. Sinking 75 piles
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3. Dewatering wells
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4. Short drive into shaft
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5. Crane installation
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6. Lifting main components
- The first phase of the recovery plan – excavation of the recovery shaft – is scheduled to be completed by mid-October (2014). Grout injection between existing segments of the underground walls originally constructed either side of Bertha’s drive to improve ground stability in the vicinity of the viaduct during the early phase of tunnelling, has already been completed. This is aimed at further improving stability and minimizing water ingress in anticipation of the next phase of the recovery plan – excavation of an access shaft ahead of the TBM via which the cutterhead, main bearing and sealing systems can be lifted and removed. Grout injection in the location at the back of the TBM shield, to further seal water out of the access shaft, has also been completed. STP crews are now installing 75 concrete piles to form the circular walls of the 120ft deep x 80ft diameter shaft that will be excavated ahead of the cutterhead and through which the TBM will then drive into.
- According to the updated schedule issued within the last week, excavation of the recovery shaft will begin next month (July 2014), for completion in October. The machine will be ready for testing in mid-February with tunnelling now expected to resume at the end of March (2015). Dixon says that the actual cause of the damage to Bertha will not be known until the main bearing and seal system are removed from behind the cutterhead and inspected in the workshop.
- Enhancements announced in documentation released by STP include:
- Installation of a new main bearing, which is to be shipped from Japan where it is currently located. The original contract specification was for a spare to be available.
- Replacement of the seals with “a more robust system,” and installation of a new outer seal ring. Adding 118 extra steel plates and ribs to the front body and a further 98 to the bearing block to “provide additional rigidity.”
- Installing extra monitoring equipment, including more sensors around the bearing seals.
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STP animated TBM recovery and repair plan
- WSDOT confirms that STP has so far submitted US$188 million of ‘change order’ requests, including $125 million “in additional compensation and time because they believe the TBM was damaged by a steel well casing originally installed by WSDOT.” The request relating to the steel well casing claim, plus a further $32 million worth of change order claims have been refused, with the remaining $31 million “under review,” said Laura Newborn for WSDOT. A complicated third party review system is in place if STP decides to contest the refusal of its change order claim, but final resolution of this could take a number of years.
- “Our position on this issue is clear: WSDOT informed STP and other prospective bidders of the well casing in documents contained within the RFP that was issued for the project in 2010. It is the contractor’s responsibility to ensure that their design and construction activities take into account all of the information provided to them. Therefore, we have denied their request,” said Newborn.
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STP Repair Plan (June 16)
TBM Bertha repairs strategy – TunnelCast, April 2014
Twelve month repair job for TBM Bertha – TunnelTalk, April 2014
Addressing the Bertha bearing seal issues – TunnelTalk, February 2014
WSDOT questions contractor TBM decisions – TunnelTalk, March 2014
TBM Bertha suffers bearing seal failure – TunnelTalk, February 2014
Hyperbaric inspections begin in Seattle – TunnelTalk, January 2014
Investigating the Seattle mega-TBM stoppage – TunnelTalk, January 2014
Dewatering to help deal with stuck Bertha – TunnelTalk, December 2013
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