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TBM Bertha’s new parts arrive

The SR 99 tunnel boring machine’s (TBM’s) new inner seals have arrived from Japan, more than a year after the machine stalled on site.

Work on the Alaskan Way Viaduct replacement project was delayed when TBM Bertha stalled in December 2013. Last month it was confirmed that damage to the machine was more extensive than initially expected.

Contractor Seattle Tunnel Partners (STP) and TBM manufacturer Hitachi Zosen chose to redesign the machine’s seal system as part of the repair plan.

The new seal system will be easier to access if necessary and will be installed in the coming weeks, along with other key components including a new main bearing; enhanced monitoring systems; added steel to strengthen the machine and accommodate the new seal system; a widened opening at the centre of the cutterhead; and extended arms to mix excavated soil in the chamber behind the cutterhead.

The new parts were offloaded at Terminal 46 and trucked a short distance north to the repair area.

The TBM was scheduled to restart in August 2015, but STP is likely to issue a revised schedule for resuming tunnelling when the full scope of repairs is clear.

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