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Seattle tunnelling machine reaches rescue shaft

Washing State Department of Transport (WSDOT) has confirmed that work to repair the tunnel boring machine (TBM) on the Alaskan Way Viaduct replacement scheme in Seattle, US reached a milestone yesterday with breakthrough into a rescue shaft.

Contractor Seattle Tunnel Partners and tunnel boring machine manufacturer Hitachi Zosen constructed the shaft to reach the SR 99 TBM that has been stalled since December 2013 following clogging of the cutter head and high temperatures.

Hyperbaric inspections in January 2014 revealed that there were no major obstructions in front of or within the cutterhead and since then work has been underway to reach the TBM to repair damage to the seal system and main bearing.

Shaft construction started in April last year and STP had expected to start testing of the machine in February 2015 with the aim of resuming tunnelling activity in late March 2015.

WSDOT has said that the issues may not delay the planned opening of the 3.2km twin-deck tunnel in November 2016 as STP had originally expected to complete the tunnel at the end of 2015.

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