TBM recovery shaft delays in Seattle20 Aug 2014

Design modifications to the shaft currently being excavated to enable access to stricken TBM Bertha have pushed back its completion by a month and eaten into the two months of ‘float’ time built into Seattle Tunnel Partners’ initial (June) recovery plan.

Confident: STP Project Manager Chris Dixon

Construction of the shaft was due to be completed under the original schedule by the beginning of October, but this has now been pushed back to the end of October or early November. The work is taking longer than previously anticipated as a result of complications surrounding installation of the exceptionally large interlocking piles that are needed to make the shaft self-supporting and thereby enable the TBM to break through. The total number of piles has increased by 11 from the original design, to 84 in total. Despite the delay, Chris Dixon of STP told reporters at a press conference in Seattle on July 29 that the latest delay will not impact on the planned resumption of the TBM drive in March 2015.

Concerned: Todd Trepanier of WSDOT

In the TunnelTalk Podcast (Podcast 1, below) Dixon details the works currently taking place and explains why changes were needed to the shaft’s initial design.

At the same press conference Todd Trepanier of the Washington State Department of Transportation (WSDOT) told reporters that the latest delays have served to increase existing concerns about the ability of its construction team to resume mining in March 2015, as stated in the original June 16 recovery plan (Podcast 2, below).

Podcast 1 – Chris Dixon explains TBM recovery shaft delays

Podcast 2 – Todd Trepanier voices WSDOT concerns

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  Seattle Tunnel Partners' June recovery plan

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  Recovery shaft excavation delays