The International Information Center for Structural Engineers

Wednesday, 30 July 2014 10:52cat

UPDATE: Bertha’s Repair Further Delayed

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Bertha's cutting face Bertha's cutting face Seattle Times

Repairing the tunnel-boring Bertha hit more delays this past week when it was announced the deep access pit that is being built to reach the front side of Bertha would be delayed by a month. Crews need more time to grind and chisel through concrete so the 120-foot deep vault in front of Bertha will be completed in August instead of July as originally planned. Chris Dixon, project director for Seattle Tunnel Partners, believes Bertha will still be fully repaired by March because the repairs had a two-month cushion added to the schedule. While Seattle Tunnel Partners is confident that the machine will be ready to complete the remaining 8,200 feet of tunneling needed for the Alaska Way Viaduct Replacement Tunnel project on time, Washington Department of Transportation is not as optimistic.

Bertha is the world’s largest tunneling machine, and it has been stuck underneath Seattle’s downtown waterfront since December 6, 2013. Bertha was built specifically for the Washington State Department of Transportation to work on the $3.1 billion Alaskan Way Viaduct Replacement Tunnel project. The machine completed a little over 1,000 feet of the expected 9,000-foot tunnel before getting stuck. In the six months since Bertha became stuck, WSDOT has determined that the machine ran into a 119-foot steel pipe that was left over from a 2002 project. The well casing was used to assess groundwater and soil conditions in the area to determine the seismic performance of the soil. Bertha is not able to cut through steel so the pipe damaged some of the machine’s cutting blades.

The pit Seattle Tunnel Partners is digging, will allow a crane to hoist Berta’s front end so the cutterhead and drive system can be repaired. The main bearing and its leaky seals will be replaced, and gaps within the cutting disc will be widened to reduce clogs when muck passes through. 

So far 53 of 84 buried columns in the pit are completed. Once the remaining columns are finished, Bertha will bore through the concrete wall and reach the access shaft. If crews can fix Bertha and the project does not have any other delays, the four-lane highway link will be finished by Fall 2016. Seattle Tunnel Partners filed a claim with the state Department of Transportation for $125 million related to repair delays. Washington DOT denied the claim, so one can expect lengthy negotiations or a legal battle between the two parties.

Sources: Seattle Times

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