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Monday, 12 May 2014 12:20cat

Seattle Tunnel Partners Setup Bertha Camera

Written by  TheStructuralEngineer.info
Bertha is the world's largest tunnel boring machine Bertha is the world's largest tunnel boring machine WSDOT Flickr

Seattle Tunnel Partners will begin digging a 120-foot deep pit this week to reach the front side of tunnel boring machine Bertha. The machine 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 battle between WSDOT and Seattle Tunnel Partners to determine who is at fault for not removing the well casing and who is responsible for cost overruns is still ongoing. WSDOT does not want the project to turn out similar to Boston’s Big Dig and end up costing taxpayers millions. A court will eventually rule on who is a fault.

In the mean time, Seattle Tunnel Partners will begin digging a 120-foot deep, 80-foot diameter pit to remove the front end of Bertha and repair the machine. WSDOT recently completed an environmental impact study for the pit. Seattle Tunnel Partners will inject concrete grout into the soil to stiffen the soil and make it easier to drill downward. They’ll install a ring of concrete columns and then remove the soil from inside the ring. The columns will be completed in July and the pit will be finished in September. The public will be able to monitor the project’s progress thanks to a camera installed by Seattle Tunnel Partners alongside the Alaskan Way Viaduct.

Workers will repair Bertha once the 120-foot pit is completed. The machine is expected to resume boring in March 2015. Seattle Tunnel Partners expects to open the tunnel in November 2016.

Sources: Seattle TimesFox News

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