The City of Seattle is replacing the two-level highway viaduct that dominates the downtown shoreline with a two-level tunnel. A very large tunnel boring machine, named Bertha in honor of an early Seattle mayor, has been excavating the tunnel for several months. In December, Bertha encountered an unknown obstruction and came to a halt. Seattleites immediately engaged in humorous speculation about what the unyielding object could be (suggestions included members of the Seahawks’ defensive line). After considerable work to access the cutterhead, it has been reported that the obstruction is, at least in part, a steel well pipe believed to have been installed in 2002 as part of a geotechnical investigation of the viaduct area. It is not yet clear whether other reasons exist for Bertha’s lack of progress. Because Bertha is the largest tunnel boring machine ever used in the United States and because of the funny suggested obstructions, Bertha was featured in some national news stories. The full story of the obstruction remains to be determined. The legal debate has already begun about whether the obstruction, whatever it is, is within the scope of risk accepted by the contractor (Seattle Tunnel Partners), or whether it is a risk that should be borne by the owner.
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