Bertha – The Tunnel is Finished, but Her Legacy Continues

September 28, 2017
John P. Ahlers - Ahlers & Cressman PLLC

The Tunnel Boring Machine (“TBM”) known as “Bertha,” built by Hitachi Zosen Corp in Osaka, Japan, was the world’s largest TBM at 57.5 ft. in diameter. The TBM was built to drill the Seattle SR 99 Viaduct replacement tunnel. Seattle Tunnel Partners (“STP”) has a contract with the Washington State Department of Transportation (WSDOT) to dig the two-mile tunnel which is now complete.

In December of 2013, tunneling was stopped ostensibly because a 119 ft.-long, eight-inch diameter steel well casing halted the TBM. See 2/15 Blog “Bertha is Stuck and She Remains Mired in Controversy.” Reports are that WSDOT installed the pipe in 2002 to measure groundwater levels and the pipe was allegedly mentioned in the reference material provided to bidders. STP had assumed that the pipe had been removed until the steel casing got stuck in Bertha’s cutting teeth, halting progress. See 1/30/14 Blog “Big Bertha Stuck: Differing Site Condition Principles Revisited.” STP had a design-build contract with WSDOT. The contract contains a Differing Site Conditions (“DSC”) clause pursuant to which if the contractor can prove that the eight-inch pipe was an unforeseen condition (not disclosed in the contract documents), and that the unforeseen condition caused the TBM’s failure, STP is entitled to an equitable adjustment of its contract.

Mr. Ahlers may be contacted at


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