Bertha (tunnel boring machine)

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Front of a model of Bertha at Milepost 31, the tunnel project information center.
Freighter Fairpartner carrying the disassembled tunnel boring machine into the Port of Seattle

Bertha, at 17.5 meters (57 ft) in diameter, is the largest tunnel boring machine in the world as of 2013,[1] built specifically for the Washington State Department of Transportation's (WSDOT) Alaskan Way Viaduct replacement tunnel project in Seattle.[2] It was made by Hitachi Zosen Sakai Works in Osaka, Japan, and the machine's assembly was completed in Seattle in June 2013. The name Bertha, after Seattle's only female mayor, Bertha Knight Landes, was chosen by a panel including the Governor and Transportation Secretary from submissions from kindergarten through 12th graders, who were asked to suggest names of a female who had significant Washington state heritage.[3]

Route map of the Alaskan Way Viaduct replacement tunnel showing location where the tunnel boring machine became stuck on December 6, 2013.

On December 6, 2013, the machine's progress was halted by an unexpected impediment.[4] After a month's investigation, WSDOT announced that the machine's cutting blades had encountered an 8 in (200 mm) diameter, 119 ft (36 m) long steel pipe, one of several well casings left over from previous drilling done in 2002 to assess groundwater conditions and soil stability in the area in case of another earthquake, like the 2001 Nisqually earthquake which led to the need for a replacement for the Alaskan Way Viaduct.[5][6] Because the machine cannot cut through metal, the pipe damaged several of Bertha's cutting blades, necessitating blade replacement before the machine could proceed.[6] The pipes' locations were known to WSDOT and were supposed to have been removed; as of yet it is not known if the state agency or a contractor is responsible for the pipes having been left behind or for tunneling having proceeded without their having been removed.[5][6] As of December 6, 2013, Bertha had tunneled 1,019 ft (311 m), or 11%, of the total 9,270 ft (2,830 m) length of the tunnel,[7] stopping about 60 ft (18 m) below ground between South Jackson Street and South Main Street.[8] In early February 2014, as Bertha was preparing to continue drilling, workers discovered that it was overheating and subsequently that a main bearing seal had been damaged and required replacement. Multiple options were discussed to fix the problem, but Bertha is expected to be out of commission until March 2015.[9]


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