The Bertha Tunnel Boring Machine, at 57.5 feet (17.5 m) in diameter, is the world's largest TBM. On July 30, Bertha began digging a tunnel beneath downtown Seattle to replace the SR 99 Alaskan Way Viaduct. According to the Washington Department of Transportation (WSDOT), an obstruction on her way, last Friday, forced Bertha to stop unexpectedly.
The TBM is working 60 ft (18.3 m) underground and has completed boring 1,000 ft (304.8 m) of tunnel, about one-eighth of the route from Sodo to South Lake Union, since July. This obstruction is the fourth delay for the project. Engineers are currently trying to identify the object, whether it is natural or man-made, and to find out the way to remove it. WSDOT reassures that Bertha wasn't damaged in any way but they don't know yet how long this delay will last and how it will affect the opening which is scheduled for late 2015.
See also: 'The information age in Geotechnics is here: US Tunnel Boring Machines tweet and people listen!'
Find tweeting Bertha here.
Sources: The Seattle Times, KOMOnews
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