Bertha Begins to Bore For Realsies

Seattle, Washington State, U.S. of A.  This thriving city is the scene of a modern technological thriller, called the ‘Viaduct Replacement’, and involves the world’s largest diameter Tunnel Boring Machine, or TBM, aptly named Bertha.  Bertha is supposed to drill a tunnel large enough to handle two two-lane roadways, over 9000 feet long, underneath downtown Seattle.  The machine started the job a couple of years ago, made it about 1,000 feet, and broke down.

After a mammoth effort, the TBM has been repaired, and has successfully mined to the last point before going underneath structures.  Mechanical failures after this cannot be addressed by digging a big hole and hauling the machine to the surface in pieces to be worked on.  Tunnel boring machines like Bertha, only smaller, are at work all over the world, and have been around for about 20 years or so.  Not only does Seattle have the world’s largest TBM, but the city is notable for being built partially on fill, which included wood, metal, concrete, cars, and probably a few bodies.  The soil is also very sandy, which makes boring a tunnel more difficult.

But this is not the first experience Seattle has had with tunnels, as two bus tunnels were bored underneath 4th Avenue in the late 1980’s, which proved to be very successful in spite of some initial problems.  Some are calling this project, which is to replace an aging and earthquake-damaged elevated highway, the ‘Big Dig’, but it is nothing like the enormous project in Boston.  Hopefully, it won’t end up being called the ‘Big Bust’ or something like that.  But even if Bertha experiences no more problems, the new tunnel will not accommodate the volume of traffic the Viaduct handles.


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