SEATTLE’S BIGGEST BORE
Digging a great big hole sounds easy. Most of us did it at least
a dozen times before the age of 5. But what if you had to dig
that hole under a swath of the Sea le metropolitan area
thick with 100-year-old structures and 30-story apartment
buildings? What if the air pressure at the deepest part of the
hole were lethal to a human being? And what if, before you
even started, you learned you had to use a brand-new 7,000-
ton tunnel boring machine—that can’t back up if you make
a mistake? That was the task the Washington State Depart-
ment of Transportation faced when it decided to replace
Sea le’s 1950s-era AlaskanWay Viaduct with a double-decker
tunnel meant to protect Emerald City drivers from earth-
quakes. Here’s how they’ll do it.
BY JACQUELINE DETWILER
HEMISPHERESMAGAZINE.COM
•
DECEMBER 2012
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ILLUSTRATION BY JAMES PROVOST
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The tunnel boringmachine, which is
being built in Japan, is too big to traverse
the Pacific whole, so it will be shipped in
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pieces and then assembled on-site.
Transporting the largest chunks—which
can weigh up to 900 tons apiece—
to the assembly area requires a weight-
spreadingmover to avoid crushing
underground pipes and power lines.
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The 600 cutting tools on the borer’s
face will need to bemaintained and pos-
sibly replaced as it cuts, which can be a
problemat such intense air pressure. To
accomplish this feat, technicians will either
crawl through themachine’s one-of-a-kind
hollow, pressurized arms or reach the
cutting face through a series of air locks,
like deep-sea divers.
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Tomake sure Seattle’s buildings
remain secure while themachine works
beneath them, multiple agencies will
monitor the ground and local structures
using state-of-the-art systems mounted
on buildings or carried by satellites. “We
have belts and suspenders andmore belts
on the suspenders,” saysMatt Preedy, the
program’s deputy administrator. “We only
have one chance to get this right.”
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INNOVATION BUSINESS GADGETRY
HOW IT’S DONE
