By Kirk Johnson, December 19, 2013
In October, workers walked through the first rings of the highway tunnel being built under Seattle’s waterfront toward the boring machine called Bertha.
SEATTLE — A secret subterranean heart, tinged with mystery and myth, beats beneath the streets in many of the world’s great cities. Tourists seek out the catacombs of Rome, the sewers of Paris and the subway tunnels of New York. Some people believe a den of interstellar aliens lurks beneath Denver International Airport.
Now Seattle, at least for now, has joined that exclusive club.
Something unknown, engineers say — and all the more intriguing to many
residents for being unknown — has blocked the progress of the
biggest-diameter tunnel-boring machine in use on the planet, a
high-tech, largely automated wonder called Bertha. At five stories high
with a crew of 20, the cigar-shaped behemoth was grinding away
underground on a two-mile-long, $3.1 billion highway tunnel
under the city’s waterfront on Dec. 6 when it encountered something in
its path that managers still simply refer to as “the object.”
The object’s composition and provenance remain unknown almost two weeks
after first contact because in a state-of-the-art tunneling machine, as
it turns out, you can’t exactly poke your head out the window and look.
“What we’re focusing on now is creating conditions that will allow us to
enter the chamber behind the cutter head and see what the situation
is,” Chris Dixon, the project manager at Seattle Tunnel Partners, the
construction contractor, said in an interview this week. Mr. Dixon said
he felt pretty confident that the blockage will turn out to be nothing
more or less romantic than a giant boulder, perhaps left over from the
Ice Age glaciers that scoured and crushed this corner of the continent
17,000 years ago.
But the unknown is a tantalizing subject. Some residents said they
believe, or want to believe, that a piece of old Seattle, buried in the
pell-mell rush of city-building in the 1800s, when a mucky waterfront
wetland was filled in to make room for commerce, could be Bertha’s big
trouble. That theory is bolstered by the fact that the blocked tunnel
section is also in the shallowest portion of the route, with the top of
the machine only around 45 feet below street grade.
“I’m going to believe it’s a piece of Seattle history until proven
otherwise,” said Ann Ferguson, the curator of the Seattle Collection at
the Seattle Public Library, who said she held out hope for something of
1890s Klondike Gold Rush vintage, when Seattle became the crazed and
booming gateway city to the gold fields of Alaska and Canada.
At the downtown storefront museum
for the tunnel project, called Milepost 31, visitors are cracking Jimmy
Hoffa jokes or spouting theories about buried train engines. Gabe
Martin, a sales clerk at a curio shop near the dig site, said he was
intrigued by the Prohibition era, when Seattle rode a tide of illegal
alcohol smuggled from Canada, and people had reason to bury things, not
wanting them found. “Bootlegger stuff,” he said.
Mr. Dixon said that efforts to drain water and reduce pressure at the
drill head, with a series of bore holes pushed down in recent days,
could allow workers to get safe access to the blocked site as early as
Friday. But working at atmospheric pressures similar to what a diver
would experience, the team could stay down only for short periods, he
said, and each visitor would then need time in a decompression chamber.
And there is something of a John Henry’s hammer theme to the tale of
Seattle’s object. Bertha is blind as a mole in front, with no
forward-facing windows or cameras, so a kind of spacewalk through
air-locked doors is required to get to the front of the machine for
inspection. And the removal or breaking up of the object is likely to be
done with jackhammers or other old-fashioned tools that a
tunnel-digging sandhog worker of generations past would recognize.
If the object can’t be broken up below ground, there would need to be
excavation down from the street. In any event, Mr. Dixon and other state
managers said, the machine’s forward progress could be halted for weeks
— though they stressed that work is continuing on the ends of the
tunnel, and that it is too early to talk about cost overruns or delays.
The tunnel is scheduled to be open to traffic by late 2015.
The tunnel is to run north and south along Elliott Bay from Century Link
Field, home of football’s Seahawks, to a point near the Space Needle on
the north, allowing demolition of an elevated roadway and improved
crosstown foot and bicycle access.
Economics and geology — two key threads of Seattle’s creation — underpin
the tunnel’s impetus. Planning for the project began after an
earthquake in 2001 revealed seismic vulnerability in the elevated
viaduct roadway, which was built in the 1950s. Businesses and real
estate interests were then sold on the idea that a tunnel, replacing the
viaduct, would open access between downtown and the waterfront.
But unlike, say, Boston or New York, where tunnels are common and
bedrock is close to the surface, getting to that end point is messy.
Seattle’s underbelly is more like pudding than soil — a slurry of sand,
gravel and clay, all jumbled and compressed by the pressures from a
3,000-foot-thick ice sheet that extended as far as Olympia, 50 miles
south. A city famous for being wet also has a high water table, only
about four to five feet down.
And because Seattle, as first encountered by European-American settlers,
was hardly conducive to being a city at all, with steep, glacier-carved
hills rolling right down to the water, the landscape was reshaped from
the beginning, with projects to grind down the hills. That in turn
created lots of landfill, which went into the waterfront to level it and
create land on which the city’s commercial center rose.
“It’s mind-boggling how much we have altered the landscape of Seattle,”
said David B. Williams, a geologist and author of a coming book about
the making of Seattle’s landscape, called “Too High and Too Steep,
Reshaping Seattle’s Topography.”
“The tunnel is just a continuation of that story,” he said as he walked
north of downtown, where a cliff face showed the layered strata of the
geologic past.
Mr. Williams, who blogs about local geology, speculated in a recent post
that the remains of a famous shipwreck, the Windward — which foundered
in 1875 and was buried near the waterfront — might be the kind of object
that Bertha encountered, though he conceded that the machine could
probably grind through a wood vessel as though it were paper.
In the end, he said, state engineers are probably right. A rock, huge in
size or in a configuration that the machine cannot quite get purchase
on to grind, is the most likely culprit. “I do hope it is not,” he said.
“It would be great to find some new mystery.”