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Seattle's 'Bertha' is a not-so-lean tunneling machine

The 'engineering marvel' is drilling a tunnel through downtown that will replace an elevated highway and help redefine the city's waterfront.

August 19, 2013|By Rick Rojas

SEATTLE — Lying in an open pit near the heart of the city, the cylindrical mass of machinery looked like a spacecraft that had crash-landed. Or, as one architect described it, a dry-docked ocean liner. Or a skyscraper on its side. One person thought it resembled a giant coffin.

But it was "Bertha," a 7,000-ton, 326-foot-long and 57-foot-tall drilling device, which is playing a central role in a project that will redefine Seattle's waterfront — and perhaps the city itself.

The drill has embarked on a project to bore a 2-mile tunnel beneath the city's downtown and replace an unsightly, 60-year-old double-decker highway that courses along the waterfront, separating the high-rises of downtown from the majestic panorama of the Puget Sound.

The $3-billion project — one of largest public works undertakings in the country — began after a decade of contentious back-and-forth, scores of proposed ideas and a few failed ballots. Since the drilling began in late July, much of the attention has been directed at Bertha, named for the city's first and only female mayor and described by experts as being as sophisticated as it is gargantuan.

"Everybody's watching Seattle," said Douglas B. MacDonald, a former Washington state secretary of transportation, "because this is the trickiest, most ambitious, most technically challenging operation now going on in the world."

The machine, with a five-story diameter, was built in Osaka, Japan, and traveled across the Pacific in 41 pieces before arriving at Seattle's port in April.

"It's the biggest thing that's ever been built of its kind," said Phillip Thompson, a professor of civil and environmental engineering at Seattle University. "I think it comes close to meeting the standard of an engineering marvel."

It was designed to handle challenges specific to this project, such as the wildly inconsistent soil created by ancient glaciers — clay, sand, silt, cobblestone and boulders up to 3 feet in diameter. Planners also had to consider the route: a path wedged between stadiums and an active port, running below a bustling commercial center.

"That all adds up to having a really, really challenging site," said Linea Laird, the project administrator with the state Department of Transportation.

The project has been difficult since its genesis.

After the highway known as the Alaskan Way Viaduct was damaged in the 2001 Nisqually earthquake, officials decided to replace it, beginning a protracted debate that reached beyond a question of transportation to something larger: a vision for the future of Seattle. As MacDonald put it, the decision would have "50, 100 years' impact on what the waterfront of Seattle will look like."

In all, the list of more than 90 options was whittled down to three: replacing the three-lane Alaskan Way Viaduct with a larger roadway; digging a tunnel from above ground — a so-called cut-and-cover, such as Boston's Big Dig mega-project; or simply putting in a surface street, which would force motorists from their cars and, advocates for this plan hoped, onto public transportation.

As those plans ended up being untenable, officials looked into boring technology, which had gone through significant advancement in recent years. The solution arrived, MacDonald said, like something out of a Greek play — it seemingly came out nowhere. "The machine became the deus ex machina," he said.

Bertha was assembled in the 80-foot-deep pit and will displace 850,000 cubic yards of soil for the double-level, two-lane tunnel running between 60 and 200 feet below the ground. The viaduct will be demolished and replaced with a surface street and public park space.

Vlad Oustimovitch, a Seattle architect who served on an advisory panel, described the machine as allowing the city to have the benefits of a tunnel — opening up acres of land between downtown and the waterfront — without the aches that the Big Dig inflicted on Boston. A cut-and-cover "would be deep abdominal surgery, and this is more like arthroscopic surgery," he said.

The project requires lane closures on the Alaskan Way Viaduct, but officials said other options would have caused more disruption. Some business owners on the waterfront feared the other options would have forced them to close.

In recent months, officials have tried to engage the public on the project. Before the machine went to work, a crowd of hundreds, included the governor, gathered for a send-off. And there was a contest to name her (a boring machine, just like a boat or a muscle car, is almost always a lady). Entries included Aurora Borealis and the Alaskan Way.

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