A Complicated Dig: Dulles Airport MetroRail Extension (Wash Post)

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[Editor's note: Explanatory graphic from this weekend's Washington Post illustrates how "Building a Metrorail Tunnel at Tysons Corner Takes Brute Force Applied With a Deft Touch" in five panels. Click image above for larger version.]

18 Feet Done, Many More to Go

Republished from The Washington Post.
By Lisa Rein. Graphic by Todd Lindeman and Brenna Maloney.
Sunday, October 18, 2009

Cars crawl down Route 123 in the afternoon rush. Forty feet below them, giant machines and men wearing yellow hard hats begin their advance under Tysons Corner to bring Northern Virginia commuters their holy grail: a new subway.

At $85 million, the half-mile tunnel is the costliest and most complex engineering feat of the 23-mile Metro extension to Dulles International Airport. It will be built while 3,500 cars and trucks cross its path each hour, while the Courtyard Marriott serves breakfast and guests swim in its pool, while hands are shaken over aerospace deals at BAE Systems. It will carry on under two miles of tangled utility lines that convey to Tysons everything from electricity to some of the nation’s most secret intelligence. As of Friday, after three months of digging and prep work, workers had hollowed out the half-mile tunnel’s first 18 feet.

One wrong move and the foundation of an office garage could settle, a top-secret communique through the U.S. Army’s microwave tower right above the tunnel’s path by Clyde’s restaurant could be lost.

“You’ve got gas lines, water lines, drainage lines, electrical duct banks, black wires and a lot more in a busy urban area, which makes for a very challenging tunneling environment,” says Dominic Cerulli, the engineer for Bechtel in charge of building the tunnel. He guides visitors on the first tour of the project on a recent weekday. “I’ve been on jobs where you’re tunneling out in the middle of a parking lot. Here you’ve got to keep businesses up and running.”

When it opens in 2013, the first leg of the rail line will extend 11.5 miles from East Falls Church through Tysons to Wiehle Avenue in Reston. The tunnel, scheduled for completion in late 2011, will connect two of the four Metro stations in Tysons. Cerulli likes to say his project is the toughest part of the line. “But don’t say I said that, because the guideway is also complicated,” he jokes, referring to the elevated section, still 18 months off, that will carry the trains 55 feet above the Capital Beltway.

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