That Is, If Subway Tunnelers Can Make It Through Gas Fumes, Cave-Ins, Ice Age Rock And All the Resultant Delays


August 18, 1991|By Doug Birch

Like the Gothic cathedrals of Europe, modern urban subways are built in pieces over decades by succeeding generations of craftsmen. They're designed to last centuries. They're supposed transport souls. And constructing one takes an unshakable faith that despite America's idolatrous worship of the auto, there is a future for public transit.

Building these huge subterranean monuments -- Atlanta's MARTA, San Francisco's BART, Baltimore's Metro -- also takes billions of dollars, small armies of workers, advanced technology and centuries-old skills. It takes patience, grit and deep pockets to cope with the perils of the underworld.

Take the twin subway tunnels being dug between Johns Hopkins Hospital and the existing Charles Center Metro stop. The distance is only about 7,600 feet, and a one-way ride is expected to last only three minutes and 36 seconds. But construction will probably take more than 5 1/2 years and cost $321 million.

Since miners began digging the Hopkins tunnels a year ago, they've choked on gasoline fumes, watched balls of flame bloom from the tunnel floor and dug out after several minor "runs," in which soil spills from the tunnel face. In November, a larger run opened a swimming pool-sized crater on Orleans Street and caused chest-deep flooding of both shafts.

No one has been killed or seriously injured. But the gasoline fumes and concern about spills caused work to halt for seven months while the state Mass Transit Administration and Kiewit-Shea A.J.V., the tunnel builder, puzzled over what to do.

As of mid-July, those delays were expected to cost $20 million. But the project's $321 million budget, 85 percent of which is being paid for by the federal government, includes more than $53 million to cover unexpected changes in the contract and other "contingencies." That means, MTA officials say, the project is still not expected to cost more than $321 million -- though it's less likely to come in under budget. Meanwhile, the MTA decided in mid-July to reduce some of the delays by beginning a separate tunneling operation from the Shot Tower station toward Charles Center.

Miners, engineers and the MTA weren't surprised by the headaches. Boring subways under a city is like performing delicate surgery -- it is a costly, dangerous and unpredictable undertaking.

The path of the subway takes it through layers of compact Ice Age sand that must be excavated carefully to avoid spills at the tunnel face. Studding the soft sand are outcroppings of rock, which must be drilled and shaved and shattered.

To keep the tunnel from caving in, miners work inside a protective TBM (tunnel boring machine), a 22-foot-diameter steel ring that lurches along as digging progresses. As it passes, the ++ tunnel walls behind them must immediately be shored up, either with steel hoops connecting oak board "lagging" or with precast concrete shells.

Chemical grout, a pungent and watery liquid that glues soil together, must be injected into loose soil to prevent settlement, which can shift and weaken the foundations of buildings or utility lines near the surface. Water may trickle up from the "invert," or floor of the tunnel, or dribble out of walls, or shoot out of rock under high pressure as it flows in rivulets or streams or vast blind underground rivers. Tunnels are hot, muddy, cramped and loud. Hydraulic fluid makes the steel machinery slick. And no one ever knows what to expect, despite extensive surveys and studies by geologists.

TUNNELING HAS ALWAYS been a perilous game of blind-man's bluff.

Twenty men died trying to build one of the first compressed-air tunnels in America, under the Hudson River from New Jersey to New York City in 1880. Seventeen workers have died building Washington's Metrorail since construction of the 78-mile system began 22 years ago. (Two died building the first 13.6 miles of Baltimore's Metro, completed in 1987.)

LaRoy "Bud" Morris, a 53-year-old fireplug of a man and a senior inspector on the Hopkins project, has been blasting and shoveling tunnels for 35 years -- helping build everything from huge wine cellars in California's Napa Valley to the tunnel networks of San Francisco's BART and Washington's Metrorail.

When Mr. Morris started tunneling in 1955, building a 6.5-mile water tunnel for a hydroelectric project in Oroville, Calif., there was a grisly rule of thumb. "Back then it was considered a man a mile, that was an old saying tunnel stiffs had," he says.

THE HOPKINS TUNNELS ARE "extremely difficult" to dig, says Peter J. Schmidt, assistant general manager for development at the MTA, because it starts above the water table and moves 20 feet below it. The tunnelers must navigate delicately between softer soil closer to the surface -- with its foundations and phone lines and sewer pipes -- and the first reefs of bedrock below.

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