Light at end of the tunnel Excavation finished on Metro extension

December 22, 1992|By Peter Jensen | Peter Jensen,Staff Writer

Excavation of the Baltimore Metro extension from Charles Center to Johns Hopkins Hospital was completed late Sunday, a holiday gift to those who have supervised the problem-plagued tunneling operation.

Mining equipment in the inbound tunnel reached the eastern wall of the future Shot Tower Station about 9:30 p.m., according to officials with the Mass Transit Administration. The site is about 60 feet below the intersection of East Baltimore and Front streets in the East Baltimore community of Jonestown.

The final link to be excavated in the 1.5-mile extension was the northerly tunnel of the twin passageways, between the hospital and Shot Tower. Outbound excavation was wrapped up Nov. 24 at a parallel point at Shot Tower Station.

"It's more a sense of relief than anything else," said Kenneth D. Merrill, the project's construction manager.

Since the mining began Aug. 7, 1990, the subway project has met numerous delays and cost overruns. Problems have resulted principally when excavators ran into, or came close to, pockets of gasoline-contaminated soil along the route through East Baltimore.

Originally expected to cost $321 million, the extension is now estimated to cost up to $337 million.

"I think that's pretty good," said Ronald J. Hartman, the MTA's administrator. "All we did was add a 5 percent margin to the price of the project, and we may still come in at budget by the time this is all over."

The subway extension is expected to open by late 1994 or early 1995.

Troubles began two months after the digging started, when workers encountered a pool of underground gasoline left at the site of a former gas station at Broadway and Mullikin Street.

That turned out to be the worst encounter with gasoline, causing a 10-month delay and adding $20 million as the tunnel environment had to be made explosion-proof.

A month later, there was a cave-in 100 feet away, at Broadway and Orleans, the result of "settling" of the ground above the tunnel and a water-main break.

That was followed by other run-ins with gasoline: in Washington Hill, the Charles L. Benton Jr. Building, and in Jonestown, not to mention an encounter with soil contaminated by leaking dry-cleaning fluid near Charles Center Station.

Compressed air is used to keep surrounding ground water out of the tunnels, which means air pressure is greater than normal in the passageways. In fact, workers must adjust to the pressure difference by using a hyperbaric chamber to reacclimate themselves without ill effects.

The problem has been that when air escapes, it has enough force to push vapors from long-forgotten pools of gasoline into the basements of homes and businesses.

After gasoline vapors were encountered in Jonestown, workers dug a system of venting wells, relocated a day-care center and removed a dozen abandoned underground storage tanks. The MTA hopes to recover some of the cost from the former owners of the tanks.

The setbacks have resulted in an 18-month delay in the excavation, which was supposed be wrapped up last January and will instead likely be completed in July.

The MTA hopes to make up some of that time in the later stages of construction.

Still, the completion of the excavation gave the MTA and its contractors reason to rejoice, if only because it means they are unlikely to run into any more surprises.

Mining is generally considered the most dangerous part of building a subway, yet the extension has not registered even serious injury.

"From here on out, there is much less uncertainty associated with the job," Mr. Hartman said.

About half the tunnels still need to be lined with a layer of concrete, and a 3-foot-thick bulkhead separates the tunnels from the stations -- kept in place because of the compressed air in the unlined tunnels.

When the linings are completed and the compressed air is removed, the bulkheads will be torn down -- most likely in April or May.

The tunneling has been performed by Kiewit-Shea A.J.V., under the supervision of DKP, a joint venture of three firms: Daniel, Mann, Johnson and Mendenhall; Kaiser Engineers Inc.; and Parsons Brinckerhoff Quade & Douglas Inc.

The excavation has removed 175,900 cubic feet of soil, sand and stone from the site, the equivalent of 1,900 dump-truck loads. The two 22-foot-wide tunnels are 6,305 feet long, with most of each below the water table.

Neither DKP nor the MTA held any official commemoration of the excavation landmark. Mr. Merrill of DKP brought in a bottle of champagne with a box of doughnuts for a 7 a.m. meeting with his staff. They drank it in paper cups.

"We had a few more problems than we anticipated in this tunneling project, but we all smiled a nice quiet smile today," said Peter J. Schmidt, the MTA's assistant general manager for development.

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