Like eager home improvers, subway construction crews broke through a wall yesterday and felt good about it.
The wall was a 3-foot-thick bulkhead leading to the east side of the future Shot Tower Station.
The event represented a significant milestone for the 1.5-mile Metro extension from Charles Center Station to Johns Hopkins Hospital. It means that the more northerly of the twin tunnels from the hospital to Charles Center now is unimpeded by barriers.
Workers can walk underground all the way from the hospital to the outer wall of Charles Center -- and even peak through a small hole that's been drilled through the concrete wall.
More importantly, it means that troublesome compressed air will no longer have to be used to keep surrounding ground water from leaking into the tunnels.
"I guess you could pass an M&M hand to hand and get it to Johns Hopkins if you want to, but the real significance is that we're no longer using the compressed air," said Peter J. Schmidt, the Mass Transit Administration's assistant general manager for development.
"I think it's a real milestone because the uncertainties of tunneling are now over with. From now on, the project is completely under our control."
The $337 million subway project is 5 percent over budget and about a year behind schedule, primarily because of encounters with gasoline-contaminated soil along the route through East Baltimore.
The problem of contaminated soil was aggravated by the presence of compressed air.
The air tended to leak out of the tunnels and push vapors from long-forgotten pockets of gasoline into the basements of homes and businesses.
Miners wrapped up excavation of the tunnels in December. But crews have been installing concrete liners inside the tunnels since then, and finally were able to turn off the compressed air Monday.
The subway extension is expected to open by late 1994 or early 1995.