Atlantic Avenue Station Rehabilitation
December 27, 2003
How to Hold Up a Subway Tunnel: Get a Big Hanger
By MICHAEL LUO
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The old entrance to the Atlantic Avenue subway station in Brooklyn was designed in 1908 by George L. Heins and Christopher G. Lafarge, who were also the architects of the Cathedral Church of St. John the Divine.
For the uninitiated, the Atlantic Avenue-Pacific Street subway station in Brooklyn has long been a daunting place, a jungle of confusing signs, dank corridors and complicated twists and turns.
A detailed map helps only slightly, revealing a tangle of 10 subway lines running through the terminal, as well as the Long Island Rail Road.
Making matters worse, over the last four years New York City Transit has been gutting the station, the fourth busiest in the system, and putting it back together piece by piece to relieve congestion underground.
The main problem was a narrow, nearly century-old pedestrian passageway under the tracks, choked with people. Engineers wanted to double the artery's width, a task complicated by the 131,000 people a day who still needed to use it and the nonstop parade of trains overhead.
"The concourses run underneath the street, underneath the 4, 5 and 2, 3 tracks and underneath the L.I.R.R. tracks," said Gary Negrycz, a project executive for the Turner Construction Company, which oversaw the work. "You've got to support all of that, mine out the earth underneath, construct the walls, new roofs, all while the trains run."
The resulting four-year nightmare of jackhammers, blocked stairwells and rerouted exits will finally end next month, and commuters will get their station back. But most will have missed the feat of engineering that unfolded all around them every day.
The traditional approach to widening the concourse would have been to simply excavate along the edges of the passageway, bolstering the roof in sections. But this was considered risky and laborious. If any of the earth slipped, even an inch, the tracks could dip and force transit officials to close the line above for repairs.
As engineers cast about for ideas, an unorthodox solution emerged: suspend the subway tunnel from its roof.
"By hanging it, the whole structure is supported before you ever take out one shovelful of dirt," Mr. Negrycz said.
At first, transit officials were skeptical. The technique was suggested by Irwin S. Toporoff, 70, an engineering consultant and tunneling expert.
"This had never been done before," Mr. Negrycz said.
Mysore Nagaraja, president of the Metropolitan Transportation Authority's capital construction corporation, said, "It was quite a radical scheme."
But Mr. Toporoff was convinced it would work. Although a subway tunnel is encased in concrete, its frame is essentially a steel box. Instead of propping it up from the bottom, Mr. Toporoff reasoned, the agency could send columns through the tunnel to bear the weight of Flatbush Avenue, while suspending the tunnel from above.
"Anytime you tunnel, you risk losing ground, which can cause settlement" of the earth, he said in an interview. "With this, you eliminate the risk."
Transit agency engineers approved the idea. In July 2000, two gaping access holes into the complex were opened, one on Fourth Avenue and the other through the floor of an old station control house on a traffic island a few hundred feet away. Engineers negotiated with the city's Department of Transportation to close two lanes of traffic on Fourth Avenue for 18 months to give them room to work.
The control house, boarded up for years and defaced with graffiti, was in many ways emblematic of the station's decline. Designed in 1908 by the same architects who designed the Cathedral Church of St. John the Divine, it served for decades as an elaborate, ornamental subway entrance. Thirty years ago, the entrance closed and the control house was converted into a newsstand. In 1980, along with several other ornamental entrances, it was designated a historic site. But in recent years it fell into disrepair.
Schiavone Construction, which did most of the work on the project, hired a company to pick up the control house and move it to a nearby parking lot on the back of a flatbed truck in the middle of the night in early 2000. Through the hole left behind, along with the other one on Fourth Avenue, workers began excacavating and taking in equipment.
Later that year, workers took steel pipes, 10 inches in diameter and filled with concrete and with a steel rod threaded through the middle, and began sinking them from the subway platform into the earth below. Ultimately, the pipes were drilled 50 feet below the platforms and extended to the ceiling of the subway tunnel.
Later, 36-foot-long crossbeams, weighing 300 pounds a foot and hauled into the station by work trains that started in the Bronx, were snaked across the tunnel, just underneath the roof. Most of the tunnel's weight would hang from the crossbeams, including the platforms, stairways and people. The weight of Flatbush Avenue would also rest on the crossbeams and the columns.
Because the roof of the concourse had to be gutted to widen the passageway, the subway tracks themselves would have been left dangling, so smaller columns and supports were placed below them to help hold them up. Most of the weight of the tunnel, however, would still hang from above.
Once all the columns and beams were in place, a pancake jack was inserted between the tunnel roof and the crossbeams, and air was pumped in. Column by column, crossbeam by crossbeam, the roof was jacked up until Flatbush Avenue, the entire subway tunnel and all the earth in between — more than 110 million pounds in all — were resting on the columns and had been raised a fraction of an inch.
"The station is completely supported," Mr. Negrycz said.
Now they could start digging underneath in the concourse. In August 2001, workers started from the hole dug below the old control house and began working their way outward in two directions. One group headed west, from the main concourse toward the Pacific Street station. The other group headed east toward the Q train platform. In all, about 350 feet of tunnel was eventually widened. The concourse used to be 15 feet at its widest point. Afterward, it became 42 feet.
For six months in 2002, while the roof of the concourse was being redone, commuters could look up and see directly into the subway tunnel. As trains rumbled by overhead, people could see sparks coming from the wheels. Groups would cluster underneath the tracks to gape.
"People who saw it the first time were a bit shaky, but they got addicted to it," said Riad Abdulazziz, Turner's project director.
Other work was going on as well. To make the station wheelchair accessible, workers sank eight elevators into the station, a difficult task because of the station's age, narrow platforms and tangle of tracks.
In all, 15 stairways were widened or added. Each operation meant a delicate act of juggling existing and new stairways to accommodate the people flowing through the station. Three platforms had a third stairway added. Workers made sure a new one was finished and open before closing an old one for repairs, so the net gain and loss of stairways for commuters was zero.
Among the most tedious tasks was making sure the complex web of signal cables that ran through the station was not interrupted. With the work done mostly more than 80 years ago and few surviving blueprints available, workers had to trace the cables to their source by hand.
Over all, the $160 million renovation of the station is one of the most ambitious so far in the long list of station rehab projects undertaken by the transportation authority. Workers redid the entire imprint of the station. "We changed the whole look of the station," Mr. Nagaraja said. "It's like night and day."
Even so, officials said, interruption of train service was kept to a minimum. Whenever engineers needed to do work on the tracks, they secured an order from the transit agency to stop train service on a line for 55 hours on a weekend. Employees worked around the clock before service restarted on Monday at 5 a.m.
Because the station had both local and express tracks, service was never completely interrupted at the station. Riders always had one platform or another. Hanging the track also saved the agency about a year's worth of work.
In March 2003, the control house was moved back to its original spot and workers began restoring it, transforming it into an elaborate skylight for the station below. At long last, the end is in sight, and regulars have begun to see the difference.
"Before, it was an old train station," said Jason Deutschmeister, a real estate lawyer. "It was dirty. It was narrow. It looked like a scene of `The Godfather,' that era, 1930's, 1940's."
The station still feels like a construction zone, littered with equipment and with parts still closed off. At the Pacific Street entrance, a new token booth sits behind the old one. On a recent morning, a group playing Incan music competed with the screech of a power saw slicing through ceramic tiles for a refurbished stairway.
As the morning rush wound down, the group packed up and left, while the power saw kept going.
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Copyright 2003 The New York Times Company
