Survey of towers' basement is completed

Engineers planning how to remove debris without damaging retaining wall

War On Terrorism

The Nation


NEW YORK - Underneath the remains of the World Trade Center, waiting silently in the gloom and dust as if for a boarding call that will never come, sits an empty PATH train nearly and neatly cut in half. Four of its cars are intact, but three more are squashed under debris from the collapse of the trade center's south tower.

After almost three weeks of exploration, engineers have completed the first survey of the seven-story, 16-acre basement under the ruined trade center complex and have found a varied pattern of destruction. Some areas are nothing but rubble; others seem almost undamaged. To the relief of the engineers, there is no evidence that the 70-foot-deep retaining wall around the basements has been damaged or breached, although the collapse of the towers left one section perilously unsupported.

The floors under the U.S. Customs House in the northwest corner of the complex, despite a gaping hole, are mostly intact and could be repaired and used again, some engineers say, while the basement floors directly under the two collapsed towers are simply rubble.

In terms of overall floor space, a little more than half of the basement is there, said Daniel Hahn, an engineer at Mueser Rutledge Consulting Engineers, which is advising New York City's Department of Design and Construction and is compiling the survey of structural damage.

Since the attacks Sept. 11, firefighters, police officers, engineers and others have crawled, floated, climbed, waded and rappelled under the trade center looking for victims, surveying the damage and looking for potential dangers. Many of their reports have made it back to floor-by-floor maps at the Mueser Rutledge offices on West 34th Street.

The `bathtub'

The engineers have been ordered to get some rest, said George Tamaro, who oversees the underground work for Mueser Rutledge. The underground work, he said, has entered a "quiet period" of thinking and planning as engineers ponder how to excavate debris from the basement without damaging the retaining wall, known as the "bathtub," that keeps the nearby Hudson River out of the site.

With the destruction of portions of the floor slabs, much of the work of supporting the wall against the water and dirt pressing in is being done by the rubble and twisted steel itself. Without adequate precautions, removing the debris could cause the wall to shift or rupture.

Last weekend, engineers began to drill wells around the outside of the bathtub wall to monitor water levels and ground movements in the next months of excavation. "The ground's going to go where the wall is going," said Tamaro.

Yesterday, engineers installed benchmarks to monitor movement along part of the wall on Liberty Street, just south of the southern tower, where a trough 70 feet deep in some places has left the wall without any support.

"Whatever went through there went straight down to the basement," said Hahn, who called that area of the wall a concern. Soil and sand are being dumped in that hole to help shore up the wall, and engineers plan to install anchors known as tiebacks in that section in the next few weeks.

Work to go in stages

To keep the wall from being damaged or moved, excavation of the basement will have to proceed in stages, story by story, Tamaro said, with such tiebacks being installed along the western and southern sides of the bathtub, where the basement floors are no longer providing enough support. Time estimates range from four months to a year.

Among the early explorers of the underground, Hahn said, were a group of police officers who traveled by raft through a flooded PATH tunnel from New Jersey. Bryan Juncosa of Atlantic Engineering, a licensed engineer as well as a commercial diver and a member of an urban search and rescue group operated by the New Jersey State Police Office of Emergency Management, spent 10 days at the site as a structural expert checking buildings and debris mounds to be sure they were safe for rescue workers.

Hahn said the engineers often entered the basement through access hatches on West Street that led down to the PATH tubes. He had been down to the B1 level, one floor down from the concourse, which, he said, was deep enough for him.

"When you watch TV you see a very antiseptic view of the WTC collapse," he said. "Down below you hear the cops shouting and getting excited. You hear construction workers talking construction worker language, you hear diesel engines of cranes. You have the aura, the smell and taste of death that's down there now. It's not a pleasant place to be."

According to the Mueser Rutlege survey, most of the entire plaza level of the trade center, with the exception of the northwest corner under the Customs House and the northeast corner under 5 World Trade Center (which is east of the bathtub area), has collapsed. The concourse, one floor below, shows a similar pattern.

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