How 4 Firms Aid In Wtc Cleanup

Real Estate Weekly, Oct 10, 2001 by Parke Chapman

Mayor Giuliani estimates that it could take an entire year to clean up the remains of the World Trade Center, despite crews working 24 hours a day, 7 days a week to clear the site.

Like armies on a battlefield, scores of contractors have divided up the site between their crews, dismantling steel beams and picking through the rubble.

The New York Times reported mat mere are over I 1,000 workers divided into four quadrants at ground zero.

The coordinated effort began only hours after the buildings collapsed, bringing together engineers, contractors, construction crews and steel workers to assess the area.

What is happening on site is far from academic, according to sources familiar with the job. The terrain is constantly shifting, so moving freely about the site is dangerous, if not impossible.

Several thousand tons of debris has so far been removed. But approximately 30,000 tons of structural steel remains.

"The site looks a lot different today than it did right after Sept. 11," said Richard Thomasetti, principal of Thornton Thomasetti Engineers, who is frequently on the site.

He credited the Structural Engineers Association of New York (SEAoNY) for coordinating efforts to inspect the area in the immediate aftermath.

"They really came together quickly to organize all of the engineering firms down there," said Thomasetti, whose own firm is still involved in the process.

A spokesperson from SEAoNY could not be reached for comment.

This process--the biggest excavation in the history of New York City--is choreographed by number of contractors, construction firms and engineers, all working together amid the wreckage. This physically as well as emotionally taxing labor since workers expect to--and often are--unearthing human remains from the debris.

The machinery brought to bear on this site dwarfs the workers who operate it. The inventory of heavy equipment on site includes a 160,000-pound hydraulic excavator, a 4100 Manitowoc crane with a clamshell and smaller cranes dangling crew baskets, among other machines. Workers must proceed cautiously since the removal of debris from within the slurry wall (also known as the bath tub) is a delicate process.

The slurry wall itself has six basement levels with a concourse level on top. According to Mueser Rutledge Consulting Engineers, the basement framing was compromised in places, particularly around the towers' 209-SF footprints.

As of the Sept. 24, engineers had not yet penetrated the tower footprint areas. Otherwise the stability of these areas is questionable. The original excavation for the World Trade Center cut 70 feet into the bedrock beneath lower Manhattan.

Just removing the massive steel segments that once sustained the towers will require blowtorches. A-published report from an engineering trade journal indicated that liquid oxygen/propane torches would be needed here while heavy equipment can remove sections that can be pulled out of the rubble.

"Much of the work that has been done is designing platforms for the cranes to rest on," said Thomasetti.

Thomasetti's firm actually used steel from the World Trade Center to create these standing platforms. Without these platforms, said Thomasetti, heavy machinery is forced to work on unstable terrain liable to shift or cob lapse at any time.

Steady rain on Sept. 30 made working conditions even more difficult, as the piles of rubble, steel and crushed concrete took on a new consistency.

Infrared cameras are used to survey the site from low-flying aircraft. These cameras can isolate the "hot spots" on the site where fires continue to burn underground.

As it was after the 1993 bombing, the highest priority for these engineers is supporting the slurry wall, since this barrier keeps the Hudson River at bay. The land that the World Trade Center rested on was reclaimed from the river.

Officials are saying that the Trade enter attacks alone will cost nearly $40 billion--a sum that includes removing debris, overtime pay and the cost of constructing new buildings and subways.

On Sept. 29, crews demolished what was left standing of 7 WTC with a wrecking ball.