The following are some pictures taken by Kevin Phillips at Ground Zero in January, 2002. As of Tuesday, September 25, 2001, in the middle of the rubble 25 feet underground was the New York City's #1&9 IRT line. The New York City (NYC) Transit called an emergency meeting and asked FPM to evaluate the possibility of flooding in the subway from a slurry wall basement collapse.
BACKGROUND
The World Trade Center basement was built with surrounding "slurry walls". These walls extend down from ground surface to about 70 feet below grade level. During their construction, they are keep structurally intact by steel cable "tie backs". When the floors were constructed, the tie backs were removed and the floors then were designed to handle the soil pressure. The NYC Transit believed that the floors have been compromised and that the only thing that was holding the slurry wall up is the debris. As more and more debris was removed, the danger of the slurry wall collapsing increases. If the slurry wall collapses because of the proximity to the Hudson River, it could cause a direct hydraulic connection to the subway network. To give you a better idea of the problem, this is a system of tunnels that is 722 miles long, much of which is below sea level (hence, the name subway).
In one day in September, 2001, FPM was joined by Dr. Carl Costantino of City college of New York (CCNY) and a dozen NYC Transit engineers who presented the relevant data and made a critical decision to isolate the 1&9 IRT subway line and hydraulically plug it with two concrete bulkheads. This effectively removed the 1&9 line from service indefinitely.
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Shot looking south from Vesey Street towards Liberty Street.
Note the existing subway (IRT 1&9 line) is damaged directly below the white truck. This is approximately where the new construction will start and head north straight through the damaged area. This is one of two locations where the subway was damaged. |
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Same shot with no zoom.
Note the existing subway is to the left (east) of the Bankers Trust Building (flag). |
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Looking west.
In the background is the World Financial Center. The yellow wall in the center of the picture is the basement wall of the building to the east of the slurry wall. The subway is right behind the yellow wall.
The large crane to the left of the picture is directly over the subway. A general observation is that it appears it will be difficult to get a dewatering system as space is at a premium. |
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Looking northwest at the intersection of Vesey and Broadway.
This is where the #7 World Trade Building used to stand. This is the second area of subway callapse.
Note: the subway will not be rebuilt for a small length right below Vesey St. due to the utilities in the area. |
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Looking west.
This shot shows how crowded this area is. It will be difficult to fit in a dewatering system in this heavily trafficked area. Consideration would be given to putting the dewatering system in between the basement wall and the subway. In that way, disturbance of this central area for staging can be reduced. |
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Looking west-northwest.
The subway is just beyond the yellow wall. |
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This is a shot of the slurry wall looking south.
This is the boundary of the #1&9 IRT line. The #1&9 IRT line is between 6 to 16 feet from the slurry wall. All of the construction and dewatering will be to the east of this wall. The slurry wall looks out of plumb and slightly askew, but seems stable. |
For more information please contact Dr. Kevin Phillips
