Robert J. Petrides is a senior engineer in charge of the World Trade Center East Bathtub construction project, which includes the underpinning of the No. 1 Line subway box.
Mr. Petrides has more than 30 years of experience in the management, design and construction of large civil works projects, primarily in the public sector. Before joining the Port Authority's World Trade Center Construction Department, he held key positions with the U.S. Army Corps of Engineers and the Metropolitan Transportation Authority.
Q. What is the maximum load that the No. 1 subway box can sustain? There appears to be four to five cranes on top of the box every day, plus materials. -- Chris, New York, N.Y.
A. Chris, this has been one of the biggest challenges we have faced to date on this project. Until the permanent underpinning is complete, the live load on top of the No. 1 subway box is limited to 200 pounds per square foot. As you mentioned, that space is critical for us to stage cranes and other equipment, so we've had to place heavy timbers on top of the box to spread out the load. We also have licensed professional engineers who carefully calculate the weight of each piece of equipment so that our load limit is not exceeded.
Q. Will any retail be built under the new Greenwich Street section? Also, when will this project be completed? -- Zack, Elkton, MD
A. The area under the Greenwich Street box is important space and will include retail space, mechanical equipment rooms and tour bus parking. Portions of Greenwich Street will be completed by September 11, 2011, which will provide critical public access to the National September 11 Memorial & Museum.
Q. Will this project create any problems for the MTA's No. 1 subway line? -- Tyler, Bonifay, FL
A. Tyler, incredibly, this project is being done with minimal disruptions to the No. 1 Line service. While the fact that a live subway bisects the site every single day hampers the productivity on the rebuilding, officials believed it was too important a service to take out during the period of construction. Having said that, there will be periodic needs to temporarily suspend service on the line to advance certain parts of the project, but these shutdowns will be scheduled to minimize any inconvenience to the traveling public.
Q. How is all of the rock for this project going to be removed? Will the general contractor be able to blast? Also, the timetable for completion of this project seems quite ambitious? Can you assure us why the public should trust the PA when it provides a timetable for this project? -- John, New York, N.Y.
A. We all understand the public's skepticism about the timetables for the World Trade Center projects, including this one to build out Greenwich Street. But following the top-to-bottom assessment that was done in October 2008, we're confident that we can meet the September 11, 2011 timetable that's been set for completion of a portion of Greenwich Street. To date, approximately 26,000 cubic yards of rock have already been removed from under the No. 1 box through both mechanical means and by blasting. Approximately 75,000 cubic yards of rock remain to be excavated.
Q. The entrance to the new Calatrava WTC Transportation Hub will be situated between Towers 2 and 3. Will passengers bound for PATH platforms be led to passageways under the No. 1 subway box? -- Joe, Cambridge, MA
A. Yes. There will be a pedestrian passageway beneath the No. 1 Line box. When completed, all of the major structures at the World Trade Center site will be interconnected with PATH and the MTA's R/W, E and No. 1 lines. Pedestrians will be able to travel from the World Financial Center to the MTA's Fulton Street Station through a climate-controlled underground mall. The Fulton Street Station will provide access to the MTA's J, Z, M, A, C, 2, 3, 4, 5 and 6 lines.
Q. Why does it seem that the building process for this project and others seems to take so long. Is there a specific reason for that? -- Mariusz, Maspeth, N.Y.
A. As I mentioned earlier, we clearly understand the public's frustration with the pace of construction. But we've made some pretty significant progress during the past year on some extremely complex projects, including the one I oversee. And we expect that level of progress to continue in the upcoming years until the projects are complete. But remember that 150,000 people move through the site through two different active rail systems every single day. The excavation of the World Trade Center's East Bathtub required that the No. 1 Line box be temporarily supported by 460 minipiles. Before excavation could begin below the water table, the entire eastern portion of the site had to be encircled by slurry walls excavated to rock. As excavation commenced, 806 tiebacks had to be drilled into rock to brace the slurry walls. This work, and other work to build the East Bathtub, all had to be done without disrupting the vital mass transit systems that serve Lower Manhattan.