For Resilience Engineers, Excavation Often Comes Down to an Educated Guess
As coastal resilience projects ramp up around the Big U of Lower Manhattan – with those along the Hudson River leading the way – planners continue to be intermittently surprised at what they find (and don’t find) below the surface. “Drawings will tell us part of what’s underneath us, but until we start going down, we actually don’t know,” said Claudia Filomena, senior director of capital projects and resiliency operations at the Battery Park City Authority. “We’ve had a lot of surprises.” Engineers involved with other Lower Manhattan Coastal Resiliency initiatives are following the work in Battery Park City with keen interest because they may face similar challenges when other nearby projects get underway.
“In the South Battery Park City Resiliency project, for example,” Ms. Filomena said, “there were a lot of utilities along Battery Place on drawings. But when we opened up the street, everything there was not on any drawing – and what was on the drawings wasn’t there.”
For this reason, pre-construction work, such as test pile drilling on land and bathymetric surveys in the water, is necessary to verify conditions. The work is scheduled concurrently with the design process, so that plans can be modified to conform to the facts underground.
As precursors to the North/West BPC Resiliency project (scheduled to begin construction later this year and continue through 2030), test pile drilling at the South End Avenue cul-de-sac and Belvedere Plaza (near the Brookfield ferry terminal) began last Tuesday, March 18. “We are trying to understand how everything fits together and how deep the piles need to go,” Ms. Filomena said. “We are drilling them until they reach resistance, and trying to figure out if our assumptions are correct.”
Nick Sbordone, BPCA spokesperson, elaborated: “As part of our effort to build a comprehensive flood protection system for Battery Park City, we are testing piles, which are structures that will support the floodwall, to reduce project costs and limit the construction timeline as much as possible.”
At Belvedere Plaza (right), two 36-inch drill shafts are being sunk, giving wide berth to the PATH tunnels below. At South End Avenue, the set-up is smaller, with five mini-piles being installed. Pile casings, powered by large air compressors, are being drilled down 50 to 75 feet, until they reach solid rock. Concrete slurry is then used around each casing to attach the concrete to both the rock and its casing. Once the concrete cures in two to three weeks, a “load test” will be conducted using steel beams and jacks to test the pile capacity. After the tests, the crews and their machines will clear out, the fencing will be taken down, and both sites restored for public access. Work at both locations is slated to be finished by mid-May.
Both test pile sites are surrounded by chain link fences covered by sound-baffling blankets. Dust and air pollution spikes, vibrations, and noise exceedances are monitored in real time. At South End Avenue, the drilling was timed to occur when the nearby nursery school was on spring break.
“The challenge is trying to squeeze in flood infrastructure in an area that’s already built out,” Ms. Filomena noted, citing the PATH tunnels, the World Trade Center pump station, and the Brookfield water intake center as examples of complicated subsurface infrastructure along the Battery Park City waterfront. “And, Battery Park City has a distinct character. It’s a neighborhood. It’s also a civic space, which makes it all the more challenging.”
For more information about the North/West Battery Park City Resiliency project, which stretches from South Cove to a high point in Tribeca on Greenwich Street, click here. For a look at the entire Lower Manhattan Coastal Resiliency plan, which encompasses Battery Park City work, click here.