PROJECT SPOTLIGHT
Ellman says that pile driving was done between May and October
in compliance with the N.Y. State Department of Environmental
Conservation moratorium in the affected part of the Hudson River
on work during the fish spawning season, from November through
April. Further, the impact hammer was used only for the finalrefusal
step to reduce the duration of noise-causing activity.
PDA testing proved the pile capacity to be over 400 tons allowable,
says Ellman, more than meeting the design capacity of
300 tons.
Immediately following the pile driving, says Foltiny, divers
became heavily involved in the project.
“We had at least one and up to four working from around
November to March.
“As cut-off elevation was at mean low water, divers were
required to cut off the piles using a Broco underwater torch,” said
Foltiny. “After the cut-offs, the divers had to grind the tops of piles
smooth to ensure precise elevation and levelness” in preparation
for installation of the galvanized steel pile caps – each a combination
of a 42-inch-diameter steel sleeve welded to a seven-footdiameter
steel plate – designed to support and connect concrete
panels that form the base of the structure.
The original plan called for the pile caps to be cast as part
of the concrete panels. Trevcon recommended a beneficial
change: decoupling the pile caps from the panels, instead
installing them as separate components.
“By making the pile caps separate, we were able to make the
through bolt connections to pile while the panels were still in the
process of fabrication,” said Foltiny. “This change also enabled a
wider degree of flexibility in terms of where the panel could fall in
relation to the pile cap.”
Before the pile caps were attached, round cages filled with
oyster shells were installed around six of the pipe piles. According
to Foltiny, “The oyster cages are intended to help develop natural
oyster habitats. I believe this may also support other marine life, as
there is an outer cage around the inner cage that holds the oysters;
the outer cage was specified to have certain opening sizes to allow
fish to get in. On a larger scale, the oyster cages are meant to be a
part of efforts to restore oyster populations throughout the NYC
area.” Ellman adds that the cages are part of the educational aspect
of the ecological platform.
A team from Trevcon had earlier filled a truck on Governors
Island with oyster shells collected from restaurants by the Billion
Oyster Project, then filled and assembled the oyster cages in its
yard in Elizabeth, N.J.
Having installed the oyster cages and anodes on each pile for
cathodic protection, the divers then attached and secured the
pile caps.
The next step in construction was to place the nine
40-foot-square, 250-ton precast concrete panels on to the
supporting piles.
The heavy-lift Chesapeake 1000 crane was used to install the
middle three panels. Because the required reach for their installation
was shorter, the remainder of the panels were placed using
a smaller Columbia crane. This work was performed at night to
minimize turbulence in the water caused by vessel traffic.
The divers were once again called on, this time to install the
bolted connections between the precast panels and the pile caps.
More than 1,600 boulders – extracted and shaped by Champlain
Stone in Fort Ann, N.Y., and weighing between two and nine tons
each – were used as a natural material in building the habitat.
Dockbuilders swing a pallet of boulders onto the platform during low tide.
In total, more than 1,600 boulders were installed for the project.
86 | ISSUE 1 2020 www.piledrivers.org