New York City is for many people the city, vibrant and rich in culture, known for its diverse communities, always moving. Even with its dense population and ubiquitous skyscrapers, the city is famed for green spaces, from the 843-acre Central Park to small, hidden gardens that provide a retreat from busyness.
A new and unique green space is being constructed in Hudson River Park, on the west side of Manhattan, where the former commercial waterfront is gaining new life. The project has been controversial and rife with delay, but is now underway and expected to be completed by Summer 2021.
Weeks Marine, Inc., a PDCA member based in Cranford, N.J., is involved in the project.
Preparation for construction: A long process
Rick Palmer, vice president at Weeks Marine, says the construction of Pier55 in the Hudson River Park has been the "most interesting and challenging project" in his 30-year career. He has worked on job sites around the world, but none have required as high a degree of precision or encompassed the range of conditions found at Pier55.
Funded by billionaire couple Barry Diller and Diane von Fürstenberg, the Pier55 development initially met with opposition from a local organization concerned with the project's selection and approval process. After multiple lawsuits, a construction stop and sustained opposition after a restart, the continuing conflicts led Diller and von Fürstenberg to reluctantly withdraw their support, shutting down the project in mid-September 2017. Work on site was halted and Weeks demobilized their barges after two weeks on the project.
High-level intervention by New York Governor Andrew Cuomo brought life back to the project a few weeks later. Governor Cuomo brokered an agreement with the opposing parties and convinced Diller to renew his commitment to the project at the end of October 2017. Weeks and the other engineers, contractors and fabricators dusted off their plans and rebooted. On May 1, 2018, a year after they had originally planned to start work, the Weeks Marine crew was back on site.
The Hudson River Park Trust, a partnership between New York State and City responsible for the four-mile park along the west side of Manhattan, is governed by the Hudson River Park Act, which mandates that the park will encourage, promote and expand public access to the Hudson River, as well as protect and conserve the critical marine habitat within the park. That mandate guided the design of the new Pier55, as well as the earlier demolition of its two neighboring piers, Pier 54 and Pier 56, which had both fallen into a state of disrepair.
The wood piles supporting the Pier 54 and 56 structures were left in place to provide a sheltered habitat for aquatic life. The Pier55 footprint overlaps portions of those pile fields; the handful of old timber piles that conflicted with the new pile locations were extracted using an ICE® 44-50 hydraulic vibratory hammer with a timber pile clamp with the Weeks 574 barge-mounted crane. Concrete debris from the two piers was also removed from the river bed using a clam shell bucket on the same crane. The demolition and debris-removal work took two weeks to complete.
Ultra-precise pile driving in challenging conditions
Over a span of just 300 feet the width of the new Pier55 the driving depth increases dramatically. At the east side of that 300-foot width, concrete piles 93 feet long will support the new structure. At the west side, piles more than 260 feet in length are required. The mica-schist bedrock into which the piles are being driven drops off from east to west at a 45° to 60° angle.
Bedrock elevations were confirmed during a week-and-a-half-long indicator probe pile program completed using a two-piece HP 18x204 steel probe, the Weeks 574 crane barge and an ICE® 110C vibratory hammer. At 35 locations, the Weeks team drove the pile to rock, splicing the upper probe segment on at each location as the rock depth increased.
The next phase comprised three weeks of precise probing to a depth of 75 feet at each of the 267 locations where the concrete piles were to be driven. The Weeks 526 derrick crane barge with its hanging fixed lead system was outfitted with an ICE® 66-80 vibratory hammer and a 130-foot-long, 36-inch-diameter steel pipe for this job. Because each pile is required to be within three inches of its planned location, the company needed to find any obstructions that would deflect or block the piles. In two locations, the probe would not advance, and the pier design was modified before production pile driving began to allow the piles to be relocated.
Throughout the probing work, Weeks Marine tested an innovative lead-mounted GPS and laser survey system, which they then utilized during the production pile driving to ensure adherence to specifications. Probe locations were double checked in real-time by a conventional land-based total station, as well.
With this phase completed, the company removed the probe pile equipment from the crane and mounted a Junttan HHK25S hydraulic hammer into the leads. This "very large" Finnish hammer, a new one for the company last year, "is the only one in the U.S. right now," according to Palmer.
The piles and the pots
While this changeover was being done, the company installed four 24-inch square concrete piles made by Jersey Precast in Hamilton, N.J. (of a total six on the project; the other two will be driven this summer).
With the Junttan hammer ready to go in the last week of June 2018, the team began the installation of 164 prestressed concrete 36-inch-diameter cylinder piles, work that lasted into the first weeks of October, completed before the end of the six-month in-water construction season. (Time-of-year restrictions require that all pile driving be completed between May 1 and October 31.) The balance of the piles another 103 are being installed this summer.
Starting on the east side of the site, where about 80 feet of organic material directly overlays the bedrock, Weeks experienced "the quickest drive times I've ever seen," said Palmer. For many of the initial piles, 30 blows or less from the hammer were all that was required to fully seat the piles into the schist, the piles having settled to within inches of the rock due to their self weight and the deadweight of the hammer. In fact, a concern for the early piles was they could be damaged by overdriving, so the refusal threshold was closely monitored and adhered to by Weeks and third-party inspectors.
Moving west along the width of the new pier, the loose material overlays clay and further still, to sand under the clay before rock is reached. Consequently, piles take longer to drive as the team moves further west, because of both the different material layers and the increased depth. Palmer expects that some piles this year may require more than a thousand hammer blows each. Further, because of the deeper driving conditions on the west side, most of the piles will require steel stingers to extend the length of the pile.
Depending on the load and conditions, a steel tip or plate is attached to the bottom of each pile. The pile designs, which include both hollow and solid concrete sections, with steel rock tips and three sizes of HP 18 stingers, require 10 separate tip types to cover all of the possibilities. The tips were manufactured by Macuch Steel Products in Augusta, Ga.
"Almost every pile is unique and tracked by its final location in the plan," said Palmer.
The concrete piles, fabricated by Coastal Precast Systems in Chesapeake, Va., are cast monolithically in steel forms, then transferred to Weeks' transport barges on the Elizabeth River.
"We tow the loaded barges up to our marine yard in Jersey City, N.J. about six miles south of the Pier55 project site," said Palmer. "Then, due to the limited water depth at the Pier55 site, we transload the piles onto smaller, shallower barges 10 piles at a time to bring them to the project for installation."
The piles are cut off after driving using a Mactech Offshore 48-inch wire saw, which results in "a very smooth, flat finish," said Palmer. The saw is "very good," says Palmer. "This was our first experience with it, and we're sold on it."
About half of the piles will support precast concrete "pots," each one unique, that are being cast as individual "petals" and "column heads" by Fort Miller Corporation in Greenwich, N.Y. The individual precast elements are trucked to the Port of Coeymans on the Hudson River, where Weeks Marine and P&M Brick erect and weld the pieces together to form the pots. Once assembled, they are loaded into Weeks Marine hopper barges and towed down the river to the Pier55 site.
The Weeks 526 crane barge, with the fixed lead system removed, is used to pick and install the pots on the piles.
The pots, the piles that support them and additional pier piles in the two to three rows closest to the outer pier edges are cast using a white concrete mix, per the design by architects Heatherwick Studios of London, England.
"This means," said Palmer, "we have two colors of piles to keep separate, and we must handle the white piles carefully to ensure that we don't mark or damage them during installation."
The team is using non-marking synthetic slings on the upper portion of the white piles to prevent scuffing and chipping, and they mark pile depths/lengths, which are typically painted directly on the pile surface, on removable tape that is taken off once the piles have been driven.
Weeks Marine anticipates finishing the pile driving in late summer this year, after constructing the first 50 percent of the pier's concrete deck over the past winter and spring. By the spring of 2020, the deck work will be complete, and the entire pier structure will be turned over to the follow-on contractors who will complete the park structures and landscaping. Palmer says the undulating surfaces the pots create, both above and below the pier, are "very artistic and truly unique. This is an exceptional project we are thrilled to be a part of."