“When I started working on the project, we weren’t really sure if it could be built,” says Celine Armstrong, Little Island project executive.

Planning for the project began in 2012, with “all the innovation and coordination happening through 2016 and 2017  between various team members before “construction really started in March 2018,” says Kevin Zimont, a project executive at construction management firm Hunter Roberts Construction Group.

Diller selected London architect Heatherwick Studio’s design after a competition, and the trust put together the local team including Arup, which provided structural, mechanical, electrical, civil and plumbing engineering as well as acoustics, safety and other consulting; cement precast solutions provider The Fort Miller Group; marine engineer Mueser Rutledge Consulting Engineers; marine contractor Weeks Marine; landscape architect Mathews Nielsen Landscape Architects; and landscape contractor BrightView Landscape Development.

“We got involved at the very beginning,” says David Farnsworth, a principal at Arup, noting that the “scheme started out as an island around the time Superstorm Sandy” had hit New York City. The storm required a design change, and the team had to make sure the pier-park hybrid would “gently slope up above flood levels,” he says.

The 500-year flood elevation level is 11 ft, so accounting for waves and sea level rise, the team decided that the flat, more traditional pier that stretches under most of the pots and houses certain services should be 15 ft above the water.

“We wanted to [reduce] damage to the landscape, and Mueser also designed it to be resilient to wave action,” Farnsworth says.

All this spurred specific construction innovations. “One of the things we realized with the elevation gain was that it created a lot of unique geography,” he says.

And that required unique solutions.

The most visible of these are the pots, which look like the petal formation of a flower. “Petal” is particularly apt, considering the fabrication of the giant cups includes putting together pieces that are also called petals. The Hudson River Park Trust had much experience rebuilding old piers, and Farnsworth said the owner decided the pots should be made with precast concrete, which is effective against corrosion, salts and other destructive elements to a water-adjacent project.

A Complexity in Every Pot

Farnsworth says one Arup engineer was racking his brain, “trying to make them look like soap bubbles” while aligning with the designer’s wish that they avoid building “rows of marching columns in a straight line.” The answer was to use a “Cairo pentagon tilting pattern,” a geometric repeating pattern common to Middle Eastern art, and the massive containers would then be “stretched [upward] at varying heights,” Farnworth says.

The team used 39 sets of formworks made after extensive 3D computer modeling to create the 132 pots. Then they could reuse the formworks and, depending on the vertical plane of each pot, pour varying “petals”—about four to six for each cup. But finding a precast concrete solution provider that could do the job was more challenging than the computer modeling.

“We were shown the concept and asked if we would be interested,” recalls Scott D. Harrigan, president of The Fort Miller Co. He says members of Hudson River Park Trust and Arup claimed they traveled along the entire East Coast looking for someone who would be interested in the work. “Apparently, they were told that the concept was crazy and not a fit for precast,” he says. “Sounds like our kind of job!”

Harrigan says final plans for the pots initially specified “very few dimensions,” although there were 3D models for all the pieces.

This was not the way his firm normally created precasts for other projects, such as bridges and the Grand Central Terminal caverns. “This is when the lump forms in the pit of your stomach … we had not been down this path before,” he says.

Eventually, Fort Miller outfitted a sister company with technology to mill and coat foam forms so workers could cast concrete on them. “A full one-third of our annual production capacity was displaced by this project,” Harrigan says, adding that his firm “essentially started a new business to serve our internal needs.”

Its workers used a robotic milling machine to create foam models of every pot piece, then laid the pieces on the floor of a 600-ft-long building that was cleared out just for the job. “It was basically like origami,” Farnsworth says. “They used an automated laser cutter and ‘folded’ them into the right shapes and then cast them in concrete.”

For “all of this geometry, we had created 3D models,” Farnsworth says. Arup engineers took modeling through to detailing of the rebar, such as bar bends, with every piece of the components “modeled by Arup and digitally transferred to Fort Miller,” he says. “It was a six- to eight-month process before we could crawl inside” the first pot, project executive Armstrong recalls.

Gather by the River

Because of their sheer size, the pots had to be assembled away from the shop. Individual petals were shipped by road from Fort Miller’s Schuylerville, N.Y., facilities to the Port of Coeymans on the Hudson River, 10 miles south of Albany and 100 miles north of New York City.

Weeks Marine would then take custody of the pieces, assemble them, weld the connecting plates and use a gantry crane to load four complete pods onto one barge. Sometimes workers would reach the end of the petal assembly process and realize, “Oh no, I’m off a half-inch,” Armstrong says. So the team would go around clockwise again until it was just right, then hold it in place and welds it together.

The barge rides took about 14 hours, floated by tugboat to the jobsite in Manhattan, Zimont says.

While the pots were being modeled, cast and assembled, marine contractors drove the pilings in stages, up to 200 ft below the river. Zimont says pilework required “a lot of planning and precision and a little bit of confidence.” The project includes a total of 267 cylinder piles, including those for the flat lower pier underneath the pots. They each support about 250 to 350 tons.

To ensure precast pilings would not tip over when topped, each had steel guide columns—metal tubes inside the hollow concrete piles, over which the pots were placed. “Because of the eccentricity of the pots and the possibility of a pot falling over, we had to develop a specific sequence of installation” of the cup onto the pile, Zimont says.

Two things necessitated driving the piles during two seasons: the constrained size of the park and an environmental restriction that only allows such work on the Hudson River to be conducted from May to November. So the team drove 164 piles during those months in 2018, then in the following off-season installed the first set of pots. The second term to drive103 more piles happened May to July of 2019.

While driving the piles, the team had to constantly probe for obstructions, then decide whether to remove the obstruction or remove the pile. Placement required extreme precision because the pots were designed to be 9 in. apart with a 3-in. variation, and also because there would be  “significant cost and impact," Zimont says.

Green Pier, Theater Works

After placing the last pot on the final piling, the team’s work was only half done. “We had to build a park on top of these things,” Zimont points out. Geofibers, which are bits of polypropylene, are placed in the soil to stabilize it on extreme slopes, he says. The team needed to have an extensive irrigation system “up and running early to ensure trees and plants and shrubs don’t die” before the park is completed, adds Zimont.

Trees as tall as 35 ft, with 12-in-dia trunks, were harvested from nurseries and planted into 4 ft of soil in the pots. Reinforced concrete slabs beneath the dirt ensure that roots can’t penetrate and grow through the cup, Farnsworth says. Using other flora as well—shrubs, grasses and perennials—each corner of the park will represent a different microclimate depending on topography, sun exposure and wind patterns.

Jewel of the Job

But the “jewel of the job,” as Zimont puts it, is the 700-seat amphitheater, which the foundation has said will present affordable performances.

“When you walk out to the park, you don’t even know the amphitheater is there until you get to the top,” he says. “You’re looking over the river and the sun sets … the team and I have had some good times there, just talking about the job.”

The flat pier portion, which is under the biggest “hill” of the park, is “where we’ve nestled the public restrooms and the changing rooms for the actors who will perform in the theater,” Farnsworth says.

The flat pier also enabled the team to use a big crawler crane.

A working theater and a large public place both require lighting, electricity, plumbing and other systems. Installing these on a pier made for specific challenges.

“We had to model all of our utilities going up and over the slab surface,” Farnsworth says.

“The reality is because of the slopes of the park, and structural capacities of where we could and could not be on the park, that 2.4 acres really shrunk down to maybe one acre to have all those people, store material, install soil and make deliveries,” Zimont says.

He likens it to building a high-rise when only one trade can use a hoist at a time. Workarounds included delivering materials and equipment from the water, using multiple cranes on site and even floating in and setting a crane by barge.

“It’s a merry-go-round, almost, trying to get in and out of the park,” Zimont says.

The team’s extreme collaboration and precision went beyond what the firms had done before, according to those interviewed.

“Every day brought more challenges as the geometry was ever changing,” Harrigan says. “Our highly skilled carpenters and production associates were pushed to the limit.”

Armstrong muses: “Maybe if it was a less interesting project we would not have had the collaboration.” But Heatherwick developed “this creative design that we all wanted to” make sure could be built, she says.

Essential Park

Little Island was considered an “essential project” that was not legally mandated to shut down during the first few months of the COVID-19 pandemic. But the team paused for about three weeks to do “an entire deep clean” and bring in hot water stations, Armstrong says, calling it “a significant amount of protocol to keep workers safe.”

Adds Zimont: “We didn’t have any outbreaks out here.”

As an outdoor jobsite, the park was safer than perhaps other projects, and it will remain a safe space once it opens this spring.

“One thing I hope this project is able to do is attract more people to step up and donate for open spaces,” Armstrong says. That’s what makes Little Island crucial, she adds, noting that the surrounding neighborhood  is a “park desert.”

Even if New Yorkers weren’t dealing with quasi-quarantine conditions and in urgent need of large, outdoor public spaces, Armstrong says Little Island’s completion will be a boon to the industry because “it can make people think about innovative construction.”