The high water table at the site of the new Imagination Playground in New York City’s Historic South Street Sea port district is a valid test for the connection integrity and watertightness of the precast concrete box culvert combined sewer system.
By Sue McCraven
The Big Apple isn’t for everyone. Not many construction contractors are tough enough to compete in New York City (NYC). Some national and international firms will not work in NYC for a number of reasons, including multiple regulatory agencies; onerous permitting requirements; congested underground utilities; and last – but certainly not least – notorious traffic.
Contractors who succeed in NYC need to be pretty savvy, like Garden State Precast located in New Jersey, who fabricated, tested and supplied the precast concrete box culvert tunnel system. This precast tunnel carries the combined sewer and stormwater flow under lower Manhattan’s Imagination Playground (see Figure 1), a new and innovative public space designed by architect David Rockwell of Rockwell Group to encourage child-directed, unstructured free play (see Sidebar A). The subsurface of the playground’s historic seaport site complicated excavation work and precast culvert assembly with a nasty assemblage of garbage, high water and potential archeological artifacts.
Burling Slip playground project: no walk in the park
In the spring of 2009, the New York City Department of Parks and Recreation began construction of Imagination Playground for the high-profile historic South Street Seaport district of lower Manhattan. More than $5 million from the Lower Manhattan Development Corporation, $3 million for utilities from The New York City Department of Environmental Protection and an endowment from Rockwell Group provided the funding for design and site development at Burling Slip.
The playground, opened in July 2010, is part of NYC’s South Street Seaport historic district and the former site of major maritime commerce. Historic importance aside, the complex underground conditions near the corner of John and South Streets had the makings for a contractor’s nightmare (see Sidebar B at the bottom of this post).
Tight tolerance challenges precast QC team
“The hurdles we faced while producing the box culvert for Imagination Playground were a bit more challenging than other jobs we have done in the past,” explains Pat O’Malley, project manager at Garden State Precast. “To meet the NYC Park Department’s watertightness specifications for this high-water installation, we needed to keep the joint tolerances very tight.”
Josh Tyler, Garden State’s QC manager, made sure the spigot tolerances of the box culvert joints were maintained within ± 0.0625 in. (± 1.6 mm). Tyler’s form set-up team performed rigorous pre-pour inspections to meet these exacting tolerances that were in compliance with the recommendations of the gasket supplier, Hamilton Kent. “Making a watertight structure is much more difficult when it is rectangular,” says O’Malley, “as opposed to when the product is round.”
“We needed to use specialized form equipment machined to a tolerance of 0.04 in. (1.0 mm),” continues O’Malley. Because of the narrow joint tolerance specified for the tunnel project, all product handling at the precast facility was monitored carefully. “We needed to make sure no damage occurred during manufacture or when we tipped the culvert sections out of the molds, and that included special care during product loading and shipping. Any imperfections to the culvert sections might have led to a joint leak.”
Sidebar A – Imagination Playground: Not Your Father’s Swing Set
After five years of research, development, focus groups and testing, Imagination Playground at Burling Slip opened in July 2010, conceived and designed pro-bono by architect David Rockwell in collaboration with the New York City Department of Parks and Recreation. Imagination Playground is part of a breakthrough playscape concept that encourages child-directed, unstructured free play; the kind of play that experts say is critical for a child’s intellectual, social, physical and emotional development. With a focus on loose parts, Imagination Playround offers a changing array of elements that allows children to constantly reconfigure their environment and to design their own course of play.
Features of this site-specific park include: a ramp; sandpit; slide; cascading water channel; rope climbing structure; masts and pulleys; and a listening forest. Inspired by the commercial activity that took place at historic Burling Slip, loose parts such as burlap bags, buckets, shovels, brooms, carts and fabric, as well as custom-designed blue foam blocks of various shapes and sizes, are incorporated within the play activities. And reflecting the proximity to the East River, buckets, sandbags and wooden dams have been integrated into the water play. Seating and storytelling are accommodated in the tiered steps of the playground’s amphitheater.
Text and architectural rendering courtesy of Rockwell Group
Hydrostatic testing of precast joints
At Garden State Precast’s Farmingdale, N.J., facility, hydrostatic testing of the culvert joints was conducted to ensure that the precast assembly complied with the watertightness specifications for the proposed combined sewer at Burling Slip. Hydrostatic testing was performed by an independent agency. An internal hydrostatic pressure of 13.2 psi (91 kPa) was placed on the assembly for a duration of 10 minutes; 13.2 psi is equivalent to 30 ft (9 m) of pressure head. No leakage was found and the inspector determined that the culvert assembly complied with job specifications (Figure 2).
The precast concrete box culvert bulkhead assembly was also inspected for watertightness under joint deflection. Applying a specified deflection of 1.0 in. (25 mm), the sealed precast box culverts were subjected to a hydrostatic pressure head of 13.2 psi (91 kPa) for 10 minutes. No leakage was detected. Joint deflection testing for watertightness was performed on two separate occasions on different box culvert castings from Garden State’s manufacturing facility.
Gasket sealing system is a lock
According to Hamilton Kent LLC, supplier of the gasket sealing system for the job, rubber gaskets have been an integral part of sealing underground infrastructures in North America for more than 60 years. “With the development of the pre-lubricated Tylox Super Seal (TSS) gasket 20 years ago,” explains Alan Siebenthaler, Hamilton Kent marketing manager, “the ease of use and performance of gaskets took a big step forward. Fast, clean, simple installations have now become the norm for contractors in many regions throughout the U.S. and Canada.”
The unique design of the TSS gasket, in combination with the radius corners and single-offset joint box culvert design, now offers the advantages of watertight connections and reduced installation time for the contractor (see Figure 3a and 3b). “This gasket has a thin layer of silicone lubricant on the inner surface of the rolling tube,” says Scott Lander, Hamilton Kent national account manager–concrete products, “so no lubricant is necessary at the job site, saving time and labor.” The gasket is applied on the spigot end of the precast box culvert at the plant, so field installation is as simple as lowering the box section into position, ensuring proper alignment, and then pushing or drawing the two culverts together.
Because the gasket is installed on the box culvert at the plant, the gasket is manufactured from synthetic rubber compounds engineered for enhanced ozone and UV resistance. This allows for storage in the precast yard for extended periods of time without material degradation. All TSS box culvert gaskets meet the material requirements of ASTM C 1677, ASTM C 443 and CSA A257, for either “Standard” or “Oil-Resistant” applications.
Precast proves watertight
“Construction of the sewer was excellently executed,” says Joseph (Joe) Atanga, resident engineer for the NYC Parks & Recreation Department. “The level of cooperation and participation of all parties was important for this project, especially Garden State Precast, who produced the concrete culverts, and Hamilton Kent, who supplied the pre-lubed gaskets for the culverts.”
“Mike Vanover of Garden State and Scott Lander of Hamilton Kent supervised the installation of the first few boxes,” explains Atanga, “and provided the needed on-the-job training and expertise for Trocom Construction to successfully complete the installation of the rest of the boxes. This level of involvement ensured that the project, which was already lagging four months behind schedule, was fast-tracked with completion almost one month ahead of schedule.”
The new sewer has been in use since March 2010, and the city conducted an internal CCTV (closed-circuit TV) inspection and video recording of the sewer two weeks after the sewer line was operational and found no leakage. “The gaskets provided the water-tight seal needed at the joints,” says Atanga, “and the precast concrete boxes made off-site and delivered ready-toinstall helped in a big way to speed up the completion of this project on time.”
Sue McCraven, NPCA technical consultant and Precast Solutions editor, is a civil and environmental engineer.
Sidebar B – Project Superintendent Tells It Like It Is
“I would rather work in a desert than in the underground conditions we faced at the Burling Slip playground site,” says David DeMartinis, Trocom Construction project superintendent. Burling Slip is in the heart of New York’s South Street Seaport historic district and is within sight of the Brooklyn Bridge and the Statue of Liberty; but it is what you can’t see, what is beneath the pavement, that has a story to tell.
People familiar with the history of the Manhatten harbor area know that the site was home to bustling water-borne commerce. NYC’s piers once handled one-third of the world’s merchant tonnage transported by sailing ships. Consequently, the current site for the playground was covered by seawater for much of its early history. City garbage and waste were routinely dumped dockside in the harbor. This historical use of the seaport site meant that the excavation materials had the makings for a constructor’s nightmare.
“Anyone who knows this area knows we’ve got a very high water table here,” says DeMartinis, “with water just about 4 ft. (1 m) below the surface. The 4 ft (4.3 m) or so that we had to excavate for the sewer line was filled with historical artifacts as well as plenty of garbage. It was like digging into a landfill – it took twice as long as normal. Our biggest challenge throughout this job was keeping the water level down in the trench; we used a tremie plug (rat slab) continuously.” Old bones and clay pottery in the subsoil necessitated the presence of a New York state archeologist during all excavation operations.
Locating and repositioning underground utilities (electric and telephone) further constrained digging at the site. To support the sewer line in the unstable substrate, Soil Solutions Inc. of New York installed 127 continuous-flight auger (augered-cast-in-place or screw) piles1, 16 in. (406 mm) in diameter and weighting 80,000 lb (36,300 kg). Beneath the precast culvert tunnel, the 45-ft (14-m) deep piles were placed in two rows, 30 in. (760 mm) apart and 6-ft (1.8-m) on-center.
“What most impressed me about the precast system,” says DeMartinis, “was the ease with which the heavy 22,000-lb (10,000-kg) precast units were positioned and assembled. The precast quality was outstanding, in my opinion, and we had the added assurance of plant inspections and a certified product.”