The New NY Bridge project reached a major milestone in late August with the installation of the first approach-span pile cap. These 300-ton concrete elements unify and “cap” the piles previously driven deep into the riverbed, and serve as foundation platforms for the bridge’s piers. Dozens of the approach span pile caps will be will be built and installed between now and the end of the year.
The caps—the size of tennis courts—are prefabricated at an offsite facility and resemble concrete tubs with holes at the bottom. Following a thorough inspection, the caps are moved onto barges and transported to the project site.
Once on site, crew members use barge-mounted cranes to position each cap atop a grouping of piles. The cranes are equipped with specially-engineered rigging to securely grip the massive tubs and place them with great precision. Holes at the bottom of the tubs allow the pile tips to slide through. Concrete is then used to seal the tubs to the exterior of the piles.
Next, the piles and tubs are fitted with a labyrinth of steel-reinforcing bars, called rebar. The tightly-hewn network of rebar is then enclosed with up to 750 cubic yards of concrete, from the project’s floating batch plants. The resulting composite material, steel-reinforced concrete, combines the strengths of both materials: The concrete can withstand enormous compression, while the steel is capable of taking on great amounts of tension.
The end product: Incredibly strong foundations that will support the new bridge well into the next century.