Underwater Infrastructure Work Prepares NYC Harbor for Megaships

Post-Panamax megaships can now navigate between Brooklyn and Staten Island to deliver cargo to the Port of New York and New Jersey thanks to infrastructure work recently completed below the water.

The $2.1 billion Harbor Deepening Program, initiated by the Port Authority of New York/New Jersey (PANYNJ) and the U.S. Army Corps of Engineers, called for a 54-foot-deep trench to be dredged in Anchorage Channel to accommodate the huge new cargo ships that dominate world trade.

Unfortunately, the proposed trench would collide with two vital water siphons that provide fresh water to Staten Island.

To address the problem WSP, in joint venture, was engaged by the New York City Economic Development Corporation (NYCEDC) to manage the construction of a single new tunnel and water main to replace the two existing pipes that run between Brooklyn and Staten Island parallel to the Verrazano-Narrows Bridge.

“The Port is the third largest in the U.S. and receives goods for 23 million people in the region annually,” said Ray Moran, WSP’s project manager. “Goods can now arrive at the Port’s six terminals by travelling through the Anchorage Channel, and this journey is possible due to some major infrastructure improvements below the water.”

“Soil conditions were extremely soft, located under the water table, and required the use of a 300-foot-long, 110-ton tunnel boring machine (TBM) known as an earth pressure balance machine (EPBM) designed for these precise conditions,” Moran said.

As the EPBM goes to work, it mines and pushes the soil and muck through a screw conveyor system that transports the residue away from the machine.

This Harbor Deepening Program was the first in New York City to use an EPBM.

“The WSP team used innovative data collection and interpreting techniques to understand and control the performance of the TBM,” said Kevin Moon, resident engineer for the project. “We monitored the earth pressures to make sure there was no over-excavation and monitored the level of wear to the rippers – the ‘teeth’ of the machine – to ensure the machine was operating properly.”

The starting point in Staten Island and the end point in Brooklyn were both located in densely populated urban areas. The tunnel passed 80 feet below the Belt Parkway, a six-lane highway along the South Brooklyn shoreline where the ground conditions were particularly challenging.

“Most of the ground was extremely soft, almost like soup; especially the fine-to-medium sand under the Belt Parkway, which proved to be very challenging to excavate,” Moon said. “Our geotechnical experts developed a sophisticated construction management plan to monitor potential settlement and observe the performance of the TBM around the clock.”

A four-shift inspection schedule provided the project with a team responsible for monitoring the muck volume, tunnel face pressure, ground settlement points and groundwater table.

In late October 2012 – 13 months into construction, as the boring machine was 1,600 feet into the project, or at about 17 percent completion – Superstorm Sandy hit New York. The surge flooded Staten Island and inundated the tunnel with seawater, severely damaging the TBM.

“At that point, discussions were had about whether to continue the project or start over,” Moran said. “In the end, the decision was made to refurbish the machine and continue forward.”

After 18 months of recovery time, mining resumed in April 2014. The tunnel was completed in January 2015 when the TBM reached the Brooklyn shaft. The new siphon was installed, connected to the existing water supply systems and activated in October 2016.

“While it was challenging to maintain the alignment and ensure safety for our workers, we were successful through the completion of the project,” Moon said. “I am very proud of what we were able to accomplish.”

The new siphon now maintains a continuous water supply to Staten Island, and ensures that New York City can now accommodate the vessels that will bring increased cargo volumes to the PANYNJ.

“The success of this project depended on the coordination of all stakeholders—not only the Port Authority, but also the New York City Department of Environmental Protection, the Corps of Engineers and other local stakeholders,” Moran said. “This was a huge undertaking and working together made all the difference.”