Project Update by Maidie Erickson, PE

McMillen Jacobs Associates is providing resident engineering and inspection services as prime consultant to the New York City Department of Design and Construction to extend water and gas services under the Bronx Kill between the Bronx and Randall’s Island. The project is challenging because of its dense urban area setting and use of trenchless technology.

In-the-wet excavation of gas main receiving shaft

The project consists of two 60-inch-diameter (1,525 mm) tunnels, each approximately 920 feet long (280 m) and installed by microtunneling. Two 20-foot-diameter (6 m), 58-foot-deep (17.7 m) launching shafts were constructed on Randall’s Island; two 64-foot-deep (19.5 m) receiving shafts were constructed on the Bronx side. Shaft excavation was in the wet with tremie base slabs. The shafts were constructed using a secant pile support of excavation system. The project also includes 1,200 feet (366 m) of near-surface water main and 2 miles (3.2 km) of gas main, flow meters, and valve chambers, all constructed by open-cut method.

After tunnel excavation, a 20-inch-diameter (510 mm) ductile iron pipe water main was installed in one tunnel and a 12-inch-diameter (305 mm) HDPE high pressure gas main in the other. The tunnels were then grouted with flowable fill. The gas main vertical riser pipes were installed up the gas main launching and receiving shafts to the new service connections, and the shafts backfilled. The remaining water main riser pipes and surface chambers will be installed inside the water main launching and receiving shafts with connections to existing services on both ends and the shafts backfilled with concrete.

Shaft construction, tunneling, and gas main work were completed by Cruz Contractors, Inc. Final gas-in from the Bronx, water main work, and shaft backfilling are expected to be completed in winter 2018/2019. Estimated date for construction completion is fall 2019.