Randall’s Island Microtunnel Crossing: Completed and Utilities Now in Service

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Project Update by Maidie Erickson, PE

As prime construction manager, McMillen Jacobs Associates provided resident engineering and inspection services to the New York City Department of Design and Construction (NYC DDC) to extend water and gas services under the Bronx Kill, a narrow strait of water between the Bronx and Randall’s Island. Shaft construction, tunneling, and gas main work were completed by Cruz Contractors, LLC. The project was challenging because of its dense urban setting and use of trenchless technology.

Randall's Island

The crossing consisted 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. The circular gas main receiving shaft was 14 feet in diameter (4.2 m) and the elliptical water main receiving shaft was 17 feet x 10.9 feet (5.2 m x 3.3 m). 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 included three watermain valve chambers, 1,200 feet (366 m) of near-surface watermain constructed by open-cut method, and 2 miles (3.2 km) of near-surface gas main constructed by open-cut and sliplining methods.

After tunnel excavation, a 20-inch-diameter (510 mm) ductile iron pipe watermain 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 watermain riser pipes and riser valve chambers were installed inside the watermain launching and receiving shafts, connecting existing services on both ends, and the shafts backfilled with concrete. Finally, site restorations were performed, including roadway repair and resurfacing, and installation of sidewalks, soccer fields, bike paths, and plantings.

The project reached substantial completion in January 2020. Gas and water utilities are now in service to Randall’s Island.

In November 2021, the American Council of Engineering Companies (ACEC) of New York announced that McMillen Jacobs Associates had received a 2022 ACEC New York Platinum Award in Category I: Special Projects for Resident Engineering Services on the Randall’s Island Project. The project also received the 2022 ACEC New York Best Panel Award, which is intended to promote communication of engineering excellence through the creation of panels that are visually exciting and representative of key design principles.


PROJECT SUCCESSES

Randall's Island

Watermain Launch Shaft on Randall’s Island

• Upgraded the water supply system to Randall’s Island.

• Brought natural gas to Randall’s Island—a “Best Management Practices” endeavor to reduce emissions from the many agencies housed on Randall’s Island, and tie-in points near each.

KEY CHALLENGES OVERCOME

• Unresolved easement issues and utility interferences required the receiving shafts to be shifted and drives extended by 340 feet (104 m). The contractor was approved to use a larger MTBM and casing pipe, and changed from fully welded steel casing to mechanically connected steel Permalok® pipe to advance the construction schedule.

• A challenging trunk main tie-in at the intersection of Brook Avenue and Bruckner Boulevard required a designed shoring system and immense utility relocations and replacements, including a 1900s 12-inch (305 mm) watermain replacement.

• Proximity to ConEdison oil-filled high transmission lines required modification of receiving shaft to an ellipse to fit between sanitary and storm sewers and a relocated high-power duct bank.

• A glacial erratic formation encountered in the watermain launching shaft was removed utilizing innovative methods of drilling and chiseling to break up and extract the 20- x 15- x 10-foot-thick (6 x 4.5 x 3 m) rock mass “in the wet”.

Read more: McMillen Jacobs Wins ACEC New York Engineering Excellence Platinum Award for Randall’s Island Microtunnel Crossing Project