The Randall’s Island Microtunnel Crossing project extends water and gas services under the Bronx Kill, a narrow strait of water between the Bronx and Randall’s Island. The project involved the microtunneling installation of two 60-inch-diameter (1,525 mm) tunnels, each 900 feet (274 m) long. Additionally, the project included the installation of approximately 1,200 feet (366 m) of near-surface water main and over 2 miles (3.2 km) of gas main.
Following the excavation of the tunnels, a 20-inch-diameter (510 mm) ductile iron pipe water main was installed in one tunnel, while a 12-inch (305 mm) high-density polyethylene high-pressure gas main was installed in the other tunnel. These mains were connected to existing services at both ends. The tunnels were grouted with flowable fill and the shafts backfilled. The project also involved extensive restoration work on roadways, sidewalks, and playfields, ensuring the area was returned to its previous condition.
Delve Underground provided resident engineering and inspection services.
The project was challenging because of its dense urban area setting; therefore, the use of trenchless technology was selected for this construction. Delve Underground addressed the following challenges:
Unresolved easement issues required shifting the two receiving shafts by 300 feet (91 m) from a parking lot to the public right-of-way.
The receiving shafts were both originally 14 feet in diameter. However, one was modified to a 10.5-foot by 17-foot (3.2 x 5.3 m) elliptical shaft because of utility conflicts, which complicated receiving shaft excavation and microtunnel boring machine extraction.
Difficult ground conditions including numerous underground boulders presented additional challenges, requiring the launch shafts to be excavated half in the dry and half in the wet, using multiple excavation methods.
Category I: Special Projects