Surface Connection Challenges
In 2011, NYC’s Department of Design and Construction (DDC) sought to connect a reach of Tunnel No.3 to the city’s distribution system using 4 access shafts. Located in several high profile areas of Manhattan, including Lincoln Center, the Theatre District and Little Italy, the scope of work includes street construction of over 18,000 feet of 48 and 30 inch diameter steel pipeline. Awarded to Waterworks, JV for a contract value of $234.8M, MED 609 is the largest such project ever undertaken by DDC.
Constructing a large-diameter water transmission pipeline in an urban environment such as Manhattan is difficult. Right-of-way within the street is tight with numerous existing utilities. Open trench is limited and shoring requirements strict. Pipeline installation is tightly regulated and must be choreographed around traffic control and other public mandates. With construction this difficult, pipe material selection is critical, and NYC only allows cement mortar lined, polyethylene tape coated steel pipe for diameters of 36 inch and larger.
New York City Tunnels for Water Security
The water supply for much of New York City is delivered through two large tunnel systems originating north of the city and extending south under its five boroughs. Located 200 -300 feet below surface, the first tunnel opened in 1917; a second tunnel opened in 1936. Both tunnels have remained in continuous service and currently cannot be taken down for inspection or repair.
Recognizing the critical need for redundancy and long term maintenance of the two existing tunnels, NYC commenced construction of a third tunnel in 1970. An initial 13 mile segment was completed in 1998. In 2013, a second 10 foot diameter, 9-mile segment was completed extending the tunnel to the southern end of Manhattan. An additional 5.5 mile segment between Brooklyn and Queens is expected to be finished by 2020.
At an estimated cost of nearly $5B, Tunnel No. 3 is considered one of the largest water supply projects currently underway in the United States. While the tunnel is impressive in scope, a significant construction challenge remains in connecting the new tunnel to the city’s existing water distribution system.
Steel Pipe Meets Difficult Construction Challenge
Steel proves to be an ideal pipe material for NYC and critical infrastructure projects like MED 609. The tightly bonded polyethylene tape coating system allows for the use of highly efficient cathodic protection, mitigating detrimental pipeline corrosion for decades, if not a century. The ability to provide steel pipe with shop fabricated fittings to almost any configuration greatly facilitates layout in difficult and congested street alignments. When unexpected field conditions arise, steel pipe is easily modified as well.
Pipe is furnished with bell and spigot ends for field lap welded joints in lengths up to 40 feet. The joint is welded inside and out, creating an enclosed annular space which can then be air tested using a small threaded outlet provided on the bell end. Because each lap joint is proof tested during installation, the completed pipeline can be placed into service without the use of bulk heads and field hydrostatic testing.