Construction starts on Delaware Aqueduct Bypass tunnel12 September 2017
USA – The New York City Department of Environmental Protection (DEP) held a ceremony on September 8 to mark the start of tunnelling for the Delaware Aqueduct Bypass Tunnel.
The USD 1bn project is the largest repair in the 175-year history of the city’s drinking water supply. The project will repair two areas of leakage within the 85-mile Delaware Aqueduct, the longest tunnel in the world, DEP said. The primary leak will be eliminated through the construction of a 2.5-mile (4km-) bypass tunnel, which will be drilled 600ft (182.8m) below the Hudson River from Newburgh to Wappinger.
Contractor Kiewit-Shea Constructors (KSC) is deploying a Robbins single shield TBM, 6.8m in diameter. The machine is built to withstand 30 bar of pressure—believed to be the most of any TBM ever manufactured, DEP said. The machine needs to withstand that much pressure because workers encountered huge inflows of water under immense head pressure when the aqueduct was first built more than 70 years ago.
The TBM is also equipped with dewatering equipment to pump 2,500 gallons per minute away from the tunnel as the machine pushes forward. In addition, the machine is outfitted with equipment to install and grout the concrete lining of the tunnel, and to convey pulverized rock to a system of railroad cars that will follow the TBM as it works. Once the TBM begins its work, DEP expects it will drive about 50ft (15.2m) of tunnel per day. Work on the tunnel will continue 24 hours a day, five days a week. Tunnelling is expected to take 20 months.
Tunnel diameter will measure 14ft (4.2m) with a steel liner and a second layer of concrete. Once finished the tunnel will be connected to structurally sound portions of the existing Delaware Aqueduct to convey water around the leaking section—an approximately six-month-long shutdown planned for October 2022. The leaking stretch will be plugged and permanently taken out of service.
Over the past several months, workers have already blasted 130 linear feet of starter tunnel, and as of September workers in Newburgh began to lower the USD 30M TBM into the launch chamber, 845ft (257m) below the ground. The machine is currently being stored in 22 pieces. It will take workers approximately four months to assemble the TBM.