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New York harbor crossing under way Sep 2011
Matthew Phair, TunnelTalk, New York Correspondent
Excavation is under way on a challenging under-crossing of New York's harbor. After long delays to address community opposition and logistical challenges, work has started on excavation of a new 9,460ft (2,883m) long siphon between Brooklyn and Staten Island to replace two existing smaller water lines.
Fig 1. Alignment of the new and existing harbor siphons

Fig 1. Alignment of the new and existing harbor siphons

Contractor Tully/OHL JV won the $300 million contract in June and has mobilized to site to start construction of the slurry wall shaft on Staten Island. Work on the Brooklyn shaft is not far behind. The installation of 26 piezometers, to measure water pressure, and inclinometers to measure ground movement above and around the tunnel and shaft excavations for collection of baseline data is also complete on Staten Island.
A Caterpillar mixed face EPB TBM will drive the 12ft (3.6m) diameter tunnel in highly variable clays and sands under full hydrostatic conditions. This is the first TBM to be ordered from Caterpillar following its acquisition of the Lovat manufacturing company in Canada. It is also the first use of EPB technology in New York City.
The TBM is designed specially for the difficult undersea drive and to withstand potential hydrostatic pressures of up to 8 bar. It is scheduled to arrive on site in January 2012 when it will launch from the 115ft deep, 28ft i.d. (35m x 8.5m) Staten Island shaft and drive toward the 80ft deep, 24ft i.d. (24.3m x 7.3m) Brooklyn shaft. Once under way, the US/Spanish Tully/OHL JV anticipates a TBM progress rate of 55ft (17m) per day.
Designed by CDM/Hatch Mott McDonald, the new siphon is part of a New York/New Jersey harbor deepening project. Dredging to a depth of 54ft below mean low water level will expose the existing siphons, which were laid in trenches on the bottom of the harbor in the early 1900s. The CDM/Hatch Mott MacDonald provided engineering services to the New York City Economic Development Corporation (NYCEDC) which is managing the project on behalf of the New York City Department of Environmental Protection (NYCDEP) and the owner of the siphons. Subsurface investigations along the alignment included 38 marine borings, 36 shaft and lands side borings, pressuremeter tests at nine locations, and field vane shear tests at eight locations.
The new siphon will be finished with a backfilled 72in welded-steel water pipe. Full backfill around the riser pipes in the shafts will also be installed. Water transmission mains connecting the tunnel to the existing system will be constructed in open cut. Microtunnelling will drive two crossings, about 325ft and 120ft (99m and 37m) long, under the Staten Island Railroad.
Once the new tunnel is complete, the existing siphons will be decommissioned and abandoned. The new tunnel will serve as a backup to the 900ft deep Richmond main water tunnel that was built under the harbor between Brooklyn to Staten Island in the 1960s through hard rock.
LiRo is acting as Construction Manager for the project, which, when complete, will provide five million gallons of water per day to Staten Island under normal conditions and as much as 150 million gallons per day in emergency conditions.
Tunnel excavation is anticipated to being in spring of 2012 with substantial completion achieved in 2014.
Reference
Contractors call for risky NY Harbor crossing - TunnelTalk, Sep 2009
Caterpillar's strategy for Lovat TBMs - TunnelTalk, April 2010

           

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