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News » US » TBM gets set for repairs to world’s longest tunnel » published 17 Mar 2017

TBM gets set for repairs to world’s longest tunnel

Manufacturing and testing has been completed for a tunnel boring machine (TBM) that will be used for repair work on the longest continuous tunnel in the world.

The TBM will be used to overhaul a section of New York City’s Delaware Aqueduct, an 85 mile-long long tunnel that delivers about 50% of the city’s drinking water each day.

Representatives from New York Department of Environmental Protection (NYDEP), consultant McMillen Jacobs (MJ), and JV contractor Kiewit-Shea Constructors (KSC) visited the Robbins facility in Solon, Ohio, to witness the factory acceptance testing of the custom TBM.

The Robbins Single Shield TBM will bore a tunnel to replace a 2.4 mile stretch of the Delaware Aqueduct.  The Delaware Aqueduct currently leaks about 20 million gallons of water per day into the Hudson River. Investigations dating back more than a decade revealed cracks in the tunnel lining. Inspections with an automated underwater vehicle showed that the cracks were stable but it was determined they could not be fixed from within the existing tunnel. New York City then decided that a new tunnel would be built under the river to bypass the leakage.

Robbins has manufactured the 21.6’-diameter Single Shield TBM to be safely sealed against pressures up to 30 bar, and to operate in variable hard rock conditions. This particular section of the tunnel lies 600’ below the Hudson River and so the inflows are under immense head pressure.

Features of the TBM to deal with difficult ground include powerful drilling, grouting, and water inflow control systems. “One unique feature of this TBM is the closeable bulkhead, which allows the excavation chamber to be sealed off,” said KSC tunnel manager Niels Kofoed. “We expect this to be a key feature in the event that groundwater flows (shunt flows) from the excavated portion of the tunnel cause washout of the annulus grout. Once the bulkhead is closed the groundwater flows are stopped and secondary grouting of the precast liner can be performed, effectively cutting off the flow path of the shunt flows.”

Robbins project manager Martino Scialpi added that “the TBM was designed with a 2,500 gallon/minute dewatering capacity. The machine is equipped with two drills in the shields for drilling through the head in 16 different positions and a third drill on the erector to drill through the shields in an additional 14 positions.  Drilling and pre-excavation grouting will be a routine job to control and minimize water inflows.”

In addition, water-powered, high-pressure down-the-hole-hammers will allow for drilling 200’ to 330’ ahead of the machine at pressures up to 20bar if necessary.

In order to provide access to launch and retrieve tunneling equipment, two deep shafts have been constructed in the towns of Newburgh and Wappinger, New York, where the bypass will begin and end.

Once assembled, the machine is expected to begin boring in fall 2017.

 

MPU

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This article was published on 17 Mar 2017 (last updated on 17 Mar 2017).

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