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Challenging New York Bay tunnel completed

Tunnelling work on the New York City Harbour Siphons Project has been completed, according to an announcement by the projects.

The tunnels that were built by OHL and Tully will replace existing shallow bores between Brooklyn and Staten Island but work was delayed by flooding and geological complications.

Work on the scheme, which will enable the Anchorage Channel to be dredged to allow larger cargo ships to pass through, started in August 2012. However, flooding during Huricane Sandy in October 2012 inundated the access shaft and tunnels at Staten Island.

According to OHL, the flood levels overtopped concrete barriers built 1m above the 100 year flood level and submerged the Caterpillar earth pressure balance tunnel boring machine (TBM) 460m into the drive.

It took almost a year for the recovery work to reach the TBM and during that time Cat pulled out of the TBM market. OHL and Tully called on TBM manufacturer Robbins to help refurbish the rusted machine. The rebuild – undertaken under water pressure – was completed in April last year enabling the tunnel drive to restart almost 18 months after it was halted.

Robbins remained on site to support the rest of the drive and helped to fit four additional thrusters when ground conditions changed from the expected marine sediments to glacial deposits with sand and hard boulders, as well as water ingress.

Now that tunnelling is complete, the stationary and tail shields will be buried at the exit shaft entrance, with the cutterhead and back-up being removed to enable the tunnel fit out work to be undertaken.

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