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TBM completes excavation of New York water tunnel

A tunnel boring machine (TBM) has completed the excavation of a new $250M (£164M) water tunnel in New York.

The new, deeper tunnel – called a siphon – will carry drinking water under New York Harbor from Brooklyn to Staten Island.

Work on the project began in August 2011 and included the construction of access shafts. The 300ft-long, 110t TBM was lowered into the Staten Island shaft in July 2012 and had progressed approximately 1,600ft towards Brooklyn when operations were suspended in October 2012 in advance of the approaching Hurricane Sandy.

The storm flooded the Staten Island shaft and the excavated tunnel with sea water and severely damaged the TBM. After the tunnel and shafts were dewatered and damage assessments were completed, months of repairs and testing of the TBM followed. Tunnelling then resumed in April 2014.

Prior to Hurricane Sandy, 389 concrete pre-cast segment rings had been put in place. In total the TBM installed 2,349 rings.

The 72in siphon has been excavated at a depth of 100ft and will replace two, nearly century old, existing water connections that run from Bay Ridge in Brooklyn to Stapleton and Tompkinsville on Staten Island. The new siphon, which will serve as the back-up water feed for Staten Island, will convey approximately 5M gallons of water each day.

The project is being funded jointly by New York City Department of Environmental Protection and the Port Authority of New York and New Jersey, and is being managed by the New York City Economic Development Corporation.

The TBM is currently being moved from the tunnel and it is expected that the siphon will be activated by the end of the year.

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