Tunnelling complete on Harbor Siphons

The tunnel, between Brooklyn and Staten Island, was designed to replace two existing shallow water lines below the bay to make way for a larger project -- dredging of the Anchorage Channel, which will allow for mega ships carrying large cargo loads to pass through.

Tully/OHL USA JV procured a 3.8m diameter EPB TBM from Caterpillar in 2012, which was designed to drive through highly variable clays, sands, weathered rock and boulders. It was launched from the 35m deep Staten Island shaft, boring towards the 40m deep Brooklyn shaft, in August 2012.

In October 2012 Superstorm Sandy hit the East Coast with winds up to 145 kph. Extreme flooding at the waterfront jobsite in Staten Island overtopped protective concrete barriers that had been designed 3ft (1m) above the 100-year flood level. Seawater rushed into the tunnel and the nearly 113m-long machine was entirely submerged only 460m into its drive.

"Obviously this was our biggest challenge," said Luis Alonso, tunnel manager for OHL. "After that, not many people thought we would be able to finish this tunnel."

The TBM was severely corroded by saltwater and sat idle until July 2013. During that time, CAT announced its impending closure of its TBM business, and the contractor looked to other manufacturers.

"OHL was always determined to finish this project," Alonso said. "After studying other options, we decided to proceed with the full refurbishment of the TBM with the help of The Robbins Company."

The rebuild took about four months, much of it done in the tunnel under water pressure, and crews were able to return to mining on April 14, 2014. Machine performance steadily increased, eventually reaching rates as high as 30.48m per day and as much as 25 rings in 24 hours in August 2014.