Suffolk County | USA

Excavation diameter

3.81 m

Tunnel length

4,328 m


Clay, silt, sand, gravel

Type of support

Prefabricated segments

Completed in



Suffolk County – Long Island (New York)

Underwater sewer tunnel in New York State made with cutting-edge techniques, freezing for the shafts and Slurry TBM for the tunnel.

In particular, soil freezing technology was used to stabilise the soil during the excavation of the shafts.

An innovative Slurry TBM was used for the excavation of the underwater tunnel, capable of advancing both with the pipe pusher system and by installing lining rings in prefabricated segments.

The sandy-clay nature of the formations required the installation of a sludge treatment plant enhanced with centrifuges and filter presses capable of separating even the finest portions of the soil.

The excavation was carried out during the most critical period of the COVID epidemic and required a special sacrifice from the workers in order to continue working despite the fact that infections often reduced worker numbers.

This project was awarded the prize for best infrastructure construction site in the US for 2021, in the category of projects under $500 million.

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