Machine recovery ends Cleaner Seas tunnelling

Tunnel works were concluded last month on the Cleaner Seas for Sussex project near Brighton, UK.

The TBM that linked the sewerage works with the long sea outfall at Friars Bay near Brighton, UK (see feature, T&TI April 2011, page 33) has been lifted from its submarine reception pit. The 1.8m i.d., 1km drive was executed by an Iseki pipe jacking TBM

The main contractor, the 4Delivery JV was comprised of Costain, United Utilities and MWH. The tunnelling subcontractor that executed the Friars Bay works was Joseph Gallagher.

The ambitious drive had to descend sharply to a second shaft at the base of the cliffs before continuing out to the outfall pipe that was laid in a trench. A submarine reception pit of approximate dimensions 13.5m x 8m x 8m was filled with a sea-dredged granular ballast gathered from near the Isle of Wight.

Prior to recovery, the machines watertight doors were shut and a positive internal air pressure applied. The cleared tunnel was flooded, floatation tanks were attached and the machine rose, ready to be recovered.

Jim MacIntyre, project manager for client Southern Water said, “Late July 2010 marked the start of the tunnelling and [the Friars Bay TBM] recovery marks the end. This is a momentous milestone for the project and takes us one step closer to completing the project and bringing cleaner seas to Sussex.”