Breathtaking end to Cleaner Seas for Sussex drives

Excavation was completed last month on the new sewer tunnel between Brighton Marina and Friars Bay in Sussex, UK. The drive was part of the Cleaner Seas for Sussex project undertaken by contracting JV 4Delivery on behalf of client Southern Water.

The 2.44m Lovat TBM named Alice broke through to Portobello on 22 June after a 3.6km drive. The other 2.44m Lovat machine, named Hollyblue, completed its 1052m drive from Peacehaven to Friars Bay in May. Previously, Alice executed a 1.8km drive between Ovingdean and Marine Drive while Hollyblue bored 2.7km from Peacehaven to Portobello.

A spokesperson for Southern Water told T&T today, “Alice achieved a maximum advance rate of 32 rings in a shift while Hollyblue achieved 37. Long term average from launch to breakthrough varied, as it was partially dependent upon drive length.

“Hollyblue’s Peacehaven to Portobello drive achieved a maximum rate of 10.5 m/shift while the Peacehaven to Friars Bay drive achieved 11.5 m/shift. Alice’s Ovingdean to Marine Drive (Belt Conveyor) bore achieved: 12.6 m/shift while the Ovingdean to Portobello (Screw Conveyor) bore achieved: 14.8 m/shift.”

The spokesperson mentioned that although most of the ground was chalk with flints, spoil from near solution features also indicated the presence of some iron minerals.

Angus Mackenzie, tunnel agent at the Peacehaven Site said “Hollyblue ultimately performed the best simply because it was specifically designed to excavate chalk with water pressures. In order to excavate in dry chalk both TBM divers had to add water under pressure as opposed to Alice, which is a more general purpose/utility machine.

Mackenzie added, “Peacehaven to Portobello and Ovingdean to Marine Drive presented no untoward challenges as such, just the normal day-to-day trials and tribulations. Peacehaven to Friars Bay was interesting as the reception shaft was very congested with equipment relating to the pipejack [see T&TI April, p. 33] that could not be disturbed by the TBM entry.

“Ovingdean to Portobello had a series of very sharp curves, the last one finishing 4.5m from the reception shaft. The skill involved in straightening the TBM out and entering the shaft in the correct place is breathtaking.”