Balfour Beatty Civil Engineering Ltd

Surface Water Link and Underground Storage Cavern, Jersey

The project comprised construction of 1,076 linear metres of tunnel, from the harbour at Weighbridge - part unlined at 3.14 metres internal diameter and part lined at 2.74 metres internal diameter - and an underground storage cavern, together with an access tunnel and shafts of 18,000 cubic metres.

The St Helier Flood Relief Scheme has been designed to alleviate surcharging of the town's sewer system during periods of high rainfall by providing separate foul and storm water systems.

Storm water, generated from catchment areas, will be conveyed in a tunnel to an existing sea outfall in St Helier Bay. Foul water from storm water overflow
chambers will flow in pipelines located within the tunnel to a centralised storage holding tank located beneath Fort Regent.

The segmentally lined tunnel drive was carried out using a modified slurry Tunnel Boring Machine and passes directly below the town centre of St Helier.

The main cavern complex and remaining tunnel sections were created using carefully controlled drill and blast rock excavation procedures. The access tunnel and associated minor openings were driven as single headings supported with rock reinforcement depending upon rock conditions and a final shotcrete lining provided as required. The project was serviced by a completely covered surface works area in the Surface Water Link and Underground Storage Cavern, Jersey, Channel Islands base of the existing Snow Hill cutting to control dust, noise and construction activity in general being accessed through the main 8m x 5m shaft.

The use of explosives required special consideration in terms of environmental impact and was subject to continuous monitoring via specialised instrumentation stations. Detailed building surveys were undertaken along the tunnel routes.

Back to selection