Hydrodemolition aids Channel Tunnel repairs…

Train services through the Channel Tunnel linking Britain and France, where scheduled to be fully restored in February 2009 following several months of repairs after a major fire in the tunnel on 11 September 2008.

A lorry caught fire on a Shuttle train carrying heavy goods vehicles bound for France through the 50 km long northern tunnel. The fire, which spread to other vehicles, raged for about 16 hours. The extreme temperatures of up to 1000ºC caused extensive damage to about 600 metres of the 7.6 metre diameter tunnel’s concrete lining, approximately 11 km from the French entrance.

The Channel Tunnel operator Eurotunnel awarded the repair contract, estimated to be between €50-60M, to a consortium of Freyssinet, Eurovia Travaux Ferroviaires and Vinci Energies. Freyssinet was appointed to look after the civil engineering works, while ETF would be responsible for track and overhead wire restoration and Vinci Energies responsible for other equipment. The technique of hydrodemolition, which uses high-pressure water jets to remove concrete from various structures, was specified as the method to remove the fire damaged concrete. Freyssinet subcontracted the concrete removal to the specialist hydrodemolition and industrial cleaning contractor Philip Lasserat.

For the hydrodemolition part of the repair Philippe Lassarat hired four Conjet hydrodemolition Robots and pumps, together with a team of experienced operators and a project manager, from Rotterdam based Doornbos Equipment, a specialist in the rental of ultra high-pressure water jetting and vacuum equipment. To meet the tight schedule Doornbos had to work three shifts round the clock and opted to use two Conjet 364s and two Conjet 322s. Conjet supplied specially modified banana shaped feedbeams, which carry the jetting nozzle, to match the curvature of the tunnel wall.

“We had to remove the damaged C45 concrete just from the walls and roof to a depth of 30 mm and managed this at an average of 650 m2/day,” says Doornbos project manager Uwe Clausen. “The total area was about 9,500 m2 over an approximate 600 m length of tunnel, including about 350 m2 directly above the fire where the damage was most severe. We removed all the fire damaged concrete in 14 working days using four Robots. We had to work non-stop round the clock in three 10 hours shifts, which included an hour in and an hour out at shift change to get through all the security.” The Robots were supported by 350 kW and 400 kW pumps operating at pressures up to 1000bar and flow of up to 240 litres/min.

After the removal of the damaged concrete Philippe Lassarat followed on repairing and replacing any fire damaged reinforcing prior to spraying on the new concrete lining. The various services and utilities were then replaced before handing the tunnel back to Eurotunnel to restart a full service of the Shuttle trains on 10 February. Eurostar, the company that operates the passenger trains running through the tunnel, anticipated services would be fully restored on 23 February.