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Amco to build Mersey tunnel escape passages

CONSTRUCTION OF three escape cross-passages in the Kingsway Mersey Tunnel is due to start next month after fears of a repeat of the Mont Blanc fire in Liverpool's Mersey tunnels.

Tunnelling contractor Amco Donelon has been awarded the £2. 2M contract to build three, 3. 3m diameter tunnels between the twin tunnel bores by tunnel operator Merseytravel.

Built between 1966 and 1973, the tunnels are 17m apart but only have cross-passages at each portal. Following the Mont Blanc tragedy in 1999, when 40 people died, safety procedures in tunnels were reviewed. This led to the decision to build the new cross passages in the Mersey tunnels, to allow motorists to escape from one bore to the other in the event of a fire.

Amco Donelon won the job after coming up with an imaginative scheme which allows the work to be carried out at night, limiting traffic disruption. Mott MacDonald is consultant for the project.

Horizontal boreholes will be driven along the length of the three cross-passage bores. Ground conditions are expected to be Middle Bunter Sandstone, some of which is heavily fissured. After drilling, the boreholes will be pressure grouted to stabilise the ground and keep out groundwater.

The cross passage location has been chosen to coincide with areas where the rock is less fissured.

The tunnels will be bored using a Brokk excavating machine, which will also place lining segments. These will then be covered with insitu fibre reinforced concrete to give a robust, low maintenance structure.

Work is expected to start in early January and finish by the summer.

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