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Mersey Loop Tunnel Drainage Project

Shortlisted schemes Civil Engineering

A decline in Liverpool's heavy industry and a parallel reduction in the use of water pumped from the underlying sandstone resulted in a rise of the natural ground water level.

A consequence of the rising water table was partial flooding of the Mersey Loop rail tunnel which led to signalling faults and disruption of train services. Railtrack sought a permanent solution and let a design and build drainage contract to Christiani & Nielsen, who brought in consulting engineer Halcrow.

It was decided to opt for a strategic long-term reduction of ground water levels, coupled with local grouting of the tunnel's precast concrete invert. Six wells up to 116m deep were drilled in the city centre and the aquifer pumped to remove about 200litres/s. Water level and tunnel movement sensors were linked via telemetry so the entire operation could be monitored.

Client

Railtrack Project Delivery North West

Cost

£3M

Principal designer

Halcrow Group

Contractor

Christiani & Nielsen

Other firms

Dragtone Building (drainage installation)

Henry Williams Electrical (electrical services)

JP Whitter (Water Well Engineers) (wellpoint boreholes)

Tri-Control (telemetry)

Stratagrout (tunnel grouting)

Inflow (mechanical services)

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