WORK HAS started on tunnelling three cross-passages between the Mersey tunnels to provide new exit routes in the event of a fire.
The £2.2M contract was awarded to Amco Donelon following a safety review of tunnels after the 1999 Mont Blanc tunnel fire when 40 people died.
Built between 1966 and 1973, Liverpool's Kingsway tunnels have cross-passages at the ventilation stations near their portals only.
Operator Merseytravel ordered the construction of three more 3.35m diameter passages. The road tunnels are 17m apart.
Amco Donelon won the contract with a proposal to do the work at night, minimising traffic disruption.
The ground encountered is expected to be Middle Bunter Sandstone which is fissile, increasing the risk of water inflow.
The cross-passages have been located where the rock is less fissured. Horizontal boreholes have been driven along the length of each cross-passage bore.
'We have found that the ground is satisfactory and we hope to start excavation work shortly, ' said Mersey Tunnels engineering manager Peter Arch.
The boreholes are being pressure grouted to keep out groundwater and stabilise the ground before excavation begins.
A Brokk excavating machine will then bore each tunnel and also place lining segments. These will then be covered with insitu fibrereinforced concrete to give a low maintenance robust structure.