With the start of work on thirty-eight cross passages connecting the northbound and southbound tunnels, the construction of HS2’s longest tunnels, which extend for 10 miles beneath the Chilterns, has entered a new phase.
Every 500m, 15m-20m long escape tunnels are bored to connect the two main running tunnels 40m below the surface.
An expert group of miners is breaking out of and excavating from one running tunnel to the neighbouring tunnel using a remotely controlled excavator.
A sprayed concrete lining supports the ground as the excavation proceeds (SCL).
Each passage is between 15 and 20 metres long and was constructed by Align, the main works contractor for HS2, a joint venture between Bouygues Travaux Publics, Sir Robert McAlpine, and VolkerFitzpatrick.
Following the installation of a waterproof membrane, a secondary concrete lining is built in the cross passage behind specialised formwork.
The safety doors can be installed at either end of the passageway once it is finished. More than 300 of these are being produced by Booth Industries, a Bolton-based company that was awarded the contract to supply them for all the tunnels between London and Birmingham.
