Half of HS2 Chiltern tunnel cross-passage mining complete

tunnels under ChilternsThe construction of HS2’s longest tunnels under Chilterns, stretching for 16 km (10 miles) passed a key milestone with mining completed for 19 out of 38 emergency cross-passages linking the northbound and southbound tunnels.

An expert team of miners use the excavators to break out of the southbound running tunnel and dig the 15-20 metres to the adjacent northbound tunnel.  As the excavation progresses the ground is supported using a sprayed concrete lining (SCL).

Once the team has completed the SCL lined tunnel, a water-proof membrane is installed followed by a secondary concrete lining constructed by placing concrete behind formwork installed in the cross passage.

“We’re making great progress on the Chiltern tunnel with approaching 9 out of 10 miles complete, and our cross-passage teams are catching up fast. Once complete, HS2 will dramatically improve journeys between London and the West Midlands, unlock tens of thousands of new homes and free up space on the busiest part of the West Coast Main Line,” Aaron Harrison, HS2 Ltd’s Project Manager, said.

The Chiltern tunnel is being delivered by HS2’s main works contractor, Align, a joint venture formed of Bouygues Travaux Publics, Sir Robert McAlpine, and VolkerFitzpatrick, which is also responsible for the nearby Colne Valley Viaduct, which also reached the halfway point last week.

Once the cross-passages are complete, they are temporarily sealed for fire safety reasons before permanent safety doors can be installed at either end. These are being manufactured by Bolton-based Booth Industries who won the contract to provide more than 300 units for all the tunnels between London and Birmingham.

Once complete, the tunnel will carry high speed trains between London and the West Midlands at speeds of up to 320 km/h (200 mph) freeing up space on the busiest part of the West Coast mainline and improving journeys between Britain’s two largest cities.

The trains will travel through two parallel tunnels under Chilterns linked by short passages for use in emergencies. Unlike the main tunnels, which are being excavated by two giant tunnelling machines, named Florence and Cecilia, these smaller cross-passages are dug using remotely controlled mini-excavators.


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