HS2 makes good progress on emerge cy cross-passage and continues tu Construction of HS2’s longest tunnels, running for ten miles under the Chilterns, passed a key halfway milestone on November 22 with mining completed for 19 of the 38 emergency cross-passages linking the northbound and southbound tunnels.
The smaller cross-passages between the two running tunnels are for use in emergencies.
Unlike the main tunnels being excavated by Tunnel Boring Machines (TBMs) Florence and Cecilia, they are dug using remotely controlled mini-excavators.
Florence and Cecilia are expected to break through at the north portal early next year.
Miners use excavators to break out of the southbound running tunnel and dig the 15-20 metres to the adjacent northbound tunnel. As excavation progresses, the cross-passage is supported using a sprayed concrete lining.
A water-proof membrane is then installed, followed by a secondary concrete lining. This is built by pouring concrete behind formwork installed in the cross-passage.
Once the cross-passages are complete, they are temporarily sealed for fire safety during tunnel construction, before permanent safety doors are installed at each end of the passage.
The doors are being manufactured by Bolton-based Booth Industries, which won the contract to provide more than 300 door units for all the tunnels between London and Birmingham.
The contract has enabled Booth Industries to establish a new facility in Bolton and create up to 50 jobs over the next ten years.
The sliding doors have been subjected to rigorous fire and fatigue testing to take account of the high train speeds, associated pressures, and train frequency.
Each running tunnel also has an emergency walkway that allows passengers to evacuate the train and walk through the cross-passages into the other tunnel, where they can be rescued by another passenger train.
Access for emergency services is from either a tunnel entrance portal or one of five ventilation/emergency access shafts.
An additional five short tunnels (known as adits and connecting the shafts to the running tunnels), are also under construction, with the mining on two of these complete.
The Chiltern tunnel is being built by HS2’s main works contractor, Align - a joint om Old Oak Com on to Euston venture of Bouygues Travaux Publics, Sir Robert McAlpine, and VolkerFitzpatrick.
Other suppliers include KVJV (responsible for ground treatment), Euro Diamond Drilling and waterproofing specialist Renesco.
Align is also responsible for the nearby Colne Valley Viaduct, which also reached the halfway point in mid-November.
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