Engineering milestone reached on HS2 (video)

HS2 Ltd has issued a new year progress update, revealing the state-of-play through a video release. We revealed in Rail 998 that construction of HS2’s longest tunnels, running for ten miles under the Chilterns, passed a key halfway milestone at the end of last year with mining completed for 19 of the 38 emergency cross-passages linking the northbound and southbound tunnels.

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Tunnel cross-passages

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.

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.

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Joint ventures

The Chiltern tunnel is being built by HS2’s main works contractor, Align - a joint 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. Despite the government-imposed ‘pause’ on building a station for HS2 at Euston, work on tunnelling from Old Oak Common towards the future terminus continues.

HS2 Ltd's Chief Railway Officer, Emma Head provides the latest in the video update, below: