HS2 Chiltern Tunnel hits construction milestone

HS2 Chiltern Tunnel hits construction milestone

Teams working on the Chiltern Tunnel, the longest tunnel on the HS2 high-speed rail project, have completed excavation of 19 out of 38 emergency cross-passages linking the northbound and southbound tunnels.

The cross-passages are essential safety features that will allow passengers to evacuate a train in an emergency and walk to the other tunnel for rescue. They are also used for emergency access by maintenance and rescue services.

"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," said Aaron Harrison, HS2 Ltd.’s Project Manager. "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.

"While invisible to the travelling public, these hidden passages have a key role in providing a safe operational railway so it's great to see such good progress."

The cross-passages are being dug using remotely controlled mini-excavators. 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.

Didier Jacques, Align's Underground Construction Director, said: "I am delighted with the progress made by our cross-passage team, working in close cooperation with our supply chain partners. In particular I would like to acknowledge the contribution from KVJV who is responsible for the ground treatment, specialist contractor Euro Diamond Drilling and waterproofing specialist Renesco."

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.

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.

"The win allowed Booth Industries to establish a new facility in the town and create up to 50 jobs over the next 10 years," said a spokesperson for the company. "The sliding doors have been subjected to rigorous fire and fatigue testing to take account of the high train speeds, associated pressures and frequency of the trains."

The Chiltern Tunnel is expected to be completed in 2029.

Photo Credit: HS2

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