Tunnel boring machines Florence and Cecilia are now nearly four miles into their 10-mile journeys and attention has now turned to the first of 38 cross passages that will link the northbound and southbound tunnels.
The first cross passage has now been completed and several more are now being prepared.
Each passage is between 15 and 20 metres in length. They are formed by a remote-controlled excavator digging from one running tunnel to the adjacent tunnel. As the excavation is progressed the ground is supported using a sprayed concrete lining (SCL).
HS2’s main works contractor for the Chilterns section is Align – a joint venture of Bouygues Travaux Publics, Sir Robert McAlpine and VolkerFitzpatrick.
Once the team completes an SCL-lined cross-tunnel, a water-proof membrane is installed followed by a secondary concrete lining constructed by placing concrete behind formwork installed in the cross passage.
Once the passageway is complete, safety doors are installed at either end. These are manufactured by Bolton-based Booth Industries, which has a contract for more than 300 units for all the tunnels between London and Birmingham.
Align project director Daniel Altier said: “The completion of this cross passage is a significant milestone for the team at Align JV, delivering the first mined cross passage on HS2 phase 1. I’m proud of the team, their hard work and collaboration to get us to this point.
“In partnership with our supply chain; KVJV responsible for the ground treatment, specialist contractor Euro Diamond Drilling and waterproofing specialist Rennesco, the sub-surface team at Align have already commenced preparation work on several other cross passages and are making good progress.”
Martyn Noak, head of tunnel engineering for HS2 Ltd, said: “HS2 is making huge progress, with 25,000 jobs supported by the project, construction in full swing between London and Birmingham and now the start of this new phase of tunnelling work under the Chilterns.
“While invisible to the travelling public, the cross passages have a key role in providing a safe operational railway. In an emergency they allow the safe evacuation of passengers into a place of relative safety – the other tunnel. Constructing cross passages is different than using a tunnelling machine as the ground is excavated in short lengths with each advance being left unsupported for a short period of time until the sprayed concrete lining is installed. It is a different set of risks and a specific skilled workforce is needed.
“It’s great to see the first one complete and I’d like to congratulate everyone involved in this important milestone, one down 37 to go.”
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