Miners start Hs2 cross tunnels under chilterns

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The construction of the longest tunnels for the HS2 project stretching for 10 miles under the Chilterns has started a new phase with the tunnelling of the cross tunnels that link the two main tunnels with 38 in total being constructed.

The escape tunnels that are 10 to 15m long are bored every 500m to connect the two main running tunnels around 40m below the surface to provide emergency access and exit routes.

A team of miners used a remotely controlled excavator to break out of and excavate from one running tunnel to the adjacent tunnel joining the two main tunnels. The tunnels are 10 to 15m in length this is then lined with a water-proof membrane before a secondary concrete lining constructed behind specialist formwork in the cross passage as shown in the image below.

The tunnels are being built HS2’s main works contractor, Align which is a joint venture formed of Sir Robert McAlpine,Bouygues Travaux Publics, and VolkerFitzpatrick.

HS2’s Head off Tunnel Engineering, Martyn Noak commented saying that : “While invisible to the travelling public, the cross passages have a key role in providing a safe operational railway.

Tunnel being sprayed with concrete
Tunnel being sprayed with concrete

 

“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.”

Daniel Altier, Align Project Director, said: “The completion of this cross passage is a significant milestone for the team at Align JV.

“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.”

Once the passageway is complete, the 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.