HS2 Constructs First of Chiltern Tunnel Cross Passages

HS2 has commenced a new phase of construction on the Chiltern tunnels, creating the first of thirty-eight cross passages that will link the northbound and southbound tunnels.

The tunnels will stretch for 10 miles under the Chilterns and will be used by high-speed trains travelling between London and the North at speeds of up to 200 miles per hour. The trains will run through two parallel tunnels, which will be linked by short passages for emergency evacuations.

To construct these tunnel cross passages, miners are using a remotely-controlled excavator to break through from one tunnel to the other. Throughout this process, the ground is supported using a sprayed concrete lining.

HS2 Chiltern tunnel cross passage
HS2 Chiltern tunnel cross passage excavation in progress

Each of the 38 passages will be between 15 and 20 metres long.

Martyn Noak, HS2 Ltd’s Head of Tunnel Engineering, 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.”

The work on constructing the tunnel cross passages is being completed by HS2’s main works contractor, Align.

HS2 Chiltern tunnel cross passages
HS2 Chiltern tunnel cross passage waterproofing

Once a passageway is complete, safety doors are installed at either end. The doors are manufactured by Booth Industries and have undergone rigorous fire and fatigue testing.

Daniel Altier, Align Project Director 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.”

Meanwhile, the two tunnelling machines, Florence and Cecilia are now almost four miles into their journeys through the Chiltern tunnels.

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