HS2

HS2 start work on first 'barn design' tunnel vent shaft

Engineers working on Britain’s new high-speed railway have begun excavating the first of 5 shafts that will bring ventilation and emergency access to the ten-mile-long tunnels. The work is currently taking place under Chiltern Hills.

The structure was designed by HS2 Ltd.’s main works contractor Align JV – a team made up of Bouygues Travaux Publics, Sir Robert McAlpine, and VolkerFitzpatrick - working with its design partners Jacobs and Ingerop-Rendel, and the architect Grimshaw and landscape designers, LDA.

Rohan Perin, HS2 Ltd.’s Project Client Director said, “the excavation at Chalfont St Peter shows how much progress we have already made in delivering the Chiltern tunnels.”

He added, "topped with a headhouse inspired by the style of local barns and agricultural buildings, the shaft is one of the few elements of the tunnel which will be visible above ground level and shows just how seriously we are taking our responsibility to protect the landscape and natural environment.”

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The single-story building will be covered in a pre-weathered grey zinc roof, with doors and vent openings picked out in a dark bronze colour, with a modest blue brick base.

Below ground-level, the shaft will reach down the twin tunnels, with fans and other equipment designed to regulate air quality and temperature, remove smoke in the event of a fire and provide access for emergency services.

To excavate the walls of the cavity, a 120-tonne drilling rig with a specialised cutting head was used, and concrete was later poured in to form each of the 16 wall panels. Now that the walls are complete, the team are excavating the chalk from inside the shaft, revealing the full depth of the structure.

Florence and Cecilia, the names of the two tunnel boring machines (TBMs), are anticipated to reach the shaft next year, and will finish their 10-mile journey in 3 years’ time. Once the TBMs have passed through, the team will build the internal vent shaft structures, basement works and install the equipment.

About 18,000 cubic metres of material is due to be excavated from the shaft, and the chalk will be reused to landscape the site once work is complete, taking trucks off local roads and helping to create new chalk grassland habitats.

Prior to construction, a temporary access road was put in place to link the site with the A413, allowing construction traffic to avoid the centre of Chalfont St Peter, stopping heavy goods vehicles (HGVs) driving past Robertswood School and the Epilepsy Society.

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There is also a new temporary marshalled lorry holding area on the A413, to help reduce congestion and queueing at the site entrance.

Align Project Director, Daniel Altier, added, “I am delighted with the progress we have made with the Chalfont St Peter shaft and the fact that we have been able to put in place measures to limit disruption to the local community. 

He concluded, “we are very conscious to ensure that any permanent structures on the project fit into the surrounding landscape and the Chalfont St Peter headhouse is no exception.”

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