Keltbray has secured the contract to provide construction services for the first two ventilation shafts and head houses on HS2's first two giant tunnel drives at Chalfont St Peter and Chalfont St Giles, on behalf of the Align Joint Venture that is delivering the Central 1 portion of HS2 Phase 1.

The shafts will provide ventilation and emergency access to the ten-mile long tunnels Align is digging under the Chiltern Hills. The scope of services Keltbray will provide include:

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• Reinforced concrete works at the base of the shafts, to create a collar structure to enable the TBMs to pass through the base of the shaft

• Internal shaft construction works to build slip-formed concrete cores and lining walls

• Excavation and substructure construction of Head House buildings.

Excavation of the first shaft to a depth of 78m located close to the village of Chalfont St Peter has already been completed, ready for Keltbray to start work. After the construction is complete the shaft will be topped with a head house inspired by nearby barns and other agricultural buildings to help it fit into the surrounding landscape.

Below ground level, the shaft will reach down to 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 maintenance and emergency services.