Work has now begun to excavate the first of five shafts that will provide ventilation and emergency access to HS2’s ten-mile long tunnels under the Chiltern Hills.
The structure was designed by HS2 Ltd’s main works contractor Align JV, 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.
Once complete, the 78 metre-deep shaft near the village of Chalfont St Peter will be topped with a headhouse inspired by nearby barns and other agricultural buildings to help it fit into the surrounding landscape.
Set back from the road, the single-story building will be wrapped in a pre-weathered grey zinc roof with doors and vent openings picked out in a dark bronze colour and a simple blue brick base.
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 the emergency services.
A 120 tonne drilling rig with a specialised cutting head was used to excavate the walls of the shaft, before concrete was poured in to form each of the 16 wall panels. Now, with the walls complete, the team are excavating the chalk from inside the shaft to reveal the full depth of the structure.
The two tunnel boring machines (TBMs) – named Florence and Cecilia – are expected to reach the shaft next year and complete their 10 mile journey in three years’ time. Once the TBMs have passed through, the team will build the internal vent shaft structures, basement works and install the equipment.
Around 18,000 cubic meters of material is expected to be excavated from the shaft, with the chalk set to be reused to landscape the site once construction is complete, taking trucks off local roads and helping to create new chalk grassland habitats.