Work well underway on first HS2 shaft

22 July 2021

Engineers working on the UK’s new high-speed railway (HS2) have begun excavating the first of five ventilation and emergency access shafts for the 16km-long tunnels being bored under the Chiltern Hills.

Located near the village of Chalfont St Peter, the 67m-deep shaft will be topped with a headhouse inspired by nearby barns and other agricultural buildings to help it blend into the landscape. The structure was designed by HS2 Ltd’s main works contractor Align JV – comprising Bouygues Travaux Publics, Sir Robert McAlpine and VolkerFitzpatrick – working with design partners Jacobs and Ingerop-Rendel, architect Grimshaw and landscape designer LDA. 

Extending down to the twin tunnels, the shaft will have 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.

A total of 16 reinforced-concrete diaphragm wall panels sunk into the chalk form the circular shaft’s perimeter. Bulk excavation of the core was achieved by a clam excavator down to 35m followed by a method using a truck loader, skip and crane to reach the final depth. Around 18,000m3 of material is expected to be excavated from the shaft, with the chalk to be reused for landscaping the site to create a new grassland habitat.

Construction of the Chalfont St Peter shaft follows the recent launch of HS2's first two TBMs - Florence and Cecilia - which are expected to pass through the shaft next year. This will be followed by installation of the internal vent shaft structures, associated equipment and basement works.