The excavation process of the first of five ventilation shafts and emergency access tunnels along the Chiltern hills (14km long), have been started by HS2 contractors.
The intended shaft, which is 78m underground and placed near the village of Chalfont St Peter will be topped with a barn-style headhouse to help meld the structure into the available landscape.
In order to dig the walls of the shaft a120t drilling rig with a specialized cutting head was used, before concrete was poured in to form each of the 16 wall panels. Currently, with the walls complete, the team is digging the chalk from inside the shaft to disclose the full depth of the structure.
At ground level 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 color and a simple blue brick base.
The location of the shaft underground level, will attain the twin tunnels and it will be equipped 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.
HS2 Ltd’s main works contractor Align JV, was responsible for this structure design, which is a team comprised 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.
Florence and Cecilia are the TBMs that are due to reach the shaft in the coming year and they are expected to complete their 10-mile drive in three years’ time. Building the internal vent shaft structures, basement works, and installing the equipment will be done by the team following the TBMs have passed through.
The amount of the materials that is estimated to be extracted from the shaft is almost 18,000 cubic meters, with the chalk set to be reused to landscape the site once construction is complete, taking trucks off local’s roads and helping to create new chalk grassland habitats.
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.”