HS2 hides Chiltern tunnel shafts in barns

HS2 has already been obliged to tunnel under the Chilterns area of outstanding natural beauty (AONB); now it is doing all it can to disguise the vent shafts too to prevent blotting the landscape.

HS2 Ltd has revealed the final design for the Chalfont St Peter vent shaft headhouse – the first of four similar structures that will provide ventilation and emergency access to the high-speed rail line’s 10 mile-long Chiltern tunnel.

Set back from the road, the single-story building will be wrapped in a simple grey zinc roof with doors and vent openings picked out in a dark bronze colour to provide contrast.

Taking its inspiration from the style of local barns and other agricultural buildings, the headhouse is designed to fit into the surrounding landscape. The pre-weathered grey zinc roof will age naturally over time, without loss of robustness or quality, while the whole structure will sit on a simple dark blue brick base, HS2 says.

Below ground level, a 60-metre ventilation shaft will reach down to the twin tunnels below, with fans to regulate air quality and temperature in the tunnels, remove smoke in the event of a fire and provide access for emergency services.

The plans have been drawn up by HS2 Ltd’s main works contractor for this section, Align JV – a team made up of Bouygues Travaux Publics, Sir Robert McAlpine, and VolkerFitzpatrick – working with its design team of Jacobs and Ingerop-Rendel (engineers), Grimshaw (architect) and LDA (landscaper).

Project client director Rohan Perin said: “HS2 remains committed to work proactively with residents, wider community and our stakeholders to be a good neighbour during the build phase.

“Once construction is complete, the headhouse at Chalfont St Peter will be one of very few structures of the Chiltern tunnels that will be visible to residents living nearby. That’s why it’s critical that we get the design right.”

Align project director Daniel Altier said: “Our stakeholder engagement team have held a series of public engagement sessions for the shaft headhouse and we really appreciate the time taken and the feedback we have received from the public at these sessions, which we have reflected in the design.”

Diane Metcalfe, associate principal at Grimshaw, said: “Chalfont St Peter ventilation shaft has been sensitively designed to complement the rural character of the Chilterns. The position and orientation of the headhouse buildings are located to conceal them within the landscape and form a courtyard similar to local farmyard arrangements.

“The pitched roof, zinc-clad buildings are a modern interpretation of the local agricultural and industrial vernacular. Design proposals are a result of close and collaborative engagement with the AONB review group.”

The plans for the headhouse will go on public display today, with local residents invited to attend a month-long virtual engagement event where they will be able to learn more about the design and construction of the vent shaft and headhouse.