When it is built, HS2’s 10 mile-long Chiltern tunnel will have five structures to provide ventilation and emergency access.
The proposed design for the Amersham vent shaft headhouse has been revealed. It will be set in the middle of a road junction just outside the town, and the circular single-storey building will be surrounded by a spiral shaped weathered steel wall designed to echo the shape of the site and the natural tones of the surrounding landscape.
In order to let light through, the upper parts of the wall will be lightly perforated with a pattern inspired by woodland foliage. On top of the building, a crown of aluminium fins will help disguise the shape of the building and soften views when viewed from further away.
Weathered steel is robust and durable and fades naturally over time to a dark brown colour. In order to let light through, the upper parts of the wall will be lightly perforated with a pattern inspired by woodland foliage.
Below ground level, a 18 metre deep ventilation shaft will reach down to the twin tunnels below, 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.
This is the second vent shaft headhouse design to be unveiled. The first, at Chalfont St Peter, was revealed in July.
HS2 engaged with the Chilterns AONB Review Group and Buckinghamshire Council during the development of the designs and has launched an online virtual engagement site to gather views from the local community.
Kay Hughes, HS2’s design director said: “Today’s reveal of the latest designs for the Amersham vent shaft and headhouse is an important milestone for the project. Inspired by the location and the form of the shaft beneath, the headhouse will be one of the few parts of the Chiltern tunnel visible to residents living nearby so it was important that we get the design right. Align and their design partners have put an incredible amount of work into these proposals and I hope the design will be welcomed by the local community.”
The plans have been drawn up by HS2’s main works contractor Align JV – a team made up of Bouygues Travaux Publics, Sir Robert McAlpine, and VolkerFitzpatrick – working with its design partners Jacobs and Ingerop-Rendel, architects Grimshaw and landscape designers, LDA Design.
Since the passing of the HS2 Act, the Align team has worked to significantly reduce the scale and visual impact of the structure. By reducing the width of the shaft, the new designs require less land for construction and fewer lorry movements on local roads.
Once construction is complete, new tree planting will be added to frame views of the headhouse and areas will be set aside for chalk grassland to help create valuable new wildlife habitats. The new planting will focus on native species typically found across the Chilterns, such as wild cherry, buckthorn and crab apple.