Design For Amersham Vent Shaft Headhouse

HS2 revealed the design for the Amersham vent shaft headhouse - one of five structures that will be built to provide ventilation and emergency access to the high-speed rail line’s 10 mile-long Chiltern tunnel. Set in the middle of a road junction just outside the town, 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.

Robust and durable, weathered steel 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. 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.

Below ground level, a 18 m deep ventilation 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.

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 to get the design right. HS2 engaged with the Chilterns AONB Review Group and Buckinghamshire Council during the development of the designs and launched an online virtual engagement site to gather views from the local community.

The plans have been drawn up by HS2 Ltd’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.