The Amersham vent shaft headhouse is one of five Grimshaw-designed structures that will be built to provide ventilation and emergency access to the high-speed rail line's 10 mile-long tunnel under the Chilterns.
The Amersham headhouse is set in the middle of a road junction just outside the town – a circular single-storey building surrounded by a spiral weathered-steel wall “designed to echo the shape of the site and the natural tones of the surrounding landscape”.
To let light through, the upper parts of the wall will be lightly perforated with a pattern sais to be inspired by woodland foliage. The weathered steel is expected to fade naturally over time to a dark brown colour.
On top of the building, a crown of aluminium fins is meant to help disguise the shape of the building and soften views from distance.
Below ground level, a 18-metre deep ventilation shaft will connect to the twin tunnels below, with fans and other equipment regulating air quality and temperature, removing smoke in the event of a fire and providing emergency access.
The designs now go out to public consultation for feedback.
HS2 Ltd design director Kay Hughes 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 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, architect Grimshaw and landscape designer LDA Design.
Align project director Daniel Altier said: "We are excited to be revealing our early designs for the Amersham vent shaft headhouse. Our designers have worked closely with stakeholders to design something that reduces local construction impacts as far as practicable during the build. We now look forward to giving the local community their opportunity to provide their thoughts on the design."
Grimshaw associate Chris Patience said: "Sited in the Chilterns, this headhouse is designed to be a local landmark on the western edge of Amersham. Its expressive architecture exploits its unique context, surrounded by roads, and its function, ventilating the high-speed rail tunnels below.
"Flint-filled gabions form retaining walls within a site that will be extensively landscaped. Retained mature trees, supplemented with new planting, will frame views of the new structures. The site compound is wrapped in a weathering steel wall which follows the curvature and topography of the site. The higher parts of the wall are perforated with varying triangular patterns, derived from the surrounding tree foliage, allowing light to filter through.
"Behind the screen, the conical headhouse shows the shape and location of the circular ventilation shaft below. The top of the building is crowned by an array of anodised aluminium fins, set out to respond to the shape of the surrounding valley and longer distance views.
"These proposals are the result of integrated work across the design team, alongside collaborative engagement with the Chilterns AONB review group."
Last month HS2 Ltd revealed the design of the Chalfont St Peter vent shaft headhouse – a rustic barn with grey zinc roof and dark bronze doors