HS2 reveals new designs for Amersham vent shaft headhouse

The headhouse will be set in the middle of a road junction just outside the town. The new designs have reduced the height of the circular single-storey building by more than 2m and the ‘crown’ of steel fins will be replaced with perforated pre-patinated zinc panels to blend with the surrounding landscape.

In response to feedback from Buckinghamshire Council, the new design also replaces the weathered steel boundary wall with a more traditional stone wall made of flint.

The twin-bore Chiltern Tunnel is the longest on the HS2 project, which is designed to improve links between London, Birmingham and the north, help level-up the economy and provide a low carbon alternative to car and air travel.

Below ground level, the 38m-deep Amersham ventilation shaft will connect to the twin tunnels. Construction is well under way: excavation is complete and structural work inside the shaft is now being undertaken.

Once construction is completed, tree planting will be added to frame views of the headhouse and areas will be set aside for chalk grassland to help create wildlife habitats. The new planting will focus on native species typical to the area.

The layout of the buildings is unchanged, with the spiral shaped walls echoing the shape of the site and the shaft beneath.

The plans have been drawn up by HS2 Ltd’s main works contractor Align JV, comprising Bouygues Travaux Publics, Sir Robert McAlpine and VolkerFitzpatrick, working with its design partners Jacobs and Ingerop-Rendel, architect Grimshaw and landscape designer LDA Design.

The Chiltern tunnel will have four ventilation/intervention shafts at Chalfont St Peter, Chalfont St Giles, Amersham and Little Missenden, with one intervention shaft at Chesham Road. Excavation is complete at all the sites except Chesham Road.

HS2 design director Kay Hughes said the Amersham headhouse was one of the few parts of the Chiltern Tunnel visible above ground so it was important to get the design right.

“LDA Landscape Architects and Grimshaw Architects have risen to the challenge with an exemplary design with local character. The curved form of the headhouse is sensitively nestled into the landscape of a local traffic island. This and the combination of natural and traditional materials provide a contextual relationship with the area’s long-standing architectural traditions and setting,” she said.

A formal Schedule 17 application for planning approval will be submitted to Buckinghamshire Council later in the summer.