Grimshaw has revealed designs for a spiral steel vent shaft, one of five structures that will be built to provide ventilation and emergency access to HS2’s 10 mile Chiltern tunnel.

With a spiral-shaped weathered steel wall surrounding a conical headhouse, designed to echo the shape of the site and the natural tones of the surrounding landscape, the structure will be set in the middle of a stretched roundabout just outside Amersham in Buckinghamshire.

Grimshaw associate Chris Patience said: “Flint-filled gabions form retaining walls within an extensively landscaped site, while retained mature trees, supplemented with new planting, will frame views of the new structures. 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 reveals the shape and location of the circular ventilation shaft below. The building is crowned with an array of anodised aluminium fins, arranged to respond to the shape of the surrounding valley and longer distance views.”

An 18m deep ventilation shaft will reach down to the twin tunnels, with equipment designed to regulate air quality and temperature, remove smoke in the event of a fire and provide access for the emergency services.

The team engaged with the Chilterns Area of Outstanding Natural Beauty Review Group and Buckinghamshire Council during the development of the designs.

Grimshaw has also designed four barn-like structures which will be positioned in rural locations elsewhere on the tunnel.