The design for Amersham Vent Shaft, a spiral steel structure was revealed by UK based architectural firm, Grimshaw Architects in August 2020. The ventilation shaft is a structure for emergency access and ventilation for the High Speed Two railway, the 10-mile Chiltern tunnel through the Chiltern countryside.
The proposed Chiltern tunnel is approximately 13.3 km long twin-bore tunnel with its two portals located between M25 and Mantle’s Wood north of the village of Hyde Heath. The tunnel depths will vary between 10m to 90m.
There are four ventilation shafts for this tunnel – Chalfont St PeterVent Shaft, Chalfont St GilesVent Shaft, Amersham Vent Shaft, and Little Missenden Vent Shaft. The compound at each vent shaft will provide a headhouse building, hard standing for maintenance and emergency access, drainage tanks, and utility connections for fire fighting and tunnel building drainage.
Grimshaw Architects, founded in 1980 by Sir Nicholas Grimshaw, is one of the pioneers of High-Tech Architecture. It has expertise in a wide range of work like the Eden Project of Cornwall and the Southern Cross Railway station in Melbourne.
It is associated with the project of Chiltern tunnel through the proposed designs for Amersham Vent Shaft along with the Chalfont St Peter Vent Shaft, resembling a barn and Colne Valley Viaduct, a landmark structure merging refined forms of concrete with engineering aspects of balancing structural loads.
Amersham Vent Shaft will consist of an 18m deep ventilation shaft reaching down to twin tunnels, providing regulated air quality and temperature, smoke removal in case of fire, and emergency access. The structure will be set in the middle of a roundabout outside Amersham in Buckinghamshire.
The design proposes a conical headhouse enclosed within a spiral-shaped weathered steel wall, in context to the shape of the site and the surrounding landscape. The wall will sit on a flint-filled gabion unfolding to a gated entrance.
An array of anodized aluminium fins will be arranged on top of the roof, which will cater to the long-distance views. The off-centrally placed headhouse will act as a landmark revealing the shape and location of the circular ventilation shaft below. The mature trees on the site will be retained with new plants providing frames for the view towards the structure.
The team collaborated with the Chilterns Area of Outstanding Natural Beauty Review Group and Buckinghamshire Council during the development of the designs. The proposal includes designing with materials that can be part of the palette of the surrounding landscape with a curvaceous layout in context to the hills around the site.
There have been public engagement sessions for the feedback by the residents on the proposed design of the shaft headhouses that can be implemented in the final proposal. The design has been on a month-long public virtual exhibition to invite public participation and communication with the stakeholders at different levels.
It exemplifies the importance of designing infrastructural projects according to the urban context that includes not only the location and its physical elements but also the role of public opinion in the subsequent development.