Chalfont St Peter ventilation shaft and headhouse
Align is working on behalf of HS2 Ltd to build 22 kilometres of the high speed rail line, running between the Colne Valley and the Chilterns. This includes the Chiltern twin-tunnels with their four vent shafts to regulate airflow, one intervention shaft and the shaft headhouses which house electrical equipment.
The headhouse provides emergency services access to support a possible incident in the Chiltern tunnel beneath, includes ventilation fans to manage the environment in the tunnel, as well as a series of plant rooms.
Set back from the road, the single-story building will be wrapped in a simple grey zinc roof with doors and vent openings picked out in a dark bronze colour to provide contrast.
Taking its inspiration from the style of local barns and other agricultural buildings, the headhouse is designed to fit into the surrounding landscape. The pre-weathered grey zinc roof will age naturally over time, without loss of robustness or quality, while the whole structure will sit on a simple dark blue brick base.
What is a ventilation shaft and headhouse?
A ventilation shaft or vent shaft, is the vertical opening that connects the tunnels to the surface and open air. It regulates air quality and temperature in the tunnel, provides access for emergency services, and allows smoke to be extracted in the event of a fire. The headhouse is the building on top of the ventilation shaft which contains fire control systems and the ventilation systems for the railway tunnels below.
For Landscape Design, your priorities ranged from replacing lost tress and hedgerows removed during construction, to considering the long-term management of the site and the apperance of the landscape. The landscape design will provide a range of habitats to support biodiversity, created and managed to complement the existing landscape. Mature trees along the existing boundary are being retained as far as possible and, once construction is complete, the whole site will be landscaped with new trees and hedgerows planted to help screen it from neighbouring properties.
In terms of Ecology, you asked that typical local habitats which might be rare or in decline should be created and for the introduction of ponds to encourage new aquatic species to colonise the area. To encourage wildlife to return, bird boxes, reptile basking banks, a grass snake laying heap and a hibernaculum will be created. Material excavated from the shaft will be used to create much of the landscaping and avoid putting extra lorries onto local roads. Habitats will be created and managed within the site to reflect the existing ecological character of the Chiltern Hills, including species-rich grassland and a new wetland.
Following your comments, the design of the Headhouse has been improved, so the single-story building is now set back from the road and wrapped in a simple grey zinc roof with dark bronze openings. Taking its inspiration from the style of local barns and other agricultural buildings, it is designed to blend into the surrounding landscape. The pre-weathered grey zinc roof will age naturally over time, without loss of robustness or quality, while the whole structure will sit on a simple dark blue brick base.
Construction was also a major consideration for you, particularly reducing the amount of earth and dirt being moved by road and reducing noise and vibrations from the construction site. We have been working closely with stakeholders to take lorries out of Chalfont St Peter and will create a temporary access road which includes a new signalised junction with the A413 Amersham Road. Noise and air quality monitoring equipment on site will help us adhere to stringent levels. If these are breached, work will have to stop. We are also carrying out regular noise and air quality levels monitoring further away from the site using mobile monitoring equipment to understand the impact of works and how to reduce them even further.
Engaging on the design of the Chalfont St Peter ventilation shaft
During design development for the Chalfont St Peter vent shaft, you gave us feedback and completed questionnaires – which influenced our approach.
You can view or download our Chalfont St Peter Ventilation Shaft ‘You said, We did’ information boards below, a key part of the design for HS2 in Chalfont St Peters.