Amersham ventilation shaft and headhouse
Our Construction Partner, Align, is working to build 22 kilometres of the high speed rail line, running between the Colne Valley and the Chilterns. It includes the 3.4 kilometre-long Colne Valley Viaduct and the 16 kilometre Chiltern tunnel with four vent shafts to regulate airflow, one intervention shaft and the shaft headhouses which contain electrical equipment.
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, you asked us to respond to the character of the site and surrounding landscape and use existing trees, hedgerows and new planting to conceal structures as far as possible. The landscaping will be sculpturally shaped to integrate with the profile of the valley, whilst woodland and shrub planting and chalk grasslands will reinforce the semi rural setting.
We will retain as much of the existing vegetation along the A413 and A404 as possible and have increased areas of native tree and shrub species to manage views of the building.
In terms of Ecology, you felt it essesntial to keep as many existing trees and hedgerows as possible and also to restore the area using planting or seeding of native and indigenous species.
We will create habitats using native plants and seeds to enhance the biodiversity value of the site. We will also undertake long-term management of land in our ownership, guided by a Habitat Management Plan for the lifespan of the project. Our plans include the creation of calcareous grassland habitat, reflective of Chilterns grassland, to allow animal foraging and movement. Existing habitat connectivity will be retained and protected, new woodland edge and scrub planting will allow for animal forgaing and movement and we will incorporate habitat features such as hibernaculum, reptile egg laying heaps and reptile and invertebrate basking bank.
Design of the headhouse
You told us to control the visual impact of the headhouse by setting the building into the landscape, while keeping the overall footprint (area) of the compound as small as possible.
We will keep as much of the building below ground as possible and have lowered the height of the headhouse and compound wall to reduce the overall visibility of the structure, while the conical shape further helps to lessen the scale of the building. The headhouse has been designed to complement and blend into the surrounding landscape, with the proposed materials embedding the building in its context, while the form reflects its valley setting.
The weathering steel wall is a low-maintenance material with a natural finish which will age over time and blend into the landscape. A surface layer of rust will steadily build up, creating a protective surface. Naturally anodised aluminium fins crown the top of the building and the reflective nature of the material means that the fins visually respond to the surrounding context and changing environmental conditions.
Vegetation has been increased across the site to further reduce the headhouse visibility, while the proposed landscaping and strengthening of existing planting will create a visual buffer between the site and its surrounding area.
For Construction, you asked us to reduce noise and vibration on the construction site, lessen noise and air pollution across the construction fleet and cut down HGV movements.
Noise and vibraion will be controlled by using automatic monitoring equipment, tackling noise at source and reviewing the location of equipment, screening and enclosing noisy activities, while we will manage air quality by regularly inspecting and monitoring the construction site and equipment, cleaning on site roads and vehicles, managing earthworks to contain dust, and also monitoring the air quality on site.
In terms of HGV movements, we have built a signalised junction to allow safe and managed access for HGVs, minimised the number of HGV movements by reducing the size of the vent shaft, created a Construction Consolidation Centre at the South Portal to act as a central hub to manage all the deliveries out to our sites, cutting down vehicle trips made, and will plan our HGV movements as much as possible to avoid peak time, holding them back so that only a certain number are on our logistics route at any one time.
View of Amersham Ventilation Shaft along the A4135
Engaging on the design of the Amersham Ventilation Shaft
In September 2020, we held a public engagement event and you gave us feedback on four topics about our design and construction.
You can view or download our Amersham Ventilation Shaft ‘You said, We did’ information boards below, a key part of the design for HS2 in Amersham.