Chiltern Tunnel designed to integrate within local landscape

Construction of the Chiltern Tunnel, the longest structure on the HS2 (High Speed Two) route linking London to Birmingham in the UK, is now complete. The 10-mile twin-bore project was designed by Tenderstream member Grimshaw with engineers Jacobs and Rendel Ingerop, within a multi-disciplinary team led by joint venture company ALIGN JV formed by Bouygues, Sir Robert McAlpine and VolkerFitzpatrick. HS2 Section C1 runs from the northern suburbs of London through the sensitive landscape of the Colne Valley Regional Park and into the Chilterns Area of Outstanding Natural Beauty.

Visible infrastructure associated with the tunnels has been integrated with the surrounding landscape design. The Colne Valley Western Slopes, 140 ha of former arable land, will be transformed through the re-use of 3 million cubic metres of chalk taken from the tunnel excavation and the creation of new chalk grassland, woodland, and wetland habitats. 

At each end, the tracks are covered by a pair of portal structures that extend the tunnels into open air. The portals dissipate air pressure, reducing train noise. To the south, the façade comprises dark painted steel louvres wrapped in a band of anodised aluminium fins while at the north, the building is expressed by a series of earth-coloured, zinc extrusions and topped with calcareous grassland roof, a habitat native to the Chilterns. Along the tunnel’s length, ventilation and emergency access is provided via five shafts and associated headhouses.

Four of the headhouses are designed to respond to the vernacular of local agricultural buildings, with dual pitch roofs reflecting simple barn forms and the compound taking on a farmstead courtyard arrangement. The headhouse located on the edge of Amersham adopts a different design approach, with a conical form that responds to the 360 degree viewing experience from surrounding footpaths. A security wall wraps the site, with the use of knapped flint referencing local geology and historic buildings.

Chris Patience, principal at Grimshaw, stated: “Grimshaw has had the unique opportunity to design all infrastructure components of the entire C1 section, from tunnel portals, shaft ventilation headhouses, and what will be the UK’s longest railway viaduct. They have all been carefully designed to celebrate the unique function of high-speed rail while respecting the sensitive landscape setting of each site. In parallel, the designs have been informed from the outset by positive dialogue with local stakeholders and the community.”

Lucy Nordberg
Tenderstream Head of Research

This tender was first published by Tenderstream on 04.02.2024 here

Start your free trial here or email our team directly at customerservices@tenderstream.com