HS2 has revealed the final designs for the North Portal of the Chiltern Tunnel, representing the last of seven key structures that will be visible for the local community.
Accompanying the North Portal are the South Portal, close to the M25, and the headhouses situated above the ventilation and emergency access shafts, which have been designed and shaped to resemble agricultural buildings.
The construction process for the twin tunnels has recently reached a major milestone as the ongoing project has passed the halfway point, seeing the two giant tunnel boring machines currently between Amersham and Little Missenden.
HS2 Ltd.’s Design Director Kay Hughes said:
“HS2 will provide zero-carbon journeys across the UK, improving links between London, Birmingham and the North, while freeing up space for more freight and local services on the existing main line.
“The Chiltern Tunnel North Portal will be one of the least visible parts of the project, but today’s reveal of the final designs is a major symbolic milestone – and I’d like to congratulate Align on getting all their Key Design Elements to this final stage of development.”
The North Portal’s design will only be partially visible from a footbridge over the railway to the north, due to it being integrated into the landscape itself between Great Missenden and South Heath in Buckinghamshire.
The structure’s ‘porous portals’ – two perforated concrete hods that cover track and extend the tunnel into open air – will avoid abrupt changes to the air pressures that stem from the trains as they traverse the tunnels.
A single-story ancillary building will accompany the portals, designed to house the mechanical and electrical equipment that will be sporting earth-coloured pigmented zinc. After receiving community feedback for the designs, the structure has subsequently reduced in size and will incorporate a green coloured roof to aid in the integration into the landscape.
Further in keeping with the integrated design process, the headhouses around the ventilation and emergency access shafts at Chalfont St Peter, Chalfont St Giles, Amersham, Little Missenden and Chesham Road, will echo and encapsulate the aesthetic of the local barns and other agricultural buildings.
The new high-speed line will be set within a cutting for 1.8 miles on the approach to the Wendover Dean Viaduct, embracing the more than 20 hectares of new woodland, shrubs and wildflowers that will aid in blending the railway into the surrounding countryside.
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