With the tunnel half-built already, Align has now completed its detailed design work.
The north portal, near South Heath in Buckinghamshire, will be one of the seven ‘key design elements’ of the tunnel visible from the outside.
The other six will be the south portal, near the M25, and headhouses above the ventilation and emergency access shafts, which are mostly designed to resemble agricultural buildings.
The design work has been completed by HS2’s main works contractor, Align JV – a team made up of Bouygues Travaux Publics, Sir Robert McAlpine, and VolkerFitzpatrick, working with consulting engineers Jacobs, Rendel-Ingerop and LDA Design, and architect Grimshaw.
Construction of the twin tunnels, which will stretch for 10 miles under the Chiltern hills, recently passed the halfway point, with two tunnel boring machines (TBMs) currently between Amersham and Little Missenden.
HS2 Ltd’s design director, Kay Hughes, said: “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.”
The north portal has been designed to lie low into the landscape between Great Missenden and South Heath in Buckinghamshire, visible only from a footbridge over the railway to the north. Two perforated concrete hoods will cover the track as the tunnel ends to soften the impact of speeding trains entering and exiting the tunnels.
Alongside the portals, there will also be a single-storey ancillary building to house mechanical and electrical equipment. This will be clad in earth-coloured pigmented zinc, with a green roof to help camouflage it.
Align technical director Alan Price said: “This is a significant achievement for both Align and our design partners in Align D, that is led by Jacobs and Ingerop-Rendel. Having the design on the shelf releases procurement and allows complete flexibility to optimise the construction programme.”
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