HS2 Ltd has revealed the design for the north portals of Chiltern Tunnel, with the intention of reducing the level of noise from trains entering and leaving at speeds of up to 320kph (200mph).
Two perforated concrete hoods will cover the tracks and extend the ten-mile-long twin-bore tunnel into the open air by up to 220 metres for trains entering the tunnel and 135 metres for those exiting.
Both extended portals will have a smooth concrete top and textured concrete to a low level, which will be porous to avoid sudden changes in air pressure from moving trains.
Set into the landscape between Great Missenden and South Heath in Buckinghamshire, the portals should only be visible from a footbridge crossing the railway to the north.
Alongside the portals, a single-storey ancillary building is also due to be built by main works contractor Align JV (comprising Bouygues Travaux Publics, Sir Robert McAlpine and VolkerFitzpatrick) to house mechanical and electrical equipment.
HS2 is currently consulting with the local community about the final design, with options including a green roof, split louvred or anodised aluminium facade.
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