UK’s High Speed 2 (HS2) has unveiled the designs of the noise-cancelling north portal of the Chiltern Tunnel, the longest tunnel on the route between London and Crewe.
The twin-bore 16km long tunnel has been designed to reduce noise from trains that enter and exit at up to 320km/h speeds.
The track will be covered by two perforated concrete hoods, helping to extend the tunnel into the open air.
Sudden changes in air pressure and subsequent noise due to trains entering and exiting the tunnels will be avoided by the porous portals.
The portals, which will be set below the landscape between Great Missenden and South Heath in Buckinghamshire, can be seen from a footbridge over the railway to the north.
One portal will be 220m long for trains entering the tunnel and another will be 135m long for the trains exiting the tunnel to enable the different levels of air pressure.
HS2 project client David Emms said: “Once construction is complete, the Chiltern tunnel will take HS2 trains deep under the Chiltern hills, linking London with Birmingham and the North and releasing space for more freight and local services on the existing mainline.”
HS2’s main works contractor Align joint venture (JV), including Bouygues Travaux Publics, Sir Robert McAlpine, and VolkerFitzpatrick, has designed the structures and will also build them.
Towards the tunnel north, the new high-speed line will be set into a cutting for 3km on its approach to the Wendover Dean Viaduct.
Six new bridges, which will connect country lanes and historic footpaths to the east and west, will cross the railway cutting.
Another HS2’s main works contractor EKFB, including Eiffage, Kier, Ferrovial Construction and Bam Nuttall, is engaged in the construction of the surface route to the north of the tunnels.