HS2’s Chiltern Tunnel

HS2 has revealed designs for the north portal of the Chiltern Tunnel. Perforated concrete hoods will cover the north portal aimed at reducing the noise of speeding trains entering and exiting the tunnel.

The two perforated concrete hoods will cover the track and exend the 10 mile twin-bore tunnel into the open air. The ‘porous portals’will stop sudden changes in air pressure, and resulting noise, caused by trains entering and exiting the tunnels at speeds of up to 320km/h.

The portals are set low into the landscape between Great Missenden and South Heath in Buckinghamshire and will only be visible from a footbridge over the railway to the north.

The portal for trains entering the tunnel will be 220metres long and the one for exiting will be only 135 metres. This will allow for the different levels of air pressure. Both are to have smooth concrete on top and textured concrete to a low level, to reduce staining and maintenance.

There is to be a single-storey ancillary building to house mechanical and electrical equipment. HS2 is to seek opinions from neighbours regarding the final design offering either a green roof, split louvred or anodised aluminium facade.

David Emms, HS2 Ltd’s project client said: “The structures, set low into the landscape and out of sight for the majority of passers by, will play a necessary role in cutting out excessive noise, and housing essential mechanical and electrical equipment. We encourage people living locally to have a look at the designs and let us know their views”.

The structures designed, and to be built by HS2 Ltd’s main works conractor for this central section, Align JV, a team of Bouygues Travaux Publics, Sir Robert McAlpine and Volker-Fitzpatrick.

Two tunnel boring machines heading north from the south portal are well underway with tunnelling, reaching Chalfont St Peter last week, they are expected to break through at the north portal in 2 years time.

Alan Price, Align HV design director said: “Our TBM’s Florence and Cecilia are making good progress each completing over 3km on the journey to the north portal”.

“As always we are very conscious of the sensitve setting for any permanent structures on the project and this includes the north portal design. Comments from local stakeholders in order that we can finalise the designs are very welcome”.

The new high speed line, to the north of the tunel, will be set into a cutting for 1.8 miles (3km) on its approach to the Wendover Dean Viaduct. The surface route to the north of the tunnels is being built by EKFB (Eiffage, Kier, Ferrovial Construction and Bam Nuttall)