In order to cut noise from trains entering and exiting the project’s longest tunnel at speeds of up to 320km/h in the north portal of the Chiltern Tunnel HS2 has published some new designs.
The process of covering the track as well as expanding the 10-mile-long tunnel into the open air, will be done by two perforated concrete hoods, while these porous portals are due to avoid sudden changes in air pressure – and resulting noise – caused by trains entering and exiting the tunnels.
Locating low into the landscape among Great Missenden and South Heath in Buckinghamshire, the portals will only be visible from a footbridge over the railway to the north.
Designing the portal for trains entering of the tunnel with 220m length will be due to allowing the different levels of air pressure, whereas the one for those exiting will be just 135m. Both will have smooth concrete on top and textured concrete to a low level, to reduce staining and maintenance.
In order to stock mechanical and electrical equipment, alongside the portals there will also be a simple single-storey ancillary building. HS2 is currently seeking views from the community about the final design, with options including a green roof, split louvered or anodized aluminum façade.
According to HS2 Ltd’s Project Client, David Emms: “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.”
He continued: “Set low into the landscape and out of sight for most passers-by, the structures will play a crucial role in cutting out unnecessary noise and housing essential mechanical and electrical equipment. We are keen to hear local views and I would encourage people living locally to have a look at the designs and let us know what they think.”
Responsible for designing and constructing these structures will be HS2 Ltd’s main works contractor Align JV – a team made up of Bouygues Travaux Publics, Sir Robert McAlpine, and VolkerFitzpatrick.
While the work’s process is well undergoing using two enormous 2,000 tones tunnel boring machines heading north from the south portal to excavate the twin-bore tunnels, in the previous week they reached Chalfont St Peter and are estimated to breakthrough at the north portal in two years’ time.
Alan Price, Align JV Design Director said: “Our TBMs, Florence and Cecilia are making good progress and have each completed over 3km on their journey to the north portal.”
“We are always very conscious of the sensitive setting for any permanent structures on the project and this includes the north portal design. We welcome comments from local stakeholders in order that we can finalize the design,” added Price.