VolkerFitzpatrick completes HS2 tunnel portal to solve high-speed rail's 'sonic boom' conundrum
VolkerFitzpatrick as part of the Align joint venture, have completed work on a pair of innovative extensions to the southern portal of its longest tunnel to eliminate the possibility of ‘sonic boom’ being created by high-speed trains entering at 200mph.
As a part of the Align joint venture consisting of Bouygues Travaux Publics, Sir Robert McAlpine, and VolkerFitzpatrick, we are constructing the C1 package of the HS2. Not only does this include delivering the record-breaking Colne Valley Viaduct which will be the longest railway bridge in the UK, but we are also constructing HS2’s longest twin-bore tunnel, reaching 10 miles long.
We have completed works on a pair of innovative extensions to the southern portal of the longest tunnel to eliminate the possibility of ‘sonic boom’ being created by high-speed trains entering at 200mph.
All trains entering tunnels anywhere in the world force air forward, creating pulses of energy that roll along the tunnel causing a small release of air pressure into the outside world at the far end. Known scientifically as ‘micro pressure waves’, they are inaudible on conventional railways. But in high-speed rail tunnels, air shoved forward without escape routes can create powerful pressure waves that emerge as an audible ‘thud’ or ‘sonic boom’.
In a first for the UK rail network, HS2’s design includes extensions on all eight tunnels where trains enter at speeds above 140mph. However, the length, physical setting and aesthetic of those at each end of the line’s tunnel beneath the Chiltern Hills mark them out as unique even to HS2.
The construction of the Chilterns Tunnel and its portal extensions was delivered by Align JV- completion of the southern portal structures was achieved in January 2025, with the northern portals scheduled for delivery in autumn 2025.
