Chipping Warden Green Tunnel

The Chipping Warden Green Tunnel will stretch for 2.5km (1.5 miles) through Northamptonshire. The ‘cut-and-cover’ tunnel is being built inside a cutting, with the earth put back on top afterwards, helping to blend the railway into the landscape and cut noise and disturbance for people living nearby. The shallow ‘green tunnel’ will also take HS2 trains under the realigned A361.

Tunnel construction

The construction of the tunnel is happening in stages, with the cutting first being excavated and then a layer of ‘blinding’ laid to form a concrete base for the structure. Designed as an ‘m-shaped’ double arch, the tunnel will have separate halves for southbound and northbound trains – each one the height of two double-decker buses. The next stage involves the assembly of five different concrete precast segments that form the ‘M’ shaped sections of tunnel.

Instead of casting the whole tunnel on site, different concrete precast segments are slotted together to achieve the double arch – one central pier, two side walls and two roof slabs. All 5,020 segments are steel reinforced, with the largest weighing up to 43 tonnes.

Similar ‘green tunnels’ are being built at nearby Greatworth as well as Wendover in Buckinghamshire and Burton Green in Warwickshire, stretching for a combined total of more than four miles. The tunnels will all have specially designed ‘porous portals’ at either end to reduce the noise of trains entering and exiting the tunnel, along with small portal buildings to house safety and electrical equipment.

Tailored landscaping design plans will be developed for each tunnel, with thousands of native trees and shrubs typical to the local area such as Silver Birch, Oak, Beech and Willow planted to create new woodland areas around the portals and recreate the hedgerows and field boundaries on top of the tunnel.