By lyndamyer
The HS2 project’s longest green tunnel, which is a shallow 2.7km-long cut and cover tunnel and designed to blend the high-speed railway into the rural landscape and reduce disruption for communities around Greatworth in west Northamptonshire, is under assembling by main works contractor EKFB. Including Eiffage, Kier, Ferrovial Construction as well as BAM Nuttall, the EKFB team will dig a cutting, build the tunnel and then bury it. For blending the tunnel into the surrounding countryside, trees, shrubs and hedgerows are going to be planted on top.
Also, over than 5,000 giant concrete segments, that have been made at a specialist pre-cast factory in Derbyshire, and assembled on site by EKFB, will be used for structure of the tunnel.
In order to boosting efficiency and decreasing the amount of embedded carbon in the structure, EKFB opted for this modular approach, rather than the traditional process of pouring the concrete on site, applying lessons from the construction of the latest French high-speed lines. This lighter-weight modular approach is expected to more than halve the amount of carbon embedded in the structure.
Greatworth is one of five green tunnels being built on phase one of the HS2 project.
According to HS2 Ltd’s project client, Neil Winterburn: “It was important to reduce the amount of carbon embedded in the high-speed line’s construction. The off-site manufacturing techniques being used will help cut the overall amount of carbon-intensive concrete and steel in the tunnel and help spread the supply chain benefits of the project across the UK.”
Considering that this tunnel has been designed as an M-shaped double arch, it will have separate halves for southbound and northbound trains, whereas five different concrete precast segments are due to be slotted together to create the double arch.
The Stanton Precast in Ilkeston, Derbyshire is the responsible for constructing the tunnel segments and all 5,410 segments will be steel reinforced, with the largest weighing up to 43 tones.
While building of the main structure is scheduled to take almost two years, the tunnel will be built in sections and the local roads and footpaths will be realigned to cross the tunnel.
Lessons learned during the construction of a similar green tunnel at Chipping Warden are being applied to the delivery of Greatworth. These include changes to quality control and the delivery and installation of the segments.
Additionally, Wendover in Buckinghamshire, Burton Green in Warwickshire and in the London Borough of Hillingdon will also host shorter green tunnels, while the common design of all the tunnels is slated to be 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.
