Modular design method

HS2 start works on pioneering green tunnel

HS2 have announced today that construction works are set to begin on the first innovative ‘green tunnel’, designed to blend the high-speed railway with the landscape around the site whilst also aiding to the reduction of disruption for communities.

Separating itself from normal underground tunnels, the contemporary design for the one-and-a-half mile Chipping Warden green tunnel in Northamptonshire is being built on the surface, using a pioneering off-site manufacturing approach. This method will speed up the overall construction time of the project, whilst also improving efficiency.

The new innovative design will involve more than five thousand giant concrete tunnel segments being made in an external factory located in Derbyshire, before being assembled on the site itself. Once constructed, the tunnel will be covered by earth, with trees, shrubs and hedgerows being planted to encase the tunnel with natural elements that will help fit within the surrounding countryside.

Chipping Warden is one of five ‘green tunnels’ that are being built on phase one of the HS2 project, which is designed to improve links between London, Birmingham, and the north, help level-up the economy and provide a low carbon alternative to car and air travel.

The off-site construction method approach has been developed through HS2’s main works contractor EFKB, who have applied lessons learned from the construction of recent French high-speed lines. EFKB are a team comprised of Eiffage, Kier, Ferrovial Construction and BAM Nuttall who are collaborating with Stanton Precast in Ilkeston Derbyshire, who are making the individual tunnel pieces. The partnership with Stanton is part of a contract that will see the delivery of up to one hundred new jobs for the local community.

HS2 Ltd’s Project Client Rohan Perin, said:

“The Chipping Warden green tunnel is a great example of what we’re doing to reduce disruption for people living close to the railway - and it’s fantastic to see the first arches in position.

 “Our trains will be powered by zero carbon electricity but it’s also important to reduce the amount of carbon embedded in construction. The off-site manufacturing techniques being used will help cutting the overall amount of carbon-intensive concrete and steel in the tunnel and make the whole process faster, more efficient, and therefore less disruptive for the community.”

The tunnel design is the shape of a double arch, which will see the tunnel have separate halves for southbound and northbound trains, each equalling the height of two double-decker buses. Five different concrete precast segments will be slotted together to achieve the double arch design, seeing one central pier with two side walls and two roof slabs. All 5,020 segments will be steel reinforced, with the largest weighing up to 43 tonnes.

The new lighter-weight, modular approach of the construction is expected to more than halve the amount of carbon embedded in the structure due to the reduction in concrete and steel usage. This method also requires less people and equipment on site, improving safety and reducing disruption for residents.

EKFB’s Project Manager, Jeremie Martin, said:

“Seeing the first set of precast units being installed is a milestone that the whole team is very proud of. This three-year construction programme will benefit from off-site manufacturing making the green tunnel build more efficient than the traditional on-site building method.

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