HS2: Northamptonshire village sees longest 'green' tunnel emerge

The first arches have been built for the 1.7-mile (2.7km) Greatworth tunnel

Work is under way on the longest "green" tunnel on the HS2 line, which looks to blend in with the countryside.

The 1.7-mile (2.7km) Greatworth Tunnel in south Northamptonshire uses a "cut and cover" process, meaning it is built in a cutting on the surface then covered with greenery.

It will be made from more than 5,000 giant concrete segments.

The cost of the project to provide fast trains from London to Birmingham and northern England is more than £100bn.

The Greatworth structure is the second "cut and cover" tunnel on the Northamptonshire landscape.

Work was delayed on the first one, just outside Chipping Warden, because quality issues were found in the pre-cast segments of the tunnel. It resumed last September.

Traditionally, tunnels have been made by boring holes in the ground, but the cut-and-cover method involves building the tunnel in a cutting and then covering it with trees and hedgerows so it blends in with the countryside.

The Greatworth structure has been designed as an M-shaped arch, with separate arms for southbound and northbound trains.

It will be made from 5,410 pre-cast concrete segments that have been manufactured in Derbyshire before being transported.

Artist's impression of a train emerging from the tunnel

HS2 Ltd said it had chosen this method of construction instead of the traditional process of pouring concrete on site to boost efficiency and cut the amount of embedded carbon in the structure.

Neil Winterburn, from HS2 Ltd, said: "Our trains will be powered by zero carbon electricity but it's also important to reduce the amount of carbon-intensive concrete and steel in the tunnel."

The first arch segments are already in place at the Greatworth site, near Brackley.

Shorter "green" tunnels are being built at Wendover in Buckinghamshire, Burton Green in Warwickshire and Hillingdon in London.

A concrete arch of the Greatworth Tunnel is lifted into place

The HS2 route has been revised several times since it was first published as costs have increased, with the current estimate being more than £100bn.

The first section of the line, between Old Oak Common and Birmingham, is expected to open in about 2030.

People living close to the construction sites in Northamptonshire have complained about traffic delays and scars on the landscape, although some communities have benefitted from HS2 funding for village halls and playgrounds.

Campaigners opposed to the high-speed railway have described the green tunnels as an example of "green-washing" by HS2.

Speaking about the tunnels last year, Penny Gaines, chairwoman of campaign group Stop HS2, said the business case was "based around saving a few minutes on train journeys, but it's far more environmentally friendly not to travel at all, and we've all seen how much business can be done through video-conferencing and other technologies".