HS2’s longest green tunnel is a step closer to completion following the realignment of a key local road, allowing for the next phase of excavations.
The new tunnel is set to stretch for a total of 2.7km, and is being built inside a shallow cutting near Greatworth, West Northamptonshire with a ‘cut-and-cover’ technique, which involves earth being put back on top afterwords in order to help it blend into the landscape.
Thus far, engineers working on the high-speed rail project have assembled the first kilometre of the structure, with the temporary realignment of the B4525 enabling work to begin on the next stage of the tunnel’s construction.
The tunnel, assembled from precast concrete segments, takes the form of an M shape with separate halves for both northbound and southbound trains – inspired by similar structures along the French high-speed network.
HS2 Ltd’s Project Manager, Sam Arrowsmith, said:I’m really pleased to see the temporary realignment of the B4525 open to drivers. This major milestone means that we can keep local traffic moving while we deliver the next stage of the Greatworth green tunnel.
Once complete, the tunnel will help protect the rural landscape and reduce disruption for people living nearby. We’ve still got a long way to go, but the lessons from Chipping Warden have helped us significantly increased productivity and I’d like to thank everyone who’s worked so hard to get us to this point.
Construction of the tunnel is handles in stages; with the cutting first being excavated before a layer of ‘blinding’ is laid to form a concrete base. Then, the the five concrete segments forming each of the M shaped section of the tunnel are assembled.
Once the structure has been assembled, a concrete ‘invert’ slab is poured to form the base for the track, the process of which has recently been sped up by changing the direction from which concrete is delivered and by introducing prefabricated reinforcing cages.
The valley in the top of the M is now being filled with an aerated concrete mix.
All construction improvements were first tested at a specially built test section of Chipping Warden’s green tunnel by EKFB.
