The Align joint venture and its subcontractors have completed construction of the 17-metre high headwall and ground reinforcement at what will become the south portal of the 16km-long Chiltern tunnel.
Align JV – a joint venture of Bouygues Travaux Publics, Sir Robert McAlpine and VolkerFitzpatrick – spent seven months excavating more than 160,000 m3 of material to create a level surface from which two tunnel boring machines (TBMs) are expected to launch in early 2021.
The TBMs, each weighing 2,000 tonnes and stretching for 170 metres are still in the Herrenknecht factory in Germany. They are scheduled to arrive at the site, near to the M25, later in the year.
Alongside the excavation, subcontractors including Roadbridge and KV JV - formed from Keller and VSL International – constructed a 17-metre high headwall through which the TBMs will break to begin their three-year tunnel drive.
The ground behind the headwall was reinforced with more than 636 soil nails – some up to 20 metres long – to hold the ground and the surface of the wall in place as the TBMs begin to break through.
Mark Clapp, HS2 Ltd’s senior project manager for this section (C1), said: “The completion of the headwall and ground reinforcement is a major step towards the start of tunnelling and delivering on that goal."
Align project director Daniel Altier added: “The completion of the soil nailing is a very visual example of how we are preparing our south portal site for the arrival of the TBMs later this year. It is now clear for all to see where the TBMs will start their journey. This has been a great team effort by all concerned, considering the challenges caused by Covid-19, including HS2, Align and our colleagues at Roadbridge and the KVJV.”
Align is delivering the C1 portion of HS2 phase 1 which includes the 16km twin bore Chiltern tunnel and the 3.4km Colne Valley Viaduct. The work is being led by an integrated project team based at the site just inside the M25.
Once work is complete, the whole construction site will be landscaped with material excavated from the tunnels and trees planted to blend it in with the surrounding countryside.