UKIS Engage: Progress at Chiltern Tunnel

The preparation for the arrival of HS2’s first giant tunnelling machines has passed a major milestone, with the completion of the 17m high headwall and ground reinforcement at what will become the south portal of the 10-mile ling Chiltern tunnel.

A specialist team who were led by HS2’s main works contractor, Align JV, a joint venture formed of Bouygues Travaux Publics, Sir Robert McAlpine, and VolkerFitzpatrick, have spent seven months excavating more than 160,000 m3 of material in order to create a level surface from which the enormous machines will launch early next year.

Weighing 2,000 tonne and stretching for 170m, the two tunnel boring machines (TBMs) are being built by German tunnelling specialist Herrenknecht and are set to arrive on the site, located near the M25, later in the year.

To reinforce the ground behind the headwall, in excess of 636 ‘soil nails’, up to 20m long, have been driven into the wall and connected to the concrete lining. The nails, consisting of steel or glass fibre reinforced polymer tendons, have been inserted using a specialised drilling rig in a delicate operation which can take up to two hours.

This reinforcement is required to hold the ground and the surface of the wall in place as the TBMs begin to break through.

Welcoming the milestone, Mark Clapp, HS2 Ltd’s C1 Senior Project Manager said: “Once complete, HS2 will transform rail travel across the UK, offering fast, reliable and low carbon journey options for millions of people across the country. The completion of the headwall and ground reinforcement is a major step towards the start of tunnelling and delivering on that goal.

“Safety is of course our top priority. The new covid-19 processes and procedures put in place by Align ensured that we were able to keep to schedule while keeping everyone safe – and I’d like to thank the whole team for pulling together during what has been a difficult few months for the whole construction industry.”

Daniel Altier, the Align Project Director 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 to deliver the C1 portion of HS2 phase 1 which includes the 10 mile long twin bore Chiltern tunnel and the 3.4km Colne Valley Viaduct with the work being lead by an integrated project team based at the site just inside the M25.

Work was paused on site for four days at the start of the COVID-19 lockdown to deep clean the work site and put in place new hygiene and social distancing procedures in line with UK Government guidance and industry best practice.

Once the work is complete, the construction site will be landscape with material that has been excavated from the tunnels and trees will be planted to blend it in with the surrounding countryside.

HS2 Ltd is a partner of the UK Infrastructure Show (UKIS), the UK’s leading infrastructure and supply chain event, which explores the latest developments across the sector. This year, UKIS is going online and will be delivered as a live, online interactive event on Wednesday 9 September 2020.

More information on what you can expect from this new digital event experience can be found by visiting the UKIS website here.

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