Bouygues, Sir Robert McAlpine, and VolkerFitzpatrick have been carrying out the work

Preparation for the arrival of HS2’s first giant tunnelling machines has passed a major milestone.

A 17m high headwall and ground reinforcement at what will become the south portal of the 10-mile long Chiltern tunnel has been completed.

A specialist team, led by HS2’s main works contractor Align JV – a joint venture made up of Bouygues, Sir Robert McAlpine, and VolkerFitzpatrick – spent seven months excavating more than 160,000m3 of material to create a level surface from which the two machines will launch early next year.

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

Alongside the excavation, a specialist team of subcontractors including Roadbridge and KV JV, formed of Keller and VSL International, also built a 17m-high headwall through which the TBMs will break to begin their three-year long tunnel drive.

To reinforce the ground behind the headwall, more than 636 soil nails – some up to 20m long – were driven into the wall and connected to the concrete lining.

Work on site was paused for four days at the start of the coronavirus lockdown to deep clean the site and put in place new hygiene and social distancing procedures.