25th Mar 2024

Final breakthrough for HS2’s longest tunnel

The second tunnelling boring machine (TBM), named Cecilia and operated by our Align JV reaches northern portal of 10-mile high-speed rail tunnel under Chiltern Hills.

The second giant boring machine (TBM) building HS2 under the Chiltern Hills broke through at the tunnel’s northern portal on Friday 22nd March, completing a journey that began in June 2021.

Named Cecilia, the TBM has driven for 10 miles underground to join twin sister machine – Florence. She arrived at the site near the Buckinghamshire town of Wendover on 27 February, after completing her adjacent tunnel drive.

Between them, the two 2,000 tonne machines have built the twin bore tunnel at depths of up to 80 metres and excavated three million cubic metres of chalk. Each machine operates like an underground factory, able to excavate the tunnels and line them with 56,000 pre-cast concrete tunnel segments, grouting them into place and moving forward at an average speed of 16 metres per day.

Final breakthrough for HS2’s longest tunnel

When HS2 is operational, trains will travel through the Chiltern tunnel – the line’s longest – at speeds of up to 200mph, helping to almost halve journey times between Britain’s two largest cities.

The new high-speed line will relieve traffic on the West Coast Mainline, freeing up space for more local services on the most crowded part of the important Victorian route. It will almost double rail capacity between London and the West Midlands, providing a more reliable service and driving economic growth.

HS2 Ltd’s head of civil works for this section of the route, Mark Clapp, said:

“This is a remarkable achievement for all concerned. Cecilia’s arrival completes excavation of HS2’s 10-mile twin-bore tunnel, but it’s only the end of the first chapter in the story of building Britain’s high-speed railway under the Chiltern Hills.

“Several years of intensive, world class engineering lie ahead of us to complete the tunnels’ four ventilation shafts plus headhouses; install the mechanical and electrical plant and machinery, slab track and overhead electrical wires before trains begin passing through at 200mph.”

Both machines launched from the tunnel’s south portal, near the M25 motorway, were operated by HS2’s main works contractor, Align – a joint venture formed of three international infrastructure companies: Bouygues Travaux Publics, Sir Robert McAlpine, and VolkerFitzpatrick. The machines are made in Germany by TBM specialists Herrenknecht.

Align’s Underground Construction Director, Didier Jacques said: “Ten miles is a long drive for a TBM, with a typical average being around three miles. The complexity and technical challenges of completing such a long drive for both our TBMs has been significant, however I am delighted that as a team, we have risen to the challenge.

“Both TBMs were designed in partnership with Herrenknecht and incorporating innovations and technologies that have been introduced on TBMs in the UK for the first time, to enhance performance and safety. This includes ‘semi-continuous boring’, allowing our TBMs to build the rings that line the tunnels without pausing.”

Each TBM is operated by a crew of around 17, working in shifts to keep the machines running when required 24/7. They are supported by over 100 people on the surface, managing the logistics and maintaining the smooth progress of the tunnelling operation.

In total over 450 people have worked on the tunnels over the last three years, including a dedicated production team who made 112,000 precision-engineered, fibre-reinforced concrete tunnel wall segments on site at a purpose build temporary factory - and a team processing the spoil from the tunnels.

Completion of tunnelling under the Chilterns follows recent publication of HS2 Ltd research showing how high-speed line’s arrival in the West Midlands will give a £10 billion economic boost over the next decade, with new development around its stations at Birmingham’s Curzon Street and near the city’s airport and the NEC. 

Latest Infrastructure news

  1. Green Apple award for project with sustainability at its core

    27 Nov 2024

    The sustainable approach to delivery taken by our AmeySRM JV team on the A533 Expressway Replacement Bridge Scheme has seen the project honoured with an international Green Apple Environment Award.

    Read more about
  2. HS2 Colne Valley Viaduct wins design award

    26 Nov 2024

    Colne Valley Viaduct named winner in the 'engineering' category  of the Royal Fine Art Commission Trust’s Building Beauty Awards - 2024 

    Read more about
  3. A19 named England’s No1 road

    08 Nov 2024

    The Strategic Roads User Survey by Transport Focus highlights the remarkable success of the A19 DBFO Project.

    Read more about

Latest news

  1. ONE Station Hill reaches practical completion

    06 Dec 2024

    Congratulations to all those who have worked on ONE Station Hill in Reading as the project completes.

    Read more about
  2. Green Apple award for project with sustainability at its core

    27 Nov 2024

    The sustainable approach to delivery taken by our AmeySRM JV team on the A533 Expressway Replacement Bridge Scheme has seen the project honoured with an international Green Apple Environment Award.

    Read more about
  3. HS2 Colne Valley Viaduct wins design award

    26 Nov 2024

    Colne Valley Viaduct named winner in the 'engineering' category  of the Royal Fine Art Commission Trust’s Building Beauty Awards - 2024 

    Read more about
View all news