19th March 2021

HS2 casts first of 112,000 wall segments for Chilterns Tunnel

Our Align JV is counting down to the launch of HS2's first tunnelling machines - Florence and Cecilia.

Preparations for the launch of HS2’s first giant tunnelling machines ramped up this week as the first of 112,000 wall segments for the Chilterns tunnel rolled off a purpose-built production line at the project’s tunnelling HQ close to the M25.

The project’s first two Tunnel Boring Machines (TBMs) – named Florence and Cecilia - are due to launch in early summer. Each of the 170m long, 2,000 tonne machines will spend more than 3 years underground, digging and slotting the wall segments into place to create the 10 mile long tunnels.

Made of high-performance fibre-reinforced concrete, the segments are being produced at a temporary pre-cast factory next to the TBM launch pads at what will be the south portal of the tunnels. This will avoid putting extra HGVs on local roads and ensure a steady supply of segments for the TBMs.

Construction of the Chilterns tunnel, and nearby Colne Valley Viaduct, is being led by HS2’s main works contractor, Align JV - a joint venture made up of three companies: Bouygues Travaux Publics, Sir Robert McAlpine, and VolkerFitzpatrick. Work on the two structures will support around 1,200 jobs.

Once construction is complete, the pre-cast factory and the rest of the south portal site, will be cleared, with the chalk excavated from the tunnels used to landscape the site and create high quality chalk grassland and other wildlife habitats.

We are using Steel Fibre Reinforced Concrete (SFRC) in the segments due to the improved ductility and durability it offers. The SFRC segments are also easier to fabricate. Once in the moulds we are using robots to polish the concrete, a task that was previously manual, to improve the quality and consistency of the final product. With 7 segments in each ring, we will be producing a total of 160 rings ahead of launch of the first TBM later this year.

Didier Jaques, Align's Underground Construction Director

See inside HS2's giant tunnel factory

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