HS2 unveils first images of preparation for new tunnel launch site

Credit: HS2 Ltd.

HS2 has revealed a series of new images showing the progress of preparation work for the arrival of the project’s first giant tunnelling machines, which will be launched from a site next to the M25 in early 2021.

The two 2,000 tonne machines – currently being manufactured in Germany – will dig the 10-mile-long Chiltern tunnels, from the site next to the M25 to near South Heath in Buckinghamshire. The new images show the excavation of the launch site and the start of work to build the concrete precast plant where more than 118,000 tunnel segments will be made.

At 136 acres, the South Portal Chalfont Lane site will be the biggest construction site on the project. From here, specialist teams will deliver the tunnelling and construction of the adjacent Colne Valley Viaduct.

HS2‘s Delivery Director, David Bennett, said: “The south portal site will have one of the most important parts to play in the story of HS2. From here, we’ll manage the construction of the Chiltern tunnels and the iconic Colne Valley viaduct. It’s great to see how much progress has been made on site – and I look forward to working with the team to deliver what will be two of the most exciting and ambitious engineering challenges on the project.”

Dedicated motorway slip-roads have been built to link the new site with the M25 and take construction traffic off of local roads, while material excavated from the tunnels will be reused as landscaping on site.

Approximately 350 staff from HS2’s main works contractor, Align JV – a team made up of Bouygues Travaux Publics, Sir Robert McAlpine and VolkerFitzpatrick, and its subcontractors – are now permanently based on site.

At peak, around 1200 people are expected to be employed in the design and construction of the Chiltern tunnels and the viaduct, with 50 opportunities for apprentices.

The ‘twin bore’ Chiltern tunnels will be the longest and deepest tunnel bores on route, with separate northbound and southbound tunnels and five ventilation shafts. The tunnels will carry the state-of-the-art HS2 trains under the Chiltern hills on their way to Birmingham, Scotland and the north of England.

Just south of the tunnel portal, the Colne Valley Viaduct – designed by Align, working with its design partners Jacobs and Ingerop-Rendel, and the architect Grimshaw – will be the longest railway viaduct in the UK. At 3.4km long, it will carry HS2 across the Grand Union Canal and surrounding lakes. Further south, the line will go into a tunnel again before arriving at Old Oak Common and London Euston.

This new route will make more space available for local and freight services on the current mainline out of Euston and offer an environmentally friendly form of transport for long distance passengers.