HS2 this week confirmed that the two enormous 2,000 tonne tunnelling machines digging the high speed rail project’s tunnels under the Chilterns have completed the first stage, up to the ventilation shaft at Chalfont St Peter.

This major achievement means that a combined total of over 3.6 miles has now been dug by the two machines – named Florence and Cecilia – since they launched from the southern end of the tunnels last summer.

The 78m deep shaft at Chalfont St Peter is the first of five that will provide ventilation and emergency access to the ten-mile-long twin tunnels – which are the longest on the project. Once complete, the shaft will be covered by a headhouse designed to resemble local farm buildings.

Designed specifically for the geology of the Chilterns, each TBM is a 170m long self-contained underground factory, digging the tunnel, lining it with concrete wall segments and grouting them into place as it moves forward.

The TBMs named ‘Florence’ and ‘Cecilia’ by local school children launched in May and June last year and are expected to break out at the north portal in around two and a half years.

Welcoming the progress, HS2 Ltd Project Client David Emms said:

“The Chiltern tunnel will take HS2 underneath the hills and safeguard the woodlands and wildlife habits above ground as well as significantly reducing disruption to communities during construction and operation of the new railway.

 “It’s great to see how much progress has been made by Florence and Cecilia – and the teams excavating the five ventilation shafts – and I’d like to thank everyone involved in getting us this far.”

These first two TBMs on the HS2 project are operated by, Align – a joint venture formed of Bouygues Travaux Publics, Sir Robert McAlpine, and VolkerFitzpatrick.

A crew of 17 people on board each machine keep them running, working in shifts and supported by over 100 people on the surface, managing the logistics and maintaining the smooth progress of the tunnelling operation.

Align Project Director, Daniel Altier commented:

Florence and Cecilia reaching our first shaft at Chalfont St Peter is a great achievement for not only the tunnelling team but also construction team involved in excavating and preparing the shaft. In particular I would like to pay credit to KVJV and Keltbray our supply chain partners, who have been working tirelessly over the last few months to ensure the shaft is ready for the arrival of Florence and Cecilia.”   

Each of the separate northbound and southbound tunnels will require 56,000 precision engineered, fibre-reinforced concrete wall segments – which are all being made in purpose build factories on site at the south portal, located just inside the M25. During their first 3.6 miles, Florence and Cecilia have combined installed more than 20,000 separate segments, each weighing around 8.5 tonnes.

Approximately 2.7 million cubic metres of material will be excavated during the construction of the tunnels and used for landscaping on the south portal site. Once construction is complete, this will help create around 90 hectares of wildlife-rich chalk grassland habitats. Chalk grassland used to be widespread across the hills of south east England and are considered habitat of international conservation significance with just 700ha left across the Chilterns.

In total there will be ten TBMs on the HS2 project - working to create 64 miles of tunnel between London and the West Midlands including major tunnels on the approach to London and Birmingham. Three machines have been launched so far.

More than 20,000 jobs and over 650 apprenticeships are already being supported by HS2, which is set to transform transport links between Britain’s major cities, free up space on the rail network for more freight and local services and support the UK’s transition to net zero carbon emissions.

source for the image and the information: HS2 mediacentre. https://mediacentre.hs2.org.uk/news/hs2-tunnelling-machines-reach-chalfont-st-peter-ventilation-shaft