This 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 10-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.
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 said: "Florence and Cecilia reaching our first shaft at Chalfont St Peter is a great achievement for not only the tunnelling team but also the 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 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 8.5t.
In total there will be 10 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.
Got a story? Email: duncan.moore@aspermontmedia.com
