Two tunnel boring machines (TBMs) have completed the first phase of HS2 tunneling work under the Chilterns south portal to the first ventilation shaft at Chalfont St Peter.
The two Florence and Cecilia TBMs have dug 5.8 km (3.6 miles) 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 16-km-long (10 miles) 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.
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 5.8 km Florence and Cecilia have combined installed more than 20,000 separate segments, each weighing around 8.5 tonnes.
These first tunnel boring machines are operated by Align joint venture comprising Bouygues Travaux Publics Sir Robert McAlpine and Volker Fitzpatrick.
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 10 TBMs which will perform HS2 tunneling working to create 103 km (64 miles) of tunnel between London and the West Midlands including major tunnels on the approach to London and Birmingham which represents the Phase One of HS2 which is expected to begin commercial operation between 2029 and 2033.
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