HS2 completes first mile under Chilterns using 170m long 'TBM'

The first 2,000 tonne, colossal tunnelling machine being used for the construction of the HS2 tunnels has successfully passed the one-mile mark.

The 170m long Tunnel Boring Machine (TBM), first launched in May, covered the first mile cutting via a mix of chalk and flint under the Chiltern hills, just out of London.

The TBM is one of two identical machines excavating the twin ten-mile-long tunnels, one of which was named ‘Florence’ by local school children, inspired by Florence Nightingale, the founder of modern nursing.

The second machine, named ‘Cecilia’, is catching up, with both TBMs expected to break out in around three years’ time.

Each machine is a self-contained underground factory and has been designed specifically for the geology of the Chilterns, digging the tunnel, lining it with concrete wall segments and grouting them into place as it pushes forward.


The process involves a team of 17 people, working in shifts, to keep the machines running, supported by over 100 people on the surface who manage the logistics and support the steady progress of the tunnelling operation.

During her first mile, Florence and her crew installed more than 5,500 separate segments, each weighing around 8.5 tonnes.

Around 2.7 million cubic metres of material will be excavated throughout the construction of the tunnels, which will then be used for landscaping around the south portal site.

Align Project Director, Daniel Altier, said “I am delighted with the progress that Florence has made since its launch in May, with Cecilia not far behind. All the spoil from the TBMs is converted into slurry before being pumped back to our South Portal site, just inside the M25, where it is processed and used for landscaping on site.”

The Projecr Manager added, “this is, and will continue to be, a huge logistical challenge, as Florence and Cecilia continue their journey through the Chilterns. Florence reaching the 1-mile point is a great achievement, however we still have a long way to go.”

Each of the separate northbound and southbound tunnels require 56,000 precision engineered, fibre-reinforced concrete wall segments, all of which are being made at the south portal of the tunnel, next to the M25.


Once construction is finally done, the operation will generate around 90 hectares of wildlife-rich chalk grassland habitats.

Chalk grassland used to be prevalent across the hills of south east England and are considered habitat of international conservation significance, with just 700ha left across the Chilterns.

HS2 Ltd Project Client, Rohan Perin, said “the 10-mile 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.”

He continued, “once complete, HS2 will offer low carbon journey options linking London with the major cities of the north and releasing capacity for more freight and local trains on our existing mainlines."


There will be ten TBMs on the HS2 project in total, all working to create 64 miles of tunnel between London and the West Midlands, in addition to major tunnels on the approach to London and Birmingham.

The Project client added, "it’s great to see how much progress has been made over the summer and I’d like to thank the crew of Florence and all the tunnelling team for their hard work.”

Over 20,000 jobs and more than 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.


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