First mile of HS2 Chiltern Tunnel completed

‘Florence’, the 170m long Tunnel Boring Machine (TBM), first launched in May. She completed the first mile, cutting via a mix of chalk and flint under the Chiltern hills, just outside London.

The TBM is one of two identical machines excavating the twin ten-mile-long tunnels. In addition, the second machine, named ‘Cecilia’, is catching up. Both TBMs are expected to break out in around three years’ time.

Each 2,000 tonne machine is a self-contained underground factory and has been designed specifically for the geology of the Chilterns. This involves digging the tunnel, lining it with concrete wall segments and grouting them into place as it pushes forward.

Process

The process involves a team of 17 people, working in shifts to keep the machines running. In addition, over 100 people work on the surface, managing the logistics and supporting 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. In turn, this 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. This is, and will continue to be, a huge logistical challenge, as Florence and Cecilia continue their journey through the Chilterns.

“Florence reaching the one mile point is a great achievement, however we still have a long way to go.”

The other eight TBMs on the project will be used to drive a further 86km of tunnels on the phase 1 route.

Environmental Awareness

According to HS2, after construction of the tunnel has been completed, they will reuse construction materials. This will include creating 127 hectares of new chalk grassland, woodland, wood pasture and wetland habitats. These will substantially enhance the local natural environment.

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

Once construction is complete, 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. They are considered a 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."

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.

“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."