HS2 launches final tunnel boring machine for Euston Tunnel

HS2 has marked a major construction milestone with the launch of its final tunnel boring machine (TBM), which has begun excavating the second bore of the 4.5-mile Euston Tunnel.

The machine, named ‘Karen’ after pioneering British train driver Karen Harrison, set off from Old Oak Common towards Euston on 16 March, completing the line-up of 11 TBMs deployed across the high-speed rail project.

Twin-bore tunnel progresses

‘Karen’ joins sister machine ‘Madeleine’, which began work earlier this year. Together, the two TBMs will construct the twin tunnels that will carry HS2 services into central London.

The Euston Tunnel is a critical section of the route, designed to increase capacity and improve reliability by enabling high-speed trains to reach a new terminus in the capital.

Major engineering operation

The 198-metre-long TBM will operate continuously, excavating soil while installing pre-cast concrete segments to form the tunnel lining.

Across both tunnel bores:

• More than 48,000 concrete segments will be installed

• Around 1.5 million tonnes of excavated material will be removed

• Spoil will be reused at sites across the UK

Part of wider HS2 progress

The milestone comes as HS2 undergoes a programme reset under chief executive Mark Wild, aimed at improving delivery certainty and refining construction sequencing.

Other major tunnels on the route, including the Northolt and Chiltern tunnels, have already been completed as work continues along the line between London and the West Midlands.

Celebrating industry pioneers

The naming of the TBM continues HS2’s tradition of honouring influential women in engineering and transport.

To mark the launch, Avanti West Coast drivers Hayley Richardson and Vicky Knight joined engineers on site and helped operate the machine.

Speaking at the event, Richardson said it was a “fantastic privilege” to take part, adding that naming the machine Karen was a fitting tribute to a trailblazer in the rail industry.

Regeneration potential

Once complete, the HS2 terminus at Euston is expected to play a key role in regenerating the surrounding area, supporting new homes, jobs and economic growth.

The start of tunnelling by the final TBM signals continued momentum for the project, as one of the UK’s largest infrastructure schemes moves closer to delivering high-speed rail services.