HS2’s London tunnelling passes one mile mark

HS2’s first two tunnel boring machines (TBM) in London have completed the first mile of twin bored tunnel in the capital.

Since launching in November last year, the 2,000-tonne TBMs have both installed more than 847 tunnel rings each, made up of 5,929 concrete segments.

The tunnel being constructed by the TBM named Sushila is the “downline” and will be where trains travelling south towards London will run once Britain’s new high speed rail line is operational. 

A second TBM, named Caroline, is constructing the “upline”, where trains will travel to the Midlands and North.

In total, the twin-bored Northolt Tunnel will be 8.4 miles long and is expected to be complete by 2025.

More 240,000 m3 of mixed soil (London Clay, chalk and sand) has been extracted during the tunnelling process so far and is being used north of the tunnel to create new wildlife habitat and landscaping.  The earth is kept within the HS2 site boundaries.

The first TBM was named by Dairy Meadow Primary School in Southall after Sushila Hirani, a local teacher with a passion for getting more girls and pupils from BAME backgrounds into STEM. The second TBM, Caroline, named after astronomer Caroline Herschell by Brentside Primary Academy School, was launched shortly after Sushila.  

Malcolm Codling, project client for HS2, said: “Work to build the HS2 network in London is gaining momentum and completing one mile of twin bored tunnel is another sign of progress on delivering the HS2 route between London and Birmingham.

“HS2 will deliver zero-carbon journeys from day one, linking the major cities of the Midlands and North with London and releasing train path capacity for local, regional and freight services.”

A team of 17 tunnel engineers from HS2’s main works civils contractor, Skanska Costain STRABAG joint venture (SCS JV), has been operating each TBM, working closely with a 60-strong team on the ground. 

James Richardson, managing director of Skanska Costain STRABAG JV, said: “Completing our first mile of tunnelling on both of our TBMs is a fantastic moment for the HS2 London tunnels programme. 

“Early next year our next two TBMs will be launched from Victoria Road crossover box, close to Old Oak Common station. All these drives will then meet at Greenpark Way in Greenford, forming the route for the initial opening of HS2 into London.

“The HS2 London Tunnels team is undertaking some of the most complex tunnelling operations ever embarked on and this milestone has been achieved through a combined effort of all parts of the team.”

The SCS JV team is now preparing to begin the construction of cross passages between the two tunnels. The link between the two parallel tunnels will be used in emergencies.

The TBMs are due to reach the first ventilation and emergency access shaft at South Ruislip in autumn 2023, after they have travelled a distance 1.7 miles. 

The 8.4-mile Northolt Tunnel will be completed with two additional TBMs which will be launched from the opposite end of the tunnel at Victoria Road Crossover Box in Ealing next winter. All four TBMs constructing the tunnel will end their journeys at Greenpark Way in Greenford in Ealing where they will be extracted from the ground.