THE first mile of twin-bored Northolt Tunnel, on the HS2 rail link, has been completed.

Since their launch in November, the 2,000-ton boring machines, named Sushila and Caroline, have each installed nearly 850 tunnel rings, made up of nearly 6,000 concrete segments.

The tunnel being constructed by Sushila is the “downline” and will be where trains travelling south towards London will run once HS2 is operational.

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.

Clay, chalk and sand extracted during tunnelling is being used to create new wildlife habitat and landscaping.  

The first machine was named by Dairy Meadow Primary School in Southall after Sushila Hirani, a teacher with a passion for getting more girls and pupils from BAME backgrounds into science and technology.

Caroline, named after astronomer Caroline Herschell by Brentside Primary School, was launched shortly after Sushila.  

The 58,000 tunnel segments for this section are being manufactured by Pacadar on the Isle of Grain in Kent.

Recently, delivery of the segments has been by rail to sidings at the West Ruislip site, reducing lorry journeys.  

James Richardson, MD of Skanska Costain STRABAG JV, said: “Early next year, our next two [boring machines] 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 Northolt Tunnel will be completed after two additional borers are launched from the opposite end of the tunnel at Victoria Road Crossover Box in Ealing next winter.

All four will end their journeys at Greenpark Way, where they will be extracted from the ground.