CONSTRUCTION of the new HS2 rail line hit another major milestone with the launch of the fourth – and final – machine being used to bore the giant Northolt Tunnel.

The 8.4-mile tunnel will run from Victoria Road in Ealing to West Ruislip, carrying trains in and out of London, and is using four huge tunnel boring machines (TBMs).

In keeping with tunnelling tradition, the fourth machine is named after a prominent woman, in this case Lady Anne Byron.

The name was chosen by Ealing people in a public vote.

Lady Anne Byron was an educational reformer and philanthropist who lived between 1792 and 1860.

She established the Ealing Grove School, England’s first co-operative school which provided education for the working classes, in an era when it was mainly for the wealthy.

TBM Anne will bore 3.4 miles from Victoria Road in Ealing, near HS2’s Old Oak Common station, to Greenpark Way in Greenford, alongside TBM Emily, which launched in February.

The other five miles of twin-bored tunnels has been under construction since 2022, with TBMs Sushila and Caroline both more than halfway through their journey between West Ruislip and Greenpark Way.

The quartet will complete their journeys next year, when they will be extracted from the ground through giant shafts at Greenpark Way.

TBM Anne was lowered in parts into the 25m deep crossover box at the end of last year, when she was reconstructed and prepared for launch.

A TBM is an earth pressure balance machine which operates like an underground factory.

It is effectively a large metal cylinder with a rotating cutting head at the front, which presses against the earth using hydraulic cylinders.

Disc cutters and scraping tools within the cutterhead loosen the earth which is then removed using a screw conveyor.

The conveyor moves the material through the back of the TBM and out of the tunnel via a conveyor belt.

As the machine moves forward, concrete rings are installed to create the tunnel walls.

The excavated London Clay is taken away from Victoria Road site via a conveyor system, removing the need for lorry movements.

From there, it is transported to HS2’s London Logistics Hub at the Willesden Euroterminal site where it is sorted, before being taken by train for re-use across the UK.