Video | Inside HS2’s twin-bored Northolt Tunnel 

Two HS2 tunnel boring machines (TBM) have completed the first mile of twin bored tunnel in London.

The TBMs, named Sushila and Caroline, have installed over 847 tunnel rings each, made up of 5,929 concrete segments, since November 2022.

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. It is expected to be complete by 2025.

The TBMs were named after local schoolteacher Sushila Hirani and German-born British astronomer Caroline Herschel following local consultation.

Naming boring machines dates back to early mining traditions, when miners and underground workers would pray to Saint Barbara, a third-century Christian martyr, to protect them from underground dangers. It was consired to be a sign of luck and respect.

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