A major engineering milestone was reached on Sunday 25 May, as teams working on the HS2 high-speed rail project successfully lifted the 850-tonne cutterhead and shields of Tunnel Boring Machine (TBM) Caroline using a giant gantry crane.

The lift follows TBM Caroline's completion of a five-mile journey from West Ruislip, arriving in an underground reception chamber in April. During the drive, the 9.48-metre diameter machine excavated over 1.2 million tonnes of earth and installed 4,217 concrete tunnel rings.


Caroline is one of four TBMs constructing the 8.4-mile Northolt Tunnel, which will eventually carry HS2 trains between Old Oak Common Station and the outskirts of London. The machine was named by local schoolchildren in honour of astronomer Caroline Herschel.

The first TBM to complete its drive on this stretch, named Sushila, arrived earlier and was dismantled in March at the Green Park Way site.