Engineers have hoisted HS2’s tunnel boring machine (TBM) Caroline from beneath Green Park Way in Greenford, marking another key moment in the construction of Britain’s new high-speed rail network.
On 25 May 2025, the 850-tonne cutterhead and shields of the 9.48m-diameter machine were lifted using a gantry crane after completing a 5-mile underground journey from West Ruislip. The operation follows Caroline’s arrival in a subterranean reception chamber in April.
Named by pupils from Brentside Primary Academy after astronomer Caroline Herschel, Caroline excavated more than 1.2 million tonnes of earth and installed 4,217 concrete rings. It is one of four TBMs building the 8.4-mile Northolt Tunnel, which will carry HS2 trains from Old Oak Common to the edge of London.
The first TBM, Sushila, was removed in March, as work progresses on the country’s largest infrastructure project in decades.
