As part of Britain’s new high-speed railway project (HS2), six tunnel-boring machines have been driving through clay, sand and ever-shifting ground beneath the streets of London. They are carving out the tunnels that will one day enable trains to reach the heart of the British capital faster. GIM International spoke to Matthew Baddeley, survey manager for the Skanska Costain STRABAG Joint Venture (SCS JV), about the challenges of guiding them there: in both line and level, and within millimetres of their intended breakthrough points. The precision engineering involved in this intriguing project includes gyroscopic control over distances of up to 8km without intermediate checks, laser scanning workflows feeding directly into design decisions, and a 21km surface traverse that reconciled two independent underground control systems: Northolt Tunnel and Euston Tunnel.
The geometry of the ‘London Tunnels’ section of the HS2 project dictates every surveying challenge. In early 2026, two tunnel-boring machines (TBMs) were launched from Old Oak Common, mining towards Euston Station for a 7.5km drive. Prior to that, in January 2024, two other TBMs had been launched from the Victoria Road Crossover Box, for a 5.5km drive to Greenpark Way Vent Shaft. This drive, called Northolt Tunnel East, was successfully completed in summer 2025. Another pair of TBMs had set out on a demanding 8km drive in October 2022 from West Ruislip back to Greenpark Way. These were for the Northolt Tunnel West drives that were completed in April 2025. At the Greenpark Way Vent Shaft, all four machines converged into two large vent shafts and had to break through into what Baddeley describes as a “steel can”: a pre-built reception structure with tight positional tolerances. “From a tolerance perspective, it was challenging for all the TBMs to meet into the shafts because of the steel can scenario and the high accuracy requirements,” he says.
