Use Case: Conventional Tunnelling

High Speed Two (HS2)

TUNNELLING TECHNIQUES FOR THE UK’S LARGEST RAIL PROJECT

High Speed Two (HS2) is the UK’s largest high-speed rail project, creating a new line between London and Birmingham with extensive underground works using a fleet of 11 tunnel boring machines (TBMs). Within HS2 Phase One, Skanska-Costain-STRABAG joint venture (SCS) is delivering the London Tunnels, combining mechanised tunnelling with complex underground structures. For the twin-bore  tunnels, TBMs—each weighing around 2,000 tonnes—enable continuous excavation and immediate segmental lining installation on mechanised drives such as the 13.6 km Northolt Tunnel or 7.2 km Euston Tunnel. These TBMs typically advance at an average rate of 15–16 meters per day, installing thousands of concrete segments to form watertight rings.
However, SCS JV also relies on conventional tunnelling methods—including roadheaders and excavators—for short, complex sections like cross passages, ventilation shafts, and intervention shafts, where flexibility and ground adaptation are critical. This hybrid approach ensures both efficiency and adaptability across the project’s diverse ground conditions.

Challenges
Tunnelling in densely populated areas is highly challenging. Tunnelling works are particularly complex because of variable ground conditions, high groundwater pressures, and strict requirements to protect existing infrastructure. While tunnel boring machines (TBMs) handle long, continuous drives efficiently, they require precise logistics and careful management in mixed geology. For shorter tunnels, cross passages and ventilation shafts, conventional tunnelling methods are essential, as these elements must provide safe exits and emergency routes. A key challenge is the integration of TBM operations and conventional tunnelling activities within a single platform.