HS2 Euston Approach Tunnels' Big Dig: Video | RailFocus

Key Takeaways

• 7.2 km tunnel built by two 7.5 m diameter TBMs
• Final 300 m constructed using mined tunnel technique
• TBMs stop a kilometre from Euston, no breakthrough
• Underground cavern splits line into north and south tunnels
• Mid‑2027 target for tunnel completion and junction

Summary

HS2’s new approach tunnels to London Euston involve a 7.2 km stretch bored by two 7.5 m diameter tunnel boring machines (TBMs). The TBMs will halt about a kilometre from the station, leaving the final 300 m to be excavated with mined‑tunnel techniques. A large underground cavern will be created to split the north‑bound and south‑bound lines, forming an underground junction. Completion of this complex segment is slated for mid‑2027.

Pulse Analysis

HS2’s Euston approach tunnels represent one of the most intricate sections of the high‑speed rail network, reflecting the broader challenges of inserting a new mainline into a densely built capital. While the majority of the 7.2 km alignment is driven by conventional tunnel boring machines, the decision to halt the TBMs a kilometre short of the station throat acknowledges the tight spatial constraints and the need to preserve surface infrastructure. This hybrid construction method—combining TBM‑driven shafts with hand‑mined sections—mirrors techniques used in other megaprojects where precision outweighs speed.

The final 300 m, excavated one metre at a time, will give engineers the flexibility to shape a massive underground cavern that functions as a split junction. Within this cavern, the south‑bound (up) line will bifurcate into two tunnels that surface separately, while the north‑bound (down) line threads between them. This configuration not only streamlines train movements into and out of Euston but also creates redundancy, allowing maintenance on one branch without halting the entire flow. Such a design showcases advanced tunnelling practices that balance structural integrity with operational efficiency.

From a business perspective, delivering this segment by mid‑2027 is pivotal for HS2’s overall timeline and budget. The specialized mined approach, though slower and potentially costlier, mitigates risk of costly surface disruptions in central London, preserving commercial activity and public sentiment. Moreover, the underground junction sets a precedent for future urban rail expansions, demonstrating that high‑speed corridors can coexist with historic cityscapes without compromising performance or safety.