TECHNICAL | SOFT GROUND TUNNELLING
FINAL HS2 TUNNEL EXCAVATION BEGINS
Excavation has begun on the final tunnel of the HS2 rail project, bringing the high-speed line towards its eventual London terminal, at Euston. Julian Champkin reports.
INTRODUCTION
The last of the London-based TBMs of the HS2 project officially launched its journey on 16th March. From a cavern at Old Oak Common in West London, TBM ‘Karen’ began excavating the second of the parallel tunnels towards Euston Station. The distance is 7.2km to build the Euston Tunnel. The first of the two TBMs got underway a few weeks
earlier and only the tail end of the backup train was still visible in the launch cavern when T&TI visited site to witness the start-up for TBM Karen. The first TBM is excavating for the up line (i.e.,
towards- London), Karen for the down line, says Eddie Edmonds, senior project manager for Skanska Costain Strabag Joint Venture (SCS JV), contractor for the London tunnels for HS2. He added that the larger conveyor structure needed for spoil removal had been completed just before TBM Karen was launched. Logistical support is a key part of the story of tunnelling in London.
Right:
TBM ‘Karen’ being prepared for HS2 Euston Tunnel drive from Old Oak Common, in west London IMAGES COURTESY OF HS2 LTD, UNLESS OTHERWISE NOTED
OLD OAK COMMON The Euston Tunnel is the final and easternmost section of the many HS2 tunnels and is being constructed with two TBMs driving from Old Oak Common. “We transported them in sections, by road; then we
partially assembled on the surface and lowered them down into the excavated cavern,” says SCS JV project manager Janagan Nithiananthan. The floor of the cavern is 23m below ground level.
The cavern will eventually serve as a main station and intersection on the route; it is some 850m long and the structure of it, including the 45,000m2
base slab, was
completed this year. Contractor for the cavern is Balfour Beatty Vinci Systra Joint Venture (BBVS JV). When completed, it will form one of the best-
connected interchange stations in the UK, with 14 platforms and more than 50 lifts and escalators. It is expected to serve 250,000 passengers per day and provide passenger connections between Great Western Railway (GWR) services to the West Country, HS2 to the
18 | May 2026
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