HS2 has successfully completed a major engineering milestone on the West Midlands section of the railway, with the installation of the second twin viaduct spanning the M6 near Chelmsley Wood.
The final section of the 4,750-tonne west viaduct was launched over one of the UK's busiest motorway corridors during a carefully planned weekend operation, allowing traffic to continue flowing beneath the structure while engineers carried out the complex manoeuvre.
The achievement means both M6 South viaducts are now structurally complete, marking the end of a significant phase of works delivered by HS2's construction partner, Balfour Beatty VINCI.
The eastbound deck, completed in 2025, will carry trains travelling towards London destinations including Old Oak Common and Euston. The newly installed west deck will carry services towards Birmingham Curzon Street and onward destinations in the north, including Manchester, Liverpool and Glasgow.
Standing just 100mm apart, the parallel weathering steel viaducts each extend 320 metres across the motorway and are supported by reinforced concrete piers. Embankment construction will now continue on either side of the structures.
Due to site constraints, the two viaducts were assembled and launched using slightly different methodologies. The east deck was installed in three stages, while the west deck required four incremental launches.
For each launch, engineers added new steel sections to the rear of the structure before using powerful strand jacks to push the entire deck forward. During the final stage, the deck's weight was fully supported by concrete piers positioned on either side of the motorway, allowing the last section to be installed safely while maintaining motorway operations.
HS2 Praises Innovative Construction Techniques
Ian Clarke, Senior Project Manager at HS2 Ltd, said:
"These viaducts straddle some of the busiest sections of motorway in the country, which is why we adopt innovative techniques that allow construction to continue without closing the carriageway whenever we can.
"We have made great progress this year and I thank motorists and local communities for their patience."
The final launch operation saw engineers move the west deck forward by 76 metres in just nine hours, achieving an average speed of around 12 metres per hour.
Although the M6 remained open throughout the programme, the M42-M6 link road was temporarily closed to establish a safety exclusion zone. The route reopened 25 hours ahead of schedule at 9pm on Saturday, 24 October.
Challenging Weather Conditions Overcome
Russell Luckhurst, the Balfour Beatty VINCI engineer leading the delivery of the project, said:
"Two neighbouring viaducts that run parallel to each other now span the busy M6 motorway near Chelmsley Wood, after the west deck was safely and successfully moved into its final position over the weekend.
"It's a huge moment for Balfour Beatty VINCI and HS2, concluding a major programme of work above the M6 – in extremely challenging weather conditions."
The successful launch came despite strong winds affecting large parts of the UK over the weekend.
However, weather conditions forced the postponement of separate parapet installation works on the nearby Water Orton Viaduct above the M42. Those activities have now been rescheduled and will require M42 closures between Junctions 6 and 9 northbound and Junctions 9 and 7 southbound from 9pm on Friday, 30 October, until 5am on Monday, 2 November 2026.
Focus Turns to HS2's Triple Box Structure
Looking ahead, HS2's motorway engineering programme will focus on the project's highly anticipated "triple box" structure near Coleshill.
The innovative rail-over-road crossing will carry four HS2 tracks over the M42 and is expected to become one of the most significant phases of motorway-related construction on the route. HS2 is continuing to work closely with National Highways to finalise the delivery schedule.
Image and video credits: HS2
