Located north of Birmingham airport, HS2’s Delta Junction is a 1.5km triangular junction that will enable trains to travel between London and Birmingham, Birmingham and Manchester, as well as directly between London and Manchester.
After leaving Interchange station at Solihull, northbound trains will curve westwards on a spur into Birmingham’s Curzon Street Station. Any northbound trains that leave Birmingham will use the northern chord to head north to meet the main HS2 line, which will connect the West Coast Main Line to Manchester. The third side of the triangle will allow trains to run between London and Manchester without stopping at Birmingham.
This is the most complex section of HS2, featuring embankments, cuttings, and 13 viaducts carrying tracks over motorways, local roads, existing rail lines, rivers, and their floodplains. The viaducts have been designed by Mott MacDonald Systra DJV for the Balfour Beatty VINCI (BBV) contract, these comprise:
- Six pre-cast segmental viaducts with standardised spans.
- River Tame East Viaduct.
- River Tame West Viaduct (one single track and one double track section).
- Water Orton 1 and 2 Viaducts.
- Coleshill East Viaduct (one single track section).
- Coleshill West Viaduct (one single track and two double track sections).
- Seven composite viaducts with decks built on weathering steel boxes or beams.
- M42/M6 link East and West Viaducts.
- River Cole East and West Viaducts.
- Watton House Viaduct.
- M42 Coleshill North and South Viaducts.
The junction’s structures will be substantial, but landscape architects have developed plans for connected and accessible areas that will include tree planting and new wildlife habitats around the Delta Junction viaducts. These will tie the viaduct structures into the local landscape, with enhancements including improved connections through the junction area, with new paths and cycle routes set within a nature-rich corridor.
M42/M6 link viaducts
The M42/M6 link viaducts are two parallel structures that will carry trains westward into Curzon Street across these roads. These were the first to be installed in the Delta project.
These are both composite bridges with concrete decks formed on full-depth concrete precast slabs carried on weathering steel girders.
Construction across these strategic links between the M6 and M42 had the potential to be extremely disruptive for road users. HS2 Ltd, BBV, and National Highways collaborated to develop and deliver a methodology that would minimise disruption.
Working either side of the carriageways, two abutments and three piers were constructed for each viaduct. The new fabricated steelwork was fabricated and delivered to the north abutment.
This project used a push-pull jacking technique that ensured a safer and more accurate launch. A temporary concrete jacking reaction beam was formed along the approach formation, the jacks engaged in sockets in this and moved the bridge forward.
The first 300-tonne push of the East Link Viaduct in February 2024 took 84 metres of girders as far as the pier. Further steel girders were welded to the back of the first section to complete the 158-metre-long structure onto which precast concrete deck slabs were placed. By installing prior to launch, the number of subsequent highway closures required to complete the composite deck was significantly reduced.
In April 2024, the second, longer push completed the installation of all 1100 tonnes of steelwork, from abutment to abutment. The operation was completed during a weekend road closure in 13 hours – 10 hours ahead of schedule – enabling motorway link roads to be reopened early. The pier-top guide frames were then removed, the girders jacked down onto their bearings, and the remaining precast deck units installed on the spans. The precast parapet panels were installed during further road closures.
The Western Link Viaduct was erected in the same way during pushes in June and September 2024, and again both were completed earlier than planned, reducing disruption to road users.
Ahead of the preparation of the rail formation, this viaduct is currently in use as an internal haul road to move material from Bromford Tunnel into the Delta Junction, taking thousands of lorries off the local road network.
Panos Psathas, senior project manager at HS2 Ltd said that the viaduct pushes were an impressive achievement for the team, particularly as these were the first huge viaduct spans to be built in the Delta Junction.
River Tame West Viaduct
The River Tame West Viaduct is a 472-metre precast segmental viaduct at the northern tip of the Delta Junction, crossing the River Tame near Water Orton. The project is being delivered by BBV and designed by MMSDJV.
In this complicated section, there will eventually be six tracks running alongside each other as they join the southern end of the Curdworth Box. The River Tame West Viaduct will carry three tracks, the River Tame East Viaduct one track and the Water Orton Viaducts two tracks.
To the south, the 1,400-metre Water Orton viaducts curve towards the M42/M6 link viaducts and on to Birmingham. The other four lines, on the River Tame Viaducts, will carry the mainline south to Interchange Station and on to London.
A total of 2,742 viaduct segments for Delta Junction structures are being made at HS2’s factory near Lea Marston using a ‘match-casting’ technique. This involves casting each segment against the following segment in a production line, with each segment fitting perfectly when assembled on site. The double track segments are 2.6 metres long, up to 13.2 metres wide, 3.5 metres high, and weigh 80 tonnes. The single-track ones are up to 84 tonnes.
Construction of the 20 piers and abutments to support the two River Tame Viaducts took place during 2023. The installation method for the viaduct as a whole requires the balancing of the cantilevered deck using cable stays anchored to the previous span. As a result, the first span of each structure was erected differently, by placing segments from the abutment end between two large 42-metre-long temporary truss girders and then moving these along on skidding trolleys.
The 16 segments were then combined into a single self-supporting 920-tonne structure by post-tensioning, before the trusses were removed and transferred to the adjacent abutment. This stage was completed in Spring 2024.
Following completion of the first spans of each viaduct, the 190 pre-cast concrete segments of River Tame West have been lifted into place using a specialist cantilever technique not used in the UK before. This patented progressive cantilever method, pioneered by VINCI, has been used on other major construction projects around the world, including the Tours-Bordeaux high speed rail project.
The temporary works give the viaduct the appearance of a cable-stayed bridge during its construction. A 22-metre-high mast is erected above the pier to support temporary tensioned cable stays and a 14-metre high, 81-tonne capacity swivel crane to erect the precast segments into final position. Four sets of masts and swivel cranes will be used across the Delta Junction site. These were designed and manufactured by Portuguese specialist, BERD.
The segments are stored in the adjacent lay down area and transported to site on a Self-Propelled Modular Transporter (SPMT). This passes beneath the mast, and the swivel crane picks up the segment and places this at the nose of construction, where it is glued with epoxy resin and connected with temporary prestressing bars to the previous sections. Then, a pair of cable stays are attached to the segment connecting it to the mast and back to the anchor of the previous span. Both stays are then stressed simultaneously.
Once all 19 segments of the 45-metre span are placed up to the next pier, permanent post-tensioning tendons are installed, stressed, and grouted, allowing the destressing and removal of the temporary cable stays. Currently each span is taking five-and-a-half days to complete.
Departure from standard
Ducted, grouted, post-tensioned bridges were banned by the Department of Transport in 1992 but National Highways has accepted a Departure from Standard for Water Orton 1 and 2 viaducts, following extensive trials and the use of modern materials to ensure full continuity and encapsulation of the tendons within their ducts.
After moving the mast forward to the next pier using the SPMT, the process is then repeated between each pier until the far abutment is reached. The crane and mast will then be dismantled and moved on to the next viaduct.
Following the completion of the structure, precast parapets are installed, followed by walkways, cable troughing, and track formation.
The erection of the River Tame West Single Track Viaduct was completed in February 2025.
Nicolas Gallone, Pre-cast Segmental Viaducts Project Manager at Balfour Beatty VINCI said that:
“This is the first time in the UK we’ve used this innovative technique to build segmental viaducts. It’s an efficient and flexible process using cable stays from the cantilever structure to keep the viaduct in place, while a mast and swivel crane are used to place each segment in place. It’s a great achievement for the whole team and work now continues using this technique on the other eight pre-cast segmental viaducts in the Delta Junction.”
The construction of all Delta Junction precast segmental viaducts is expected to be completed by September 2026, and the completion of equipment installation and superstructures by summer 2027.
Image credit: HS2