Engineers working for the HS2 project have slid the first part of a major 320-metre-long viaduct into position that will carry high speed trains across the M6 near Birmingham Airport.
The first stage of the project – delivered this weekend – saw the ‘East Deck’ of the M6 South viaduct slid 119m out over a slip road adjacent to the motorway.
To reduce disruption for motorists, the viaduct deck is being assembled to one side and slid across the motorway over three weekends, with each part pushed out before later sections are added behind them.
This multi-stage process means that the weight of the deck will increase with each push from 1,3000 tonnes this weekend, to 3,290 for the final slide. These subsequent slides will take the deck out over the main M6 carriageway and then finally the M6-M42 link roads.
The weight includes pre-cast concrete deck slabs on top of the steel structure. Launching the viaduct with the deck units already in place further reduces the number of closures of the motorway.
The East Deck will carry two tracks taking trains towards London while an adjacent ‘West Deck’ will carry a further two tracks for services heading to Birmingham and further north. This will be assembled and slid out next year using the same technique.
Liam Kenney, HS2 Ltd’s Senior Project Manager said:
“It’s great to see the first section of the East Deck in position over the weekend. Once complete, these twin viaducts will carry high speed trains over the M6 helping to improve journeys and free up space on the existing rail network for more freight and local services.
“I’d like to thank everyone who is worked so hard to deliver the first slide safely and efficiently opening the road to traffic 11 hours early."
The complex operation is being led by HS2’s main works contractor, BBV – a team made up of Balfour Beatty and VINCI, supported by specialist steelwork company Victor Buyck Steel Construction (VBSC). The team are working closely with National Highways and other key local stakeholders including the NEC and Birmingham Airport.
Victoria Lazenby, National Highways Regional Director for the Midlands, said:
“We know that any work on our roads affects drivers and local communities and always try to keep that disruption to a minimum. So we are delighted by the innovation shown by HS2 and BBV in this complex engineering feat to reduce the impact on road users.
“We will continue to work very closely with HS2 to ensure minimum disruption on our roads and are grateful to people for their patience while this major infrastructure scheme is delivered.”
The viaduct section was moved using a series of winches, known as strand jacks, at an average speed of twelve metres per hour, sliding across non-stick pads to reduce friction – a material usually found to the surface of a household frying pan.
A 36-metre-long temporary launch nose was installed to the front of the structure, to guide the viaduct on its launching path and reduce the weight of the cantilevered section.
The viaduct, and the launch nose, will remain in its current position while the next section is assembled. The viaduct is restrained temporarily by equipment located on the piers and the abutments.
Russell Luckhurst, the Balfour Beatty VINCI’s engineer leading the delivery of the works, said:
“This complex viaduct spanning the M6 motorway and adjoining slip roads is really beginning to take shape, now we’ve successfully moved the first section into place.
“It’s a huge achievement for the dedicated project team who’ve worked tirelessly over the past three years to reach this point. We’re now focussed on delivering the next phase, which includes two further launches later in the year.”
Each viaduct span is formed of a hollow double-box structure made of weathering steel. This kind of steel boasts a natural protective layer of oxidisation which gives it a characteristic ‘rusty’ appearance and reduces maintenance by eliminating the need for regular repainting.
Four pairs of concrete piers support the viaducts with tallest one 9.9m in height. A 4.5m high parapet will be provided on the side facing the Chelmsely Wood to reduce noise and disturbance from passing trains.
The structural design has been carried out by Balfour Beatty VINCI’s Design Joint Venture, made up of Mott MacDonald and SYSTRA.
Tom Dutton, Senior Design Co-ordinator for the Mott MacDonald SYSTRA DJV, said:
“The launch of the first deck of the two-deck M6 Motorway South Viaduct marks an exciting milestone following years of dedicated design work. We have seen the design take shape as the foundations, piers, and abutments were constructed, and now the moment has arrived for the deck to be launched.
“The launch design is a fantastic example of collaboration between Mott MacDonald SYSTRA DJV colleagues in the UK and France, BBV, and their steelwork and launching contractor, Victor Buyck Steel Construction. Together, we have addressed the complex challenges of the temporary works and the fabrication of the steel diaphragm—not to mention the feat of launching the viaduct decks over the M6 motorway itself.
“This achievement is a testament to our collective effort and a fantastic milestone for the immediate team and the whole project.”
