The challenge
Nuneham Viaduct plays an important role in the Oxfordshire rail network, carrying the CrossCountry and Great Western Railway services, as well as freight trains to and from Southampton Docks, across the River Thames between Didcot and Oxford. While the steel bridge was installed in 1909, the abutments and timber piles are thought to significantly pre-date this, being a part of the original bridge from the 1840s. The age of the structure recently became apparent after monitoring revealed significant movement in the structure. This movement, caused by poor ground conditions and deterioration to the south bank abutment and its timber piles, resulted in the viaduct being closed to passenger and freight trains in April 2023.
It was decided that the existing abutment would be demolished and rebuilt, alongside a new bearing shelf. To support the new abutment and overcome the challenging ground conditions, eight steel piles would be driven up to 25 metres into the River Thames embankment.
To enable these major structural works to be carried out, temporary works were a key part of this project, required to support and physically lift the bridge off the failed abutment, enabling Network Rail’s engineers to then demolish and rebuild the southern bank support structure. As well as the time constraints, with the railway line and part of the river having to be closed to traffic, the location was an additional challenge. We were asked with delivering these temporary works, appointed to design, supply and install a propping and jacking system.
Our solution
Colin Campbell, Senior Engineer at Mabey Hire explained: “Working closely with Network Rail and Balfour Beatty engineering teams, we designed a bespoke propping and jacking scheme. The end solution had to allow us to span 20 metres off piles driven into the River Thames and have a jacking arrangement on top, enabling us to lift the 200-tonne bridge structure up by 650mm to its original level.”
The scheme was formed of our Mass 25 grillage beams connected together to form a 22m long truss with Mass 50 and Mass 25 vertical and diagonal components. On top of the two trusses, three jacking platforms were installed, using bespoke beams to enable a jack and pack operation.
Colin continued: “When it came to the installation, 24 15-metre-long steel piles were first driven into the bed of the River Thames to create a solid platform for our temporary propping structure, which would in turn support the weight of the viaduct. A 750-tonne capacity crane was employed to lift our temporary propping structure onto barges, which were floated underneath the bridge. Once on the river, the crane then lifted both ends of our propping truss (22 tonnes) into position on a steel grillage set onto the piles.
“It was an incredibly challenging installation, requiring excellent collaboration between engineering teams and extensive planning, not just for consideration of the lift itself but also the logistics of getting the support structure into place.”
Once in position and the bridge was successfully supported and lifted, Network Rail engineers were able to demolish the damaged abutment, removing around 3,000 cubic metres of material from the embankment to create space, and build the new abutment.
Andrew Jones, Contractors Engineering Manager at Balfour Beatty Rail UK, commented: “Mabey Hire were involved in every step of the temporary works, from the initial design to the implementation on site. Colin and the wider team are a credit to their industry and clearly are the leading experts in their field.”
In addition to our temporary propping and jacking equipment, our monitoring expertise also proved invaluable on the project. As well as monitoring and measuring displacement at the centre pier, prisms were attached to both the bridge structure and the temporary works trusses to continually monitor displacement during the jacking process and the new pier construction. What’s more, during the jacking process, monitoring equipment was attached to the two lattice girders and the centre girder, all connected to a data logger, enabling the hydraulic engineer to control and measure the lift to keep the existing structure level during the jacking.
The works on the bridge took just over two months to complete, with our team having de-jacked the steel structure back down onto the new support abutment on 4th June 2023. The railway viaduct reopened to traffic on 9th June 2023.
