Final phase of Barmouth Viaduct restoration to begin following successful test lift of span

The 154 year old, 820m long single track railway viaduct is the UK’s oldest and longest timber viaduct. As well as the railway, the bridge carries a pedestrian and cycle pathway owned by Gwynedd County Council.

The £30M project to restore the bridge involves the replacement of timber and metallic elements on a like for like basis. Network Rail expects that the restoration will safeguard the structure for up to 60 years.

Work on site started in 2020 and has been split into several phases across three years to minimise impact on rail services, the local community and economy. During the first two phases Alun Griffiths focused largely on replacing and repairing the decayed timber elements of the viaduct.

The final phase involves replacing and restoring the structure’s metallic elements and renewing 130m of track on its northern edge, near Barmouth Toll House. The viaduct will be closed for 12 weeks between 2 September and 24 November for the works on the metallic elements to be carried out, while the track renewal will take place from the 25 November to the following weekend.

Among the tasks to be executed in the 13 week period is the removal of two old metallic spans and their replacement with new 160t ones. Each new span will be lifted onto the viaduct and transported using rail trailers inside the one it will replace. Once in position, a dedicated team will carefully take apart the old span placing the elements onto a pontoon in the Mawddach Estuary. As the replacement of all elements has to be on a like for like basis, when the old span is removed the project team will make adjustments to the new one to achieve that outcome.

Due to the complexity of the installation method, the project team decided to carry out a practice operation ahead of the actual one. The practice operation took place on a purpose built mock railway track just outside Barmouth, with 15 people testing the cantilever and jack system that will be used to lift the span onto the viaduct. A total of 16 jacks, with capacities ranging from 20t to 100t, as well as six rail trailers were used for the test.

Barmouth Viaduct's two new metallic spans will weigh 160t each

The test lift of the span was successful. According to Network Rail, the process to install the two news spans on the viaduct will take two days.

Network Rail Wales & Borders route director Nick Millington said: “We’re delighted to begin the final, and most visually exciting, stage of our multi-million-pound restoration of Barmouth Viaduct, with our focus now on restoring the metallic elements on a like-for-like basis.

“A huge part of this phase of work has been planning the replacement of the 160t metal spans, a feat of engineering that has involved months of preparation to develop a unique delivery and installation system. We have also worked closely with our partners at Natural Resources Wales to ensure we’re doing everything we can to protect the delicate ecology of the Mawddach Estuary.

“As the railway and footpath across the viaduct will need to be closed for the duration of our work to ensure everyone’s safety, I would like to thank everyone for their patience as we carry out this vital work, which will protect this important and iconic rail link for years to come.”

Like what you've read? To receive New Civil Engineer's daily and weekly newsletters click here.