The replacement of Barmouth viaduct metallics: from concept to construction

Barmouth viaduct metallic spans required replacement after over 100 years in the marine estuary environment in north-west Wales. In 2020, Network Rail instigated a tender process to choose a design and build team to replace the metallic trusses. The five trusses to be replaced, located on the environmentally sensitive coastline, at the end of the longest timber railway viaduct still in operation in the UK, required a highly technical and innovative construction method as traditional techniques using jack-up barges and cranes introduced additional risk to the project. This paper describes the development of the concept, the design of the new permanent trusses, the temporary works to install the new bridge and the construction period. The previous structure was Grade II* listed and the new structure replicates it while staying true to modern fabrication methods and retains the original abutment and caisson substructure. The new trusses were transported carefully along the timber viaduct to the south and were used in the temporary case to support the old structure as it was demolished and lowered to pontoons below. The whole construction was successfully carried out to programme within a tight 3-month track blockade in the autumn of 2023.