Restoration of the 156-year-old barmouth viaduct

Barmouth Viaduct is a 150-year-old Grade II* listed structure and a significant landmark on the north-west coast of Wales in the UK. The bridge is an access route, carrying a single-track railway, a public footpath and cycleway over an estuary. The 820m long structure consists of the longest timber railway bridge in Great Britain and five metallic spans over the navigation channel.

In 2020 it was recognised that the metallic spans were life expired and a design and build contract was awarded for their replacement. As the bridge is in a tidal estuary classified as a site of special scientific interest (SSSI) with very limited access, the project had to minimise environmental impact during the works and ensure no construction presence in Barmouth during the tourist season. It also reduced the carbon footprint through the reuse and refurbishment of the existing substructure. Great care was taken to replicate the aesthetic and structural form of the original structure, ensuring the new bridge maintained the heritage status and iconic nature of the original bridge while meeting modern standards.

An innovative method for reconstruction of the structure was needed as traditional methods using jack-up barges and cranes were not cost-effective and introduced additional risk to the project. The construction method developed by Tony Gee and Partners in collaboration with Griffiths, consisted of transporting the new girders across the timber viaduct by rail and installing the new girders inside the existing structure to enable the replacement. The new girders were then used as temporary works to support the existing bridge and facilitate the removal of the existing superstructure via a bespoke gantry crane supported on temporary works above the new girders. The new girders were then lowered and jacked apart, and deck panels installed.

This presentation will cover the technical aspects related to the detailed design of the new metallic spans including the main temporary works and the construction methodology adopted for the successful delivery of the heritage structure.