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Loughor trestle viaduct, site of
Loughor Estuary, between Llanelli and Swansea, Wales, UK
Loughor trestle viaduct, site of
associated engineer
Isambard Kingdom Brunel
date  opened 17th September 1852
UK era  Victorian  |  category  Railway Viaduct  |  reference  SS558981
photo  Stephen K. Jones collection
The Victorian Grade II listed rail viaduct that once crossed the tidal estuary of the River Loughor, carrying the south Wales main line, was the last surviving example of a Brunel timber viaduct. In 2013, after a series of refurbishments and alterations, the viaduct was demolished and replaced by a new steel and concrete rail bridge.
Isambard Kingdom Brunel (1806-59) designed the 18-span timber Loughor Viaduct to carry two tracks of the South Wales Railway, authorised by the South Wales Railway (Chepstow to Fishguard) Act 1845. Apparently the tracks were laid originally as multi-use, both standard gauge (1.435m between rails) and Brunelís broad gauge (2.14m).
The viaduct was 228.6m long between stone-faced bankside abutments with a swing bridge at the Swansea (east) end providing a 12.2m clear opening, and had 17 other spans of similar size. Its timber trestles were supported on three-pile piers, the piles being driven 4.3m into the river bed.
Brunelís assistant, Lavington Evans Fletcher (1822-97), was resident engineer and also designed the movement mechanism for the swing bridge.
The first train crossed the viaduct on 17th September 1852 and a regular public service began on 11th October 1852. The delay was apparently caused by a shortage of Barlow rails for the permanent way. In May 1872, the South Wales Railway changed from using broad gauge to standard gauge.
In the 1880s, the trestles were replaced and/or reinforced with wrought iron. The timber deck was replaced by three longitudinal wrought iron girders topped by an iron deck made from surplus Barlow rails laid transversely.
The swing bridge was last used in 1887, and was later replaced by a fixed girder. Its opening was closed permanently to river traffic by major work carried out on the viaduct during 1908-9.
During the 1908-9 works, Brunelís original three-pile pier groups were cut off at lower waling level. New four-pile timber pier groups were driven to support the deck, which was reconfigured by replacing the longitudinal wrought iron deck girders with four deeper steel plate girders.
In 1979-81, the viaduct was refurbished sympathetically, re-using as much of the existing timber as possible. The work was supervised by Christopher Loudon Wallis (1935-2006), a civil engineer specialising in timber engineering and youngest son of bouncing-bomb inventor Sir Barnes Wallis (1887-1979). Serious erosion of the river bed was discovered during the contract, necessitating tipping stones to protect the timber piles.
In 1986, the viaduct was limited to single-track operation following British Rail concerns over structural safety. Freight and passenger trains were also subject to speed restrictions, with consequent delays. Loughor Viaduct was Grade II listed in October 1998.
In March and April 2013, as part of the redoubling of 8.4km of railway between Llanelli and Swansea, Network Rail replaced the viaduct with a seven-span steel and concrete rail bridge. The new bridge was constructed alongside the old, then jacked sideways into position after the viaduct was demolished. The new bridge incorporates one span of the original substructure at the Llanelli (west) end and retains its abutments.
Timber pile viaducts used to be a notable feature of Welsh coastal railways, though few now survive. To preserve the heritage value of Loughor Viaduct, a two-span section of the old structure, from deck to waling level, has been relocated (SS559980) to railway land north west of the new viaduct.
Resident engineer: Lavington Evans Fletcher
Resident engineer (1979-81): Christopher Wallis
Research: SKJ, ECPK
"Timber Viaducts: Loughor and Pont Brewit" by Stephen Jones, in ICE Wales Cymru Newsletter, November 2013

Loughor trestle viaduct, site of