The Crumlin Viaduct was a railway viaduct located above the village of Crumlin in South Wales, originally built to carry the Taff Vale Extension of the Newport, Abergavenny and Hereford Railway (NA&HR) across the Ebbw River.
Hailed as "one of the most significant examples of technological achievement during the Industrial Revolution", in its 107 years of service until being dismantled in 1965, it remained: the least expensive bridge for its size ever constructed; the tallest railway viaduct in the United Kingdom; the third tallest viaduct in the world, after the aqueduct at Spoleto, Italy, and the timber viaduct in Portage, New York state.
Background
During the Industrial Revolution, and the mass-extraction of coal from South Wales, there was a resultant growth in construction of railways into the South Wales Coalfield. The Taff Vale Railway so monopolised the trade of shipping coal to Cardiff Docks, that mine owners were desperate for competitor railway companies to both improve speeds of shipping, provide access to new markets, and hence reduce shipping rates.
The London and North Western Railway had developed a route for the industrialised West Midlands and Northwest England, by controlling the Llanfihangel Railway and the Grosmont Railways as feeder lines into the Hereford Railway, and hence onwards via the joint GWR/LNWR controlled Shrewsbury and Hereford Railway. This allowed shipment of goods from Pontypool and the Ebbw Valley to Hereford. However, access to the productive Rhymney Valley and Rhondda Valley coalfields was at best restricted, through having to route trains south to Cardiff along the TVR, then along the South Wales Railway to Newport via the GWR, before being able to access LNWR controlled track.
The UK Parliament approved an Act of Parliament on 3 August 1846, the construction of the Taff Vale Extension, which would connect Coedygric North Junction at Pontypool with the TVR/GWR at Quakers Yard, and hence allow direct and LNWR controlled access. The LNWR approved the required capital expenditure, and merged the existing three railways and the extension project in the new Newport, Abergavenny and Hereford Railway.
Construction
The route for the Taff Vale Extension required the construction of two significant viaducts across two major river valleys: one across the Ebbw River; and one across the Rhymney River, the Hengoed Viaduct.
The Ebbw Valley posed two significant challenges through its geography: Its height, created both a structural problem and a wind problem, as the valley funnelled and hence increased wind speed It is actually two valleys, the Ebbw and the smaller Kendon
Chief Engineer Charles Liddell concluded that stone would be a poor choice for construction of a suitable bridge, as additional stone would need to be shipped to the valley, and the height of the resulting structure would result in an unstable and high-maintenance bridge. Further, the solidity of a stone structure would create additional compressed wind flow around the rail tracks, resulting in a possible safety hazard for passengers and train crew. Overall, the required over-engineered result would also have been very expensive. His recommendation therefore to the board was for a cast iron structure.
Two tender responses were received by August 1852, with Liddell's recommendation for a design by Scottish civil engineer Thomas W. Kennard, using an amended design using the Warren truss. Contracts were signed in December 1852, with a stipulated completion date of 1 October 1857. After further experimentation of his design system at his father's Blaenavon Ironworks, the iron structures were cast at Kennard's Falkirk Ironworks and shipped to Newport Docks.
Kennard began construction in October 1853 by building the Crumlin Viaduct Works on the east bank. Here castings from Falkirk were brought together with wrought iron from Blaenavon, and all fitting and fabrication work took place. After shortening the spur from the Monmouthshire and Brecon Canal, and with the natural land between the two valleys acting as the ninth pier, the first girder was hoisted into place on 3 December 1854. The completed structure linking Pontypool Clarence Street railway station in the north via the Bryn Tunnel () to the viaduct east end, came by the end of May 1857.