Crumlin Viaduct - Construction

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 October 1st 1857. After further experimentation of his design system at his fathers 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 to the Bryn Tunnel (398 yards (364 m)) in the south by the end of May 1857.

Testing began that same month, in front of the Board of Trade Inspector, Colonel Wynne. Six locomotives loaded with pig iron or lead weighing a total of 370 long tons (380 t) were placed in charge of locomotive driver "Mad Jack" of Pontypool, who before making his first crossing had visited every public house in Crumlin. After a series of tests, during which a deflection of less than 1.5 inches (38 mm) was measured, the bridge was approved for use in the same month.