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Meldon Viaduct
Meldon, near Okehampton, Devon, UK
associated engineer
W.R. Galbraith
date  1874, 1878 - 1879
era  Victorian  |  category  Railway Viaduct  |  reference  SX563924
ICE reference number  HEW 270
Meldon Viaduct crosses the River Okement valley 3.2km south west of Okehampton, and once carried the railway between Exeter and Plymouth. It is a Scheduled Ancient Monument, and one of only two structures of this type of wrought iron construction in Britain.
The first viaduct was built in 1874, to convey the mainline London & South Western Railway between Waterloo and Plymouth on a single track. The first train crossed the structure on 12th October 1874.
In 1878 it was decided to increase capacity to double track and a second similar viaduct was built parallel to the first. The new structure carried the 'down' line and the older one the 'up' line. An extended deck linked the two, with additional bracing at the tops of the trestle piers.
The viaducts were built by W.R. Galbraith, at a gradient of 1 in 77 rising towards the west and to horizontal curves of approximately 600m radii. Each has six equal spans of 27.4m, comprising two Warren girders. The trusses are 2.8m high deployed at 1.5m, 2.3m and 1.5m centres, with the older trusses having a bottom tension member of a vertical flat only.
The deck is 43.9m above river bed level, and its five piers range in height from 14.6m to 36.6m. The tapering piers are formed from four wrought iron columns, in sections 3.2m long, braced both horizontally and diagonally at each joint. Column sections are made in six parts with longitudinal riveted joints, and are supported on 7.3m wide masonry bases. Cross braces are in wrought iron, with the older trestles having more slender bracing.
The end spans of the viaducts rest on cast iron sliding bearings, founded on concrete filled cast iron tube piles in front of the abutments. The piles are between 4.6m and 17.1m deep.
In 1927, a speed limit of 32km per hour (20mph) was imposed after concerns were raised about dynamic loading from wind and trains travelling over the structure. The bottom chords of the 1874 trusses were braced in 1938.
Strengthening work was carried out before and during World War II (1939-45) and the trestle columns were weighted with concrete to resist uplift. This allowed heavier trains to cross the viaduct. The piers of the 1874 viaduct were strengthened further in 1959, with collars around the columns and heavier bracing.
The railway was returned to single track running in April 1966, with trains crossing the earlier structure. Through railway traffic ceased on 6th May 1968, although the line continued to be used as a head shunt for Meldon Quarry.
In 1970, a concrete road was laid over the viaduct for use by construction traffic involved in building Meldon reservoir and dam. The rails were lifted in 1990.
In summer 1996, Carl Bro Group carried out a 650,000 refurbishment contract funded by CAMAS Aggregates and British Rail Property Board. New work included decking in treated softwood, handrails, repainting, steel work repairs, masonry repairs to the abutments, and river bed scour protection to the piers.
Meldon Viaduct was then incorporated into the Granite Way footpath and cycleway across Dartmoor. It is now owned by the Meldon Viaduct Company, a non-profit-making company set up in February 1999.
After some further work, the structure was reopened on 6th July 2002 by Adam Hart Davis.
Research: ECPK
reference sources   CEH South

Meldon Viaduct