Scottish viaduct receives gentle treatment from National Highways

The masonry repairs on the soffit of the arch were made from cradles and by rappelling on the voussoirs.

As the video below shows, the 16-arch viaduct spanning the River Avon on the border of West Lothian and Falkirk has been returned to its former glory thanks to a £2m renovation program funded by the Historical Railways Estate (HRE).

Work on the Westfield Viaduct included masonry repairs, waterproofing and the installation of 19 blanket bricks, six bat tubes and two bat boxes. It took 18 months to complete and should see the structure, built in the 1850s, last for a few more generations.

HRE civil engineer Colin McNicol said he was satisfied with the progress of the work. “The viaduct had a number of issues that needed attention to ensure it remained safe and in good condition and the work that has been completed makes any future plans to reopen the viaduct as an active route for pedestrians, cyclists and other users a real possibility.” he said.

The Westfield Viaduct is among 3,100 former railroad structures maintained by the National Highways Historical Railways Estate (HRE) on behalf of the owners, the Department of Transportation. Although National Highways has no remit for roads in Scotland – that is a matter delegated to the government – ​​it still looks after the railway viaducts that are no longer in use.

The Westfield Viaduct was built between 1854 and 1855 as an extension of the Monkland Railway. This branch ran from Blackston Junction on the Slamannan Railway to Bathgate to meet the Wilstontown, Morningside and Coltness Railway before turning west to run to the mines around Crofthead before becoming part of the North British Railway in 1865.

The structure has 12 large arches about 47 feet wide and two smaller ones at each end. In total, it spans 660 feet over land and water and is 60 feet from the top of the arch to the riverbed.

Before renovations could begin, two rounds of bat surveys were conducted at different times of the year, including a summer re-entry survey to ensure bats had not returned to the work areas for hibernation. Surveys included rappelling under the direction of licensed bat ecologists, checking cracks in masonry with endoscopes (a long, thin tube with a camera inside) for signs of bat activity. Drones were used for additional checks.

Any crevices that showed signs of bat droppings or dark spots on the stones, and crevices that were too difficult to inspect properly, were fitted with exclusion devices that allow bats to exit but not re-enter. All surveys were completed under a NatureScot bat license.

Temporary bat boxes, pipes and bricks were installed in areas of the structure where work was not taking place for the bats to use safely during the hibernation season. Several bricks, boxes and bat tubes were then built into the viaduct as permanent bat shelters.

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Other work included extensive vegetation clearing and repairs to all 16 spans, along with repairs to the north and south parapets and waterproofing work. New cast iron support plates, manufactured to match the originals, were also installed to replace the damaged elements and the stone repairs were matched to the unworn original material.

The National Highways HRE team is often criticized in the media for rather clumsy shortcuts in its Victorian bridge maintenance, simply filling the voids under the arches with rubble and concrete, thus preventing any development of green routes along the derelict railway alignments under the arches.

In June last year, the former Chairman and Chief Executive of the Strategic Railway Authority, Richard Bowker, was so outraged by what happened to the Great Musgrave Bridge in Cumbria’s Eden Valley that he said: ‘I never really liked ‘ and now heads must roll’ but, at least on this occasion, the CEO of National Highways must formally apologize as well as scrap this policy of wanton vandalism.

Replace protection plates

New stave stones and cast iron cladding plates, cast to match the originals
New stave stones and cast iron cladding plates, cast to match the originals

Millar Callaghan Engineering Services was awarded the contract to replace the damaged and broken skid plates and tie rods that hold the structure together at the top of the 16 arches.

Detailed research verified the detailed dimension and design of the existing steel cast iron plates to the new replacement plates would match exactly. The new plates and tie rods were manufactured at Millar Callaghan’s workshop in Irvine.

A spider crane was positioned at the top of the viaduct to assist in the removal of the old ones and the installation of the new protection plates. Motorized access platforms were used to access both the outer face and the underside of the arch to remove and install steelwork.

The old cracked and damaged boards removed were carefully and skillfully removed to ensure they did not break during removal. The new plates and tie rods were then installed and tightened into position. A fresh coat of paint was applied to freshen up both the new and existing steel structure.

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