A Scottish viaduct is given a gentle treatment by National Highways

Masonry repairs of the arched ceiling were made of cradles and descents on voussoirs
Masonry repairs of the arched ceiling were made of cradles and descents on voussoirs

As the video below shows, the 16-arch viaduct that spans the River Avon on the border between West Lothian and Falkirk has been restored to its former glory thanks to a £2 million refurbishment scheme funded by the Historical Railways Estate (HRE).

Work on the Westfield Viaduct included masonry repair, waterproofing and the installation of 19 bat bricks, six bat tubes and two bat boxes. It took 18 months to complete and the structure, built in the 1850s, should stand for several more generations.

HRE civil engineer Colin McNicol said he was pleased with how well the work went. “The viaduct has had a number of issues that required attention to ensure it remains safe and in good condition, and the completed work makes any future plans to reopen the viaduct as an active travel route for pedestrians, cyclists and other users a viable option,” he said.

The Westfield Viaduct is one of 3,100 former railway structures maintained by the National Highways Historical Railway Estate (HRE) on behalf of the owners, the Department for Transport. Although National Highways is not responsible for Scotland’s motorways – it is a devolved government affair – it still looks after the railway viaducts there that are no longer in use.

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

The structure has 12 large arches spanning approximately 47 feet and two small ones at each end. In total, it extends 660 feet above land and water and stands 60 feet from the top of the arch to the riverbed.

Before restoration could begin, two rounds of bat surveys were conducted at different times of the year, including a summer re-entry survey to ensure that bats did not return to the work areas to hibernate. Surveys included abseiling under the direction of bat-licensed conservationists inspecting cracks in the masonry with endoscopes (a long thin tube with a camera inside) for signs of bat activity. Drones were used for further inspections.

Any crevices that showed evidence of bat droppings or dark spots on the stones, as well as crevices that were too difficult to examine properly, were fitted with closures that allowed the bats to exit but not re-enter. All studies were conducted under a NatureScot bat license.

In places where no work was carried out, temporary bat boxes, pipes and bricks were installed so that bats could safely use them during the hibernation period. Subsequently, many bat bricks, boxes and tubes were built into the viaduct as permanent shelters for the bats.

Related information

Other work included extensive vegetation removal and repairs to all 16 spans, as well as repairs to the north and south parapets and waterproofing work. New cast iron profile plates, made to match the originals, were also installed to replace damaged components, and stone repairs were color-matched to the original indestructible material.

The HRE National Highways team is usually under fire in the media for somewhat boorish shortcuts in maintaining a Victorian bridge, simply filling empty spaces under the arches with rubble and concrete, thus preventing the development of greenways along disused railway lines under the arches.

Last June, the former Chairman and Chief Executive of the Strategic Rail Authority, Richard Bowker, was so enraged by what happened to the Great Musgrave Bridge in Cumbria’s Eden Valley that he said “heads must roll”, but at least on this occasion the director National Highways General must formally apologize and also reject this policy of gratuitous vandalism.

Replacement of patress plates

New voussoir stones and cast iron pattress plates, cast to match the originals
New voussoir stones and cast iron pattress plates, cast to match the originals

Millar Callaghan Engineering Services was awarded the contract to replace damaged and broken profile plates and tendons that connect the structure at the top of the 16 arches.

A detailed study showed that the detailed dimensions and design of the existing cast iron steel plates would exactly match the new replacement plates. The new tie plates and tie rods were manufactured at Millar Callaghan’s Irvine workshop.

A spider crane was placed on top of the viaduct to assist in the removal of old and the installation of new paving slabs. Powered access platforms were used to access both the outer surface and the underside of the arch to remove and install the steelwork.

Removed old, cracked and damaged boards were carefully and skillfully removed to ensure they would not fall apart during removal. New tie rod plates and tie rods were then fitted and tightened in the correct position. A fresh coat of paint was applied to refresh both the new and existing steelwork.

do you have a story? Send an email to news@theconstructionindex.co.uk

Leave a Reply

Your email address will not be published. Required fields are marked *