A major £8.2m project to protect and strengthen a historic viaduct at Yarm in North Yorkshire is nearing completion.

Network Rail engineers have drilled more than 600 piles deep into the ground to secure the piers of the 43-arch viaduct on the Northallerton to Eaglescliffe line.

When it was built in the Victorian era between 1848 and 1852, the foundations of many piers were built into the bedrock. However, 14 of the foundations were not sunk into the bedrock, and being made from timber, they have deteriorated over time.

Over time, the structure has suffered varying degrees of support along its 690-metre length, which has resulted in slight movements at some points along the viaduct.

In a similar way to subsidence in a building, this can eventually cause structural issues such as cracks to appear.

To prevent cracks appearing, Network Rail worked with its contractor AMCO Giffen to develop a 21st century civil engineering solution to strengthen the 19th century viaduct.

Through the bottom of each pier engineers cut a series of holes through which steel beams were pushed horizontally. Some steel was left poking out and exposed at each end, which was then encased in a block of concrete through which a piles were drilled 13-metres deep.

A video has been released showing the sheer scale of the structure and footage of the strengthening work.

In total, 656 piles attached to the concrete block above were sunk into the bedrock. With the new steel beams encased inside the concrete blocks, the modern and the old are fused together.

As the viaduct is close to residential properties, a practical solution to keep noise and disruption to a minimum was devised to avoid disturbing residents during the 14-month work. A hydraulic solution known as Jack Piling was used to drive the piles as, unlike Hammer Piling, it causes very few vibrations and being much gentler, is also beneficial for the structure itself.

Earlier this year a plaque commemorating the viaduct’s construction was restored, and a £6m project to strengthen a 160-year-old viaduct on the line between Glasgow and Motherwell in Scotland was completed.

“The Victorians did a great job in building this huge structure high over Yarm, but they did not know the same about the geology deep underground as we do today, leading to some of the foundations not being as strong as the others. Without this multi-million-pound investment, eventually it could have affected the stability of the historic viaduct and resulted in lengthy delays to passenger and freight trains. Doing this preventative work all while keeping trains running normally above secures not only the future of the viaduct for our passengers but also its future as a much-loved icon for people in the town”

Jon Calvert, Network Rail portfolio delivery director