Major work to protect and strengthen Teesside’s historic Yarm Viaduct for passengers and freight is nearly complete.

Network Rail is securing the Grade II listed structure’s supports – known as piers – by drilling more than 600 piles deep into the ground.

The £8.2m investment into the 43-arch Victorian viaduct on the Northallerton to Eaglescliffe line will make future journeys more reliable for passengers and freight.

When Yarm Viaduct was built between 1848 and 1852, the foundations of many of its piers were built into the bedrock.

However, 14 were not. And with some of the foundations being made from timber, they have deteriorated over time.

With varying degrees of support across the structure, it has caused slight movements at some points along the 690-metre-long viaduct.

Just like subsidence in a building, eventually this can lead to structural issues, such as cracks appearing.

To prevent that from happening, and from potentially significant delays to trains in future, Network Rail and its contractor AMCO Giffen have found a 21st century civil engineering solution to strengthen the 19th century railway icon.

A series of holes were cut through the bottom of each pier inside which steel beams were pushed horizontally, leaving some steel poking out at each end.

The steel left on show was then encased in a block of concrete, and down through each block a series of piles were then drilled 13-metres deep.

A total of 656 piles - which act like massive nails - were fixed into the bedrock underground.

As they're attached to the concrete block above, with the new steel beams encased inside which go through the base of each of the viaduct's piers - the modern and the old are fused together.

Jon Calvert, Network Rail portfolio delivery director, said: “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.”

Rob Cox, TransPennine Express operations director, added: “The Yarm Viaduct is a crucial part of our network and I’d like to thank our colleagues at Network Rail and fellow train operators for their support and hard work throughout this project.

“The work to this historic structure will mean we can keep passengers on the move in the future.”

The 172-year-old structure carries trains overhead for practically the whole length of the town, but it is nestled in between Yarm’s narrow terraces so the viaduct’s scale isn’t ever entirely seen from street level.

Being so close to properties meant the team had to come up with a practical solution to avoid disturbing residents over the 14-month programme.

To keep noise and disruption to a minimum, a driven piling method powered by hydraulics was adopted, otherwise known as ‘Jack piling’, which hardly makes any vibrations - unlike hammer piling.

This vastly reduces the noise but is also beneficial for the structure itself – being much gentler for the Victorian viaduct.

This work completes in the same year as Railway 200, marking the bi-centenary of the invention of the first passenger railway between Darlington and Stockton in September 1825.