National Highways harnesses cosmic rays to inspect abandoned Scottish rail tunnel | So Good News

Using a new process called muon imaging, which harnesses cosmic rays to create X-ray-like images, National Highways hopes to reveal defects and voids in the Balgray Tunnel without having to be in physical contact with the tunnel walls and ceiling.

Traditionally, National Highways inspections use techniques such as ground-penetrating radar, drilling and visual inspections to look for hidden shafts and highlight potential problems.

Built in 1896, the Balgray Tunnel curves 640 meters below the Kelvinside area of ​​Glasgow, and although it has been closed since 1964, it still needs regular inspections to ensure it remains safe and in good working order.

National Highways is charged with maintaining the structure on behalf of the Department for Transport (DfT), as part of the Historical Railways Estate (HRE) programme.

Geoptic has adapted the muon process for use in railway tunnels and the Balgray survey is the first time the technology has been used on an HRE tunnel. If deemed a success, it could be applied to more HRE structures.

National Highways manager of the Historical Railway Estate program Helene Rossiter said: “Ensuring that all our structures remain safe and in good condition is our priority and we are very keen to see the results of this unique technique and evaluate how it can help us to carry out some of our tunnel surveys more efficiently in the future.

“Inspections of all our historic rail tunnels are a key part of the maintenance routine and if the Balgray Tunnel trial is successful, we may look to use the technology in other tunnel investigations in HRE.”

What is Muon Tomography?

Muon tomography relies on cosmic rays, which are high-energy particles produced by the Sun and other astronomical sources that hurtle through space at near the speed of light. When they enter the Earth’s atmosphere, they collide with the oxygen and nitrogen molecules that trigger a cascade of other particles. Most of these particles are stopped in the atmosphere, but muon particles reach the ground.

A muon is 200 times heavier than an electron, and its weight and speed give it an advantage over X-rays in penetrating dense materials. At sea level, around 10,000 muons pass through every square meter of ground every minute, and these can be used to image the interior of large technical infrastructure.

Muon detector takes measurements from the back of a truck moving slowly through the tunnel.

Muons can penetrate hundreds of meters through materials such as brick, stone and concrete.

In 2017, the technology was used to map the Great Pyramid of Giza, leading to the discovery of secret chambers and rooms untouched by human hands since the pyramid was built over 4,500 years ago.

Muon tomography has also been used to search for magma chambers inside active volcanoes and image the Fukushima nuclear reactors.

Geoptic technical director Lee Thompson added: “Geoptic is delighted to be working with National Highways to provide the first HRE muon tunneling survey and we hope this is a collaboration we will be able to continue in the future.

“Before the survey began, we needed to develop a digital twin of the tunnel using detailed geological data that informs us how many muons we expect to see at any given time in the tunnel. Then, inside the tunnel, we use our instruments that detect muons to measure the number of muons at different points.

“Differences between what we expect to see and what we actually observe can be interpreted as differences in density in the structure of the tunnel compared to what we assumed in our digital twin. In addition to identifying hidden voids and shafts, our instruments can return valuable information about the shaft’s position, size and scope.”

The HRE is managed by National Highways on behalf of the DfT and comprises 3,100 bridges, tunnels and viaducts, including 77 listed structures.

National Highways has been criticized for its management of the structures in recent years with engineers expressing “shame” on their profession after the infill at Great Musgrave Bridge in Cumbria in 2021.

National Highways has since been ordered to remove the infill by the local authority. It has also developed a new way of assessing historic structures following an intervention by the DfT.

Earlier this month, campaigners questioned the legality of a further four bridge fillings carried out by National Highways between January 2019 and May 2021.

Jacobs acts as “sole supplier” (designer) for the Historical Railways Estate with six contractors supporting Jacobs in carrying out any work, including Dyer & Butler and Balfour Beatty.

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