National Highways video info reads:

Were using the same cosmic ray technology used to find hidden chambers in the Great Pyramid at Giza to help unlock the secrets of a 100-year-old historic railway tunnel, located deep under the streets of Glasgow.

Balgray Tunnel is just one of 3,100 former railway structures maintained by National Highways Historical Railways Estate (HRE) on behalf of owners, the Department for Transport.

Constructed in 1896 and curving for 640 metres under the busy West End area of the city in Kelvinside the disused tunnel has been closed to the public since 1964.

Until now we've used ground penetrating radar to gather information about our structures. A novel process, muon imaging harnesses cosmic rays from space to create powerful x-ray like images, to search for potential defects and voids without having to be in physical contact with the tunnels walls and ceiling.

Working with our partner, 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 a HRE tunnel.

The work will help our partner develop their technology and improve their methodology for locating blind shafts.

Full story at:

https://nationalhighways.co.uk/our-work/historical-railways-estate/historical-railways-estate-project-profiles/project-profile-balgray-tunnel/