The Glasgow Subway, opened in 1896, is the world’s third‑oldest underground railway, after London and Budapest, and consists of two 10 km circular tunnels running in opposite directions. Serving over 40,000 passengers daily, it is currently undergoing a major modernisation programme by SPT covering stations, trains, signalling, and ongoing tunnel lining maintenance and improvements.

  • Client
    Strathclyde Partnership for Transport (SPT)
  • Principal Contractor
    Freyssinet
  • Phase one
    2015 - 2018
The Glasgow Subway comprises of two tunnels: a clockwise Outer Circle and an anti-clockwise Inner Circle, each 10 km long. The form of construction varies depending on soil type, depth below surface and proximity to rivers, and includes brick horseshoe, concrete horseshoe, brick and concrete circular, and cast iron linings.

The scope

The bulk of the repairs were undertaken in the tunnels running between Hillhead and Buchanan Street stations in the city centre, a section that also incorporated Kelvinbridge, St George’s Cross and Cowcaddens stations. Another high‑priority section was located on the south side of Glasgow between Shields Road and Kinning Park. These high‑priority areas totalled 8,019 linear metres of tunnel, and works executed by Freyssinet included:

  • Cleaning of the tunnel lining, track bed, cess and drainage channels.
  • Investigation and assessment of the condition of the tunnel lining, including removal of steel drip sheets.
  • Recording of inspection data using the ScanPrint tablet‑based data management tool.
  • Probe hole investigations to determine tunnel lining thickness and the presence and extent of voids behind the lining, involving approximately 5,500 probe holes of 50 mm diameter.
  • Design of the required repairs.
  • Annulus grouting using cement grout, requiring approximately 3,000 m³ of grout and around 46,000 injection holes of 32 mm diameter.
  • Convergence monitoring between five reference points around the tunnel circumference to confirm that no unexpected movement of the lining occurred during critical works.
  • Concrete lining repairs comprising hand‑placed concrete patch repairs and up to 2,700 m² of sprayed concrete repairs.
  • Brickwork lining repairs including brick replacement, stainless steel pinning, and up to 1,600 m² of repointing.
  • Resin injection leak sealing to brick and concrete linings, requiring an estimated 17,000 injection holes and 9,000 litres of resin.
  • Installation of weep pipes to manage water ingress.
  • Re‑caulking of cast iron joints.
  • Track bed repairs to seal cracks and prevent the ingress of water and silts.

Additional works were carried out in the medium‑priority areas, which totalled 6,672 linear metres. These works included cleaning of the tunnel lining followed by investigation and assessment of its condition to inform the prioritisation of future phases.

SPT sought to avoid a full‑scale shutdown of the subway and elected to carry out the works during night‑time closures between 00:30 and 05:00 over a two‑year period. The workforce averaged around 80 personnel, with peak operations involving up to 130 people working within the tunnels.