Aberdovey Tunnel No. 1 (Frongoch) - Network Rail Tunnel

Network Rail
Engineering Services - Network Rail Design Delivery
June 2020 — December 2023
Services performed
Tunnel visual inspection, ground investigation requirements, site support, rock sample test schedules, input to ground investigation report; development of specialist options for tunnel lining repair and replacement, constructability advice, cost & programming of repair/replacement options.
Frongoch tunnel is 183 meters long and was built in the 1860s. The tunnel is fully lined using slate or brick which appear to have been installed in stages as there are circumferential construction joints. Significant water ingress is present at some locations in the crown and shoulders. The inflow of water has caused damage to the existing tunnel lining and significant gaps in the lining are present.
Dr. Sauer & Partners are supporting NetworkRail Design Delivery in the development of specialist options for the tunnel lining repair or replacement of the Frongoch Tunnel. During the tunnel site visit the team inspected the current state of the tunnel and lining and developed ground investigation and survey work scope requirements.
The British Geological Survey (BGS) data available for this site suggests that bedrock geology consists of mudstones of the Borth Mudstone Formation. The BGS geological mapping indicates that the Borth Mudstone Formation dips at 64° in a south easterly direction at the Frangoch Site.
Frongoch, Aberdyfi, Aberdovey, Wales, UK


  • Slate and brick lined Victorian Rock Railway Tunnel
  • Tunnel refurbishment
  • Ground investigation

Slate Lined Section

Brick Lined Section