This disused railway tunnel is now a popular trail for pedestrians and cyclists, forming part of the Strawberry Line route in Somerset. Failure of the existing simple plastic mesh installed to the roof of the tunnel was allowing debris to fall from the tunnel crown, presenting a significant risk to users. Further areas of unstable rock were also identified in the tunnel portal approach cuttings, creating additional risks even before entering the tunnel.
Main contractor Kier won the contract to install a new water main through the tunnel, with their package of works including a requirement to address the rockfall issues. CAN were brought in as the geotechnical specialist to provide a design and build solution and worked with design consultancy Jubb to develop the solution.
The developed approach combined rock bolts, rock netting and catch fences across the site. De-vegetation and scaling loose rock from the approach cutting slopes took place first, followed by installation of Geobrugg 100KJ rock catch fences to intercept rock fall from the portal headwalls. With the access routes made safe, work commenced in the tunnel itself, with 110 rock bolts drilled upwards into the roof using an excavator mounted drill rig. Deltax rock netting was then installed, secured by the rock bolts and acting to contain any loose rock in future.
With all the work taking place at height in difficult to reach locations, a combined approach was required to access the various work areas. The steep rock faces around the tunnel portals required the use of industrial rope access technique, with mobile elevated work platforms used to assist installing the catch fences and to access the roof inside the tunnel. Completion of this important work means that this route can remain open and safe for public use for many more years to come.
Duration: 9 weeks
Location: Winscombe, North Somerset