Britain must urgently maintain its Victorian railway tunnels. Traffic, speeds, and loading sizes have all increased. Therefore, these historic structures need reinforcement. Moreover, safety and reliability remain non-negotiable. The Sugar Loaf Tunnel in Mid-Wales highlights both the challenge and the solution.
Tunnel linings continue to deteriorate. As a result, bulging causes gauge loss. Furthermore, water dripping increases rail wear. In winter, icicles form and block tunnels. However, addressing these issues takes time. Maintenance must cover hundreds of tunnels. Still, significant investments aim to extend tunnel life by ten years.
Victorian engineers built tunnels using brick and masonry. Initially, they surveyed routes with ropes and simple telescopes. Then, they constructed shafts—about 2.7m wide—along the alignment. These shafts allowed ground checks and access. Next, timber headings ran from shaft bases to drive the tunnels forward.
Workers excavated in 4m lengths. They timbered the openings, built sidewalls, then completed the brick arch using formers. Consequently, many tunnels developed ‘cold’ joints and open joints. These now let in water and weaken the structure.
In 1868, engineers completed the 900m-long Sugar Loaf Tunnel. They built it along a fault line. However, the northern end had low ground cover and heavy water ingress. By 1992, engineers had to install a 200mm thick concrete lining. But issues persisted. Because of limited possession times, repairs needed to be fast and train-compatible.
The repair team prioritised water control and structure support. Therefore, they adopted a rail tunnel shotcrete approach. They applied 1.5m-wide, 150mm-thick concrete strips at each joint. These acted as support ribs. Additionally, they anchored the ribs with fibreglass rock bolts. Then, they added an ‘egg-box’ plastic drainage layer. This directed water away from the tunnel lining.
Natural Cement’s Shotcrete Products proved essential. Their fast setting and water tolerance met tunnel demands. As a result, the team applied shotcrete efficiently. They used a dry-spray method. Moreover, pre-packaged bags reduced waste and rebound. This approach saved time during short possession windows.
The repair method worked. Engineering tests confirmed a 23% strength increase in the tunnel. First, the crew pressure-washed the lining. Then, they drilled for stainless steel dowel pins. Finally, they sprayed the shotcrete. Natural Cement’s steel fibre-reinforced mix added strength. Importantly, it avoided the complications of traditional steel mesh.
Five years later, inspections showed no deterioration. The tunnel support strips remained intact. Additionally, rail wear had decreased. No icicles formed. Water drainage continued working effectively. As a result, the tunnel stayed dry and safe.
Conclusion
The use of Natural Cement Sprayed Concrete products in maintaining and repairing Victorian railway tunnels like Sugar Loaf Tunnel offers a durable, efficient solution that respects the historical construction methods while ensuring modern safety and reliability standards. As we look to the future, embracing these innovative materials and techniques will be crucial in preserving our railway heritage for generations to come.
For more information on Natural Cement’s range of repair products for the Rail Industry or to arrange a Lunch & Learn CPD session please contact enquiries@naturalcement.co.uk.
Date added: 18/06/2024