Network Rail engineers have designed an innovative repair solution to fix an underground tunnel in Liverpool city centre.
Although city dwellers wouldn’t have noticed anything engineers have been working very hard for the last 6 months on a £3.5m project. The project involves strengthening and waterproofing the ceiling of High Neck Tunnel between Liverpool Central and Brunswick stations. The 130 year old tunnel needed upgrading in order to repair and fix leaks and loose Victorian Brickwork. This will enable more reliable rail services between Southport and Hunts Cross.
Before spraying the roof with concrete a steel ‘ram-arch’ tension system was installed to strengthen the tunnel roof for the next 100 years.
Engineers from Network Rail came up with this unique solution by using computer aided design (CAD) technology. The engineers also used specialist LiDAR laser surveying technologies to create a 3D computer model which mapped out every inch of the tunnel’s interior. The technology was so good that it captured every uneven lump and brick of loose stonework. Scaffolding teams were then able to build a massive temporary platform which was referred to as “the dance floor,” so that they were able to work safely above the tracks whilst trains passed underneath as normal.
In numbers the work involves:
- Installing 100t of scaffolding over 125m
- Securing 5t of ‘ram-arch’ steel mesh to existing brickwork
- 2,500 bolts connecting the arch reinforcements
- Spraying 820m2 of concrete (240m3 volume)
- When set, the concrete will weigh approximately 575t
- From track to the arch peak High Neck tunnel is 15m high
Network Rail works delivery supervisor Helen Little said: “In the past some previous repairs to High Neck Tunnel caused major disruption because accessing the tunnel ceiling is so difficult and the railway needed to be closed entirely. Building on similar repairs in 2017 – it was our priority this time to once again make sure we didn’t disrupt present day journeys while we fixed the structure for the future.
“It’s been great to train up to install the ‘ram-arch’ system ourselves and the team now has the skills to take this on to further work within Network Rail and save taxpayers’ money. The CAD also improved efficiency because it’s enabled us to plan the project right down to the last bolt – minimising materials being wasted.”
All the while Merseyrail passengers have been blissfully unaware that above their heads this major engineering project has been underway since March.
Merseyrail chief operating officer Zoe Hands said: “We are pleased to work with our partners at Network Rail as they utilise cutting edge technology to ensure vital work on our network can be undertaken without impacting on the service we offer to our passengers. We hope to see more works of this nature undertaken in this way going forward, so that we can continue to offer the best possible train service to the people of the Liverpool City Region.”
The final phase of the project, where concrete is sprayed into the reinforced metalwork, starts this month with the underground upgrades expected to finish by the end of 2022.
This will complete work started in 2017 and will mean the entire length of the 125m long tunnel has a reinforced concrete roof needing minimal to no maintenance for decades to come.
Image Credit New Civil Engineer