Innovative engineering at Eden Brows
Source: RTM Feb/Mar 17
Last year disaster struck the iconic Settle to Carlisle railway line in Cumbria when a 500,000-tonne landslip occurred. Rhiannon Price, project manager for infrastructure projects at Network Rail, gives RTM an update on the innovative technique being used to repair the route.
As RTM went to press, plans to reopen the Settle-Carlisle railway line were gathering apace, with the route expected to be open to passenger services by the end of March.
The line, as readers will recall, has been closed for the last 12 months after the winter storms led to a 500,000-tonne landslip in February 2016, caused by severe erosion of the embankment base near the River Eden.
Due to the complexity of the site, it wasn’t until July last year that Network Rail revealed its innovative £23m piling and slab solution to repair the line at Eden Brows.
Rhiannon Price, who has been involved with the project from the start, told RTM: “We deal with a lot of storm events and emergencies, but we hadn’t seen something as significant as what happened last year at Eden Brows, especially in terms of the location and complications surrounding it.
“We initially anticipated it could be a £4-5m scheme to repair the line, but after we did the initial ground investigations we knew the situation was much more serious, and a more complex solution would be needed for us to get the desired amount of poor spoil out.”
That is why, Price noted, the infrastructure owner pursued a new type of engineering solution, which includes a concrete and steel-tunnel-like structure that will sit beneath the railway, to fix the problem.
Network Rail has taken the approach to drive two rows of high-strength piles, filled with concrete, deep into the bedrock. These piles act as a corridor on which a 1.5m-thick concrete slab is placed. This then forms a solid base for the tracks.
“It is completely innovative,” said Price. “We still haven’t located another place or situation where this has happened. We did do something fairly similar on the same stretch of line to Kirkby several years ago after sink holes appeared, but this was just slabbed [floating] over, and no piles were involved.”
The difference at Eden Brows, she added, was that the team needed to get into the bedrock, which is why piles 18m and 20m-long have been used.
“It needed to be a really stable structure for the slab, not a floating one,” noted Price. “We have installed 208 piles altogether, and we have poured the slab in five different pours.”
Discussing the challenges of such a complex scheme, Price told us one of the toughest aspects of the project was that, for quite some time, people thought that nothing was happening. Work to install the Van Elle piles, for instance, didn’t start until early December.
“We had to get the piles fabricated, which was a long process, and they had to come from abroad,” she said, adding that because the solution was not an ‘off-the-shelf repair job’ it meant the infrastructure owner had to undertake a lot of negotiations before things started happening on the ground.
While the main repair works didn’t start until late 2016, Network Rail was able to do a lot of enabling works during the summer months, removing a lot of spoil, and getting down to the required levels before winter set in.
Then from September through to November, the team carried out extensive stabilising work on the rock face.
“At the start of December we started piling, and it has been 24/7 since then. It has been really intense and heavy going,” said Price. “The piling went as anticipated. We knew it was going to be slow, we knew we were going to struggle to make any extra time up on these works because it is so unique and the piles are so big.”
At the time of our interview with Price, Network Rail was just completing the fourth of its fifth pour for the 100m-long concrete slab. Following this work, the infrastructure owner started to install all the drainage around the slab.
“Then we’ll start installing the track and ballast, but even then we still have a lot to do to get it back into service,” she told RTM. “We have test trains to run and driver training to complete, because it has been closed so long. So even when the track is back there is a lot of work left to do. We have about seven days at the back end of the programme to do all that, and we have 200m of track to relay.”
Once the work on the line, which is due to reopen by the end of March, is complete, the Network Rail team will also be carrying out scour protection work during the summer months.
“This is so that River Eden doesn’t erode any more of the embankment,” said Price. “We will be putting some quite substantial scour protection in. Following on from that, we will install a multitude of drainage throughout that slope. There will be a significant amount of drainage put in place.”
The infrastructure owner is also in discussions to install a monitoring solution at the site.
Discussing this ongoing work, and the lessons learned, Price said: “Eden Brows was quite unique. It wasn’t on anyone’s radar as being a poor site.
“There was minimal slippage a number of years ago, but nothing compared to this nature. But when we’ve done the explorations we’ve found that there was an original failure many, many years ago – over 100 years ago.
“This project highlights the importance of having good local records in place, and making sure we maintain our assets. We’re always aspiring to improve our processes and systems, and we do have this locally, but ultimately we need something that ties everything together. I know that the asset managers are looking at how we do this collectively.”
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