Let’s give full credit to the designers and builders of the Settle and Carlisle railway. Having set out to construct a line it didn’t really want, the Midland Railway Company didn’t hold back. Everyone is familiar with the spectacular result – a railway that is justly famous for its viaducts, tunnels and grandiose wild scenery.
So proud and confident were the Midland Railway directors of their new line that they boasted it would endure for a thousand years. Built largely by muscle power, the quality of this Victorian engineering marvel was, and still is, truly outstanding.
…or might there have been a few bodge jobs along the way?
That’s probably an unfair question, and we probably shouldn’t criticise, but, in the line’s 140-year history, there have been some ongoing problems. Excepting the inevitable viaduct, bridge and tunnel repairs, the problems have been with landslips, formation sinking, and at least one cutting that should perhaps have been a tunnel. Now a location, never before much heard of, has gained notoriety – Eden Brows.
On the night of 6 December 2015, Storm Desmond did its worst. The flooding and devastation in the north of England, and especially in Cumbria, were unprecedented. It followed three days of torrential rain that had fallen onto already saturated land. Many rivers reached record levels, overtopping defences, swamping towns and villages and washing out bridges.
On the Settle and Carlisle, things didn’t seem too bad at first. Heavy rainfall in Cumbria is nothing new, after all, but this was to turn out to be something rather different.
Eight miles south of Carlisle, the railway passes through a steep wooded gorge near to the Eden Brows estate. Some 200 feet above the River Eden, the railway runs along a ledge cut into the valley side – or at least it seemed that way. Down at the base of the slope, the flooded river, by now well out of its normal channel, was busy eroding material with great effectiveness. The result, widely reported, was a slow-moving land slippage triggered by the unloading of the embankment foot. The entire hillside was on the move, and with it the Settle and Carlisle railway!
It soon became clear that the ledge, rather than being cut into the hillside, had been built up using material excavated from nearby cuttings and tunnels. Even as the line was being built, there were landslip problems here.
A contemporary account reported: “Shortly after we began to tip, a landslip took place and the whole ground – some five acres – began to move. The ground between the line and the river blew up, on account of being unable to resist the pressure of the embankment; and the whole thing slid down towards the water.”
The Midland Railway engineers, led by John Crossley, had considered a tunnel further to the west, but this was deemed impractical. It was only after a ‘massive drainage scheme’ was instigated that tipping to form a ledge could recommence. It involved sinking vertical shafts with deep drains connecting them. These shafts were afterwards filled with rocks and, as well as providing drainage, were intended to act as a ‘friction bed’ to prevent further land movement. Both the drainage scheme and the built-up ledge have given trouble ever since.
On Tuesday 9 February, Network Rail closed the Carlisle to Appleby section. Subsequent periods of heavy rainfall had only added to the problems. Ongoing ground and aerial drone surveys showed that, in the two months since Storm Desmond, the railway formation had dropped by 1.5 metres due to a rotational slump.
The ledge, and indeed the entire hillside, initially estimated at 500,000 tonnes of material, was still on the move. Subsequent borehole testing has shown that figure to be an underestimate, with the area of land involved measuring approximately 150 metres by 70 metres.
Network Rail was quick to announce that the problem would be repaired and Story Contracting was employed to undertake investigative and preparatory work. The location is remote and difficult to reach, so Story’s work would include the construction of a large compound, tree clearance and the laying of extensive access roadways.
On 7 July, Network Rail announced that the Settle and Carlisle railway would be fully reopened by the end of March 2017, following the construction at Eden Brows of a massive steel and concrete structure to support the tracks. Story Contracting has been appointed to undertake the work. This £23 million engineering solution was one of six that were considered. Other options included:
- Significantly moving the course of the Settleand Carlisle railway;
- A less major alteration to the course of therailway;
- Building a bridge;
- Digging out the entire gorge embankmentand filling it with solid material;
- Ground works involving multiple criss-crossing rock-anchored supports.
The structure to be built will be almost completely buried. It will comprise two rows of contiguous bored piles supporting a one metre thick by 75-metre long concrete slab. Upon this the new track formation, three metres thick, will rest.
It is thought that 230 piles will be required, with approximately 130 of these on the failure (river) side and 100 on the cutting (rear) side. The piles themselves will be mainly 660mm in diameter and formed of reinforced concrete protected by steel outer casings. The reinforcement will comprise seven B40 bars with 16mm shear reinforcement.
All piles are to be sunk into the bedrock, with rock sockets being used to form a stable base. The piling depth will vary across the site. On the cutting side, the overall depth will typically be 18 metres, of which about 5.5 metres will be drilled into the bedrock. On the failure side, the overall depth will be about 20 metres, with 7.5 metres encased in the bedrock. They are to be installed at 750mm centres.
Installation of the piles, using an air-drilled system, is subcontracted to Van Elle. The piling work is made slightly more difficult by the presence of two fault lines that pass through the work site at right angles to the railway. There are differences in the bedrock material on each side of these fault lines. Extensive ground investigation works have been undertaken by Central Alliance, Geotechnical Engineering and others to build up a profile of the embankment and the geology beneath it. This has involved the drilling of many 30-metre deep boreholes.
Story Contracting has divided the works programme into nine phases. The first of these has involved the construction of access ramps to bring the piling rigs onto site. This has been followed by the installation of temporary piles (steel tubes filled with concrete) to provide a stable platform for the piling rigs.
Meanwhile, spoil trains have assisted in removing the old track bed. The piling work will take place four metres below rail level, which has required approximately 16,500 tonnes of material to be removed. Transportation of the spoil by rail has also ensured positive relations with the nearby village communities of Armathwaite and Cumwhinton. Another added bonus is that the unloading of the embankment has helped to stabilise the slippage.
The first row of continuous piles is being installed along the cutting side of the site. After this, piling work will continue with the second row. The concrete slab, which incorporates a three-metre-high ballast retention wall along its front face, will be laid over the piles to form the structure. A layer of compacted aggregate three metres thick will cover the slab and then, finally, the ballast and tracks will be laid.
Phase eight involves driver training prior to the re-opening of the shut section of line and the final phase will involve follow-up works, landscaping and restoration of the surrounding woodland areas. Once the railway is reopened, Network Rail plans to carry out earthworks improvements to the foot of the embankment below the line and above the River Eden. This is an additional £5 million scheme that includes the installation of rock fill and an elaborate drainage scheme. Rock armour will be added to prevent any further river erosion and a programme of tree planting will help to stabilise the land.
As the work progresses, a close eye is being kept on the land movement by means of aerial surveys and ground monitoring. Through liaison with Leica Geosystems and design consultant Aecom, the latter is achieved by means of continuous automated laser scanning that is linked to a sophisticated alarm system.
Environmental issues have been very much to the fore. The area surrounding the work site includes ancient woodland and there is a Site of Special Scientific Interest at the foot of the embankment. In addition, badger setts within the woods are protected by 10-metre radius exclusion zones.
Both Network Rail and Story Contracting have worked closely with Natural England on these matters and continual monitoring takes place. Natural England will also advise on the tree replanting.
Whilst the line is closed, Network Rail has made use of this opportunity to bring forward other works on the line already planned for CP5. The installation by Babcock Rail of new level crossing barriers, wig-wags, fencing and road surfacing has been undertaken at Culgaith Crossing and at Low House Crossing. Meanwhile, just a few miles from Eden Brows in the Baron Wood area, J. Murphy & Sons has also been busy. Here the River Eden also cuts close to the railway in a situation not dissimilar to that at Eden Brows. The events further down the line dictated that preventive action be taken at Baron Wood.
For passengers, freight operators and supporters of the much-loved Settle and Carlisle, the reopening can’t come too soon. Martin Frobisher, Network Rail’s route managing director, said: “This is a vital rail link across the north of England and I am very aware of how important the railway is to the local community and local economy. I can assure everyone that we are doing all we can to design a lasting solution and to reopen the railway as quickly as possible.”
It’s generally agreed, however, that, after these and other repairs are completed, the Settle and Carlisle railway will be in probably its best-ever condition. It should be good for at least another century. That’s still rather short of the Midland’s proud thousand-year boast, but things could have been worse. Crossley’s solution was problematic, but it did last for 140 years. He would surely have been impressed by today’s engineering solution.
Rail Engineer will be revisiting this project as the work progresses.
Written by Stuart Marsh