The Eastern Union Railway was not the first railway to reach Norwich. It had been beaten to the post by the Eastern Counties Railway Company in 1845. It wasn’t until 1849 that a fast, direct line linking this major East Anglian port with the capital opened. The result of all this may well have been that the Eastern Union did not have first choice of alignment into the city. The Eastern Counties company had slid along the Yare valley for the last few miles and had avoided any major earthworks.
If you look at the alignment of the line from London on the Ordnance Survey map, you can almost see a last minute ‘squiggle’ to get to its destination. After miles of dead straight railway there’s a seemingly illogical sharp left and a sharp right. Perhaps their ideal route had been taken already?
And what do we know of this sharp left and right piece of railway today? It’s in a deep sided cutting at a place now known as Markshall Farm just to the south of the A47 dual carriageway.
Rabbits, lots of them
If this cutting had been a second thought by the line’s builders it might explain why the sides are so steep. Cut out of glacial soils (that’s sand and gravel with subordinate clay bands apparently) they have been a source of irritation to track engineers over the generations. Low- grade landslips have the potential to disrupt traffic and the gradual leaching down of fine soil particles have done for the track drainage. And when the rabbits took up 23 residence and formed their own coney city, the likelihood of the Markshall curve being a major problem became ever more likely. 160 years after it was constructed, it was time to finally sort out the cutting.
Network Rail is required to assess all cuttings and embankments and to rank them in order of risk of failure and the impact on the safe running of trains. Not surprisingly, the Markshall Farm curve was on the list. Despite being some 115 miles from London, this is a commuter line with trains in each direction every 30 minutes. There really are people who get up to catch the 05:30 (or earlier!) and, having invested that amount of energy to rising so early, any disruption due to rabbits is not going to be appreciated.
Work on a solution had been programmed for CP5 but, with the ORR prepared to release funds early to pre-empt any likely disruption, a scheme was assembled to start in CP4.
The site is 600 metres long with access only at one end. Disruptive possessions were out of the question. The line is electrified with 25kV OLE. The combination of all these restraints steered the designers, Byrne Looby Partners – commissioned by main contractor B&M McHugh in conjunction with Aspin Foundations, the company undertaking the work – to specify a solution that involved the minimum of heavy machinery and the use of relatively lightweight equipment that could be manually handled.
The requirement, in very broad terms, was to provide a way of stopping the gradual flow of soil down into the track and to stabilise areas where there had been historic slippages of the cutting slope due to a mixture of the cutting gradient and deteriorating crest drainage. One area needed the loose material to be removed using long reach excavators and replaced with coarse granular. This part of the project did require possessions, but only during no-train periods.
The prevention of the underlying soil movements required some specialist kit, specialist installation techniques and above all specialist knowledge and experience.
After the rabbits had been persuaded to leave and their burrowings demolished, the solution throughout the site was to lay a heavy mesh material over the cutting slope and to anchor it.
The material chosen was Macmat® type R combined erosion matting/mesh and the anchor systems were supplied by Platipus Anchors. It sounds like a short remit, but it’s worth looking at the materials and techniques in more detail.
Firstly the Macmat. This has been used extensively in many countries. It is manufactured by the Maccaferri Industrial group which has its worldwide headquarters in Bolgna, Italy, and was supplied by Maccaferri Ltd – the UK subsidiary.
Maccaferri meshes are three-dimensional structures for the consolidation of natural topsoil for revegetation and erosion control applications. MacMat® R with Steel Mesh Reinforcement has a high voids content and is made from a polyolefin mono-filament matrix, heat-bonded at the contact points with a variable profile and thickness, reinforced by a double-twist steel mesh. This product is an excellent fascia system when used with ground anchors as the integral low-strain steel mesh transfers loads between the anchor load plates. Having an erosion/ root stabilisation mat and reinforcement combined in one product reduces installation time.
Platipus Anchors developed its anchoring system back in the early eighties. Ingeniously simple, the system involves a narrow anchor that is driven into the soil using drive rods, taking with it a wire tendon. When it has been driven to the required depth, the drive rod is removed and the wire tendon tensioned. This tensioning causes the anchor to rotate in the ground, compressing the soil above it.
Over the years, Platipus has developed a wide range of anchoring solutions that are used not only in civil engineering and construction but also in landscape and utility sectors. They perform exceptionally well in granular soils which is why they were an obvious choice for the Markshall Farm site. In addition, the system can be easily installed using conventional hand-held equipment.
Installing such materials and equipment on steep slopes right next to an electrified and high-speed railway requires specialist skills. Aspin, which has extensive railway geotechnical earthworks experience, was able to turn around a fast efficient delivery carrying out the earthworks and installing the Platipus anchors – all with their own IRATA (Industrial Rope Access Trade Association) qualified staff.
At peak activity, Aspin had up 35 operatives working on the site. On average there were four drilling teams installing about 80 anchors a day, although on a number of exceptional days over 100 anchors were placed. In all, 2,919 ground anchors were required – 1,850 type S6 and 597 type S8 anchors were installed at a depth of four metres while a further 472 type S8 were installed at 4.5 metres. All anchors were manufactured in aluminium bronze with stainless steel accessories offering a design life of 120 years. In addition, Platipus supplied temporary anchors to act as abseil points so the Aspin team could access the slope safely.
The anchors and mesh were installed over a 12-week period between February and May 2014. Dubbed “an excellent example of calibration from design, supply and installation”, the project was delivered on time and without delaying East Anglian commuters.
And does it really matter what political and financial shenanigans went on in the 1840s or why there seems to be a squiggle on the main line as it approaches Norwich? For the bleary eyed folks on the 05:30 to London, all this is pretty irrelevant.
Understandably, they’re more concerned with arriving in the Capital on time. By successfully delivering this £2.2 million scheme, the combined efforts of Network Rail, B&M McHugh, Aspin, Maccaferri, Byrne Looby Partners and Platipus Anchors have made sure that they will.