Anyone familiar with Boston in the USA ten years ago may know of the project to put the city’s overhead viaduct road system into tunnels. Known as the ‘Big Dig’, it became notorious because of its late running and huge overspend.

Equally notorious has been the Bluebell Railway’s own Big Dig – to clear Imberhorne cutting of waste and allow the railway to reach East Grinstead. There have been many spectacular achievements in the history of heritage railways but this project must rank as one of the most ambitious ever attempted. Its notoriety did not mirror the Boston problems but the challenges that had to be overcome were equally taxing. The Rail Engineer met with Chris White, the Bluebell infrastructure director, to understand exactly how it had been achieved.

Project history

The line had closed in 1958 but the double track section from East Grinstead to Horsted Keynes was kept on a care and maintenance basis until 1964 and used to store surplus rolling stock. It was lifted soon after and the Imberhorne cutting, just south of East Grinstead, was acquired by the local authorities.

During the late 1960s and early 1970s it was used for the dumping of domestic waste until it was completely full. The cutting is 380 metres long, 18 metres wide at the bottom and around 40 metres wide at the top, and had a maximum depth of 13.5 metres. An estimated 125,000 cubic metres of waste was dumped, protected by clay capping to an average depth of 3 metres. Vegetation soon took over with little evidence that a cutting had once existed.

Meanwhile, the Bluebell Railway had acquired the section of track between Horsted Keynes and Sheffield Park and began running trains in 1960. Even then, a fanciful vision was always to extend northwards to East Grinstead but, in the early days of the preservation movement, no- one quite knew how to go about this, let alone where the finance would come from. Many years were to pass before the ‘Northern Extension Project’, or NEP as it became known, was to progress to planning stage. Eventually the railway was re-instated in stages to Kingscote by 1994 with rails laid to the south cutting face by 2003

Environmental requirements

Planning permission had been granted in 1985 for the Northern Extension but with strict conditions relating to Imberhorne cutting. Condition 7 of the agreement stated that the cutting must be ‘sufficiently cleared of domestic waste to allow the railway to be re-instated’. This wording was to prove fortuitous once work actually started. Other requirements were that the Bluebell had to demonstrate to the Local Authority and the Environment Agency that the work would be carried out safely, not interfere with local residents and that waste must be taken away to an appropriate and registered landfill site.

Environmental requirements loomed large as planning of the actual work took place. Control of odour and prevention of leachate escape (contaminated water in waste) were dominant and this required a survey of all underground and surface waterways to ensure none could or would be polluted. Trial borings in the late 1980s had indicated that only domestic waste was present, officially classified by the EA as municipal solid waste (MSW), and in 2004, following the drilling of more extensive bore holes and detailed analysis, nothing toxic was found.

Waste removal was still going to be a major undertaking and a feasibility study by Atkins in early 2000 explored alternative means of the railway reaching East Grinstead. One idea was to create a diversionary route on adjacent land and another was to create a tunnel. Both would have been much more expensive. Thus the big dig was the only practical way forward and acquiring the right expertise and people would be crucial.

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Atkins became the principal contractor for the design and with its team came environment director David Barry, whose knowledge was to prove invaluable. All the key civil engineering guidance came from former railway engineer Dick Beckwith who is Bluebell’s regular professional advisor.

Also involved was Jonathan Atkinson, the Environment Regulator for the South East, with these experts having the task of supporting the Bluebell and satisfying the Mid Sussex District Council Environment Officer that the project was fit for purpose.

One significant consideration was the cutting ownership as the owner (West Sussex County Council) was liable if things went wrong. Thus ownership had to transfer to the Bluebell Railway who then took on the associated risks. It took five years to get ‘ticks in all the boxes’ but eventually agreement to proceed was given in 2009.

Removal process

Further test bores in 2004 revealed that the south end of the cutting either side of Imberhorne Lane bridge contained only earth and not waste and was thus suitable for use on other engineering projects rather than go to landfill. This saved considerable cost and was dug out by Bluebell staff and volunteers. Transported by rail to Horsted Keynes, it was used to build up the embankment for the future re-instatement of the Ardingly branch to an Atkins design. This was a useful starter and gave visual evidence that things were happening.

A pilot scheme at the north end led to a contract being let to Land and Water of Guildford who took 5-6 weeks to dig out 10 metres of waste. This was very successful but the use of road transport involved extensive infrastructure fixed costs including provision of a weighbridge, a wheel wash facility and the use of banksmen. 10,000 tons over the full cutting width were taken away at a cost of £45 per tonne. A cost review indicated that this method was never going to be affordable.

A decision was then taken that the Bluebell Railway would become the main contractor, employing subcontractors to provide plant and carry out the work. This saved a considerable sum but required the railway to take on all the risk and fulfil CDM (Construction (Design and Management) Regulations 2007) requirements for a construction site including the production of all documentation and the provision of training for the large volunteer workforce which would provide all the on-site support. In parallel, various former senior railway managers were able to facilitate a deal with GB Railfreight to take the waste material out by rail and a contract was arranged with Shanks Waste to unload the waste at the landfill sites. A trial of this arrangement in 2010 showed the cost could be reduced to £24 per tonne and thus it became the chosen method.

The East Grinstead line has weight limitations imposed by the various viaducts along the route so the make up of the spoil train had to be carefully controlled. At midday, a train with 20 wagons would arrive at East Grinstead and, via the access siding, move south to the Bluebell station. Using the newly constructed run-round loop, the train was split in half with 10 wagons being propelled to the loading dock some half a mile southwards.

Once loaded, the 10 wagons would be exchanged for the empty ones, these being loaded in a similar manner. No wagon was permitted to carry more than 70 tons. The train would depart at 21:00 for the land fill site and be unloaded at 02:00 the next day. Once empty, it would return to East Grinstead and thus a daily cycle was created.

Initially the waste went to Stewartby on the Bedford- Bletchley branch and later to Calvert on the erstwhile GC main line. The reason for the change was to accommodate land fill operators licences that permit only so much to be dumped each year and the considerable volumes produced by the Bluebell cutting caused the first site to reach its quota. Superb co-operation was given by both Network Rail and Southern in terms of granting paths and alternative berthing arrangements for EMU stock at East Grinstead.

To dig out the rubbish, the Bluebell employed L&W (Billingshurst) for the provision of plant and operators. Three excavators were supplemented by dumper trucks to take the waste to the loading dock. Every day, the machines would dig longitudinally into the cutting side. Moving the waste around and loading it into the wagons was almost as big a task as the actual digging work. Early on it was realised that the waste material was very stable as it did not contain granular material and had been kept dry by the clay capping.

Smart thinking

The original cutting width was very generous even for a double track railway but, with planning permission only allowing the re- instatement of a single track, the question was asked, did the railway need to dig out the full width? By having slightly steeper gradients on both the north and south approaches, it was possible to reduce the cutting depth from 13.5 to 11 metres. These two factors considerably reduced the amount of waste that had to be removed, hence the importance of Condition 7 in the planning agreement that only sufficient waste need be removed to allow the railway to be reinstated.

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Another critical factor was the Landfill Tax Credit legislation that was to be abolished in April 2012, after which the removal cost would rise to £94 per tonne. A certain focussing of minds resulted and all necessary waste was removed by the due date.

Between April 2012 and March 2013, the remaining waste was re-engineered within the cutting site. Work was due to finish in October 2012 but the appalling weather during the year prevented the planned completion until almost opening day. The cutting sides are profiled to about 60o and are capped in Mypex, a horticultural product that encourages growth of vegetation and prevents any surface material blowing away. On top of this is a geotextile grid that provides the necessary reinforcement and through which the vegetation will grow.

The tops of the cutting are clay capped, it being realised that preventing ingress of water is vital. Good drainage has been installed throughout the Northern Extension, there being seven miles of drains in the two mile section, plus all culverts being repaired. ‘Look after your drains and the rest looks after itself’ being an adage worth remembering.

Costs, opening and ongoing work

Test trains were run for two weeks before the opening on 23 March 2013. Safety verification was undertaken in accordance with the ROGS procedures (The Railways and Other Guided Transport Systems (Safety) Regulations 2006). This demonstrated that the railway had been built in accordance with the design, crew training was performed, a maintenance regime was in place and the whole railway could be operated safely. The opening day duly took place in a snowstorm and patronage of the railway since that time has increased significantly.

A project of this magnitude was never going to be cheap and, for a heritage line, could be viewed as mountainous. Digging out the cutting has cost £1.75 million, the provision of the railway and the new Bluebell station at East Grinstead cost £450,000, repairs to the brick Imberhorne viaduct since 2002 have cost £400,000 and the track from Kingscote through the cutting has worked out at £1,500 per 60’ panel. Although expensive, it is actually less than the original estimate of around £6 million. Reducing the cutting size has been the key factor.

Raising funds to pay for it all has been an inspiration to the heritage movement. The initial share issue produced £700,000, the ‘tenner for the tip’ and ‘fiver for the finish’ initiatives raised £120,000 and there have been some very significant donations by individuals as the work progressed. No grants were received from public bodies other than one from East Grinstead Town Council for some station work, and there has been no borrowing from banks.

The Big Dig project officially closed on 19 July but some rearrangement of soil and waste within the site are continuing. What do they do next? Well, reinstatement of the line to Ardingly is on the cards and other than a bridge replacement, should not pose the same challenge as that of the Big Dig. A station at West Hoathly is a possibility but, with a longer bigger railway, keeping it all in fine fettle could well be the challenge for the next few years.

Particular thanks are extended to the army of Bluebell volunteers who have given hundreds of man hours to support the contractors’ work and without whom, this project could not have happened. In addition to Chris White, mention must be made of Matt Crawford, the infrastructure manager and to the previously named experts who steered the project in the right direction.