Nearly 100 years later, after BR singled the line in 1971 in preparation for the use as a test track, the line between Old Dalby and Upper Broughton was slewed so as to be in the centre of the formation. Although there was vehicle access alongside the line for most of the test track this section was not included as there was little room alongside the track due to further subsidence

Approx 130 years after the first time it occurred and following a prolonged period of heavy rain in June 2007 a further serious bank slip occurred.

The following is based on a technical article by Colin Carr of Balfour Beatty Rail Projects which appeared in the January 2009 edition of the Rail Engineer and describes the extensive repairs necessary to return the track to running order.

Ideal test track

The line was first resurrected by the Research Division of British Rail in 1970 for testing the gas turbine-powered experimental Advanced Passenger Train (APT-E). The curves, cuttings, high embankments and tunnels - plus the fact that line speeds of over 125 mile/h could be achieved, created an ideal set of conditions for a test track, the only high speed one in the UK.

Old Dalby is probably best remembered for a spectacular planned collision in 1984. A remote-controlled class 44 locomotive was used to race down the track and collide with a nuclear container that had been strategically placed across the track. This was a spectacular event, guaranteed to top the YouTube video charts if it were repeated today. The underlying intention was to reassure a nervous public that those potentially lethal nuclear containers, travelling up and down the network could withstand anything that could be thrown at them.

Today the Old Dalby test track is owned by BR (Residuary) Ltd., part of the Department for Transport which, following privatisation of the railways in 1994, took over the remaining functions of the British Railways Board, including the former BR Property Board. After a few years with minimal use by DM&EE and Serco, the lease was re-negotiated in 2000 and transferred to Alstom Transport Limited who upgraded and electrified the line during 2001, specifically to test and commission the Virgin Pendolino trains.

Preparing for new role

After completion of the Pendolino testing at the end of 2005, the line remained hardly used for a couple of years and looked as if it might be closed altogether. Then, in 2007, it was announced that Metronet (now part of London Underground) had taken control of the line for its own future testing of the new subsurface London Underground train fleet. Serco Assurance became the Infrastructure operator. In addition, Balfour Beatty Rail Projects were invited to undertake a dilapidation survey and submit proposals to over £3 million of work needed to bring the site up to the standard required for its new role.

The most pressing requirement was to repair a major bank slip that had occurred about one mile from the village of 0!d Dalby itself, right in the middle of the route. At this point the track was doubled and one line was virtually hanging over the 100m long slip.  As you would expect, the overhead line electrification structures, which run the whole length of the route, were in a very precarious state at this point. The rural environment made access throughout the route very difficult so effective access by rail was critical if all the engineering problems were going to be addressed.

Dangerous kick back

A roadway was constructed across farmer's fields and the first task was to remove the entire length of suspended concrete sleepered track from the site, James Dowle, Balfour Beatty Rail Projects' Project Manager for all the work at Old Dalby, explained that this work was not as simple as it might appear. Special care was needed to ensure that staff were well clear when the rail was cut because of the inevitable kick back caused by the tension in the rail. Disc cutters were set up, the site cleared and the kick back was observed from a safe distance.

James described the weather conditions throughout the contract as being very wet and windy, and the ground conditions became very unstable as well as unpredictable. This manifested itself when they tried to remove the twisted and insecure OLE stanchions overhanging the slip. It proved to be a much bigger challenge than they expected and it was decided that the best method was to bring in two telescopic cranes to remove them safely. Also, as they were removing the debris caused by the slip, a secondary slip was exposed. However, once the stanchions had been successfully removed and the debris cleared, a seven tier gabion wall was constructed. A rock fill base was installed behind the gabion wall and layers of compacted geotextile soil were placed close to the top of the embankment, at a height of more than 10m and covering the 100m length of the slip.

The sub-contract chosen to carry out the civil engineering work was Weldon Plant. James was very appreciative of their efforts. He was particularly pleased with their commitment to getting the job done and their positive response to the many unpredictable challenges emerging every day. Clearly James appreciated their work and application, emphasising the point that they were always proactive in resolving the problems they encountered. They were great team players as well.

Deep seated settlement

A close second to the slip in terms of priority was the requirement to address very difficult ground conditions which had caused a deep seated settlement to the formation. This problem was located about four miles from the slip site, a location where it was thought that access could only be obtained by rail. The engineering solution both for this site and the slip site was designed by Coffey Geotechnics. Their solution was to drive a grid of 60 sheet piles forming three rows and varying in length from 3,6m to 9m. They were designed to form a grid, tied together, providing stability for the formation contained within the grid.

The practical engineering expertise was provided by Aspin Foundations. They have gained a wealth of experience over the years, developing road/rail piling rigs to drive piles alongside track formations for signal gantries and stanchions. Unfortunately, in the past this site has been subjected to all sorts of remedial treatments including grouting - always a nightmare for piling. This was compounded by a very troublesome concrete gantry base and, as a consequence, additional piling equipment had to be employed to do the work and combat the unpredictable ground conditions.

The design was revised and a grid of two rows of piles, 6m and 9m Song, were successfully driven and tied together. Large quantities of rubble, grout and spoil had to be removed, adding a little spice to the challenge.

Four other sites, ranging from 400m to 1000m lengths, were identified for track renewal and an additional 4000m of  track was also refurbished. This involved the removal of BJB fastenings in concrete sleepers and the installation of NTF 1501-type concrete sleepers to accommodate a 3rd and 4th rail. In addition, jointed track needed to be repaired and prepared for hot/cold weather conditions. Required skills of this work were provided by ISS Facility Services.

As we all know, there is no point fettling track unless the drainage and formation is working effectively, so the impressive and very effective Balfour Beatty Drain Train was used to clean culverts and track drains throughout the route. This work was required in areas to re-establish I25 mile/h running over a select length of track, with 60-90 mile/h speeds throughout the rest of the route.

New trains for the Underground

The Old Dalby workshop has been refurbished and the inspection pit removed so that ballasted track with 3rd and 4th rail can be installed. The expectation is that the test track will be used for the next seven years primarily for Bombardier's new  'S' stock trains which are being built/assembled in Derby. From 2010, these will replace the A, C and D stock currently used on the Circle, District, Hammersmith & City and Metropolitan lines. This new stock will contribute to an increase in capacity by more than 40% which will be a welcome relief to many commuters

Environmental matters

James was very pleased with their environmental record on this site.  More than 30,000 tonnes of spoil were removed and recycled some being used by the local farmers in recompense for access. 'Envirosand' was used for the first time, it consists of ground glass that is used as substitute sand for drains and other applications. Kestrels were nesting and care had to be taken not to disturb the feeding chicks. There were also the inevitable badger sets and all that that entails. The slip site was re-seeded using local grass seeds it's all good stuff and they are,  justifiably, applying for a Civil Engineering Environmental Quality Award (CEQUAL) by the ICE and I think that they deserve some recognition for their work in this area.

Proving the reliability of the new trains

Metronet (London Underground) intends to keep the track in its used and worn condition in order to maximise the endurance testing of the new trains. By simulating six months to a year's service in just one month, it will allow the trains' reliability to be fully proven. The facilities at Old Dalby will save many nights of testing for the trains on the Underground. This time can now be used to carry out maintenance work and improve the track, as well as for installing new signalling systems - a critical factor in the overall upgrade of the London Underground system.

Furthermore, if the testing of the trains had been carried out on the Underground, it would have exposed the system to the risk of further breakdowns, causing delays to the start of traffic the next morning. Fortunately, this will not happen as a result of the work that has been completed by Balfour Beatty Rail Projects and it marks the next stage of Old Dalby's determination to play a role in the future of our railway system. It's not going to go away.