Dinmore tunnel is actually two railway tunnels located on the former Shrewsbury to Hereford line between Hereford and Leominster. The tunnels are split level with the track on the Up line to Leominster being higher than the Down line to Hereford. The Up tunnel was built in 1853 and the Down tunnel in 1891. Both tunnels are approximately 1,000 metres long. The line speed through the tunnels is 80mph.

Maintaining track

It would be difficult to think of a more challenging location for Network Rail engineers to carry out maintenance than in a long single bore tunnel. If the drains are clogged up, the formation saturated, the ballast riddled with pumping red clay and there is nowhere to move the CWR or the concrete sleepers, there are not many options. They could spend the next twelve months hand-digging the contaminated ballast out but it would be tedious work, progress would be slow, temporary speed restriction would be necessary for long periods of time and it would be expensive.

A Kirow Crane could lift sections of track out in front of itself and then diggers could remove the contaminated ballast, but how would they get the ballast out of the tunnel? They might have to consider welding rail (in a tunnel) and then possibly destressing the track. It all gets very complicated, expensive and, whatever method was chosen, the effect on the train service would be detrimental to say the least. Worst of all, it is quite probable that the drainage system through the tunnel, often the root cause, will still remain ineffective.UK Ra2 4 cropped [online]

Newly-designed RailVac

Ian Harris, Network Rail’s assistant track maintenance engineer, Hereford, was the man with just this problem. The track formation within the Down tunnel was suffering from poor drainage and contaminated track ballast which was making it very difficult to maintain the track within acceptable parameters for the line speed specified.

To address these problems, Network Rail decided to utilise a RailVac machine owned by Railcare, Sweden. This machine gained product approval just over twelve months ago and it is a development of a Swedish UIC model which has been used in this country since 2006. However, that machine had to be transported by road because it did not comply with the UK structure gauge.

Railcare, working in partnership with Bridgeway Consulting, successfully steered the newly-designed machine through Network Rail’s robust product approval process. It is now classed as a flat wagon when forming part of an engineer’s train so can travel at up to 100km/hr. When working independently within a possession it will travel at a maximum of 16km/hr. Steve Mugglestone is Railcare’s project manager responsible for the RailVac, its performance, productivity and future workload. He explained the scope of work that Network Rail wanted carried out during a 48-hour possession.

The work included the excavation and re-ballasting of approximately 200 metres of plain line situated in three separate areas, to clear the channel drain and remove the contaminated ballast shoulder throughout the length of the tunnel. Steve explained that a road-rail vehicle (RRV) fitted with a clamshell bucket, located at the south portal of the Down tunnel, loaded ballast that had previously been stock piled in the cess onto a road-rail dumper. This was fitted with a conveyor belt that could offload ballast across the formation, in front of the dumper. It is a simple but very useful item of plant supplied by A P Webb Plant Hire Ltd.

At the north portal of the tunnel was another RRV, also fitted with a clamshell bucket. Its role was to manage the excavated material, dropped off by the RailVac after working in the tunnel. When all the work in the tunnel is completed the RRV would then load the material into empty wagons to be taken away.

The RailVac itself was brought to site as part of an engineering train, along with the wagons. They were detached ready for work whilst the train completed a run round so that it was in position to pick up the RailVac and wagons at the end of the possession. So when all movements of the machines and train have been completed the engineering supervisor gave permission for the RailVac machine to commence work.

The ‘Manipulator’

The RailVac is similar in size to a tamper. It has an engine, cab, generators, pumps and valves designed to create the required vacuum and suction as well as two hoppers, all neatly designed and packed away. Then you notice the vacuum machine ‘Manipulator’ which has a long 250mm diameter flexible tube with two metres of hardened steel nozzle at its end. It is a bit like an elephant’s trunk and its function is very similar in that it sucks up anything that is within 50mm of the nozzle end. Nothing gets missed, especially life-expired ballast contaminated with wet pumping clay from the formation.

The RailVac has all the necessary requirements for safe working – cameras, lights and electric sensor beams that can stop the machine if it is moving too close to another object. It can move in either direction but is planned to reverse away from the excavated track with the operator standing at the cab end of the machine where it is possible to control the movements of the vacuum manipulator by means of a ‘remote control box’. This is clearly a skilled activity, preferably performed by a person who has gained considerable experience using game machine controls. Certainly the operator in control at Dinmore was very adept, ensuring that everything from around and under the sleeper was sucked up by the Manipulator down to a depth of between 250 and 300mm below sleeper bottom.

Loading fresh ballast outside the tunnel portals (Collin Carr) [online]

Depending on the condition of the ballast being removed, the machine will work for about 1.5 hrs sucking up about 18 cubic metres of spent ballast and clearing about 15m of track and shoulder. Try doing that with a shovel! There are two operators who share the task of operating the control box. The debris is sucked into the hopper positioned in the middle of the machine. The RailVac then travels out of the tunnel, the hydraulic hopper doors open, deflector plates are extended out below the hoppers and vibration helps the spent ballast to be discharged for the RRV to deal with.

Although the machine moves at a very slow pace an exclusion zone of six metres is set up and maintained around the machine as it works. The only personnel working in the immediate area of the machine are the operator, the machine controller and technical personnel. However, because of the nature of the work, usually two additional track workers follow the machine with rakes to ensure that all the debris is sucked up. If necessary the machine stops to enable this work to be done safely. It is a tight operation with only 5/6 additional support staff needed. Steve uses people who are now familiar with the process, supplied by Quantum Construction Leeds.

Ballast vibrators

To ensure that line and level of the track is maintained, Duff jacks are placed between the RailVac and the ballast discharging dumper which is distributing the ballast from its conveyor belt in 100mm layers across the excavated formation. The ballast is then vibrated using handheld Robel tamping machines that are similar in size to Kango packers and are designed to vibrate rather than compact the ballast. They only recently started to use these machines but, so far, they are very pleased with their performance.

Once the heavy excavation work is complete, the RailVac removes the ballast covering the drainage troughing lids which are then manually removed so the machine can suck out all the debris. It’s a simple job with the RailVac but it is often the critical job that does not get done when other methods of repair are used. When all the work is complete and the site cleared, a tamper runs through the tunnel to ensure line and level are within tolerances, ready to receive the first train at the end of the possession. A TSR of 50/30mph is applied initially then raised to 80mph the following week after a further tamp.

As Steve explained, the beauty of this process is that at the end of the shift you have a clean, tidy site and the track is fit for purpose. They have never overrun a possession with this or the previous machine. No cables need to be disconnected so there is no signalling involvement and, if need be, they could hand back a possession at short notice. The process is ideal for all those locations, such as S&C layouts and underbridges, which are most difficult to maintain. Certainly Ian said he was very pleased with the work that they were doing.

A few more of these machines may be seen around the network in the future. For maintenance engineers with a problem that possibly keeps them awake at night, they might want to try the RailVac. Suck it and see!