Article appeared in the February 2012 edition of Railway Strategies magazine
One of the main challenges for the rail sector is that the state, type and indeed location of its drainage infrastructure can be very unpredictable.
Scattergun growth, the different construction practices of multiple contractors and privatisation have all meant that that railway drainage is far from uniform. The drainage underneath our nation’s railways is frequently in poor condition and structured in unorthodox ways.
Drainage may be located at the side of the track, under the track, or located in the middle of the track. Indeed, we have encountered instances where sections of railway have been built without any drainage infrastructure in place. It is not uncommon for surface water to be drained out into a nearby ditch, and for this only to cause problems when the ditch becomes blocked.
The sometimes inadequate nature of railway drainage has the potential to be calamitous given the great capacity of faulty drains to cause enormous damage to railway infrastructure and consequently cause failings on the network, with the attendant sanctions for railway companies and inconvenience for passengers.
Pipes underneath railways tracks are subject to a great many stresses. In addition to the wear and tear, root ingress and erosion caused by abrasive substances that all drain infrastructure is affected by, they are also put under great pressure by the weight of the trains that pass over them every day.
If the area around the pipes is not structured properly, sufficiently bedded and protected by the ballast materials, then the sheer weight of the overhead trains will cause piping to fracture and collapse. Once this has occurred, the weight of the train going over the track serves to pump the leaking drainage to the surface, much like the weight of a foot on sand pumps seawater to the surface. After it is present at ground level, liquid can do great damage to the track and the surrounding area.
Surface water will quickly cause degeneration of the track, which will require expensive replacement. The moisture will cause electronic mechanisms, such as signals, to trip, meaning signal failure and delays to services.
Repair and replacement
The signs that the drainage underneath a track is in need of specialist attention are usually easy to spot. Visible signs include a pooling on the track bed, sections of track that are damp or an area which repeatedly floods.
Once serious drainage problems have been identified, usually the only option is the repair or replacement of the offending pipe in order to get the track back to full working order.
This work cannot be avoided, but it is understandable that the mention of large scale drainage replacement will send a shiver down the spine of the senior management of rail companies. Any sort of infrastructure replacement will mean cost and disruption on some scale, and the situationis made all the more acute by the fact they are fined £200 pound fine for every minute a train is delayed.
No dig technology
The positive news for the sector is that in our experience 80 per cent of problematic track drainage can be replaced using no-dig techniques. This method, analogous to the keyhole surgery now prevalent in UK medicine, allows us to carry out permanent and watertight localised repair of sewers and drains without having to excavate the area. These can be used on a wide variety of pipes, including pitch fibre, which can often be problematic.
The use of no dig technology has several benefits to the customer. Because no invasive action is required, the risk to assets is enormously reduced and the length of the procedure is drastically shortened. Because no fuel heavy apparatus is required – a carbon output reduction of up to 90 per cent can be achieved, and there is minimal noise, meaning decreased noise pollution near stations or residential areas.
How we do it
The first step is for our operative is to clean the drain or sewer, normally using high pressure water jets. This ensures that the damaged area is not hidden by scale, debris or sludge. We then put a CCTV camera down in order to clearly identify the broken section of drain.
Once the area that must be repaired has been identified, we will then undertake the no-dig repair. The two most common types of no-dig repairs are ‘cured in place pipe’ (CIPP) lining, either for the full length of the sewer or drain, or a part length ‘patch’ repair.
A CIPP lining is a repairing pipe in the form of a flexible tube impregnated with a resin, which is placed and inflated within the original ‘host’ pipe. This then produces a new pipe within the host pipe after the resin cures.
When a pitch fibre pipe has collapsed or become deformed, it can be re-rounded by a special tool which is mechanically drawn through the pipe. As it moves, the tool expands the pipe back into its correct shape. We then use a CIPP liner which is inserted and, using water pressure or air, applied to the inside of the old pipe. This reinstates the original structure of the pipe, and provides a permanent repair.
Where the affected area is more localised, a patch repair, which usually have a projected lifespan of 50 years, is often more appropriate.
The patch, which we prepare on site to match the size of the specific area in question, consists of a glass fibre mat impregnated with resin which has a time delay catalyst. Once the patch is prepared above ground, we wrap it around an inflatable pipe packer which is used to transport the patch from above ground to the affected area in the drain.
Using a CCTV camera to check that everything is properly aligned, we then position the packer within the pipe to ensure that the patch adequately covers and repairs the broken section.
The packer is then inflated with air, which applies pressure against the patch on the pipe wall in order to bond it in place. In this way, the patch is held in position until the resin has cured and it is effectively glued against the wall. Only then is the packer deflated and removed, leaving the patch in place over the damaged section and the pipe back in full working order.
Of course, in some situations, excavation is unavoidable. However, a good drainage engineer will always explore all the available options before suggesting that digging up the area is the only solution.
Perhaps the most important thing to remember is that, just like in medicine, prevention is better than cure, and the sooner a problem is identified and diagnosed, the more likely it is that it can treated without the need for invasive procedures, and costly downtime on our railway network.