HEAVY-HAUL railways are generally built to serve areas with high concentrations of mineral deposits, which tend to be in some of the hardest to reach, most inhospitable areas of the world. Railways that travel through this difficult terrain, where temperatures can vary between 40oC and -40oC and tonnage transported can exceed 200 MGT/annum, require a rail fastening that is able to meet these challenging conditions.
Many heavy-haul railways are also having to cope with increasing tonnage as commodity prices and world volumes recover from the low of a few years ago. A lot of heavy-haul railways were constructed at a time when demand for minerals was much less than it is today and were therefore not designed for the volume of traffic they are currently carrying. In the United States, for example, the heavy haul freight network uses alignments that were set out in the 19th century and some lines still have wooden sleepers and cut spike and anchor rail fastenings.
The growth in tonnage on some railways has resulted in premature deterioration of the track geometry and issues with the fastenings, particularly if these were originally specified incorrectly.
In these situations, which by their very nature are in remote, difficult-to-reach locations, a fastening system is needed that requires minimum intervention and will perform reliably over the long term.
It is not unusual for a heavy-haul railway to carry 200 million tonnes per annum, compared with around 20 million tonnes per annum on conventional lines. Even on heavy-haul railways, the actual tonnage shipped far exceeds that which the track systems were originally designed for, which places increased stress on the rails, fastenings and sleepers. With this much greater tonnage, maintenance or replacement of fastenings is required much more frequently than on conventional lines. When replacing an existing fastening system it is therefore important to identify a low-maintenance solution that can withstand the rigours of modern heavy-haul traffic.
When it comes to heavy-haul fastenings, the cost of maintenance and replacement is low compared with the cost of labour and track possessions. Most heavy-haul operators plan to replace small track components only when other maintenance work, such as re-railing, is being carried out. Considerable savings can therefore be made by ensuring the life of fastening components exceeds that of the rail. This, however, becomes more challenging as rail lifespans and tonnage carried increase. For example, the major US heavy-haul railways now expect rail in tangent track to withstand 3 billion tonnes of traffic before replacement. This means the net savings from investing in durable fastening components can soon be recouped.
High traction forces can cause longitudinal track stresses and therefore affect the specification. On conventional railways, once track has been designed to cope with forces due to thermal expansion and contraction, the maximum expected braking forces will then by default be strong enough to withstand the applied traction forces. However, in heavy-haul applications with higher traction forces, this can induce track failure. This first manifests itself in the uneven movement of sleepers, which become skewed and displaced relative to the rails and the ballast.
The solution to this problem lies in designing, constructing and maintaining a high-quality track bed and by paying special attention to the specification of rail fastenings with appropriate longitudinal shear elasticity. Tests on different types of rail pad have demonstrated quite different performance in terms of mitigating the effects of high traction forces.
The third factor affecting fastening specification results from the fact that most heavy-haul railways are planned by mining companies rather than established railway operators. The railway therefore becomes part of the mining project because it is the most economical and reliable way to move bulk commodities from source to consumer. In most cases, the design, build and even operation of the railway is put out to competitive tender in the same way as any other capital investment.
This should require a heavy-haul track technical performance specification, however there is no established technical standard that takes into account the kind of factors that affect heavy-haul railways. In practice, simply adopting technical specifications from one railway and applying them to another in a different part of the world is rarely sufficient. The heavy-haul industry does have a strong record of sharing technical knowledge through organisations such as the International Heavy-Haul Association (IHHA), which has helped to develop best practice which can be exported to new and more challenging projects which in turn is helping to shape the fastener specification.
The location of heavy haul railways in extremely harsh climates can present a challenge to the materials being used in rail fastening systems. Steel and concrete function well in extremes of climate, but for other materials, such as plastics, this can prove a challenge. Plastics are widely used within the rail fastening system to provide electrical insulation, resilience and sometimes sacrificial wear elements.
Working in inhospitable climates also poses challenges for track workers. A great deal of manual labour is still involved in track construction and maintenance, so there is a drive towards introducing more automation and extending maintenance intervals.
Reverse rail cant
One heavy-haul railway which has helped to shape the specification of heavy-haul sleeper plates was the US Class 1 railway Norfolk Southern (NS). For this project, Pandrol worked with NS to pioneer the development of a standard asymmetrical 18-inch sleeper plate in locations where reverse rail cant was an issue. NS uses timber sleepers, but all the sleeper plates available at the time with elastic fasteners had a small footprint. The challenge was driven by higher locomotive horsepower, dynamic braking, increasing freight traffic, larger rail sections and sleeper strength variation, which when combined meant a new specification was needed for a heavy-haul sleeper plate design.
The most critical specifications were maximum bearing area contact with the sleeper, increased bearing area contact with the sleeper, increased bearing area asymmetry toward the field side, a clip housing centred on the sleeper plate, space for four screw spikes and two cut spikes and ultimately financial savings over a cast plate.
We introduced the Victor plate, which had the same footprint as a standard asymmetrical 18-inch Arema sleeper plate and incorporated a cast swaged-in shoulder that used a standard Pandrol e-clip to secure the rail to the plate. The Victor plate is designed to accommodate high axleloads on wooden sleepers.
The location selected was in a 290m-radius curve on a 0.09% gradient with 90mm of superelevation, which was used mainly by coal trains carrying around 40 MGT annually. Cut spikes were used to secure the plate to the sleepers as NS is primarily a cut-spike railway. The Victor plate was monitored and found to perform well with respect to reduced sleeper plate cutting and gauge widening, which lowered maintenance requirements for this curve.
Victor sleeper plates maximise the bearing area, while the use of Pandrol resilient fasteners with their good holding power help to prevent rail rollover and reduce maintenance.
NS has also specified the use of Victor plates with screw spikes for bridge applications and to date NS has installed over 3 million plates. The plates have proven beneficial in reducing plate cutting, reverse rail cant and gauge widening, as well as providing rail roll-over restraint. By addressing these factors, NS has been able to reduce maintenance costs and increase efficiency.
It is clear that heavy-haul rail fastenings require enhanced performance to be able to withstand the axleloads and curvature that can lead to issues such as reverse rail cant and the need for ongoing maintenance. Heavy-haul operators are increasingly turning to fastenings designed for high-output mechanisation to reduce installation costs for contractors and repeat those efficiencies in stressing operations, re-railing and rail maintenance throughout the life of the fastening system.
Innovation in this sector has led to solutions that overcome many of these problems and help railways to achieve lower maintenance and longer lifespans for their fastening systems.