Track


Is customised maintenance the answer to track stress?


With heavy-haul operations placing significantly more stress on track structures and components, railways should consider customised maintenance schedules and practices, as Dr David Rhodes, Pandrol’s technical director, explains.


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N the face of it, rail fastenings are not required to do anything more in heavy-haul


applications than they are in any other railway. Heavier rail sections and closer sleeper spacing can compensate for higher axleloads and the loading on the fastenings does not need to be any higher than usual. However, in practice the demands of the specialist heavy-haul operators are such that quite different approaches to track component design are usually necessary.


The detailed design of rail fastening systems affects parameters such as track gauge, track stiffness and rail inclination, all of which affect, in turn, wheel-rail interface mechanics. Of course this makes fastening specifications a critical factor in keeping railways running smoothly. However, in the case of heavy-haul railways three additional factors are


IRJ February 2013


highlighted which combine to make these requirements even more challenging. First, compared with conventional railways, the annual passing tonnage on heavy-haul lines can be very high. In conventional applications, 20 million tonnes per annum constitutes a busy line, but in heavy-haul operations 200 million tonnes per annum is not unusual.


This means that if components still


require maintenance or replacement after the same accumulated passing tonnage, maintenance intervals are naturally much shorter. What is less obvious is the effect on life- cycle cost analysis. Maintenance activities which would be discounted to a negligible net present value on a conventional railway because they occur so far in the future are much more significant on a heavy- haul railway.


At the detailed level of the rail fastenings the cost of maintenance and replacement does not lie in the cost of the components themselves but in the cost of labour and track closures. There are considerable economic benefits in replacing small track components only when other maintenance work, such as re-railing, is being carried out. This suggests that considerable savings can be made by ensuring the life of fastening components exceed the life of the rail. Inevitably this becomes more of a challenge as rail life is extended, with the major US heavy-haul railways now expecting rail to last for 3 billion tonnes of traffic in tangent track. In the case of a heavy-haul line with high annual passing tonnage the net present value of such savings is high enough to justify investment in more durable components.


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