Assessing the damaging effects of railway dynamic wheel loads on railway foundations

Dynamic train wheel loads, which can be significantly greater than static loads, occur due a variety of factors and unless they are properly considered in track structural design, significant unplanned maintenance and premature track failure may result. This is particularly so for traditional ballasted railways built on soft foundations because although ballast lends itself to maintenance, it is often problematic and costly to repair damaged foundations. To address this, a rigorous combined analytical-numerical approach is described to predict and characterize, for the first time, the damage to which railway foundations can be subjected as a result of dynamic loads. The approach marries a sophisticated three-dimensional dynamic model of the train-track system incorporating vertical track quality, foundation soil distress models, statistical analysis methods and results of field investigation.
The resulting analyses demonstrate that the magnitudes and distributions of dynamic loads are a function of train speed and track quality and that specific locations experience significantly higher amounts of damage which can lead to a variety of track faults. The approach is illustrated via a study of a heavy haul railway line in China where the wheel loads and tonnage carried are set to increase significantly. The study suggests that the thickness of the ballasted layer would need to increase by over 20% to prevent premature foundation failure provided that the track is maintained in good condition, and by significantly more should the track condition be allowed to deteriorate.