Railway track degradation: The contribution of rolling stock

Abstract

During train operation, geometrical irregularities develop in soil-supported ballasted railway tracks as a function of the carried tonnage. This form of degradation is combatted by periodic tamping using specially equipped trains, in order to guarantee predefined levels of structural performance. The growth of irregular settlements depends on both track properties (such as sleeper spacing, bending stiffness of the rail, and geotechnical properties of the subsoil) and the intensity of variations in the longitudinal stiffness (variations in soil profile, switches and crossings, transitions, etc.). These variations affect both the static and dynamic, frequency-dependent stiffness of the track under the moving wheels. In addition, the nature of the loading exerted by the rolling stock has an important influence. Trains running at a constant speed exert quasi-static loads on the infrastructure due to the constant axle loading. Also, a dynamic loading component may occur as a result of non-perfect wheels, with frequencies that are a function of both the speed and the wheel tread geometry. In general, the design of a railway track can be optimized with respect to its structural performance over the whole lifecycle. However, for existing lines this is difficult, and the only way to limit degradation and associated costs is to influence the condition of the rolling stock. The present study discusses the theoretical background of track degradation in the form of differential settlements. It then shows the results of an analysis of the loading conditions on Dutch railway lines, at network and local levels, based on actual measurements. Conclusions are drawn regarding deterioration and the effects of different loading types. The obtained results show that huge improvements are possible on mixed lines, and in particular, on freight lines, with reductions in geometrical degradation up to 52% of actual values. The main driver of excessive degradation appears to be the low-frequency component of the dynamic axle loading.