Detection of local instabilities based on typical wheel-rail-forces (EPIB 2)

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The ballasted track superstructure achieves the required load distribution and the damping of dynamic traffic loads in correspondence with its actual stiffness properties provided by superstructure and substructure/subsoil. However, these properties are not constant along the track, e.g. caused by changes of substructure performance but also from one rail support to the next because of individual support conditions of the sleepers provided by the ballast. Deviations of geometry along the loaded track define the initial quality as well as the track borne source of dynamic wheel rail forces. Because of plastic deformations within the ballast layer or within substructure/subsoil the track geometry and the superstructure stiffness are facing load cycle dependent and time dependent (climatic impacts) changes. Along a track section with single, local defects, an increasing degradation of track quality and therefore early need for track maintenance will be observed, because of the high local vehicle-track reactive effects. To achieve the goal of the joint project, the subproject EPIB 2 will study and determine the effect of local instabilities within substructure/subsoil to wheel rail forces using simulations based on a calibrated vehicle-track-substructure interaction model. For model calibration in-situ investigations are needed, which are already accepted by DB Netz AG and ÖBB INFRA. The model will cover a certain length of the track, because the dynamic wheel rail forces are dependent on the geometry of the loaded track and are in interaction with stiffness properties and vehicle based parameters (Inertia, properties of springs and dampers, speed). The intension is to achieve a high flexibility of the model and applicability to different ballasted track systems. Main goal of work package EPIB 2, as part of the joint project, is to make the detection of local instabilities as simple and as early as possible, long time before significant deviations of track geometry occur. Local instabilities will cause increasing plastic deformations because of local weaknesses of cohesive soils within rail substructures. Local weakness can be detected by changes in wheel rail forces, which are also superimposed by dynamic forces generated by the actual, general track quality. Typical dynamic excitations (according to frequencies and amplitudes) of wheel rail forces, which are indicators for the presence of local instabilities, can be extracted from continuous readings of vertical wheel forces or axle box accelerations of measurement trains or regular trains and may be implemented into the track management system. This would also strengthen the results of ground penetrating radar measurements with respect to the determination of stiffness properties along the track.