Railway-induced ground vibrations in the presence of local track irregularities and wheel flats

Rapid growth in railway infrastructure has led to numerous environmental technical challenges. This includes ground-borne vibration, which is becoming an increasing problem, particularly in urban environments. A common source of this vibration is local defects (e.g. rail joints, switches and crossings) which cause large amplitude excitations at isolated locations. Modelling this type of excitation mechanism using typical linear frequency domain analysis is challenging and therefore non-linear time domain methods are required. Therefore, in this study a validated and comprehensive time domain, three-dimensional ground vibration prediction model is used to investigate the vibrations generated at the wheel/rail contact due to local rail and wheel surface defects. Different types of rail and wheel defect are mathematically modelled, including rail joints, switches, crossings and wheel flats. The track is modelled as a typical ballasted track, using a two-step approach where the vehicle/track dynamics and ground wave propagation are simulated separately. The first step models the effect of railway vehicles (using a multibody approach with many degrees of freedom) on the dynamic excitation of the track and incorporates a non-linear Hertzian contact law at the wheel/rail interface. The second step applies these track-vehicle model forces to a finite/infinite element model to accurately generate vibration time histories for required ground-borne vibration assessment. This work focuses on the AM96 trainset, largely used in the Brussels Region (Belgium). The geometries of a variety of local defect types are analysed and a sensitivity analysis is undertaken based on the defect size and train speed. It is found that defect type and geometry have a significant influence on vibration levels, and that only selected geometry types are effected by train speed.