Sections of railway line associated with variations in track stiffness often have an increased maintenance requirement owing to the relatively rapid deterioration of track geometry. Variations in stiffness could arise from changes in ground conditions, transitions from free track onto a fixed structure and other localised features. Increased dynamic loads may be responsible for track degradation at sites with these characteristics. This is especially relevant to future high speed rail infrastructure, where increased operating speeds have potential to increase dynamic loading on the track significantly. At present, there is little direct physical evidence linking increased dynamic loading to accelerated geometry deterioration, and monitoring of problem sites is needed to investigate their real behaviour. This paper presents some findings from an ongoing study of a ballasted viaduct on a high speed railway, at which ballast migration has been found to occur in the vicinity of a structural expansion joint leading to the occurrence of unsupported sleepers.. The response of the structure and the track to the passage of high speed trains has been monitored using geophones. Using the resulting data supported by appropriate theoretical modelling, mechanisms for the enhanced track degradation are proposed. The results of the study provide insights into the interaction between trains, the track, the ballast and the structure, and can be used to inform the cost-effective maintenance and design of existing and future high speed rail infrastructure.
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