Keywords: railway track, tamping operation, ballast density, discrete element modelling.

The tamping operation is essential in railways since it allows the correction of the track geometry defects. However, on tracks already consolidated by the traffic, the tamping affects the ballast layer, reducing the track stiffness, which later may yield new geometry defects. In contrast, this operation needs to densify the ballast on newly-built or renovated tracks to maintain geometry quality for longer periods. In the Carajas Railway (heavy haul line in Brazil), the practical experience of maintenance indicates that the tamping of a single insertion has not been effective on newly-built or renovated tracks. For such cases, the multiple insertion has been more efficient. Nevertheless, for the authors' better knowledge, there are no studies that evaluate/measure possible differences between these tamping types, for heavy haul lines such as the Carajas Railway. Due to these aspects, this paper aims to evaluate two types of tamping operations: single and multiple insertions of the tamping tines, to evaluate its effectiveness in promoting the ballast compaction. For this purpose, ballast density measurements were carried out in the field. Complementary simulations using a discrete element modelling were made. As results, the field tests showed that the multiple insertion generated a densification 15% higher than the single insertion. In the laboratory, it was observed that the materials used to determine the ballast density in the field presented particle size distributions and particle’s shape without significant differences, meaning that the higher compactness achieved in the multiple insertion probably comes from a greater packing of the ballast particles. Through numerical simulations, an analysis of this densification throughout the ballast layer was done, so the arrangement of the aggregates may be better observed. The region underneath the sleeper, where the tamping tines operated, displayed higher densification when compared to the track axis region. Aligned to the field results, the multiple insertion indicated a better compacted zone under the rail. In this way, when applying the multiple insertions, it is expected to achieve a more stable ballast layer with a smaller number of tamping passages to keep the track within the required design limits.

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