A Numerical Study on the Stress Changes in the Ballast Due to Train Passages.

The long-term settlement of railway tracks is a consequence of permanent deformations taking place in the track granular layers and subgrade. In the ballast layer, which experiences the highest stress amplitudes during train passages, these permanent deformations strongly depend on the loading conditions, which in turn depend on several factors as the train speed and axle loads, sleeper-ballast initial pressure, or track geometry quality. Moreover, under the action of moving loads from trains, further to a very significant increase of the vertical stress, the ballast layer experiences the rotation of the principal stresses, which is another aspect that significantly influences the long-term structural behaviour. This paper numerically analyses the stress changes in the ballast due to train passages, aiming at showing how these stresses may vary depending on the loading conditions. A numerical program of dynamic simulation is used that considers the nonlinear resilient nature of the ballast and the three-dimensional representation of the track-ballast-soil system using the FEM. The paper shows that dynamic effects due to trains travelling at very high speeds can significantly influence the stress path followed during loading and the principal stresses rotation inside the upper layers of the track. The paper also shows the importance of the consideration of the ballast nonlinear behaviour in the rotation of the principal stresses. [ABSTRACT FROM AUTHOR]