Characterizing the Influence of Ballast Flying

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Addis Ababa University


Ballast flying is understood as cause of track deterioration in many countries over where high train speed is operated. The deformation and degradation behavior of ballast under static and dynamic load cause the ballast to fly early from under the track. In this thesis, the railway ballast particle force equilibrium is analyzed through basic mechanics and mathematical formula and a discrete element model is set up to discover the factors and influences. Ballast flying is correlated with ballast shape and mass, especially the ballast shape mass ratio corresponding to operation speed. Ballast interlock ability governs the ballast flying possibility and severity. Ballast flying possibility increase with ballast bed acceleration. The performance of ballasted track depend not only on its design, but also the way and quality of maintenance ,ballast needed to analyze the shape and mass of ballast material used to reduce the flying of ballast under track. This thesis investigated the effect and influence of ballast flying using a Discrete Element Modeling (DEM) approach. Results show that ballast flying particle is correlated with ballast shape and mass, aggregate gradation and ballast interlock ability. From DEM output it can be conclude that finer and non-uniformly graded aggregate are easily fly under railway track during operation and ballast with high angular shape resulted in the highest shear resistance or high stability. Acyclic loading analysis was conducted for angular particles relatively low confining pressure for analysis of particle fragmentation the generated assembly of angular particles undergoing fragmentation at various load cycle. from the simulation observe that though the mechanical load increase the fragmentation of railway ballast increases and finally leads to ballast displacement which lead to ballast flying. As the applied normal force increased, the shear force also increased primarily influenced by the shape effects of aggregate angularity and surface texture. Yet, a rough surfaced rounded particle had shear strength higher than that of a smooth-surfaced angular particle. The fact that rounded gravel particles have less aggregate interlock compared to crushed angular aggregate to transfer shear force can be explained by the bilinear contact force paths for the rolling and climbing up of the rounded particles. Angularity and cubical particles have high resistance to the vertical displacement under traffic loading because the inter particle force high when compared with the spherical and rounded/circular particles.



Ballast flying characterization, discrete element modeling, ballast interlock ability, ballast mass