Characterizing the Influence of Ballast Flying
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Date
2016-03
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Addis Ababa University
Abstract
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.
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Keywords
Ballast flying characterization, discrete element modeling, ballast interlock ability, ballast mass