Behavior of Fresh and Fouled Railway Ballast Subjected to Direct Shear Testing: Discrete Element Simulation
Publication: International Journal of Geomechanics
Volume 14, Issue 1
Abstract
This paper presents the three-dimensional discrete element method (DEM) that was used to study the shear behavior of fresh and coal fouled ballast in direct shear testing. The volumetric changes and stress-strain behavior of fresh and fouled ballast were simulated and compared with the experimental results. Clump logic in particle flow code in three dimensions () incorporated in a subroutine was used to simulate irregular-shaped particles in which groups of 10–20 spherical balls were clumped together in appropriate sizes to simulate ballast particles. Fouled ballast with a various void contaminant index (VCI) ranging from 20 to 70% VCI was modeled by injecting a specified number of miniature spherical particles into the voids of fresh ballast. The DEM simulation captures the behavior of fresh and fouled ballast as observed in the laboratory, showing that the peak shear stress of the ballast assembly decreases and the dilation of fouled ballast increases with an increasing VCI. Furthermore, the DEM also provides insight to the distribution of contact force chains and particle displacement vectors, which cannot be determined experimentally. These micromechanical observations clearly justify the formation of a shear band and the evolution of volumetric changes during shearing. The reduced maximum contact force associated with increased particle contact area due to fouling explains the decreased breakage of fouled ballast. An acceptable agreement was found between the DEM model predictions and laboratory data.
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Acknowledgments
The authors are grateful for the financial support provided by CRC for Rail Innovation. The laboratory assistance of Mr. Alan Grant is also appreciated.
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Published In
International Journal of Geomechanics
Volume 14 • Issue 1 • February 2014
Pages: 34 - 44
Copyright
© 2014 American Society of Civil Engineers.
History
Received: Apr 30, 2012
Accepted: Oct 3, 2012
Published online: Oct 4, 2012
Published in print: Feb 1, 2014
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