Abstract
The morphologies of coarse particles are usually irregular and play a dominant role in the mechanical behaviors of the particle assemblies. This paper quantitatively studies the effect of particle shape on the angle of repose, which is an important macroscopic parameter for ballast materials, via laboratory tests and numerical simulations by means of the discrete element method (DEM). Forty ballast particle templates and four simply created clump templates are reconstructed using an image-based method and quantified with two shape factors, sphericity and convexity. A series of simulations are conducted with the coefficient of sliding friction between particles changing from 0.2 to 0.6 at an interval of 0.1 to study its influence on various shapes of particles, and an appropriate value of sliding friction coefficient is chosen for the comparison of particle shape effect. The results show that increasing sphericity and convexity can significantly decrease the angle of repose, and the real ballast model gives a more realistic angle of repose behaviors as that of laboratory tests compared to simply created models. By analyzing the characteristics of particle motions and contacts from a microscopic perspective, the mechanism of particle shape attributed to the formation of granular aggregation is also discussed and revealed in this research.
Highlights
Granular materials such as powders, grains, soils, and gravels are extremely common in industrial, agricultural, and engineering fields. erefore, thorough understandings of their mechanical properties are required for better application of these granular materials in practical
By comparing the discrete element method (DEM) modeling results for different particle shapes and that of the experimental tests, the mechanism that contributes to the difference of repose angle between various granular assemblies concerning the particle shapes is discussed
Based on an image-processing method, four types of simple clumps together with 40 real ballast templates have been reconstructed and quantified with sphericity and convexity to study the impact of particle shape and the interparticle friction coefficient on the angle of repose on a ballast-size scale in DEM simulations
Summary
Granular materials such as powders, grains, soils, and gravels are extremely common in industrial, agricultural, and engineering fields. erefore, thorough understandings of their mechanical properties are required for better application of these granular materials in practical. Compared to soils or sands, coarse large-sized matters such as crushed rocks in dam engineering or ballast used as bearing materials in the railway system tend to have irregular morphologies, and the interlocking effects between particles are much more pronounced than that of small-sized substances, leading to different behaviors and properties in typical angle of repose tests. A series of DEM simulations for the angle of repose tests were carried out for both simple-shaped and irregular-shaped particles to numerically study the particle morphology effect on the formation of piles for coarse aggregates. A laboratory experiment using the cylinder lifting test (CLT) was conducted in parallel, and the experimental results were compared to that obtained with DEM models to verify the important effects of particle shape on the mechanical behaviors for coarse aggregates
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