Shape analysis of railway ballast stones: curvature-based calculation of particle angularity

Bettina Suhr,Roger Lewis,William A Skipper,Klaus Six

doi:10.1038/s41598-020-62827-w

Bettina Suhr, Roger Lewis + Show 2 more

Open Access

https://doi.org/10.1038/s41598-020-62827-w

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Abstract

Particle shape analysis is conducted, to compare two types of railway ballast: Calcite and Kieselkalk. Focus lies on the characterisation of particle angularity using 3D scanner data. In the literature, angularity is often characterised using 2D data, as these types of data are easier to collect. 3D scanner data contain a vast amount of information (e.g. curvatures) which can be used for shape analysis and angularity characterisation. Literature approaches that use 3D data are often not thoroughly tested, due to a lack of test cases. In this work, two new curvature-based angularity indices are introduced and compared to one from the literature. Analytical test bodies with shapes ranging from spherical towards cubic are used for a first plausibility test. Then, 3D scans of ballast stones are compared to artificially rounded meshes. Only one out of three evaluated angularity indices seem to be suited to characterise angularity correctly in all of the above tests: the newly introduced scaled Willmore energy. A complete shape analysis of the scanned ballast stones is conducted and no difference between the two types of ballast can be seen regarding form, angularity, roughness, sphericity or convexity index. These findings of shape analysis are set in the context of previous works, where experimental results and DEM simulations of uniaxial compression tests and direct shear tests were presented for the same ballast types.

Highlights

Particle shape analysis is conducted, to compare two types of railway ballast: Calcite and Kieselkalk
Particle shape analysis has strongly benefited from advances in measurement techniques, considerably increasing the amount of information available
If a particle has concave parts, including edges and corners, these can be expected to increase particle interlocking, which influences the bulk behaviour of granular materials

Summary

Introduction

Particle shape analysis is conducted, to compare two types of railway ballast: Calcite and Kieselkalk. A complete shape analysis of the scanned ballast stones is conducted and no difference between the two types of ballast can be seen regarding form, angularity, roughness, sphericity or convexity index. These findings of shape analysis are set in the context of previous works, where experimental results and DEM simulations of uniaxial compression tests and direct shear tests were presented for the same ballast types. To characterise particle form, so-called 1D form factors are used For their calculation the particle’s longest, intermediate and shortest axes (L, I, and S respectively) are sought, see[2] for different definitions and measurement/calculation approaches. As the particles considered in this work show pronounced corners and edges in concave areas, roundness is not considered as an advantageous shape descriptor for these materials

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