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

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.

Simple particle shapes for DEM simulations of railway ballast: influence of shape descriptors on packing behaviour

“…sharp edges and corners. Moreover, clumps are not constructed to approximate the shape of ballast stones with respect to the volume error, but to approximate shape descriptors, which are known from previous work, [51]. Details on all clumps constructed in this paper can be found in the supplemental material provided with this work.…”

“…The shape of two types of railway ballast, Calcite and Kieselkalk, was analysed in [51]. The stones under investigation were composed of sharp corners and edges as well as rounded areas and their angularity was analysed.…”

“…The stones under investigation were composed of sharp corners and edges as well as rounded areas and their angularity was analysed. Another important shape characteristic of ballast stones is their nonconvexity, which was evaluated in [51] using the convexity index. Both sharp corners and edges as well as non-convex shapes can be expected to significantly influence the ballast bulk behaviour as they yield a big interlocking potential.…”

“…The obtained simulation results were in very good accordance with the experimental results. A shape analysis of the same two types of ballast was conducted in [51]. Regarding form, angularity, sphericity, convexity index no difference could be seen between both ballast types.…”

“…Packing porosity as well as coordination number and isotropic fabric, will strongly influence the simulated bulk behaviour. Aiming at simplicity and efficiency, clumps of three spheres will be constructed using information available from the shape analysis, [51]: elongation, flatness, convexity index and sphericity. For the different clump shapes, the packing behaviour will be addressed with respect to porosity (densest and loosest packing to be generated for a shape) coordination number and isotropic fabric.…”