Roundness and Sphericity of Soil Particles in Assemblies by Computational Geometry

The use of computational geometry methods for determining soil roundness (R) and sphericity (S) were evaluated and extended to particles segmented from images of three-dimensional particle assemblies. Two Adobe Photoshop lasso tools were used to delineate particles with full projections from the assemblies. Results were in excellent agreement with values published in traditional roundness and sphericity charts, thus confirming that the computational method can replace the much slower and less objective chart methods. Complete volume-based distributions of particle roundness and sphericity were presented for three soils with vastly different particle shapes. Values of R and S obtained from images of three-dimensional assemblies were almost indistinguishable from values obtained using images of detached particles showing their largest projected areas. Mean R values were also computed for 10 different soils of various geologic origins. As expected, crushed sands exhibited the smallest mean values of R whereas alluvial and glacio-fluvial soils showed the largest values.