Comparison of 2D Optical Imaging and 3D Microtomography Shape Measurements of a Coastal Bioclastic Calcareous Sand

Abstract

This article compares measurements of particle shape parameters from three-dimensional (3D) X-ray micro-computed tomography (μCT) and two-dimensional (2D) dynamic image analysis (DIA) from the optical microscopy of a coastal bioclastic calcareous sand from Western Australia. This biogenic sand from a high energy environment consists largely of the shells and tests of marine organisms and their clasts. A significant difference was observed between the two imaging techniques for measurements of aspect ratio, convexity, and sphericity. Measured values of aspect ratio, sphericity, and convexity are larger in 2D than in 3D. Correlation analysis indicates that sphericity is correlated with convexity in both 2D and 3D. These results are attributed to inherent limitations of DIA when applied to platy sand grains and to the shape being, in part, dependent on the biology of the grain rather than a purely random clastic process, like typical siliceous sands. The statistical data has also been fitted to Johnson Bounded Distribution for the ease of future use. Overall, this research demonstrates the need for high-quality 3D microscopy when conducting a micromechanical analysis of biogenic calcareous sands.

3D image scanning of gravel soil using in-situ X-ray computed tomography

“…14d, AR sl-2D corresponds to AR il-3D , but not to AR sl-3D . A similar tendency regarding the aspect ratios is also found in literature 16 . Comparisons of the sphericity in Fig.…”

“…(v) Computing the particle size and shape characteristics (for 3D images) Because the particle morphology, i.e., particle size and shape characteristics, can influence the mechanical properties of granular material, various parameters that characterize them have been proposed and investigated 13,14,16,[42][43][44][45][46][47][48][49][50][51][52][53] . In this study, the particle morphology was evaluated using SPAM functions 38 with the parameters listed in Table 4: the diameter of an equivalent sphere that has the same volume as a target particle (D eq-3D ); lengths of the minor (L s-3D ), intermediate (L i-3D ), and major axes (L l-3D ) of an ellipsoid fitted to the target particle; aspect ratios calculated by L s-3D /L l-3D (AR sl-3D ) and L i-3D /L l-3D (AR il-3D ); and true sphericity (S t-3D ) calculated using S eq /S 42 .…”

“…S eq denotes the surface area of a sphere with the same volume as the target particle, and S denotes the surface area of the particle. These size and shape descriptors were selected because they were often adopted to compare particle morphologies in 2D and 3D images 13,14,16,46,49 , even though there is no general agreement on the types of descriptors that are the most comparable. Regarding sphericity, various definitions for 2D and 3D images have been proposed 42,45,53 .…”

“…Therefore, regardless of whether intact soil samples are obtained in the field, the observation, quantification, and evaluation of natural sedimentary structures are essential.X-ray computed tomography (CT) is a widely used non-destructive technique for examining objects in medical and industrial applications, as well as in research 10,11 . This technique is useful in geotechnical engineering for observing sedimentary structures or discontinuous planes, such as fissuring, in soil samples 12 ; to quantify physical properties, including particle size and shape characteristics [13][14][15][16] ; to investigate pore and contact fabrics 17,18 ; or to characterize mechanical properties such as shear responses 19,20 primarily using the discrete element method (DEM) [21][22][23][24] or three-dimensional (3D) printing technology to replicate synthetic samples [25][26][27][28][29][30] based on CT images. Such a new paradigm based on imaging, image processing, and computing properties is…”

Shape‐dependent settling velocity of skeletal carbonate grains: Implications for calciturbidites

“…Moreover, two‐dimensional shape descriptors cannot fully quantify the shape of three‐dimensional particles (e.g. Su & Yan, 2019; Beemer et al ., 2022), in particular for calciturbidite deposits wherein grain orientation by hydraulic sorting is important. In the case of skeletal carbonates, the first‐order shape descriptor form is likely to be the most meaningful shape parameter, although roundness‐related parameters can explain additional retardation of the settling velocity.…”