Efficacy of 3D dynamic image analysis for characterising the morphology of natural sands

Abstract

Two-dimensional Dynamic Image Analysis (DIA) is gaining acceptance in geotechnical engineering research. Three-dimensional (3D) DIA extracts features from 8-12 projections of a particles thus it is believed to verge on the true particle morphology. DIA is fast, efficient, and convenient for characterizing thousands of particles quickly; nevertheless, it captures shapes that are fundamentally different than the 3D morphologies reconstructed using micro-computed tomography (μCT). In DIA particle features are interpreted using external images of a particle, which fail to account for differences in imaging perspectives. In addition, 2D and 3D shape descriptors are influenced by differences in dimensionality projection owing to variations in definition, dimensionality, and perspectives of the particle images employed which causes them to differ from their 3D counterparts. In this study we compared sand particle size and shape descriptors obtained using both DIA and μCT for three natural sands having wide granulometries. 3D DIA offers significant advantages in terms of efficiency, while providing adequate representation of Feret dimensions, Sphericity and Convexity. However, the study demonstrates that 3D Roundness is difficult to characterize using DIA and that shape measurements of complex irregular calcareous sands obtained from 3D DIA are not comparable to those obtained using μCT.

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

“…The histograms of shape parameter for this coastal calcareous sediment are non-normal. This was also seen in [ 22 , 23 ] for the 2D DIA of Ledge Point and the Browse #1 hemipelagic calcareous sand. For this study, the Bounded Johnson Distributions [ 34 ] were fitted to all of the shape parameter histograms; fit lines are shown in Figure 6 and Figure 7 .…”

“…This would explain how Cx 2D and S 2D can be correlated ( Figure 8 c), but Cx 2D does not show the same variation in size that S 2D does ( Figure 5 b,c). The Correlation of sphericity with convexity in 2D DIA methods have also been shown by [ 22 ] and [ 24 ] for both siliceous and calcareous sands.…”

“…Li et al [ 22 ] argued that 3D μCT should be used to assess the shape parameters of calcareous sediments in order to resolve internal voids within the grains and that DIA methods can result in dimensionality projection errors that make particles appear larger in projection (this type of error would have a minimum impact on thin platy particles). The angular projection error presented here for biogenic platy and shelly particles that results in a statistical increase in the measured aspect ratio and sphericity in DIA provides an additional reason for using μCT for measuring the shape parameters of complex calcareous sands.…”

“…The complex shape of the grains in these calcareous sands contributes to their poor geotechnical behavior [ 16 , 17 , 18 , 19 , 20 ], such as pile running [ 21 ]. Although a few studies have examined the impact of 2D and 3D imaging techniques on the measurements of sand grains [ 22 , 23 , 24 ], there have been no direct comparisons of 2D DIA methods to 3D μCT of bulk samples. This paper investigates the impact of 2D DIA and 3D μCT imaging methods on the measured shape parameters, aspect ratio, convexity, and sphericity, of calcareous beach sand.…”

Recent Advances in Particle Characterization

“…Moreover, 3D DIA may produce particle size distribution using Feret and EQPC diameters and offers particle shape descriptors like aspect ratio, convexity, and sphericity. These three points of a particle's dimensions are closer to the real shape of the particle [7].…”