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

Two-dimensional (2D) dynamic image analysis (DIA) is gaining acceptance in geotechnical engineering research. Three-dimensional (3D) DIA extracts features from 8–12 projections of a particle and thus it is believed to verge on the true particle morphology. DIA is fast, efficient and convenient for characterising thousands of particles quickly; nevertheless, it captures shapes that are fundamentally different from 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, the sand particle size and shape descriptors obtained using both DIA and μCT are compared for three natural sands having wide granulometries. Three-dimensional 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 characterise using DIA and that shape measurements of complex irregular calcareous sands obtained from 3D DIA are not comparable to those obtained using μCT.