The morphology of two types of complex calcareous sand was investigated in this study. The materials were selected owing to their different geologic and biologic origins. Ledge Point is a bioclastic coastal sand, while Browse #1 is a hemipelagic sand. These two sands fall outside the range of common data sets used to correlate mechanical properties to particle shape parameters. Morphologic analysis of these calcareous sediments can aid with understanding the engineering behavior of calcareous soils. Moreover, sediments source tracing information could also be inferred from particle shape analysis. Two-dimensional Dynamic Image Analysis (DIA) was employed to capture five million and eight million particle images of each sand, respectively. A number of size parameters including diameter of equivalent projected circle (EQPC), Feret minimum, and Feret maximum diameter were efficiently obtained for each captured image using DIA, and used to investigate particle size distribution of these sediments. In addition, samples of over 800,000 particles were used to assess statistical distributions of various particle shape parameters including Aspect Ratio, Convexity, Sphericity, and Roundness-DIA (by volume). A Johnson family of distributions was found to provide a better fit to particle shape parameter distributions than the normal distribution for both sands. It is also shown that the Sphericity and Aspect Ratio are size independent, while Convexity and Roundness-DIA are correlated with particle size. Convexity is likely correlated with Sphericity for both calcareous sediments owing to their biogenic origin. Correlations of Roundness-DIA, Sphericity, Convexity, and Aspect Ratio and particle size are also observed but need more analysis.

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.

Sandy hemipelagic calcareous sediments are quite complex soils. In some instances, they can consist entirely of the skeletal remains of microorganisms, such as foraminifera tests. These calcium carbonate test (shell) producing protozoa are common in marine environments, accounting for the majority of the calcium carbonate in the open ocean. Foraminifera come in a variety of species, each with unique test morphological adaptation suited to their local environment. For example, planktic species have relatively low density tests and live in the water column, while benthic species have dense shells and live on the seafloor. This paper explores the impact of biologically driven morphology on the physical properties (e.g. crushing) of calcareous sand from the Browse Basin, offshore North West Australia. X-ray microtomography scans were performed to visualize and measure the test structure and the Weibull statistic of particle strength for Trilobatus sacculifer, a common planktic foraminifera, and Cibicidoides sp., a benthic foraminifera. These are compared with clastic siliceous and calcareous sands. Overall it is shown, that the biological taxonomy can play a significant role in the crushing behavior and mechanical properties of deep sea calcareous sediments.

Calcareous sediments are prominent throughout the low-latitudinal offshore environment and have been known to be problematic for offshore foundation systems. These fascinating soils consist largely of the skeletal remains of single-celled marine organisms (plankton and zooplankton) and can be as geologically complex as their onshore siliceous counter parts. To enable an adequate understanding of their characteristics, in particular, their intra-granular micro-structure, it is important that geotechnical engineers do not forget about the multifaceted biological origins of these calcareous sediments and the different geological processes that created them. In this paper, the 3D models of soils grains generated from micro-computed tomography scans, scanning electeron microscope images, and optical microscope images of two calcareous sediments from two different depositional environments are presented and their geotechnical implications discussed. One is a coastal bioclastic sediment from Perth, Western Australia that is geologically similar to carbonate sediments typically used in micro-mechanics and particle crushing studies in the literature. The other is a hemipelagic sediment from a region of the North West Shelf of Australia that has historically been geotechnically problematic for engineers. The results show there is a marked difference between coastal bioclastic and hemipelagic sediments in terms of geological context and the associated particle micro-structures. This brings into question whether a coastal bioclastic calcareous sediment is a good micro-mechanical substitute for a hemipelagic one.

This article discusses particle size distribution (PSD) by sieving as it relates to variable granular density soils such as hemipelagic calcareous sediment and pyroclastic pumice. These soils tend to have low-density porous sand-sized particles and high-density solid silt and clay-sized particles. When mass fraction passing each sieve is used to create the gravimetric PSD, the quantity of sand-sized particles in these soils can be underestimated, because of their low density. This article presents the volumetric PSD as a new method to account for granular density variation in these unique sediments.