The Granular Structure of Two Marine Carbonate 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.