Quantification of the morphology of shelly carbonate sands using 3D images

Abstract

This is the published version of the paper.This version of the publication may differ from the final published version. Shelly carbonate sands proliferate in regions of the world where construction of offshore structures is in high demand. These structurally weak sands have high intra-granular voids and complex angular grain shapes. To improve the understanding of the mechanical properties of the material, a detailed morphological quantification is required. This paper presents a three-dimensional characterisation of the morphology of shelly carbonate sands based on analyses of X-ray computed tomography images. Two sands from the Persian Gulf with distinct grading were investigated. An adaptive watershed segmentation technique was developed to identify the individual grains for subsequent grain-scale analysis, which overcomes the challenges posed by the intricate microstructure of these sands. Non-invasive measurements of size, intra-granular void and various shape parameters were carried out, and statistical analyses were conducted, to characterise the grains. The results help to better understand the mechanisms of grain interlocking, and the role of grain angularity and intra-granular void ratio on the mechanical behaviour of shelly carbonate sands. Permanent repository link

Shape analysis of railway ballast stones: curvature-based calculation of particle angularity

“…While it is convenient to reduce all information from a 3D mesh to a single number, it is even more important that this number makes best use of the available information. In 19 , the curvature at each mesh vertex is calculated to identify corners. Then, the ratio between the surface area associated with these corners and the total surface area is defined as the angularity index, thus the calculated curvature values are not directly used.…”

“…For comparison, the angularity index I A , introduced in 19 , will also be considered in this work. For its calculation, the radius of the largest inscribed sphere, r inscr , has to be calculated.…”

“…The developed angularity index in 18 includes the integrated mean curvature and is similar to the one introduced later in this work. In 19 an angularity index was introduced, where the area of the particle's edges and corners is divided by the total particle surface area. This index will be considered later for comparison.…”

Image-Based Modelling of Shelly Carbonate Sand for Foundation Design of Offshore Structures

“…In-house imaging processing codes were developed to first binarise the images using Otsu's thresholding and subsequently apply an iterative watershed algorithm to separate the grains touching. The codes are fully described in [8]. The key advantage of the watershed code, when compared with previously used codes, is its ability to overcome the challenges posed by the diversity and complexity of the shapes associated with the bioclastic nature of shelly sands.…”

“…An additional parameter, the angularity index (I A as defined in [5]), is used to quantify the major surface irregularities, i.e., edges and corners. The index is defined such that rounded grains will yield low I A and angular grains will have high I A values, more details in [8]. These parameters definitions were such that the values will vary between 0 and 1, the latter corresponding to an ideal shape.…”