Particle classification and intra-particle pore structure of carbonate sands

Carbonate soils, known as bioclastic deposits, have been classified as ‘problematic soils’ in many offshore and ocean engineering applications. Carbonate soils have many complicated mechanical properties, e.g., low shear strength and high compressibility, mainly determined by their unique microstructures that include weak car-bonate minerals, complex particle morphology, and abundant intra-particle pores. However, current knowledge of these microstructures, especially regarding intra-particle pore structure, does not yet match our understanding of the complicated behaviors of the soils. In this context, this paper presents a detailed quantitative study of the particle morphology and intra-particle pore structure of carbonate sand particles based on the results of X-ray micro-computed tomography (μCT) scanning and image processing techniques. By investigating particle shape, this paper first introduces a triangular classification method for carbonate particles in terms of their aspect ratios. The continuous pore size distribution, fractal dimension, and Euler characteristic are then defined to characterize the cumulative volume fraction, complexity, and connectivity of the precisely reconstructed intra-particle pore structure, respectively. The classification results indicate that the proposed classification method is a significant step toward the establishment of a novel classification framework for carbonate soils in engineering applications. The quantitative results characterizing the topological properties of the intra-particle pore structure and their statistical analysis provide deep insight into the hydro-physical permeability and biogeologic origins of car-bonate soils.