Quantifying the Morphology of Calcareous Sands by Dynamic Image Analysis

It is commonly accepted that the macroresponse of soil depends significantly on the microscopic particle characteristic features, such as size, shape, and roughness. These parameters can be obtained readily by dynamic image analysis of each individual particle, enabling the quantification of particle morphologies. This study investigated the variation of calcareous sand morphology before and after the one-dimensional normal compression. The tests employed a large oedometer cell (231.6-mm inner diameter and 155-mm height) and coarse calcareous particles (10–20 mm). It was found that samples of different particle shape mixtures have almost the same compressibility due to continuous breakage and gradual fining of coarse sand particles. The particle breakage can be effectively quantified by the change of total particle perimeters in the dynamic image analysis. The mixture of branched particles in blocky sands can effectively increase the particle breakage factor because the branched structure can be easily crushed due to localized stresses during the compression. The breakage of coarse particles can produce a large number of fine particles with an exponential frequency distribution (by number). These fine particles generally are more elongated and flatter than the coarser particles. After the compression tests, all particles tended to be slightly smoother and more spherical, due mainly to the particle asperity damage. In particular, the rounded (spherical) particles were much smoother than the angular ones. The relevance of particle morphology change to geotechnical engineering practice also is established.