Quantifying the particle shape and surface roughness of sands

Particle shape and surface roughness affect both the macro- and micro-mechanical behaviour of natural sands. In geotechnical practice, the global shape of sands is generally characterized by visual comparison to reference charts or by static image analysis with a limited number of particles. Meanwhile, due to the difficulty in measuring surface roughness of sand grains, it is usually ignored in the quantification of particle morphology. In this study, the global shape of four types of natural sand, Leighton Buzzard sand (LBS), beach sand (BS), carbonate sand (CS), and completely decomposed granite soil (CDG), was measured by a dynamic particle shape analyser, and quantified using three parameters, i.e., aspect ratio, sphericity and convexity. The influence of mineralogy, depositional environment, and particle size on the global shape has been thoroughly discussed. Among the four sands, the shape descriptors of LBS are the highest, indicating the most spherical and rounded shape, because of the aqueous traction transportation. The sphericity of CDG increases with decreasing particle size due to the abrasion or collapsing of asperities of coarser particles under subsequent weathering. The surface roughness of LBS, BS and CS was successfully measured by an optical interferometer, and quantitatively characterized by the flattened root-mean square roughness (RMSf). The RMSf of particles with different mineralogy and sizes all tends to be stable at relatively larger size of field of view. Among the tested granular materials, the surface of CS particles is the roughest and most variable, and the finer the CS particles, the rougher the surfaces.

Automated summary

The shape and surface roughness of natural sands play significant roles in their macro- and micro-mechanical behavior. Existing methods for characterizing sand shape typically rely on visual comparison or static image analysis, without considering surface roughness. This study measured the global shape of four types of natural sand using a dynamic particle shape analyzer and quantified it using aspect ratio, sphericity, and convexity. The influence of mineralogy, depositional environment, and particle size on shape was discussed. Additionally, the surface roughness of the sands was measured using an optical interferometer, and the roughness characteristics were analyzed. The results showed that the shape descriptors of Leighton Buzzard sand were the highest, indicating a more spherical and rounded shape, while the surface roughness of carbonate sand was the roughest and most variable.