Effects of Particle Morphology on the Interface Friction Angle of Sands

Abstract The particle shape of coarse-grained soils, such as sand, influences its geotechnical properties, including the interface friction angle (δres)–a crucial parameter for characterizing soil-pile and soil-pipe interactions in offshore geotechnics. This paper presents an experimental investigation of the effects of particle morphology on sand interface friction angle using a Bromhead ring shear device. We tested three sands –fine silica sand, Hokksund sand, and Ottawa sand—against a smooth steel interface, medium rough sandpaper, and rough sandpaper under normal stresses ranging from 10–50 kPa, corresponding to an equivalent depth of approximately 5–8 meters in typical offshore soils. We determined the shape factors characterized by sphericity and roundness based on image analysis and mathematical computation. Synthesized glass beads with a monodisperse size distribution were also tested as an idealized model system for comparison. Results indicate that particle shape plays a more dominant role than particle size in controlling the interface friction angle. Sands with greater angularity (Hokksund and silica sands) exhibited higher friction angles, whereas rounded Ottawa sand behaved more similarly to spherical glass beads, particularly on rough interfaces. Results revealed a potential competition between particle shape and surface roughness, controlling the dominant frictional mode. These findings offer new insights into the morphologically-driven mechanisms influencing interface friction, providing valuable input for geotechnical design, modeling, and foundation analysis in offshore environments.