Exploring Sand Interface Friction Angle: Effects of normal stress, surface roughness, and substrate hardness

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4. Exploring Sand Interface Friction Angle: Effects of normal stress, surface roughness, and substrate hardness

This study investigates the effects of surface roughness, substrate hardness, and normal stress on sand residual interface friction angle using a Bromhead ring shear device. Three sands - a fine silica sand, Hokksund sand, and Ottawa sand - were tested against three interface materials (steel, silicon carbide sandpapers, and polypropylene) subject to normal stresses ranging from 10 to 50 kPa, corresponding to an equivalent depth of approximately 5 - 8 meters in typical offshore soils. Additionally, the inherent variability of the tested sands allows for an investigation into the effects of gradation and particle shape on the interface friction angle. A new parameter, the substrate-to-sand hardness ratio, was introduced to account for the influence of interface hardness. Results revealed that higher normal stresses increased the residual interface friction angle, likely due to enhanced grain-interface interlocking, though the effect was less pronounced for Hokksund sand and silica sand with irregular particle shapes and higher angularity. For polypropylene, the inherent smoothness of the interface dominates over surface roughness, suggesting roughness alone is insufficient to fully characterize interface properties. An empirical model was developed to predict the residual interface friction angle based on key parameters, including surface roughness, hardness, applied normal stress, sand internal friction angle and median particle size. Our findings provide new insights into the role of interface geometry and material-dependent properties in controlling sand-interface friction, enhancing geotechnical predictive modeling and design.

5th International Symposium on Frontiers in Offshore Geotechnics (ISFOG2025)

3 - Constitutive models and soil behaviour modelling