Rate-Dependent Shear Behaviour of Silt-Steel and Sand-Steel Interfaces

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4. Rate-Dependent Shear Behaviour of Silt-Steel and Sand-Steel Interfaces

This paper presents the viscous effects during rate interface tests on medium-dense Fontainebleau sand and normally consolidated silt in contact with steel plates of different roughness. Six types of surfaces are used - four made of steel (smooth and polished surface; newly manufactured slightly rough surface; rusted medium rough surface, and sand-blasted medium rough surface) and two made of sandpaper to mimic the rusted steel. The tests were carried out in Bromhead type ring shear apparatus under constant normal load (CNL) and constant volume (CV) conditions. There is characteristic roughness (R_neutral) for silt-steel interface that returns neutral viscous effects in undrained conditions. Below R_neutral the undrained shear strength of silt-steel interface decreases with increasing shearing rate. When the surface roughness is higher than R_neutral, the interface undrained shear strength increases with increasing shearing rate. The shear strength behaviour on medium-dense sand-steel interface is more complex. The rate-dependency of sand is influenced by normal stress, displacement level, and surface roughness. The steady state interface shear stresses can be consider as rate-independent during shearing under high normal stresses. However, when low normal stress level is applied, rate-dependency phenomenon can be observed for smooth interfaces and it weakens with increasing interface roughness. For medium-dense sand viscous effects were found when R_a (arithmetic average roughness) is lower than 1 m. Furthermore, this research shows influence of surface texture origin and topography on mobilized interface shear strength. It also presents how classical roughness parameters (i.e., R_a, R_n) might be misleading is interface shear strength interpretation.

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

3 - Constitutive models and soil behaviour modelling