Rate effects on the interface shear behaviour of normally and overconsolidated clay

This paper presents a study on the effects of shearing velocity, surface roughness and overconsolidation ratio on the strength and deformation behaviour of fine-grained soil–structure interfaces. The results of shear box direct interface shear tests, augmented with soil deformation measurements from particle image velocimetry analyses, indicate that shearing velocity (i.e. velocity at which the continuum surface is displaced) has a controlling effect on the drainage conditions mobilised during shearing. As shearing velocity was increased, undrained conditions were progressively mobilised, characterised by smaller interface strength and volumetric changes for tests on normally consolidated specimens. Increases in shearing velocity resulted in increases in interface strength for overconsolidated specimens. The results presented herein indicate that, as the magnitude of surface roughness was increased, drained shearing conditions were favoured for a given shearing velocity. Soil deformation measurements indicate that the shear zone where localisation occurs becomes thicker as the surface roughness increases, and the magnitude of soil deformations decreases as shearing velocity is increased. The findings presented herein are relevant for prediction and interpretation of soil–structure interface behaviour, as well as for development of constitutive models that capture the combined effect of shear rate, surface roughness and stress history.