An experimental study of the initial volumetric strain rate effect on the creep behaviour of reconstituted clays

Clayey soils tend to undergo continuous compression with time, even after excess pore pressures have substantially dissipated. The effect of time on deformation and mechanical response of these soft soils has been the subject of numerous studies. Based on these studies, the observed time-dependent behaviour of clays is mainly related to the evolution of soil volume and strength characteristics with time, which are classified as creep and/or relaxation properties of the soil. Apart from many empirical relationships that have been proposed in the literature to capture the rheological behaviour of clays, a number of viscid constitutive relationships have also been developed which have more attractive theoretical attributes. A particular feature of these viscid models is that their creep parameters often have clear physical meaning (e.g. coefficient of secondary compression, Cα). Sometimes with these models, a parameter referred to as initial/reference volumetric strain rate, v̇₀ has also been alluded as a model parameter. However, unlike Cα, the determination of v̇₀ and its variations with stress level is not properly documented in the literature. In an attempt to better understand v̇₀, this paper presents an experimental investigation of the reference volumetric strain rate in reconstituted clay specimens. A long-term triaxial creep test, at different shear stress levels and different strain rates, was performed on clay specimen whereby the volumetric strain rate was measured. The obtained results indicated the stress-level dependency and non-linear variation of v̇₀ with time.