Dynamic properties of a sand-nanoclay composite

The paper describes the influence of 1-3% (by dry mass of sand) Laponite, a highly plastic synthetic nanoclay, on the dynamic properties of Ottawa sand, based on undrained resonant column tests. The effect of Laponite depends on the amount added, the confining stress and consolidation time. With 1% Laponite, there is an increase in the very small-strain shear stiffness at all confining stresses, which increases with extended consolidation time, reflecting the thixotropic nature of the nanoclay. Added Laponite also produces an increase in small-strain damping, an extension of the linear strain threshold; and it delays the generation of excess pore pressure, degradation of shear modulus and increase in damping with shear strain. These effects, which become more significant with increasing Laponite content, can be attributed to the impact of the clay on the fabric and grain-to-grain contacts. Evidence is provided that Laponite interferes with direct interaction between the sand grains, and the thickness of the clay layer present at the contacts appears to control the small-strain behaviour of the sand-Laponite mixtures. The formation of a gel-like pore fluid from the hydration of Laponite in the voids, and the degree to which it occupies the pore space, are responsible for the behaviour in the non-linear region.