Effects of Particle Characteristics on the Viscous Properties of Granular Materials in Shear

Abstract

The viscous properties of a wide variety of unbound granular materials (GMs) were evaluated by drained shear tests. The specimens were reconstituted ones that were loose or dense and air-dried or moist or saturated, of mostly natural sands and gravels, having different mean particle diameters, uniformity coefficients, fines contents, degrees of particle angularity and particle crushabilities. The tests were mostly triaxial compression (TC) tests and partly plane strain compression tests, both at fixed confining pressure, and direct shear tests at fixed normal pressure. The viscous properties of GMs were evaluated by stepwise changing the loading rate and performing sustained loading (SL) tests during otherwise monotonic loading (ML) at a constant loading rate. The viscous properties are characterised in terms of the rate-sensitivity coefficient (β), the viscosity type parameter (θ=βr/β) and the decay parameter (r1). Correlations among these parameters and effects of particle characteristics on these parameters are analysed. Creep strains are compared with residual strains by cyclic loading under otherwise the same TC conditions. As the particles become less angular, as the grading becomes more uniform and as the particles become less crushable, the viscosity type deviates more from the Isotach type (i.e., θ=1.0) changing toward the P & N type (i.e., θ<0) associated with a decrease in β and r1, while creep strains by SL decreases and residual strains by many unload/reload cycles increases. It is shown that the loading rate effects observed in the experiments can be simulated well by the three-component model taking into account the effects of particle characteristics on the viscous property parameters.