Viscous Property of Granular Material in Drained Triaxial Compression

Abstract

The viscous properties of a wide variety of reconstituted loose and dense unbound granular materials, including natural sands and gravels, were evaluated by a series of drained triaxial compression (TC) tests at fixed confining pressure. In total sixteen granular materials having different mean particle diameters, D50, coefficients of uniformities, Uc, fines contents, FC, degrees of crushability and particle shapes were newly tested. The viscous properties were quantified basically by many times changing stepwise the axial strain rate and partially by performing drained sustained loading during otherwise drained monotonic loading (ML) at a constant strain rate. It is shown that the viscous properties can be represented by the rate-sensitivity of the stress upon a step change in the strain rate, the decay rate of a viscous stress increment during the subsequent ML at a constant strain rate and the dependency of the residual stress during ML at a constant strain rate. The effects of the particle characteristics on the viscous properties were evaluated by summarising the results from the present and previous studies. As a new and surprising fact, with poorly graded unbound round granular materials, the stress for the same strain during ML at a constant strain rate decreases with an increase in the strain rate.