The effect of consolidation on undrained behaviour of granular materials: experiment and DEM simulation

Abstract

The characteristic features of undrained responses of granular materials, for example, stress ratio at instability ( η IS) and phase transformation ( η PT) states and the critical state (CS) behaviour, are often influenced by the consolidation history. However, there are limited studies in the literature, and a consensus has not yet been reached. This study combined the triaxial test of yellow silty sand and the three-dimensional discrete element method (DEM) simulation of ellipsoid particles under a triaxial condition to evaluate the effect of isotropic and K 0 consolidations. Triaxial test data formed non-unique CS lines (CSLs) in the e–log(p′) space for isotropic and K 0 tests, whereas the CSL was unique for DEM simulations; where e and p′ are the void ratio and mean effective stress, respectively. The micromechanical quantities, coordination number (C N) and fabric anisotropy (F vM) at the CS, also showed a unique relation with p′. The characteristic features, η IS and η PT, showed good correlation with the state parameter (ψ ) and the density indices. It was found that the η IS decreased with ψ, and the correlation was dependent on consolidation type. The micromechanical analysis suggested that F vM is a better parameter than C N to characterise the macromechanical behaviour. This study unambiguously supports the applicability of CS theory and provides insights into micromechanics of granular materials.