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

The characteristic features of undrained responses of granular materials, for example, stress ratio at instability (eta(IS)) and phase transformation (eta(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, eta(IS) and eta(PT), showed good correlation with the state parameter (psi) and the density indices. It was found that the eta(IS) decreased with psi, 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.