Exploring the undrained behaviour of granular clumps after isotropic and Ko-consolidation paths using DEM

This paper investigates the undrained behaviour of granular clumps after isotropic and K_o-consolidation paths using a three-dimensional discrete element method (3D-DEM). Four randomly chosen clumped particles with a wide range of densification indexes, I_D, and mean confining stresses, p' were considered. The specimens were sheared to the deviatoric strain, ${\epsilon }_q$ of 40 % to reach the critical state (CS) conditions. It was found from the results that a unique critical state line (CSL) was achieved, irrespective of consolidation paths. The micro-mechanical quantities such as the average coordination number (CN) and von Mises fabric in terms of the second invariant of deviatoric fabric, F_vM, also reached CS values. Irrespective of the consolidation paths, unique relationships were found between $e-\log \left(p^{\prime }\right)$and $CN-\text{log}\left(p^{\prime }\right)$. The stress-fabric joint invariant, K_F established a unique relationship with $p^{\prime }$and e, which forms a relationship in the $K_F-p^{\prime }-e$ space and the projection of this relationship in the $e-\log \left(p^{\prime }\right)$ plane confirms the classical CSL. Moreover, the flow potential (u_F), stress ratio at instability (${\eta }_{IS}$), and average coordination number at instability (CN_IS) showed no dependency on the consolidation paths, while a dependency was observed for the second-order deviator fabric, F_vM.