Characteristic behavior of drained and undrained triaxial compression tests: DEM study

Undrained and drained triaxial compression tests were simulated using the discrete element method (DEM). It was found that the transition states between contractive and dilative behavior of dense specimens, that is, the characteristic (Ch) and phase transformation (PT) states for drained and undrained conditions, respectively, are the same state in terms of stress ratio and fabric quantity (F_vM). The transition was not due to the change in number of particle contacts, that is, coordination number (CN). A unique critical state (CS) line was obtained for a large range of mean effective stresses (p') for both drained and undrained simulations, which facilitates further analysis in term of the state parameter (ψ). Because PT, Ch states, and CS were representative of sand behavior, the SANISAND model was adopted to predict DEM simulations. Despite some limitations, the model can predict overall trends of shearing response and produce adequate qualitative behavior such CS, PT, or Ch states of DEM simulations.