Exploring packing density, critical state, and liquefaction resistance of sand-fines mixture using DEM

A series of monotonic and cyclic triaxial shearing tests are simulated by discrete element method (DEM) to explore packing density, critical state, and liquefaction resistance of sand-fines binary mixtures. It is found that there is a threshold fines content (FCth) that makes void ratio reach the minimum value and it is affected by the relative density of the mixture. A unique critical state line (CSL) is obtained in equivalent skeleton void ratio-mean effective stress (e*-p') plane regardless of the fines content. The critical stress ratio of the mixture slightly increases as fines content increases, and its average value is around 1.20. The e* and ψe* (state parameter based on e*) can unifiedly characterize the cyclic liquefaction resistance of the mixtures with different fines contents. The active particles of binary mixtures that participate in the force chains are explored from a microscope perspective. It reveals that there is a unique micro CSL in the mechanical coordination number-mean effective stress (MCN-p') plane despite of fines contents, and the micro state parameter (ψMCN) can also successfully and unifiedly characterize the cyclic liquefaction resistance of sand-fines mixtures.