Discrete element analysis of cyclic shear behavior of sand considering particle morphology and suffusion effects

To investigate the cyclic response characteristics of sandy soil under the combined effects of particle morphology and suffusion, coarse particle skeletons with varying elongation and flatness indices were constructed based on the discrete element method (DEM). A fines removal algorithm incorporating stress states and geometric topology is introduced to prepare gap-graded specimens with different degrees of suffusion, followed by undrained cyclic shear simulations. The results indicate that fines loss accelerates the decline of mean effective stress, and the failure modes of the specimens change from cyclic mobility to flow liquefaction as the degree of suffusion increases. Particle morphology significantly affects the suffusion sensitivity of the skeleton. Compared with spheres, complex-shaped particles maintain cyclic mobility characteristics at low fines loss ratios and delay liquefaction. Meso-scale analysis reveals that the liquefaction resistance is not entirely determined by the magnitude the equivalent intergranular void ratio. A specific flattened morphology can resist the reorganization of the skeleton more effectively than mere high packing density. The evolution of the mechanical coordination number further confirms that contact networks constructed by complex particle shapes possess greater resilience, effectively inhibiting the premature collapse of force chain systems.