A discrete element study on sand response to cyclic loading: macro-micro perspectives

The discrete element method (DEM) is used to simulate the behavior of a model sand under cyclic stress. Two approaches are employed in the contact model to account for the effect of anisotropic particle shape: (1) spheres with a rolling resistance moment and (2) clumps of spheres. Model parameters are calibrated using experimental results from drained monotonic triaxial tests on NE34 sand. Then, a series of cyclic triaxial tests is done on a homogeneous elementary volume sample with varying density index (\(I_D\)) and cyclic stress ratio (CSR). Both macroscopic and micromechanical characteristics of the material are examined under cyclic loads. In particular, the evolution of Young’s modulus (E) and the damping ratio (D) with strain amplitude are evaluated at varying \(I_D\) and compared with values from the literature. An analysis of the coordination number (Z), orientation of strong and weak contact forces, friction mobilization, sliding contacts and fabric evolution links the observed macroscopic behavior of energy dissipation to the phenomenon of frictional sliding at the grain scale.