DISCRETE ELEMENT ANALYSIS OF THE RESPONSE OF GRANULAR MATERIALS DURING CYCLIC LOADING

Soil can experience cyclic or repeated loadings in a range of situations and prediction of cyclic soil response is obviously important to geotechnical engineers. The particulate nature of soil results in highly complex, non-linear response characteristics, and developing models that can capture soil response under cyclic loading is non-trivial. The distinct element method (DEM) can be used to study the fundamental, particle-scale mechanics of granular materials, and offers much promise as a tool to advance understanding of soil response. The first stage in adopting DEM to model cyclic soil response is to quantitatively demonstrate that a DEM model can replicate physical test data, as analytical validation of DEM models for random assemblies of particles under repeated loading is not viable. This paper describes a series of strain-controlled cyclic triaxial tests on an ideal granular material (steel spheres) that were used to validate the capability of an axi-symmetric DEM model to analyse cyclic loading. The DEM model was then used in a parametric study to examine the particle-scale mechanics of the response of specimens of uniform spheres to 50 cycles of loading with various strain amplitudes. The distribution of contact force orientations and magnitudes during testing was examined. The simulations indicate that both the fabric anisotropy and coordination number continued to evolve over the 50 cycles considered. While the variation in the macro-scale response was less marked, there is a clear relation between the micro-scale parameters and the overall specimen response.