Energy dissipation in granular materials in DEM simulations

Soil has generally been treated as a continuum from as early as the eighteenth century. Since then the analysis of soil behaviour in practical engineering analyses and development of constitutive models has depended on a continuum assumption. However, in order to gain a deeper understanding of the behaviour of soils and their particulate nature, there is a need to move from continuum mechanics to discrete models. Such modelling is possible using the Discrete Element Method (DEM). In this thesis an open source DEM particle simulation software, LIGGGHTS is used to study the relationships between grain scale parameters and energy dissipation in granular media in one-dimensional compression. In order to measure the dissipated energy, changes in energy terms are traced at every time step and the principle of energy conservation applied. The influence of particle size distribution, initial void ratio, and inter-particle friction coefficient on energy dissipation are studied and discussed. It is shown that increasing the coefficient of uniformity decreases the energy dissipated; lowering the initial voids ratio results in steeper energy dissipation curves; and a higher inter-particle coefficient of friction yields more energy dissipation. It is hoped that the knowledge gained of the relationship between grain scale parameters and energy dissipation can be built upon to formulate constitutive relationships within the hyperplasticity framework. It is envisioned that relating grain scale parameters to constitutive models will allow the formulation of models that are purely based on the micro-mechanics of granular media.