Micromechanical Analysis of Sheared granular Materials Using the Discrete Element Method

Abstract

This PhD thesis was written at the Department of Geosciences at the University of Bremen in Germany and funded through MARUM Center for Marine Environmental Sciences . The work was undertaken from May 2009 to September 2013. The data analyzed in this thesis were produced by the author through the application of numerical Discrete Element simulations. Based on this approach, different methods of analyzing the microfabric of granular materials were applied and developed. This thesis contains five chapters including three research papers that improve the understanding of the effect of the microfabric on the shear strength of granular matter. The introduction gives a general overview of granular matter and its relevance in nature and industry. After that, the focus is on the empirical concepts of friction, strength, and failure as controlling factors for the granular stability. This is followed by a description of the typical physical and mechanical properties of granular matter, such as the composition, the grain size and shape, and the packing and porosity. The introduction also includes a description of the motivation and the main objectives of this research and provides general open scientific questions that will be addressed in the subsequent chapters. The first chapter closes with a detailed description of the different types of model setups and lists all relevant numerical methods applied in this research. The body of the thesis is represented by three manuscripts (Chapters 2 - 4). Each of them focuses on the coefficient of friction whose behavior is equivalent to the bulk shear stress according to the Mohr-Coulomb criterion. Within the first study, the influence of the model dimensionality, 2D vs. 3D, on shear behavior was investigated. The focus of the second study was the contact formation and evolution of complex particle shape arrangements. Therein, the microfabric of three different basic particle shapes was compared. The third study was designed to examine pore volume changes caused by grain shape variation. The final chapter of the thesis synthesizes the main conclusions from the three manuscripts and presents some future perspectives.