Numerical Study of Oscillating Particle in Viscous Fluid

V Roubtsova

In the proceedings of: GeoVancouver 2016: 69th Canadian Geotechnical Conference

Session: PROBLEMATIC SOILS - III Loose and Liquefiable Soils

ABSTRACT: A micro-hydromechanical model was developed to simulate liquefaction phenomena under strain control on granular media. It combines the discrete element method (DEM) for modelling of the solid phase and the Marker and Cell method (MAC) for pore-scale flow modelling. The flow modelling is based on the full Navier-Stokes equations for incompressible fluids. In order to validate the results of pore-scale numerical simulations, they were compared with results obtained experimentally. This comparison shows that the developed model can precisely describe the flow around an oscillating cylinder immersed in a viscous, incompressible fluid. An example of simulation on a sample consisting of spherical particles shows some of the possibilities that SiGran can provide to explain liquefaction phenomena at the particle scale.

RÉSUMÉ: Un modèle hydromécanique a été développé pour simuler le phénomène de liquéfaction sous un chargement en contrôle de déplacement. Ce modèle combine la méthode des éléments discrets (DEM) pour la phase solide et la méthode Marker and Cell (MAC) pour la modélisation des écoulements. La modélisation des écoulements est basée sur les équations complètes de Navier-Stokes pour les fluides incompressibles. Dans le but de valider les résultats obtenus par les simulations u pore, une comparaison avec ceux obtenus expérimentalement a été effectuée. Cette comparaison montre que le modèle développé peut décrire correctement les écoulements cylindre qui oscille dans un fluide incompressible. Un exemple de simulation, sur un échantillon constitué de particules sphériques, montre quelques- 1. INTRODUCTION When loose, saturated soils are subjected to cyclic shear strain, the soil particles tend to rearrange into a more dense packing with smaller voids, as water in the pore spaces is forced out. In undrained shear testing, no volume change is possible; therefore excess pore pressure is generated. This leads to the transfer of stress from the soil skeleton to the pore water, which causes liquefaction (Xiao, 2015). Liquefaction is one of the most interesting, complex and controversial topics in geotechnical earthquake engineering (Kramer, 1996). Although significant progress toward the assessment of liquefaction resistance has been made in laboratory tests and numerical simulations, major challenges still remain. These challenges are compounded by the complex and variable nature of earthquakes, which are characterized by non-uniform and multidirectional cyclic loading and are therefore difficult to reproduce in laboratory testing. The main objective of this paper was to gain new insight into fluid flow in porous media constituted of spherical particles subjected to cyclic shear displacement. This article further presents the possibilities of a simulation tool named SiGran, developed for producing and testing granular media in drained and undrained conditions. 2. BACKGROUND FOR SOILS AND FLOW MODELLING Although many studies examine the modelling of the undrained behaviour of soils subjected to cyclic loading using continuum approaches, the liquefaction phenomenon has not been well explored at the particle scale. The continuum approach cannot explore the physical microscopic mechanisms that lead to liquefaction, and may therefore fail to explain some of the phenomena associated with liquefaction. It does not provide information about grain movement, contact orientations or inter-particle contact forces. The discrete approach, on the other hand, takes into consideration the discrete nature of the particles. This approach is a powerful tool that can help to simulate the microscopic response and provide the fundamental deformation characteristics of saturated soil in an undrained cyclic shearing test. Among these characteristics, the most important is internal slippage due to grain rearrangement, which leads to a change in the microstructure of the tested specimen. To study the pore flow, the granular media are generally simulated by a regular lattice network, which is made up of pore bodies located on lattice points and connected by pore throats. The simplest capillary model of the linear case is one representing a porous medium by a bundle of straight parallel capillaries of uniform diameter. This model was upgraded by putting

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V Roubtsova (2016) Numerical Study of Oscillating Particle in Viscous Fluid in GEO2016. Ottawa, Ontario: Canadian Geotechnical Society.

@article{3828_0720100836,author = V Roubtsova,title = Numerical Study of Oscillating Particle in Viscous Fluid,year = 2016}