INVESTIGATION OF BEHAVIOR OF PARTICULATE MEDIA USING DISCRETE ELEMENT METHOD E. Seyedi Hosseininia, Department of Civil Engineering, Faculty of Engineering, University of Tehran, Tehran, Iran A. A. Mirghasemi, Department of Civil Engineering, Faculty of Engineering, University of Tehran, Tehran, Iran ABSTRACT Many attempts have been made to find various relationships for different parameters and some kinds of constitutive models studying behavior of particulate media. All these models are based on concepts of continuous media which some of them have considered elastic behavior of soil too. Using a numerical method such as Discrete Element Method, one can figure out what is happening through a discontinuous media where soil particles have the main rules in introducing the shear strength and deformation characteristics of the media. The behavior of the media is more important when the particles have the ability of fragmentation. But most of the models presented before, have not consider this phenomenon. In this paper, the hyperbolic elastic model is investigated for an assembly of polygon shaped particles in two different test series. Also evolution of different macro parameters of the assembly such as volume strain, angle of friction, angle of dilatancy and elastic modulus are studied during the tests both for non-breakable and breakable soil particles. RÉSUMÉ Beaucoup de tentatives ont été faites de trouver de divers rapports pour différents paramètres et quelques genres de modèles constitutifs étudiant le comportement des médias particulaires. Tous ces modèles sont basés sur des concepts des médias continus que certains d'eux ont considérés le comportement élastique du sol aussi. En utilisant une méthode numérique telle que la méthode discrète d'élément, on peut figurer hors de ce qui se produit par des médias discontinus où les particules de sol ont les règles principales en présentant les caractéristiques de résistance au cisaillement et de déformation des médias. Le comportement des médias est plus important quand les particules ont les capacités de la fragmentation. Mais la plupart des modèles ont présenté avant, démuni considèrent ce phénomène. En cet article, le modèle élastique hyperbolique est étudié pour un ensemble des particules formées par polygone de deux séries différentes d'essai. En outre l'évolution de différents macro paramètres de l'ensemble tels que la contrainte de volume, l'angle du frottement, l'angle de l'épaississement et le module élastique sont étudiés pendant les essais pour les particules non-cassables et cassables de sol. 1. INTRODUCTION The crushability of soil particles has been studied experimentally by a number of researchers and Influence of particle breakage on internal friction angle and deformability of granular materials have been investigated with tests such as triaxial and unconfined compression tests (Marsal 1967, Bertacchi et al. 1970, Fumagali et al. 1970, and Marachi et al. 1972, Venkatachalam 1993, Varadarajan et al. 2003). Triaxial tests of sands show a strong dependence of strength and dilatancy behavior on both relative density and stress level, relating to grain crushability (Bolton, 1986). An empirical characterization of peak angle of internal friction of sands in relation to those two parameters was reasonably successful, although inherent anisotropy due to bedding was also seen to be important. In recent years, along with the progress of numerical methods and computer technology, different methods have been used to model breakage of brittle bodies with the help of Discrete Element Method (DEM). Discrete element simulation of perfectly elastic and infinitely strong grains provides many insights into the deformation of granular media (Thornton, 2000). Among these methods, are the method based on simultaneous utilization of Molecular Dynamics (MD) (Kun et al. 1996) and the 3D approach used by Robertson & Bolton (2001) and McDowell & Harireche (2002). Breakage of particles is very important whereas it influences on the stability and the deformation of an earthwork structure where there is a high pressure on the layers. This is happening in the underlying layers, bearing significant weight of the upper layers. The soil grains in the underlying layers are subjected to significant stress magnitudes. The induced high stresses may cause the particles to be broken. Particle breakage and crushing of large particles to smaller ones, results in changes in grain size (gradation) curve;