S.A.Sadrnejad - Associate Prof., Civil Engineering Dept., K.N.Toosi University of Technology, Teheran, Iran

Natural granular materials are often geometrically anisotropy while is considered in a gravitational field, because the particles have a preferred orientation. Moreover, natural anisotropy of sand is a fully geometrical aspect depends on the orientation of applied load respect to bedding plane known to be due to different responses of granular materials to a given stress. In the other words, this kind of anisotropy is due to micro-fabric created by the arrangement of the particles.The internal friction angle as a main feature of strength characteristic in granular materials is of particular importance, whatever its physical meaning, it is not constant around any point through a given soil, even though the void ratio or relative density is fixed, but rather changes greatly depending on many other factors.The main objective of this paper is to outline a methodology for modeling the elasticplastic behaviour of inherent anisotropy of soil due to a certain kind of plane of deposition and orientation of applied load. The micro fabric behaviour of sand on a sliding plane is known to be composed of two perpendicular components of sliding anisotropy.The constitutive equations of model are derived within the context of slip theory and elastic behaviour of whole medium and plastic sliding of interfaces of predefined multiplanes.The formulation incorporates explicitly the notion of the preferred direction, which defines the orientation of material fabric based on a simple numerical integration

Natural anisotropy, Multi-plane, micro-fabric, sliding mechanism