Semi-Micro Bounding Surface Model for Anisotropic Sand   Seyed Amirodin Sadrnejad Professor, Dept. of Civil Engineering, K.N. Toosi University of Technology, Tehran, Iran e-mail: sadrnejad@kntu.ac.ir
			ABSTRACT

This paper deals with the development of a numerical model providing reliable estimates of the loading of a sand box with buried steel pipe subjected to cyclic loading. The reliability test is based on two physically and statistically independent sets of experiments. The first set is related to elastoplastic material modeling and the second set to structural model verification. Since model verification can be accomplished successfully, the developed model is well suited to provide prognoses of the loading of a sand-buried steel pipe for dynamic loading scenarios. Accordingly, an induced anisotropic plasticity model predicting dynamic behaviour of sand is presented. The model incorporates the critical/steady state concept that postulates the existence of a state where sand continuously deforms at a certain constant effective stress depending two main parameters of both initial bulk parameters (i.e. void ratio or relative density) and stress level (i.e. mean stress). The local instability of saturated sand within post-liquefaction is highly dependent on the residual inherent/induced anisotropy, bedding plane effects, and stress/strain path.
Most of the models developed using stress/strain invariants are not capable of identifying the parameters depending on orientation such as fabric. This is mainly because stress/strain invariants are quantities similar to scalar quantities and not capable of carrying directional information with themselves.
The constitutive equations of the model are derived within the context of non-linear elastic behaviour of the whole medium and plastic sliding of interfaces of predefined multi-planes.
The proposed multi-plane based model is capable of predicting the behaviour of soils on the basis of plastic sliding mechanisms, elastic behaviour of particles and possibilities to see the micro-fabric effects as natural anisotropy as well as induced anisotropy in plasticity.
The comparison of model results with experiments under both drained and undrained tests show the capability and power model in predicting of soil behaviour under any condition in soil structures.

Keywords: Multi-plane, Elastic-plastic, Model, Bounding surface, anisotropic sand

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