الفهرس 
IntroductionOnly 14 pages are availabe for public view
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Abstract
Formulation of proper constitutive models for engineering materials and the accurate, efficient, and robust implementation of the models are considered major challenges in computational mechanics. In the dissertation, several important computational issues are addressed in the context of constitutive modeling for geotechnical engineering problems. First, it is shown that the consistency between the numerical scheme used to integrate the constitutive equations and the global strategy used insolution of nonlinear finite element equations is very important if an efficient and stable analysis is to be achieved. This is demonstrated by considering the integration of classical Drucker-Prager model. Within the framework of an implicit integration technique, the so-called consistent Jacobian for Drucker-Prager model is derived in closed form. Through numerical simulatios of several boundary value problems, it is shown that the use of consistent Jacobian leads of significant improvement in efficiency of the numerical solutions. Moreover, recognizing the numerical difficulties involved in the use of Mohr-Coulomb model in the analysis of geotechnical problems, a modified implemented by using both implicit and explicit integration methods. The modified Mohr-Coulomb model is then used to investigate the effect of soil dilatancy on the stability of soil embankments. It is shown that consideration of soil dilatancy is of paramount significance in the slope stability calculations and the use of an associative glow rule leads to unconservative stability numbers. This dissertation also addresses the modeling of cyclic behavior of clays by extending the modified Cam clay to a simple bounding surface model. Again, using an implicit integration scheme, the consistent Jaccobian is derived for this new model in closed form. The numerical simulations show the nobustness of the implementation and demonstrate the realistic behaviour of the model . Realizing the fact that localization of deformation is the a major effect in the response of soil structures near faillur, an enhance finite element was implemented to accommodate the localized faillure and to capture the develped shear bands. Numerical simulations show the advantages of this new element and its ability to simulate the localization phenomena.