PLASTICITY MODELING OF SOILS AND FINITE ELEMENT APPLICATIONS
Abstract
In this dissertation, emphasis is placed on critical assessment of the applicability of plasticity-based material models of soil within the context of their finite element implementations, and on computational studies of the progressive failure behavior of several geotechnical engineering problems. Recently developed advanced plasticity models as well as classical models are reviewed and discussed with respect to their advantages and limitations for application to geotechnical engineering problems. Incremental constitutive matrices of isotropic material models are then presented in a form that is suitable for direct numerical analysis, under both associated and non-associated flow rule assumptions. Further, incremental equilibrium equations considering the effect of large deformation or geometric change of soil are derived by utilizing the updated lagrangian formulation. For elastic-plastic finite element analyses, integration techniques such as the mid-point integration rule and initial stress iterative method are employed to demonstrate the finite element implementation of existing plasticity models. Here, the plasticity models adopted for computer implementation are (i) the Drucker-Prager model (elastic perfectly plastic model); and (ii) the strain hardening cap models (plane and elliptic cap models). The computer implementation has been completed and its procedures have been coded ina subroutine of the finite element program "SOILSLP" developed at Purdue University. The cap models are evaluated experimentally and analytically in a comparative study with the Drucker-Prager model. In the analytical study, these plasticity models are applied to a footing problem and a slope stability problem under static or seismic loading conditions. The finite element solutions corresponding to different material models are compared to each other. They are also evaluated from the viewpont of the limit analysis method. Finally, the applicability and limitations of the plasticity models as applied to geotechnical engineering problems in general and earthquake induced landslides problems in particular are discussed, based on the results obtained from these present finite element analyses.
Degree
Ph.D.
Subject Area
Civil engineering
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