Implementation and comparison of a generalized plasticity and disturbed state concept for the load-deformation behavior of foundations

A nonlinear finite element method with an eight-noded isoparametric quadrilateral element is used for the prediction of load-deformation behavior including the bearing capacity of foundations. A Disturbed State Concept (DSC) with a Hierarchical Single-Surface (HISS) plasticity model with an associated flow rule, and a Generalized Plasticity Model (GPM) with a non-associated flow rule are used to characterize the constitutive behavior of soils. The DSC model, however, can allow for non-associative behavior through the use of disturbance. Both models are able to simulate load-deformation including softening behavior. However, the GPM is based on the continuum approach while the DSC can allow for discontinuity due to factors such as microciaching. Predictions by both models show good agreement with laboratory data. A comparison between the DSC/HISS and generalized plasticity model is presented and it is found that the DSC/HISS model has certain advantages over the generalized plasticity model. A modified Terzaghi theory is developed for the bearing capacity based on the dependence of material behavior and in-situ stress; it can be used to compute the bearing capacity affected by in-situ stress. © Sharif University of Technology, June 2009.