| Soil-skeleton dilation effects (cyclic mobility) is of paramount importance in dictating the extent of shear (lateral) deformations under seismic loading conditions. The main objective of this thesis is to develop a mixed stress/strain-space constitutive model capable of modeling this phenomenon during dynamic earthquake excitation. This constitutive model is based on the original Prevost (Princeton University) stress-space plasticity theory for frictional cohesionless soils. Mainly, the following two new distinct phases of soil response were added: (i) A perfectly-plastic slip strain phase (without contraction or dilation) represented by a robust strain-space formulation, followed by (ii) a strongly dilative/contractive phase beneath the failure envelope. Applicability of numerical optimization procedures for systematic calibration of model parameters is also investigated.;The developed constitutive model is incorporated in a two dimensional finite element program CYCLIC, which implements a Biot-type soil-fluid coupled formulation. CYCLIC is employed to analyze the effect of spatial permeability variation on site liquefaction potential and the corresponding deformation patterns. A port dike retaining structure is also studied and the results are compared to other available liquefaction analysis programs. Currently, an Internet-based computational program CYCLIC 1D (http://casagrande.ucsd.edu), a one dimensional version of CYCLIC, is already available to remote users for conducting on-line seismic analysis. |
