Disturbed state modeling for dynamic and liquefaction analysis

Although a number of models have been proposed to characterize behavior of geological materials including elastic, plastic, and cyclic loading responses, few constitutive models have been developed for the behavior of fully saturated sands and interfaces including liquefaction under dynamic loading. Such realistic constitutive models play an important role in analyzing and predicting the response and design of soil-structure interaction systems. Also, in the engineering view of the complexity of the material behavior, it becomes necessary to develop and use computer procedure (finite element method) for the analysis and prediction of behavior of geotechnical problems. A general concept, called the disturbed state concept (DSC), that can characterize behavior of geological material is developed in this dissertation for the behavior of saturated sands and sand-steel interfaces. The DSC model is an unified approach and allows hierarchical use of the model for factors such as elastic and plastic strains, damage, and softening and stiffening. The model parameters for a saturated sand and a sand-steel interface are evaluated using data from comprehensive laboratory tests; truly triaxial test device for the saturated sand and cyclic multi-degree-of-freedom device (CYMDOF-P) for the interface. The laboratory test results are also used for the verification of DSC model. In general, the model predictions were found to provide satisfactory correlation with the test results. The DSC model with the foregoing parameters is implemented in a nonlinear dynamic finite element program(DSC-DYN2D). It is used to solve two boundary value problems-an axially loaded pile and a shaking table test-involving the interface behavior for pile and the liquefaction for shake table. A new and highly efficient method is used to determine the liquefaction in saturated materials. This method is based on the changing microstructure of the material and allows identification of liquefaction based on the critical disturbance, Dc which is the point where the curvature of the disturbance function is the minimum. Based on the results of this research, it can be stated that the DSC model is capable of characterizing the cyclic behavior of saturated sands and interfaces and the liquefaction instability under dynamic and earthquake loading