Energy-based modeling of liquefaction and earthquake site response

A methodology for the effective stress analysis is developed to simulate the local site response during earthquakes, especially for liquefiable soil deposits. The energy method which correlates dissipated energy and pore pressure buildup, and stress dilatancy, is successfully combined with multi-yield surface plasticity constitutive model.; The work in this dissertation consists of four parts, which take steps for generalization of the constitutive relation. First part investigates the possibility of the energy method through laboratory test results by computing energy from experimentally obtained hysteresis loop. Then the method is combined with a simple backbone curve given by a G-gamma curve to simulate pore pressure buildup under undrained cyclic loading with constant shear strain amplitude. A method to construct liquefaction strength curve from a G-gamma curve is also proposed. Then for arbitrary loading, the method is combined with one dimensional multi-yield surface plasticity model.; Second part investigates the applicability of one-dimensional model to site response. Firstly, total stress analysis is conducted to validate the model by comparing results with that of equivalent linear model. Secondly, a centrifuge test and an observed vertical array record are simulated. Model parameter can be determined by widely accepted material properties in geotechnical earthquake engineering. Results show fairly good agreements with measured data.; Third part generalizes the constitutive model from one- to three-dimension. The pore pressure model in compression is totally embedded in the constitutive relation as a form of volumetric flow. For unloading in dilation, a new elastic matrix is introduced to give similar stress path as one-dimensional model. Upon computation, a class of return mapping algorithm is used for an accuracy of numerical integration.; Fourth part applies the three-dimensional model to site response analysis. The model is first validated through the simulation of total stress analysis. Then the same centrifuge test as one-dimensional model is simulated. To see the effects of multi-directional shaking, the same vertical array data, but with two simultaneous input motions, i.e. NS and EW components, are used as an input. Results clearly show the effects of multi-directional input, and the effects of NS component seem dominating on pore pressure buildup.