Numerical analysis of seismically induced deformations in saturated granular soil strata

The problem of cyclic soil mobility associated with seismic activity is of significant practical importance and may induce detrimental effects on super- and sub-structures. Nevertheless, challenges still remain in predicting liquefaction induced lateral spreads and settlements. In this thesis, a computer code based on an existing fully coupled Biot-type formulation is implemented in order to develop a numerical seismic analysis tool at Rensselaer Polytechnic Institute (RPI). This code complements the RPI seismic centrifuge experimental capabilities and addresses the currently standing challenges in numerical predictions of seismic permanent deformations. A new constitutive effective stress model is developed to simulate the seismic loading response of saturated granular soils. A novel computational mechanism to model soil densification due to liquefaction is developed to account for settlements before re-solidification of the liquefied stratum. This mechanism is also useful in simulating the possible evolution of water inter-layers trapped between horizontal layers of different permeability.; Site amplification at the Lotung array in Taiwan is numerically simulated to validate the developed computational code. Critical assessment of state-of-the-art predictive numerical tools based on a recent model testing program (as part of the centrifuge VELACS project) is presented. A close look is taken at the evolution of settlements due to liquefaction. Deficiencies in currently existing constitutive models are highlighted. Using the developed code, numerical simulations of two VELACS Models that mimic infinitely extended saturated soil deposits are found to reasonably model many aspects of the recorded response. The behavior of saturated soil at very low (near liquefaction) effective stresses is shown to be critical in dictating the ensuing lateral deformations.