9523092 Prevost Though extensively studied during the last 30 years, the phenomenon of soil liquefaction is still one of the main causes of catastrophic damage during major earthquakes. The aim of this project is to obtain a better understanding of soil liquefaction mechanisms, aimed at more realistic liquefaction risk assessment methods and appropriate seismic design countermeasures, and emphasizing the importance of spatial variability exhibited by soil properties. Natural soils are variable in their properties. The scarcity of field test results, and the degree of disorder exhibited by soil properties, leads to the use of statistical methods to describe the distribution of those properties. In this context, the various geomechanical soil properties are modeled as the components of a multi-variate, multidimensional (mV-nD) stochastic field. The characteristics of the stochastic field are evaluated based on statistically significant sets of "in- situ" measurement results. Two- and three-dimensional finite element simulations of the behavior of horizontally layered sandy soil, as well as of structures founded on liquefiable soil and subjected to seismic loads, are performed using the multi-yield soil constitutive model implemented in the computer code DYNAFLOW. The numerical simulation results for predicting excess pore- pressure buildup, liquefaction index, and liquefaction induced deformations -- obtained using stochastic input constitutive parameters -- are compared to deterministic input simulation results; and the influences on these results of spatial correlation distances, probability distributions of soil properties, cross-correlations between various soil properties, finite element discretization mesh size, as well as the effects of the 2-D simplification vs. true 3-D behavior are examined and quantified. Verification of the method for constitutive parameter calibration and for the performance of the analysis procedure is made by comparison with "in-situ" behavior recorded during past earthquakes. Recommendations will be made for updating current analysis and design procedures for structures founded on liquefiable soils, in order to account for the degree of spatial variability of soil properties. This research will provide a sound basis for liquefaction risk assessment and for characterization of spatial variability of soil properties. ***
