Effects of Stochastic Variability of Soil Properties on Liquefaction Resistance

9523092普雷沃斯特尽管在过去的30年里进行了广泛的研究，但土壤液化现象仍然是大地震期间灾难性破坏的主要原因之一。 本项目的目的是更好地了解土壤液化机制，旨在更现实的液化风险评估方法和适当的抗震设计对策，并强调土壤特性所表现出的空间变异性的重要性。 天然土壤的性质是可变的。 田间试验结果的缺乏，以及土壤性质所表现出的无序程度，导致使用统计方法来描述这些性质的分布。 在这种情况下，各种地质力学土壤特性建模为一个多变量，多维（mV-nD）随机场的组成部分。 随机场的特性基于统计上显著的“原位”测量结果集来评估。 采用多屈服土本构模型，对水平层状桑迪土以及在可液化土上建立的结构物在地震荷载作用下的行为进行二维和三维有限元模拟。 用随机输入本构参数预测超静孔压恢复、液化指数和液化诱发变形的数值模拟结果与确定性输入模拟结果进行了比较;以及空间相关距离、土性概率分布、土性间的互相关性有限元离散网格尺寸，以及2-D简化与真实3-D行为的影响进行了检查和量化。 本构参数校准和性能的分析程序的方法进行了验证，通过比较与“原位”的行为记录在过去的地震。 将提出建议，以更新目前的分析和设计程序的结构建立在可膨胀的土壤，以考虑到土壤特性的空间变异程度。 这项研究将提供一个良好的基础，液化风险评估和表征土壤性质的空间变异性。 ***

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. ***