Effects of Stochastic Variability of Soil Properties on Liquefaction Resistance

9523092 Prevost 尽管在过去的 30 年里进行了广泛的研究，土壤液化现象仍然是大地震期间造成灾难性破坏的主要原因之一。 该项目的目的是更好地了解土壤液化机制，旨在制定更现实的液化风险评估方法和适当的抗震设计对策，并强调土壤性质所表现出的空间变异性的重要性。 天然土壤的特性各不相同。 由于现场测试结果的缺乏以及土壤特性所表现出的无序程度，导致使用统计方法来描述这些特性的分布。 在这种情况下，各种地质力学土壤特性被建模为多变量、多维 (mV-nD) 随机场的组成部分。 随机场的特征是根据统计上显着的“原位”测量结果集来评估的。 使用计算机代码 DYNAFLOW 中实现的多屈服土本构模型，对水平层状砂土以及建立在可液化土上并承受地震荷载的结构的行为进行二维和三维有限元模拟。 将使用随机输入本构参数获得的用于预测超孔隙压力累积、液化指数和液化引起变形的数值模拟结果与确定性输入模拟结果进行比较；并检查和量化了空间相关距离、土壤特性的概率分布、各种土壤特性之间的互相关、有限元离散化网格尺寸以及 2-D 简化与真实 3-D 行为的影响对这些结果的影响。 通过与过去地震期间记录的“现场”行为进行比较，对本构参数校准方法和分析程序的性能进行了验证。 将提出更新当前基于可液化土壤的结构的分析和设计程序的建议，以考虑土壤特性的空间变异程度。 这项研究将为液化风险评估和土壤特性空间变异性表征提供坚实的基础。 ***

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. ***