Static and Dynamic Instability of Liquefiable Soils

可液化土壤的静态和动态不稳定

• 批准号: 0201317
• 负责人: Ronaldo Borja
• 金额: --
• 依托单位: Stanford University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2002
• 资助国家: 美国
• 起止时间: 2002-10-01 至 2007-09-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0201317&HistoricalAwards=false
• 关键词: Static; Dynamic; Instability; Liquefiable; Soils

Abstract0201317, Ronaldo Borja, Stanford University"Static and Dynamic Instability of Liquefiable Soils"The objective of this project is to develop a finite element model for analyzing the dynamic instability and flow liquefaction of soils, including the accompanying lateral flow and large ground movement during and following an earthquake. The model is based on a two-phase mixture theory with the following essential components: (a) a constitutive model that replicates the buildup of excess pore pressure prior to liquefaction; (b) a criterion for the onset of flow liquefaction instability; and (c) a constitutive response at residual state following flow liquefaction. A bounding surface plasticity model is used to model the anisotropic cyclic stress-strain behavior of soils before the onset of flow liquefaction, as well as to predict the accompanying pore pressure buildup. Large deformations are employed through the use of a finite deformation theory based on a multiplicative decomposition of the deformation gradient.A major component of the project is devoted to analyzing the results of monotonic undrained triaxial tests and cyclic undrained simple shear tests as a boundary-value problem. A universal assumption employed in interpreting the results of these tests is that the specimen is deforming homogeneously, suggesting that any measured specimen response may be interpreted as a material response. However, there are strong indications that this is far from being correct. Among the issues addressed by performing boundary-value problem simulations is whether or not the quasi-steady state condition commonly observed in saturated sand specimens of intermediate density is non-local. Also being investigated are the effects of imperfections and other perturbations on the response of soil specimens taken as a structural system. Finally, a systematic methodology is being devised for re-calibrating the constitutive model parameters in the finite deformation regime, and the finite element model is used to reanalyze the collapse of the Lower San Fernando Dam following the San Fernando earthquake of 1971.

摘要0201317，斯坦福大学罗纳尔多·博尔贾（Ronaldo Borja），“液化土壤的静态和动态不稳定性”，该项目的目的是开发一个有限的元素模型，用于分析泥土的动态不稳定性和流动液化，包括伴随的侧向流动以及在地震期间和之后的横向流动和大地面运动。 该模型基于具有以下必需组成部分的两相混合理论：（a）一个本构模型，该模型在液化之前复制了过量孔隙压力的积累； （b）流动液化不稳定的标准； （c）流量液化后在残留状态下的本构响应。 边界表面可塑性模型用于模拟流动液化发作之前土壤的各向异性循环应力 - 应变行为，并预测伴随的孔隙压力积累。 通过使用有限变形理论，基于变形梯度的多重分解来实施大变形。该项目的主要组成部分致力于分析单调不渗透的三轴测试的结果和环状不流失的简单剪切测试作为边界值问题。 解释这些测试结果的一个通用假设是，样品是均匀变形，表明任何测量的试样响应都可以解释为材料响应。 但是，有很强的迹象表明这远非正确。 在通过执行边界值问题模拟解决的问题中，在中间密度的饱和砂样本中通常观察到的准稳态状态是否是非本地的。 还研究了缺陷和其他扰动对被视为结构系统的土壤标本响应的影响。 最后，正在设计一种系统的方法，用于重新校准有限变形方案中的本构模型参数，并使用有限元模型重新分析了1971年圣费尔南多地震后下部San Fernando大坝的崩溃。