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][201317]，斯坦福大学，c罗·博尔哈，“可液化土壤的静动力失稳”，本项目旨在建立一个有限元模型来分析地震期间和地震后土壤的动力失稳和流动液化，包括伴随的侧向流动和大的地面运动。该模型基于两相混合理论，具有以下基本组成部分：(a)复制液化前超孔隙压力积累的本构模型；(b)流动液化失稳发生的判据；(c)流动液化后残余状态下的本构响应。采用边界面塑性模型对流动液化发生前土体的各向异性循环应力-应变行为进行了模拟，并对随之产生的孔隙压力进行了预测。通过使用基于变形梯度乘法分解的有限变形理论，采用了大变形。该项目的一个重要组成部分是将单调不排水三轴试验和循环不排水单剪试验的结果作为边值问题进行分析。在解释这些试验结果时采用的普遍假设是试样均匀变形，这表明任何测量的试样响应都可以解释为材料响应。然而，有强烈的迹象表明，这种说法远非正确。在进行边值问题模拟时，要解决的一个问题是，在中等密度的饱和砂土中，通常观察到的准稳态状态是否是非局部的。此外，还研究了缺陷和其他扰动对作为结构系统的土样响应的影响。最后，设计了一种系统的方法来重新校准有限变形状态下的本构模型参数，并使用有限元模型重新分析了1971年圣费尔南多地震后的下圣费尔南多大坝倒塌。