Finite Element Analysis of Strain Localizaion in ExcavationsResearch into Network Algorithms and Related Problems

基坑应变定位有限元分析网络算法及相关问题研究

• 批准号: 9700426
• 负责人: Ronaldo Borja
• 金额: $ 17.87万
• 依托单位: Stanford University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 1997
• 资助国家: 美国
• 起止时间: 1997-10-01 至 2001-09-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9700426&HistoricalAwards=false
• 关键词: Finite; Element; Analysis; Strain; Localizaion

This project involves the study of strain localization on the stability and deformation behavior of open and supported excavations. Previous studies have demonstrated the usefulness of the standard finite element (FE) method in modeling the process of sequential excavation and construction particularly when the soil mass is deforming homogeneously. However, when a narrow band of intense shearing forms within the soil, the standard FE interpolation becomes inadequate because it is incapable of representing the effect of shear bands which could form across the finite elements. Therefore, in the regime of intense shearing, the standard FE method would predict a stiffer structural behavior even though a bifurcated response is already in order. In braced and tied-back excavations, this implies that the predicted movements and support loads will be smaller, and so the standard FE solution will err on the unsafe side. This research will address this problem by modeling strain localization as a problem of strong discontinuity, which involves jumps in the displacement field. The idea of slip lines in soil mechanics is consistent with this analysis. Within the context of FE analysis, problems involving strong discontinuities result in solutions that are completely independent of the FE mesh, in particular showing a sharp resolution of the discontinuities even in unstructured meshes. Furthermore, this approach admits the use of traditional rate-independent models of continuum mechanics, even those which do not offer a characteristic length scale, since the discontinuities are now assumed to correspond to sets of measure zero in the mathematical sense. The investigation will cover drained and undrained behavior using a finite deformation theory based on multiplicative plasticity, and will involve the use of J2 plasticity and modified Cam-Clay plasticity models. There are numerous field cases where strain localizations are known to have formed during the process of sequential excavation, and these will be used to test the accuracy of the proposed analytical methodology.

该项目涉及对开挖和支持发掘的稳定性和变形行为的应变定位研究。 先前的研究表明，标准有限元（FE）方法在建模顺序发掘和构造过程中的有用性，尤其是当土壤质量均匀变形时。 但是，当土壤中狭窄的强烈剪切带形成狭窄的带时，标准的Fe插值变得不足，因为它无法代表剪切带的效果，而剪切带的效果可能会在有限的元素中形成。 因此，在强烈的剪切状态下，即使已经有分叉的响应已经按顺序进行，标准FE方法也会预测结构性较硬的行为。 在支撑和绑扎的挖掘中，这意味着预测的运动和支撑载荷将较小，因此标准的FE解决方案将在不安全的侧面误。 这项研究将通过将应变定位建模为强烈不连续性的问题来解决这一问题，这涉及流离失所领域的跳跃。 土壤力学中滑动线的想法与此分析一致。 在FE分析的背景下，涉及强烈不连续性的问题导致解决方案完全独立于FE网格，特别是在非结构化的网格中也表明了不连续性的急剧解决。 此外，这种方法承认使用传统的与速率无关的连续性力学模型，甚至那些不提供特征长度尺度的模型，因为现在假定不连续性在数学意义上与量度零相对应。 该研究将使用基于乘法可塑性的有限变形理论涵盖排水和不排水的行为，并将涉及使用J2可塑性和改良的CAM-Clay可塑性模型。 在许多现场案例中，已知在顺序发掘过程中已形成菌株局部定位，并且这些局部将用于测试所提出的分析方法的准确性。