NEESR-CR: Properties of Cohesionless Soil Subsequent to Liquefaction and Resedimentation

NEESR-CR：液化和再沉降后无粘性土壤的特性

• 批准号: 0936421
• 负责人: Ronaldo Borja
• 金额: $ 81.3万
• 依托单位: Stanford University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2009
• 资助国家: 美国
• 起止时间: 2009-10-01 至 2014-09-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0936421&HistoricalAwards=false
• 关键词: NEESR; CR; Properties; Cohesionless; Soil

This award is an outcome of the NSF 09-524 program solicitation "George E. Brown, Jr. Network for Earthquake Engineering Simulation (NEES) Research (NEESR)" competition and includes Stanford University (lead institution), Arizona State University (subaward), and Bucknell University (subaward). This project will utilize the NEES equipment sites at the University of California at Davis, and at the University at Buffalo. The project will experimentally and numerically investigate the properties of resedimented soil following liquefaction, including void ratio distribution and shear strength. To investigate the properties of cohesionless soil subsequent to liquefaction, a series of coordinated physical model tests, numerical analyses, imaging analyses, and laboratory shear strength tests will be conducted. Physical model testing will include laboratory column testing, small- and large-scale shake table testing, and centrifuge testing. Numerical analyses will include simulations of the impact of non-homogeneities (as revealed by the physical model testing) on shear banding and the undrained shear strength of cohesionless soil, and novel computational fluid dynamics- (CFD-) based analyses of resedimentation of cohesionless soils. Laboratory testing will include shear strength testing on specimens recovered from the physical models, using special techniques to preserve their structure. Imaging will include bright field microscopy (BFM) and computer-aided tomography (CT) scanning of recovered specimens to evaluate their structure prior to and after liquefaction.Uniform and non-uniform sands will be liquefied and allowed to reconsolidate at different stress levels. Solidified soils will be removed and freeze-dried for cutting into smaller samples. The heterogeneity of the smaller samples will be quantified through CT, BFM, and digital image processing (DIP). The numerical modeling program will utilize sedimentation theories and CFD implemented in Eulerian framework. The mathematical model will consist of three layers: clarified water, fully liquefied soil, and solidified soils. Shock fronts will be tracked using the volume of fluid (VOF) method. Two numerical modeling schemes will be pursued, the first aimed at predicting the heterogeneity of liquefied soils, and the second aimed at studying the effect of heterogeneity on the post-liquefaction strength.This year's NEES solicitation seeks "ground-breaking and transformative basic research" requiring the use of NEES equipment sites. Much progress has been made in studying and modeling the phase transition process when a soil with a well-defined solid skeleton liquefies and eventually behaves like fluid. The reverse phase transition, in which a liquefied soil solidifies and forms a new solid skeleton, has not received the same level of attention, yet this process could dramatically alter the post-liquefaction properties of such soil, including its shear strength. The proposed work, requiring the use of two NEES testing facilities and focusing on a problem rarely addressed in the literature, satisfies the definition of a ?transformative basic research.? The project will advance discovery and understanding of the sedimentation, liquefaction, and consolidation processes while promoting teaching, training and learning in the graduate and undergraduate levels, as well as in high school and K-12 levels. A teaching module on the subject of liquefaction will be integrated into the University Consortium on Instructional Shake Tables (UCIST), a partner of NEES, and will ensure an active undergraduate participation. Visualization tools demonstrating solid-fluid interaction will enhance education and research. Every effort will be made to get underrepresented students and women involved in this project. Data from this project will be archived and made available to the public through the NEES data repository.

这个奖项是一个结果的NSF 09-524计划征求“乔治E。小布朗地震工程模拟网络（NEES）研究（NEESR）”竞赛，包括斯坦福大学（牵头机构），亚利桑那州立大学（子奖项）和巴克内尔大学（子奖项）。该项目将利用位于戴维斯的加州大学和位于布法罗的大学的NEES设备站点。该项目将通过实验和数值方法研究液化后沉降土的特性，包括孔隙比分布和抗剪强度。 为了研究液化后无粘性土的特性，将进行一系列协调的物理模型试验、数值分析、成像分析和室内抗剪强度试验。 物理模型试验将包括实验室柱试验、小型和大型振动台试验以及离心试验。 数值分析将包括模拟非均匀性（如物理模型试验所示）对剪切带和无粘性土壤的不排水剪切强度的影响，以及新的基于计算流体动力学（CFD）的无粘性土壤再沉积分析。 实验室测试将包括对从物理模型中回收的样本进行剪切强度测试，使用特殊技术来保护其结构。 成像将包括明场显微镜（BFM）和计算机辅助断层扫描（CT），以评估其结构之前和之后的液化。均匀和不均匀的沙子将被液化，并允许在不同的应力水平重新固结。将去除固化的土壤并冷冻干燥，以切割成较小的样品。将通过CT、BFM和数字图像处理（DIP）定量较小样本的异质性。数值模拟程序将利用欧拉框架中的沉降理论和CFD。该数学模型将包括三个层次：澄清水，完全液化的土壤，固化的土壤。将使用流体体积（VOF）方法跟踪激波阵面。两个数值模拟方案将继续进行，第一个旨在预测液化土壤的非均匀性，第二个旨在研究非均匀性对液化后强度的影响。今年的NEES征集寻求“突破性和变革性的基础研究”，需要使用NEES设备场地。具有明确固体骨架的土壤从冻结到最终表现为流体的相变过程的研究和模拟已经取得了很大的进展。逆相变，其中液化土壤固化并形成新的固体骨架，没有得到同样程度的关注，但这个过程可能会显着改变液化后的土壤性质，包括其抗剪强度。拟议的工作，需要使用两个NEES测试设施，并专注于一个问题，很少在文献中解决，满足的定义？基础研究的转型？该项目将推进沉积，液化和固结过程的发现和理解，同时促进研究生和本科生以及高中和K-12水平的教学，培训和学习。 关于液化主题的教学模块将被整合到大学教学摇表联盟（UCIST），NEES的合作伙伴，并将确保积极的本科生参与。演示固体-流体相互作用的可视化工具将加强教育和研究。将尽一切努力让代表性不足的学生和妇女参与这一项目。该项目的数据将通过NEES数据库存档并向公众提供。