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

该奖项是NSF 09-524项目招标“小乔治·e·布朗地震工程模拟（NEES）研究网络（NEESR）”竞赛的结果，包括斯坦福大学（牵头机构）、亚利桑那州立大学（次级奖项）和巴克内尔大学（次级奖项）。该项目将利用加州大学戴维斯分校和布法罗大学的NEES设备站点。该项目将通过实验和数值研究液化后再沉积土的特性，包括孔隙比分布和抗剪强度。为了研究液化后无黏性土的特性，将进行一系列协调的物理模型试验、数值分析、成像分析和实验室抗剪强度试验。物理模型测试将包括实验室柱测试、小型和大型振动台测试以及离心机测试。数值分析将包括模拟非均质性（如物理模型试验所揭示的）对无黏性土壤剪切带和不排水剪切强度的影响，以及基于新型计算流体动力学（CFD）的无黏性土壤再沉降分析。实验室测试将包括对从物理模型中恢复的标本进行剪切强度测试，使用特殊技术来保存其结构。成像将包括对恢复的标本进行明场显微镜（BFM）和计算机辅助断层扫描（CT）扫描，以评估其液化前后的结构。均匀砂和非均匀砂将被液化，并在不同的应力水平下重新固结。固化的土壤将被移除并冷冻干燥，以便切割成更小的样品。小样本的异质性将通过CT、BFM和数字图像处理（DIP）来量化。数值模拟程序将利用沉降理论和CFD在欧拉框架中实现。数学模型将由三层组成：澄清水、完全液化的土壤和固化的土壤。将使用流体体积（VOF）方法跟踪激波锋面。本文将研究两种数值模拟方案，第一种方案旨在预测液化土壤的非均质性，第二种方案旨在研究非均质性对液化后强度的影响。今年的NEES招标寻求“突破性和变革性的基础研究”，要求使用NEES设备站点。在研究和模拟具有明确固体骨架的土壤液化并最终表现为流体的相变过程方面取得了很大进展。相反的相变，即液化土壤固化并形成新的固体骨架，还没有得到同样程度的关注，但这一过程可能会极大地改变这种土壤的液化后特性，包括其抗剪强度。建议的工作，需要使用两个NEES测试设备，并关注文献中很少提及的问题，满足a ？变革性的基础研究。该项目将促进对沉积、液化和巩固过程的发现和理解，同时促进研究生和本科阶段、高中和K-12阶段的教学、培训和学习。一个关于液化的教学模块将被纳入NEES的合作伙伴- - -震动台教学大学联盟（UCIST），并将确保本科生积极参与。展示固流相互作用的可视化工具将加强教育和研究。我们将尽一切努力让代表性不足的学生和妇女参与到这个项目中来。该项目的数据将存档，并通过NEES数据储存库向公众提供。

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.