NEESR-SG: Experimental and Micromechanical Computational Study of Pile Foundations Subjected to Liquefaction-Induced Lateral Spreading

摘要：将对斜坡和滨水地区桩基在剪切力作用下的横向扩展问题进行深入研究。 这是造成地震损失的主要原因，损失高达数十亿美元。 在目前的工程方法中，已经确定了一个很大的知识缺口，以评估桩基础对液化砂施加的横向载荷的弯曲响应（极限平衡（LE）和p-y方法）。 不确定性的一个来源是必须对桩群施加侧向压力的面积、单独桩的面积之和或桩之间的土壤。 这两个假设之间的差异可以产生桩弯矩变化的三倍。 不确定性的另一个来源是土壤渗透性的重要性，不包括在目前的LE方法，但全尺寸和离心振动试验表明，可以产生一个变化的弯矩的一个因素。 室内和足尺振动台试验以及现场试验和初步分析表明，液化砂土在单桩和群桩附近的反应是复杂的。 包括液化土壤的硬化，由于过量的负孔隙水压力引起的土桩相互作用;水从自由场流动，最终膨胀;和，软化的液化土壤附近的基础，在一个复杂的时间依赖性的方式。一个基本的和全面的方法，使之成为可能的NEES，将被用来解决这个问题，使用一系列现有的实验和分析工具。研究的目的是了解在桩基础附近的横向扩展过程中的砂土液化现象，以解决如何设计桩基础的工程问题，无论是在简化的条款，以及在提供一个基本的理解，为适当的分析平台，并澄清正确的方式使用离心模型在未来的研究和工程应用。 这是通过一项实验研究计划完成的，该计划使用了布法罗大学的1克二维振动、6米高的层状箱式容器NEES设施和RPI NEES离心机设施，包括使用新型先进传感器测量振动期间的土壤加速度、变形和压力;以及RPI、加州大学圣地亚哥分校和杜兰大学的微机械离散元数值实验和有限元分析;所有这些都由适当的识别和分析框架集成，包括系统识别和可视化能力。 的DEM数值实验，验证了1克和离心物理试验，旨在提供第一次详细的信息，在单个土壤颗粒和颗粒组的水平上，对桩基础附近的液化土的响应，包括应变局部化，剪切带和桩周围的流动，从基本的微观力学原理计算。 DEM的见解将被用来完善FE分析中使用的本构关系的重要未解决的方面。 来自美国、日本（包括日本合作者）和其他国家的广泛工程师和研究人员参加的第三年研讨会将评估研究结果。该项目将采用一套新的研究工具和整合这些工具的方法。该项目的互动网站将定期更新结果和解释。研究生和本科生参与研究，重点是招募代表性不足的学生，在顶点和类似课程的学期项目，在项目结束时准备1-2个教育模块，以及对K-12学生及其教师的具体努力，旨在加强该项目的影响。

Abstract: Critical research will be conducted on the problem of pile foundations subjected to liquefaction-induced lateral spreading in sloping ground and near waterfronts. This is a major cause of earthquake damage with costs in the billions of dollars. A large knowledge gap has been identified in current engineering methods to evaluate bending response of pile foundations to the lateral loading applied by the liquefied sand (limit equilibrium (LE) and p-y methods). One source of uncertainty is the area over which the lateral pressure must be applied for pile groups, the sum of the areas of the piles alone, or also soil between the piles. The difference between these two assumptions can produce pile-bending moments varying by a factor of three. Another source of uncertainty is the importance of soil permeability, not included in current LE methods, but which full scale and centrifuge shaking tests indicate can produce a variation of bending moments by a factor of seven. Centrifuge and full-scale shaking table tests, as well as insitu testing and preliminary analyses, suggest a complicated response of the liquefied sand in the neighborhood of individual piles and pile groups. Included is stiffening of the liquefied soil due to excess negative pore water pressures caused by soil-pile interaction; water flowing from the free field with eventual expansion; and, softening of the liquefied soil near the foundation, in a complicated time-dependent manner. A fundamental and comprehensive approach, made possible by NEES, will be used to tackle the problem using a range of available experimental and analytical tools. The objectives of the research are to understand the phenomenon of sand liquefaction during lateral spreading near pile foundations; to solve the engineering questions of how to design pile foundations against lateral spreading both in simplified terms as well as in terms of providing a basic understanding for appropriate analytical platforms; and, to clarify the correct way to use centrifuge modeling in future research and engineering applications. This is done through an experimental research plan using the University at Buffalo 1g 2D shaking, 6m-tall laminar box container NEES facility and the RPI NEES centrifuge facility, including use of novel advanced sensors to measure soil accelerations, deformations and pressures during shaking; and micromechanical Discrete Element (DEM) numerical experiments and finite element (FE) analyses at RPI, UC San Diego and Tulane University; all integrated by an appropriate identification and analysis framework including system identification and visualization capabilities. The DEM numerical experiments, validated by the 1g and centrifuge physical tests, aim at providing for the first time detailed information at the level of individual soil grains and groups of grains, on the response of the liquefied soil close to pile foundations including strain localization, shear banding and flow around the piles, calculated from basic micromechanical principles. The DEM insights will be used to refine important unsolved aspects of the constitutive relations used in the FE analyses. A Year 3 Workshop with the participation of a broad range of engineers and researchers from the US, Japan (including Japanese collaborators) and other countries, will evaluate the results of the research. The project will exercise a new set of research tools and ways to integrate them. The Interactive Web Site of the project will be periodically updated with results and interpretations. Graduate and undergraduate involvement in research, with emphasis on the recruitment of under-represented students, term projects in capstone and similar courses, preparation of 1-2 Educational Modules at the end of the project, and specific efforts toward K-12 students and their teachers, are aimed at intensifying the impact of the project.