NEESR Payload: Characterization of Dynamic Soil-Pile Interaction by Random Vibration Methods

该奖项由2009年美国复苏和再投资法案(公法111-5)资助。该奖项是NSF 09-524项目征集“小乔治·E·布朗地震工程模拟(NEES)研究网络(NEESR)”竞赛的结果。该有效载荷项目将由爱荷华州立大学领导，并将利用加州大学洛杉矶分校的NEES设备和NEESR-SG项目“了解和改善软粘土中桩基础的地震行为”(奖项#0830328)中的实验现场测试装置。该项目的总体目标是改进实验和计算工具，以弥合实际多方向荷载下土壤-基础系统的理论和观测之间的差距。尽管多年来在理论和试验研究方面取得了重大进展，但一般三维动力桩-土相互作用的试验测量结果与理论预测之间仍存在显著差异。这些差异可能部分归因于一系列因素，如复杂的土-桩接触条件，进行全尺寸动态试验的困难，以及土的工程性质的统计变化，以及现场测量的挑战。当前预测能力中的这些缺陷可能会导致不安全的设计不足或代价高昂的过度设计。该有效载荷项目的重点是扩展现有的NEES技术和测试能力，以表征土-桩动态相互作用，并提高现有分析和计算模拟工具的准确性。现场振动试验将对安装在改良和未改良软粘土中的桩进行，以基本了解桩在这些土壤条件下的地震反应。该项目的具体目标是；(1)评价使用伺服液压惯性质量振动器和宽带随机激励来表征改良和未改良粘土中桩的动力行为的有效性；(2)通过将传统分离的竖向和水平简谐激励组合成具有垂直和水平-摇摆同步运动的单一多模式随机振动试验来改进当前测试技术的效率；(3)研究涉及混沌脉冲加载的实验技术的使用，该实验技术在缩尺模型离心机试验中已被证明是非常成功的；(4)比较使用正弦、随机和混沌脉冲激励类型来表征土的弹性动力响应的相对有效性，(5)评估现有分析和计算技术对改良和未改良粘土中桩的实测响应的预测能力，并在必要时进行修正，以及(6)调查最近在砂土中桩的离心机研究中观察到的试验性状是否延伸到粘土中的桩。该项目将产生一些实用的实验方法和一个实质性的数据库，以更全面地了解动态土-桩相互作用的基本行为。待开发的具体工具包括使用非破坏性随机振动技术对土-桩相互作用进行现场动态表征的创新方法、改进的计算模拟工具以纳入桩安装和应力依赖对土壤剪切模量和阻尼的影响，以及对现有工程理论的修改，这些修改可以立即应用于实践。从长远来看，从这个项目中学到的经验教训将扩展到理解更大范围的土壤条件和群桩的动态行为。这项研究产生的实验和计算模拟技术将提高我们对基本土-基础-结构相互作用的理解，使基础设计能够更准确地模型，并导致地震减灾方面的改进。该项目将通过远程参与使NEES社区参与进来，并将创建一个网站，其中包括为向K-12学生、普通公众和地震工程界传播研究成果而量身定做的部分。桩的初步动态实地测试将被纳入ISU土壤动力学的研究生课程，在该课程中，学生可以选择在学期项目中分析数据以获得学分。该项目的数据将被存档，并通过NEES数据库向公众提供。

This award is funded under the American Recovery and Reinvestment Act of 2009(Public Law 111-5).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. This Payload project will be led by Iowa State University (ISU) and will utilize NEES equipment from the University of California, Los Angeles and the experimental field-test setup from the NEESR-SG project entitled "Understanding and Improving the Seismic Behavior of Pile Foundations in Soft Clays" (Award #0830328). The overall goal of the project is to contribute to improved experimental and computational tools to bridge the gap between theory and observation for soil-foundation systems under realistic multi-directional loading. Despite many years of significant advances in theoretical and experimental research, significant discrepancies remain between experimental measurements and theoretical predictions of general three-dimensional dynamic pile-soil interaction. These discrepancies may be partially attributed to a host of contributing factors such as complicated soil-pile contact conditions, difficulties in performing full-scale dynamic tests, and the statistical variation of the engineering properties of soils coupled with the challenge of their in-situ measurement. Such shortcomings in current prediction capabilities can lead to unsafe under-design or costly over-design. The focus of this Payload project is to expand the existing NEES technologies and testing capabilities for characterizing dynamic soil-pile interaction, and to improve the accuracy of current analytical and computational simulation tools. Field vibration tests will be performed on piles installed in improved and unimproved soft clays to gain a fundamental understanding of the seismic response of piles in these soil conditions. Specific goals of the project are to; (1) evaluate the effectiveness of using a servo-hydraulic inertial mass shaker and broadband random excitation for characterizing the dynamic behavior of piles in improved and unimproved clays, (2) improve the efficiency of current testing techniques by combining the traditionally separate vertical and horizontal harmonic excitation cases into a single multi-modal random-vibration test with synchronous vertical and coupled horizontal-rocking motions, (3) investigate the use of an experimental technique involving chaotic impulse loading which has shown great success in scaled-model centrifuge tests, (4) compare the relative effectiveness of using sinusoidal, random and chaotic impulse excitation types for characterizing the elastodynamic response of the soil, (5) evaluate the predictive capabilities of current analytical and computational techniques against the measured responses of piles in improved and unimproved clays and develop corrections if necessary, and (6) investigate whether experimental behavior observed in recent centrifuge studies of piles in sands extends to piles in clays. This project will generate a number of practical experimental methods and a substantive database towards a more complete understanding of the fundamental behavior of dynamic soil-pile interaction. Specific tools to be developed include an innovative method for dynamic in-situ characterization of soil-pile interaction using non-destructive random vibration techniques, improved computational simulation tools to incorporate effects of pile installation and stress-dependence on the soil's shear modulus and damping, and modifications to current engineering theories which can be immediately applied in practice. In the long term, lessons learned in this project will be extended to understanding the dynamic behavior of a greater range of soil conditions as well as pile groups. The experimental and computational simulation techniques generated by this research will improve our understanding of fundamental soil-foundation-structure interaction, enabling more accurate models for foundation design and leading to improvements in earthquake hazard mitigation. This project will involve the NEES community through teleparticipation, and a web site will be created with sections tailored for disseminating the research results to K-12 students, the general public, and the earthquake engineering community. Preliminary dynamic field-tests of a pile will be incorporated into a graduate course in soil dynamics at ISU, where students will have the option of analyzing the data for credit in a term project. Data from this project will be archived and made available to the public through the NEES data repository.