Characterization of Dynamic Soil-Pile Interaction by Random Vibration Methods (NEES-2010-0940)

<p><strong>Title:</strong> Characterization of Dynamic Soil-Pile Interaction by Random Vibration Methods (NEES-2010-0940)</p> <p><br /> <strong>Year Of Curation:</strong> 2013</p> <p><br /> <strong>Description: </strong>This project utilized 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. </p> <p><br /> <strong>Award:</strong> http://www.nsf.gov/awardsearch/showAward?AWD_ID=0936627</p> <p><br /> <strong>PIs & CoPIs:</strong> Jeramy Ashlock</p> <p><br /> <strong>Dates:</strong> August 15, 2009 - July 31, 2012</p> <p><br /> <strong>Organizations:</strong> Iowa State University, IA, United States</p> <p><br /> <strong>Facilities:</strong> University of California, Los Angeles, CA, United States</p> <p><br /> <strong>Sponsor:</strong> NSF - 0936627 </p> <p><br /> <strong>Keywords: </strong>Dynamics, Soil-Structure Interaction, Oklahoma, Payload,clay, Pile Foundations, pile vibration, shaker, inertial shaker, piles, random vibration, transfer function, boundary element method, 3D elastodynamics, CDSM, deep soil mixing, soil improvement, soft clays, computational simulation, computational modeling</p> <p><br /> <strong>Publications: </strong></p> <p>"Characterization of Dynamic Soil-Pile Interaction by Random Vibration  Methods: Experimental Design and Preliminary Results "                    </p> <p>"Characterization of Dynamic Soil-Pile Interaction by Random Vibration Methods"  </p> <p> </p> <p> </p> <nb:citations></nb:citations>

<strong>标题：</strong>基于随机振动方法的动态土-桩相互作用特性表征（NEES-2010-0940）
<strong>整理年份：</strong>2013
<strong>项目说明：</strong>本项目使用了来自加州大学洛杉矶分校（University of California, Los Angeles）的美国国家地震工程模拟系统（Network for Earthquake Engineering Simulation，简称NEES）设备，以及NEESR-SG项目的现场试验装置，该项目标题为"软黏土中桩基抗震性能的认知与优化"（资助编号：0830328）。本项目的总体目标是开发更完善的试验与计算工具，以弥合实际多向荷载作用下土-基础体系的理论与实测结果之间的差距。尽管多年来理论与试验研究取得了显著进展，但通用三维动态土-桩相互作用的试验测量结果与理论预测之间仍存在显著偏差。这些偏差部分可归因于诸多因素，例如复杂的土-桩接触条件、开展全尺寸动态试验的难度，以及土体工程特性的统计变异与原位测量的挑战。当前预测能力的此类不足可能导致不安全的欠设计或高成本的过设计。本有效载荷项目（Payload project）的重点是扩展现有NEES技术与试验能力，以表征动态土-桩相互作用，并提升当前分析与计算模拟工具的精度。研究将对加固与未加固软黏土中的桩体开展现场振动试验，以深入认知此类土体条件下桩体的地震响应。项目的具体目标包括：(1) 评估采用伺服液压惯性振动台与宽带随机激励来表征加固与未加固黏土中桩体动态行为的有效性；(2) 通过将传统分离的竖向与横向简谐激励工况整合为同步竖向与耦合横向摇摆运动的单模态随机振动试验，提升当前试验技术的效率；(3) 研究混沌脉冲加载试验技术的应用，该技术在缩尺模型离心试验中已展现出良好效果；(4) 对比正弦、随机与混沌脉冲激励三种方式在表征土体弹性动力响应方面的相对有效性；(5) 基于加固与未加固黏土中桩体的实测响应，评估当前分析与计算技术的预测能力，并在必要时提出修正方案；(6) 探究近期砂土中桩体离心试验中观测到的试验行为是否适用于黏土中的桩体。本项目将生成一系列实用试验方法与大量数据库，以更全面地认知动态土-桩相互作用的基本特性。拟开发的具体工具包括：采用非破坏性随机振动技术开展土-桩相互作用动态原位表征的创新方法，改进的计算模拟工具以纳入桩体施工效应与土体应力相关性对剪切模量和阻尼的影响，以及可直接应用于工程实践的现有工程理论修正方案。从长远来看，本项目的研究经验将推广应用于更广泛土体条件以及桩群的动态行为认知。本研究生成的试验与计算模拟技术将提升我们对土-基础-结构相互作用基本特性的认知，为基础设计提供更精确的模型，并推动地震减灾工作的改进。
<strong>资助链接：</strong>http://www.nsf.gov/awardsearch/showAward?AWD_ID=0936627
<strong>项目负责人与联合负责人：</strong>Jeramy Ashlock
<strong>项目周期：</strong>2009年8月15日 - 2012年7月31日
<strong>依托单位：</strong>美国爱荷华州立大学，艾奥瓦州，美国
<strong>试验设施：</strong>美国加州大学洛杉矶分校，加利福尼亚州，美国
<strong>资助方：</strong>美国国家科学基金会（NSF）- 0936627
<strong>关键词：</strong>动力学、土-结构相互作用、俄克拉荷马州、有效载荷项目、黏土、桩基、桩体振动、振动台、惯性振动台、桩体、随机振动、传递函数、边界元法、三维弹性动力学、CDSM、深层搅拌法、土体加固、软黏土、计算模拟、计算建模
<strong>发表论文：</strong>
"基于随机振动方法的动态土-桩相互作用特性表征：试验设计与初步结果"
"基于随机振动方法的动态土-桩相互作用特性表征"