NEESR - II: Mechanisms and Implications of Time-Dependent Changes in the State and Properties of Recently Liquefied Sands

NEESR - II：最近液化的沙子的状态和性质随时间变化的机制和影响

• 批准号: 0530378
• 负责人: Roman Hryciw
• 金额: --
• 依托单位: Regents of the University of Michigan - Ann Arbor
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2005
• 资助国家: 美国
• 起止时间: 2005-09-15 至 2010-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0530378&HistoricalAwards=false
• 关键词: NEESR; II; Mechanisms; Implications; Time

Abstract The objectives of this research are to develop a better understanding of the mechanisms and implications of time-dependent changes, commonly referred to as "aging," in the state and properties of recently liquefied sands; and, to develop a quality assurance metric for remedially densified sand that accounts for aging effects. Aging effects in sand, such as increases in penetration resistance with time after deposition, densification, and/or liquefaction, are known to occur in-situ, but the causes of these effects are not fully understood. Nonetheless, these effects have important ramifications in earthquake engineering. First, the lack of understanding of the phenomenon is an impediment to quality assurance (QA) for ground densification projects aimed at mitigating the damaging effects of liquefaction. Also, aging effects introduce considerable uncertainty in field-based liquefaction susceptibility correlations, as the influence of aging on the in-situ test indices used to develop correlations is unknown but certainly varied among the case histories in the liquefaction database. Within the realm of probabilistic based earthquake engineering (PBEE), a probabilistic quantification of the influence of aging on in-situ indices is required. Previous investigations into the underlying mechanisms of aging of sands have been inconclusive, sometimes raising more questions than resolving. Unfortunately, the boundary conditions for most published field studies have been too numerous and variable to conclusively identify the mechanisms underlying aging. Nevertheless, the results of such field studies add to the evidence that the aging phenomenon exists. Building on the lessons learned from previous studies, this research entails synergistic field and laboratory investigations to be performed collaboratively by the University of Michigan and by the University of Rhode Island. Also included on the research team is Dr. Wilhelm Degen, Senior Vice President, Vibrofoundation, Inc., who will be donating equipment time and expertise and Dr. James K. Mitchell (Virginia Tech), one of the foremost experts on the aging phenomenon. The field investigation will involve inducing liquefaction by explosives, vibroflotation, and vibroseis at adjacent locations. The former two techniques were selected because they are ground densification methods in which the aging phenomenon has been observed. However, both methods introduce foreign elements into the soil: explosives - blast gases; vibroflotation - heavily aerated water. On the contrary, the vibroseis (NEES equipment), only introduces seismic waves into the ground, and thus, will allow discernment of the contribution of blast gases and heavily aerated water on the aging phenomenon. In conjunction with the field investigation, an aging study will be performed in the laboratory using soil and groundwater from the field site, with the purpose of discerning the scale and different stress state effects on aging. There are several broader impacts stemming from the proposed research. For society at large, this research will help minimize losses from earthquakes by improving the current methods for liquefaction risk assessment and mitigation. Technology transfer will be ensured, as the corporate partner will have input on the testing plan, as well as direct access to the research findings, with other interested parties having access to the data/findings via the NEESgrid. The educational impacts will not only result from the increased technical understanding of the subject matter, but will also result from the collaborative nature of the proposed research and the educational outreach program with Bates Elementary School, Dexter, Michigan. Regarding the outreach to women and underrepresented minorities, the PI participates in several University of Michigan programs tailored for such purposes: Grace Hopper Project, Marian Sarah Parker Scholars Program, Summer Research Opportunity Program, and the Summer Engineering Exploration Camp. Through these programs, several undergraduate women and/or underrepresented minorities will be involved in the proposed research, with the exact nature and level of the involvement depending on student availability and research schedule.

摘要本研究的目的是更好地了解近期液化砂的状态和性质中随时间变化的机制和影响，通常称为“老化”;并制定一个质量保证指标，用于补救密实砂，说明老化效应。 砂中的老化效应，例如沉积、致密化和/或液化后随着时间的推移贯入阻力增加，已知会在原位发生，但这些效应的原因尚未完全了解。 尽管如此，这些影响在地震工程中具有重要的影响。 首先，对这种现象缺乏了解是旨在减轻液化破坏性影响的地面致密化项目质量保证（QA）的障碍。 此外，老化效应在基于现场的液化敏感性相关性中引入了相当大的不确定性，因为老化对用于开发相关性的原位测试指标的影响是未知的，但在液化数据库中的案例历史中肯定会有所不同。 在基于概率的地震工程（PBEE）领域内，需要对老化对原位指标的影响进行概率量化。以前对沙子老化的潜在机制的研究一直没有定论，有时提出的问题比解决的问题更多。 不幸的是，大多数已发表的实地研究的边界条件已经太多和变量，最终确定的机制老化。 然而，这些实地研究的结果进一步证明了老龄化现象的存在。 从以前的研究中吸取的教训的基础上，这项研究需要协同现场和实验室的调查，由密歇根大学和罗得岛大学合作进行。 研究团队中还包括Vibrofoundation公司高级副总裁Wilhelm Degen博士，他将捐赠设备、时间和专业知识，米切尔（弗吉尼亚理工大学），对老化现象的最重要的专家之一。 现场调查将涉及在邻近地点通过炸药、振冲和可控震源诱导液化。选择前两种技术是因为它们是已经观察到老化现象的研磨致密化方法。 然而，这两种方法都将外来元素引入土壤中：爆炸物-爆炸气体;振冲法-大量充气的水。 相反，可控震源（NEES设备）只将地震波引入地面，因此，将允许识别爆破气体和大量充气水对老化现象的贡献。 结合现场调查，将在实验室中使用现场的土壤和地下水进行老化研究，目的是辨别规模和不同应力状态对老化的影响。 拟议的研究产生了几个更广泛的影响。 对于整个社会来说，这项研究将有助于通过改进目前的液化风险评估和缓解方法来最大限度地减少地震造成的损失。 将确保技术转让，因为公司合作伙伴将对测试计划提供投入，并直接访问研究结果，其他有关各方可以通过NEESgrid访问数据/结果。 教育的影响将不仅从增加对主题的技术理解，但也将从拟议的研究和教育推广计划与贝茨小学，德克斯特，密歇根州的协作性质。 关于对妇女和代表性不足的少数民族的宣传，PI参加了密歇根大学为此目的量身定制的几个项目：格雷斯霍珀项目，玛丽安萨拉帕克学者计划，夏季研究机会计划和夏季工程探索营。通过这些计划，一些本科妇女和/或代表性不足的少数民族将参与拟议的研究，参与的确切性质和水平取决于学生的可用性和研究时间表。