NEESR-II: In Situ Determination of Soil Modulus and Damping as a Function of Level of Strain

NEESR-II：现场测定土壤模量和阻尼与应变水平的关系

• 批准号: 0421275
• 负责人: Giovanna Biscontin
• 金额: --
• 依托单位: Texas A&M Engineering Experiment Station
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2004
• 资助国家: 美国
• 起止时间: 2004-09-15 至 2009-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0421275&HistoricalAwards=false
• 关键词: NEESR; II; Situ; Determination; Soil

One of the two main sources of uncertainties in geotechnical earthquake engineering and soil-structure interaction analysis is the knowledge of the soil properties "in-situ" under the existing state of stresses and of their dependence on the level of strains. In recent years there has been tremendous progress in our ability to determine the values of the shear modulus in the field at various depths for very low levels of strain (Gmax). It has been noticed that these values can be very different from those reported from laboratory testing. The profession still relies, however, on laboratory tests to estimate the dependence of the modulus and damping on the amplitude of the shear strains. The basic assumption has been that the variation of the modulus, once normalized by dividing it by Gmax, and of the damping will be the same in the field and in the laboratory. Under the NEES program, the University of Texas at Austin has developed now equipment that allows us, for the first time, to obtain reliable measures of modulus and damping as functions of strain directly "in-situ." This is a very significant development, but additional work has to be done in order to develop and validate procedures to infer the values of modulus and damping from the recorded data (velocities or accelerations) at various points under a mat. Intellectual merit: The objective of this work is to conduct a series of tests with the new NEES equipment of the University of Texas at the National Geotechnical Experimentation Site (NGES) located on the Texas A&M Riverside campus, developing and evaluating the techniques needed to interpret the data and obtain in the field curves of modulus and damping versus shear strain. The research will contribute to the fundamental understanding of laboratory versus field measurements of the dynamic properties of soils. Numerical tools to estimate modulus and damping as function of levels of strain from the recorded data will be developed and calibrated. The resulting software will be made available to the NEES network. Broader impact The research will provide fundamental understanding of the response of soils subjected to cyclic loading in the field and how it relates to the properties measured in the laboratory. This is a significant contribution to the field of earthquake engineering and will allow researchers to better calibrate their simulation tools for field response and seismic design in general. Undergraduate education and K-12 outreach will play a significant role in this NEES research project. Students will participate in summer REU programs at the University of Texas, Austin and Texas A&M University. The project is well suited for the involvement of undergraduate students in the research work, especially as support to the field work, data collection and data reduction. The undergraduate students will be able to work with the PIs and the graduate students. Outreach efforts will be directed towards K-12 students, through demonstrations and teacher involvement in the research activities. Summer workshops for teachers will be developed within the "E3 Teacher Summer Research Program for Secondary Math and Science Teachers" already in place at The Dwight Look College of Engineering at Texas A&M. Regularly scheduled workshops for the graduate and undergraduate students involved in the research will be organized to promote exchanges and interactions. The educational and outreach plan addresses diversity by promoting pedagogies, such as hand-on activities, increased interaction and integration of research and education, which research has shown to be effective in the retention of underrepresented ethnic groups and women in engineering.

岩土地震工程和土-结构相互作用分析中不确定性的两个主要来源之一是对现有应力状态下“原位”土壤性质及其对应变水平的依赖性的认识。近年来，我们在很低应变水平（Gmax）下确定不同深度现场剪切模量值的能力有了巨大的进步。已经注意到，这些值可能与实验室测试报告的值非常不同。然而，该专业仍然依赖于实验室测试来估计模量和阻尼对剪切应变幅度的依赖性。基本假设是，模量的变化（通过除以Gmax进行归一化）和阻尼的变化在现场和实验室中相同。在NEES计划下，德克萨斯大学奥斯汀分校开发了一种设备，使我们能够第一次直接“原位”获得模量和阻尼随应变变化的可靠测量结果。“这是一个非常重要的发展，但必须做更多的工作，以开发和验证程序，从记录的数据（速度或加速度）在垫下的各个点推断模量和阻尼值。智力优点：这项工作的目标是在位于德克萨斯A M滨江校园的国家土工实验场（NGES）使用德克萨斯大学的新NEES设备进行一系列测试&，开发和评估解释所需的技术数据并获得模量和阻尼与剪应变的现场曲线。该研究将有助于对土壤动态特性的实验室与现场测量的基本理解。将开发和校准用于根据记录的数据估算模量和阻尼随应变水平变化的数值工具。由此产生的软件将提供给NEES网络。更广泛的影响这项研究将提供基本的理解土壤的反应受到循环荷载在外地和它如何涉及到在实验室测量的属性。这是对地震工程领域的一个重大贡献，将使研究人员能够更好地校准他们的模拟工具，用于现场响应和一般的抗震设计。本科教育和K-12外展将在这个NEES研究项目中发挥重要作用。学生将参加夏季REU课程在得克萨斯大学，奥斯汀和得克萨斯州A M大学。该项目非常适合本科生参与研究工作，特别是支持实地工作，数据收集和数据减少。本科生将能够与PI和研究生一起工作。将通过示范和教师参与研究活动，向K-12学生开展外联工作。教师暑期讲习班将在“E3教师暑期研究计划的中学数学和科学教师”已经到位，在德怀特看工程学院在得克萨斯州A M。定期为参与研究的研究生和本科生举办研讨会，以促进交流和互动。教育和外联计划通过促进实践活动、增加互动以及研究和教育的结合等方法来解决多样性问题，研究表明，这对留住工程领域代表性不足的族裔群体和妇女是有效的。