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

在岩土地震工程和土-结构相互作用分析中，不确定性的两个主要来源之一是了解土体在现有应力状态下的原位性质及其对应变水平的依赖关系。近年来，我们在确定非常低应变水平(Gmax)下不同深度的现场剪切模量值的能力方面取得了巨大的进步。已经注意到，这些值可能与实验室测试报告的值有很大不同。然而，该行业仍然依赖于实验室测试来估计剪切应变幅度对弹性模量和阻尼值的依赖性。基本假设是，一旦将模数除以Gmax进行归一化，在野外和实验室中，模数的变化和阻尼值的变化将是相同的。根据NEES计划，德克萨斯大学奥斯汀分校现在已经开发出设备，使我们能够第一次获得作为应变函数的可靠的弹性模量和阻尼的测量结果。这是一个非常重要的发展，但为了开发和验证程序，从垫子下不同点的记录数据(速度或加速度)推断模量值和阻尼值，必须进行额外的工作。智力优势：这项工作的目标是在德克萨斯A&A&M河滨校区的国家岩土试验场地(NGES)使用德克萨斯大学的新NEES设备进行一系列测试，开发和评估解释数据并在现场获得模数和阻尼值与剪切应变关系曲线所需的技术。这项研究将有助于从根本上理解土壤动态特性的实验室测量与现场测量。将开发和校准从记录的数据中估计作为应变水平函数的模数和阻尼值的数值工具。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从根本上了解土壤在现场循环加载下的反应，以及它与实验室测量的特性之间的关系。这是对地震工程领域的一项重大贡献，并将使研究人员能够更好地校准他们的模拟工具，用于现场响应和总体地震设计。本科生教育和K-12外展将在这个NEES研究项目中发挥重要作用。学生们将参加德克萨斯大学奥斯汀分校和德克萨斯农工大学的暑期REU项目。该项目非常适合本科生参与研究工作，特别是作为对野外工作、数据收集和数据整理的支持。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，面向K-12学生开展外联工作。在德州农工大学德怀特工程学院已有的“中学数学和科学教师E3教师暑期研究计划”范围内，将为教师举办暑期研讨会，定期为参与研究的研究生和本科生组织研讨会，以促进交流和互动。教育和外联计划通过促进教学方法，如实践活动、增加互动和研究与教育的结合，解决多样性问题，研究表明，这在留住未被充分代表的族裔群体和从事工程工作的妇女方面是有效的。

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.