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对现有应力状态下“原位”土性质及其对应变水平的依赖的了解。近年来，我们在非常低应变水平（Gmax）下确定不同深度现场剪切模量值的能力取得了巨大进展。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模量和阻尼对剪切应变振幅的依赖关系。基本的假设是，模量的变化，一旦归一化，除以Gmax，和阻尼的变化将是相同的，在现场和在实验室。在NEES项目下，德克萨斯大学奥斯汀分校已经开发出现在的设备，使我们第一次能够直接“就地”获得作为应变函数的模量和阻尼的可靠测量。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）推断模量和阻尼的值，还需要做额外的工作。这项工作的目的是在位于德克萨斯A&amp；M河滨校区的国家岩土实验基地（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所需的技术，并获得模量和阻尼与剪切应变的现场曲线。这项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。将开发和校准从记录数据中估计作为应变水平函数的模量和阻尼的数值工具。由此产生的软件将提供给NEES网络。更广泛的影响该研究将提供对土壤在田间循环荷载下的响应的基本理解，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，用于现场反应和一般的地震设计。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。学生将参加德州大学奥斯汀分校和德州农工大学的夏季REU项目。该项目非常适合本科生参与研究工作，特别是作为实地工作、数据收集和数据简化的支持。本科生将能够与pi和研究生一起工作。通过示范和教师参与研究活动，推广工作将针对K-12学生。针对教师的暑期工作坊将在“E3中学数学和科学教师暑期研究计划”的框架内开展，该计划已经在德州农工大学德怀特·洛克工程学院实施。定期为参与研究的研究生和本科生举办研讨会，促进交流和互动。教育和外联计划通过促进教学方法解决多样性问题，例如动手活动、加强研究和教育的相互作用和一体化，研究表明，这些方法在保留代表性不足的族裔群体和工程领域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.