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.
