The goal of this CAREER research project was to develop an integrated research and education program aimed at advancing fundamental knowledge on dynamic pile-soil interaction for pile groups. Piles are long, slender types of deep foundation elements that are typically used in groups, and are driven or vibrated into the ground by large hammers. They are generally used when stronger or stiffer building foundations are needed relative to simpler shallow foundations. Dynamic pile-soil interaction problems have been a source of considerable challenge in earthquake engineering and soil dynamics for over a half-century due to the many complex physical mechanisms involved. Examples of these challenges include pile installation effects (how the pile damages or alters the soil during insertion), pile-soil separation and interfacial contact stresses under loading, nonlinear stress-dependent material properties of soils even under small strain, complex wave propagation in three-dimensional soil domains, and the dependence of the soil's response on the in-situ and load-induced spatial variation of the shear modulus and damping (i.e., how the soil weight as well as loads from the structure alter the strength and stiffness of the soil surrounding a pile). Although a wealth of knowledge has been gained from past analytical and experimental studies, significant contributions to earthquake loss reduction stand to be realized through more accurate prediction and design of the behavior of soil-pile systems under dynamic loads.  

Regarding the intellectual merit of the project, integrated computational studies and full-scale tests of pile foundations were conducted to address the aforementioned project goals. Specifically, coupled vertical-horizontal-rocking vibration tests with broadband excitation and random vibration signal processing techniques were used to efficiently characterize the dynamic response of soil pile-group interaction in the time and frequency domains. The vibration tests induced small strains in the soil, and were followed by large-strain quasi-static cyclic tests which slowly pushed and pulled the pile foundations by large displacements until failure. Concurrent with the experimental phase of the study, three-dimensional inhomogeneous disturbed-zone computational models were developed for single piles and pile groups using a custom 3D Boundary Element code. The sensitivity of the theoretical pile response was determined through parametric studies of the model parameters, including; (1) soil shear modulus and damping profiles in the disturbed zones around the piles, (2) modulus and damping profiles in the far-field, (3) size and shape of the disturbed zones, and (4) pile-soil contact conditions. Upon characterizing their relative contributions to the overall elastodynamic response, these parameters were then calibrated to the observed experimental responses in a system-identification optimization approach, to produce calibrated computational disturbed-zone models of the observed pile-soil interaction. The new computational models provide an approach that can be used for improved prediction of the dynamic response of soil-pile systems under multi-directional dynamic loads. Results of the models were distilled into impedance functions which can be immediately applied in engineering practice.

Regarding broader impacts, the education, outreach and training (EOT) goals of the CAREER project were to strengthen the analytical and teaching skills of graduate and undergraduate students, while reaching out to K-12 students to introduce them to topics of geotechnical engineering and inspire them towards careers in Science, Technology, Engineering and Mathematics (STEM). To maximize the impact of the EOT program, the activities were conducted in cooperation with established university outreach and diversity programs having proven records of inspiring K-12 students towards STEM fields while increasing participation of under-represented minorities in engineering. Among the several EOT activities for this project were development of a liquefaction demonstration unit and lectures on geotechnical and earthquake engineering which were used in several educational and outreach events. Additionally, a Science Bound Saturday event was organized and held, in which local junior high students from underrepresented minority groups learned about the project as well as careers in geotechnical engineering, participated in several hands-on demonstrations, and were given a tour of four geotechnical labs at Iowa State University. The project also involved support, training, and mentoring of two PhD students, two post-doctoral scholars, eight undergraduate research assistants, and one visiting scholar PhD student. To help address the underrepresentation of females in engineering, one female PhD student and two female undergraduate students were supported on the project.

Last Modified: 06/05/2020
Modified by: Jeramy C Ashlock