IOWA STATE UNIVERSITY OF SCIENCE AND TECHNOLOGY
A critical component of earthquake and tsunami loss reduction is the accurate prediction and design of the response of pile-soil systems under dynamic loading. Despite many years of significant advances in theoretical and experimental research, significant discrepancies remain between experimental
measurements and theoretical predictions of general three-dimensional dynamic pile-soil interaction.
These discrepancies may be partially attributed to a host of contributing factors such as complicated soilpile contact conditions, difficulties in performing full-scale dynamic tests, and the statistical variation of the engineering properties of soils coupled with the challenge of their in-situ measurement. Such shortcomings in current prediction capabilities can lead to unsafe under-design or costly over-design.
The focus of the proposed NEESR Payload project is to expand the existing NEES technologies and testing capabilities for characterizing dynamic soil-pile interaction, and to improve the accuracy of current analytical and computational simulation tools. The Payload project will make use of the field-testing phase of the existing NEESR-SG project entitled “Understanding and Improving the Seismic Behavior of Pile Foundations in Soft Clays” (Award #0830328), which utilizes NEES equipment and instrumentation deployed to a full-scale test site in Oklahoma. Field vibration tests will be performed on piles installed in improved and unimproved soft clays to gain a fundamental understanding of the seismic response of piles in these soil conditions.
The goals of the project are to: (1) evaluate the effectiveness of using a servohydraulic inertial mass shaker and broadband random excitation for characterizing the dynamic behavior of piles in improved and unimproved clays, (2) improve the efficiency of current testing techniques by combining the traditionally separate vertical and horizontal harmonic excitation cases into a single multimodal random-vibration test with synchronous vertical and coupled horizontal-rocking motions, (3) investigate the use of an experimental technique involving chaotic impulse loading which has shown great success in scaled-model centrifuge tests, (4) compare the relative effectiveness of using sinusoidal, random and chaotic impulse excitation types for characterizing the elastodynamic response of the soil, (5) evaluate the predictive capabilities of current analytical and computational techniques against the measured responses of piles in improved and unimproved clays and develop corrections if necessary, and (6) investigate whether experimental behavior observed in recent centrifuge studies of piles in sands extends to piles in clays.
Intellectual Merit: The project will generate a number of practical experimental methods and a substantive database towards a more complete understanding of the fundamental behavior of dynamic soil-pile interaction.
Specific tools envisioned include an innovative method for dynamic in-situ
characterization of soil-pile interaction using non-destructive random vibration techniques, improved computational simulation tools to incorporate effects of installation and stress-dependence on shear modulus and damping, and modifications to current engineering theories which can be immediately
applied in practice.
In the long term, lessons learned in this project will be extended to understanding the dynamic behavior of pile groups and a greater range of soil conditions.
Broader Impacts: The project will involve the NEES community through teleparticipation and a web site will be created with sections tailored for disseminating the research results to K-12 students, the general public, and the earthquake engineering community.
Preliminary dynamic field-tests of a pile will be incorporated into a graduate course in soil dynamics at ISU, where students will have the option of
analyzing the data for credit in a tem project.