NEESR pilEs Payload

Funding: NEESR-SG; Understanding and Improving the Seismic Behavior of Pile Foundations in Soft Clays PI; J. Ashlock; Award #0830328

The overall goal of the project is to contribute to improved experimental and computational tools to bridge the gap between theory and observation for soil-foundation systems under realistic multi-directional 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 soil-pile 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 this 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. 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. Specific goals of the project are to; (1) evaluate the effectiveness of using a servo-hydraulic 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 multi-modal 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.

This 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 to be developed 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 pile installation and stress-dependence on the soil's 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 a greater range of soil conditions as well as pile groups. The experimental and computational simulation techniques generated by this research will improve our understanding of fundamental soil-foundation-structure interaction, enabling more accurate models for foundation design and leading to improvements in earthquake hazard mitigation.

Test site in Miami, OK

Shaker on the specimen