Static and Dynamic Axial Response of Drilled Piers. I: Field Tests
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Volume 137, Issue 12
Abstract
A prototype pier load test program was performed to study the load-deformation and energy-dissipation characteristics of the response of drilled piers under static and dynamic axial loads. The field tests consisted of six fully instrumented drilled concrete piers 61–76 cm (24–30 in.) in diameter and 5.8–9.1 m (19–30 ft) in length. The piers were constructed on a stiff, sandy clay site adjacent to the University of California, Berkeley campus. A dynamic Fundex pile load test (PLT) was performed on each pier, followed by a static-compression or tension test and a second PLT. The field tests revealed that the stiffness and capacity of a soil-pier system depend significantly on the loading rate. For the type of piers and soil considered in the field test, the increase in dynamic stiffness versus static stiffness is approximately 20–40% at almost all displacement levels. The ultimate dynamic capacity increases approximately 30% compared with the static case. The multiple PLTs conducted on the same drilled pier also indicated that a pier may experience up to 50% stiffness and strength degradation when subjected to full load reversal. The test program showed that the PLT is a fast, innovative method to get useful site-specific information for seismic design of the pier foundation.
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Acknowledgments
The PLT and static pier load tests were performed by American Piledriving, Inc. (API) of Pleasanton, California, under the direction of Rutherford and Chekene Consulting Engineers. Their cooperation and support are gratefully acknowledged. FISO Technologies of Canada fabricated the optical strain bars based on parameters provided by Lymon C. Reese and Associates, and the electrical strain bars were custom-built by Lymon C. Reese and Associates, which also monitored all the tests. An automated electronic data-acquisition system was provided on loan by FISO. The writers also appreciate the support and advice of Craig Comartin of Comartin Associates, the University of California, Berkeley, Capital Projects group, and FISO Technologies throughout the test program. The financial support for the test program was provided by University of California, Berkeley, Capital Projects, and the research was supported by Pacific Earthquake Engineering Research (PEER) Center under the National Science Foundation Award No. NSFEEC-9701568. The first writer also acknowledges support from the University Grants Committee (UGC) of Hong Kong—Strategic Initiatives UNSPECIFIEDRPC11EG27, and the Li Foundation Heritage Prize. Finally, we thank anonymous reviewers for their helpful comments to improve the quality of the paper.
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Published In
Journal of Geotechnical and Geoenvironmental Engineering
Volume 137 • Issue 12 • December 2011
Pages: 1133 - 1142
Copyright
© 2011 American Society of Civil Engineers.
History
Received: Dec 24, 2007
Accepted: Apr 8, 2011
Published online: Nov 15, 2011
Published in print: Dec 1, 2011
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