Cyclic Lateral Load Behavior of a Pile Cap and Backfill
Publication: Journal of Geotechnical and Geoenvironmental Engineering
Volume 132, Issue 9
Abstract
A series of static cyclic lateral load tests were performed on a full-scale pile group driven into a cohesive soil profile. Twelve 324-mm steel pipe piles were attached to a concrete pile cap in plan and in height. Pile–soil–pile interaction and passive earth pressure provided lateral resistance. Seven lateral load tests were conducted in total; four tests with backfill compacted in front of the pile cap; two tests without backfill; and one test with a narrow trench between the pile cap and backfill soil. The formation of gaps around the piles at larger deflections reduced the pile–soil–pile interaction resulting in a degraded linear load versus deflection response that was very similar for the two tests without backfill and the trenched test. A typical nonlinear backbone curve was observed for the backfill tests. However, for deflections greater than 5 mm, the load-deflection behavior significantly changed from a concave down shape for the first cycle to a concave up shape for the second and subsequent cycles. The concave up shape continued to degrade with additional cycles past the second and typically became relatively constant after five to seven cycles. A gap formed between the backfill soil and the pile cap, which contributed to the load-deflection degradation. Crack patterns and sliding surfaces were consistent with that predicted by the log spiral theory. The results from this study indicate that passive resistance contributes considerably to the lateral resistance. However, with cyclic loading the passive force degrades significantly for deflections greater than 0.5% of the pile cap height.
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Acknowledgments
The Utah Department of Transportation and the Federal Highway Administration provided funding for this project. Their support is gratefully acknowledged. However, the views and recommendations expressed in this paper do not necessarily reflect the views of the sponsors. The writers also wish to thank David Anderson, the Civil Engineering Department technician, who provided assistance with the testing set-up and instrumentation for this study.
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© 2006 ASCE.
History
Received: Sep 15, 2004
Accepted: Dec 2, 2004
Published online: Sep 1, 2006
Published in print: Sep 2006
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