Abstract
A series of centrifuge tests were performed to investigate the behavior of laterally loaded pile groups in improved and unimproved soft clay. The soil profile consisted of four lightly overconsolidated clay layers overlying a dense layer of sand. The pile groups had a symmetrical layout consisting of piles spaced at 3.0 and 7.0 pile diameters (D). After improving the soft clay in situ using simulated cement deep soil mixing (CDSM), pile foundations were driven into the improved ground. Centrifuge tests revealed that CDSM is an effective method to increase the lateral resistance of pile foundations. The lateral resistance of the improved pile group at 7D spacing increased by 157%. Due to pile–soil–pile interactions, the lateral resistance in the 3D pile group increased by only 112%. In both improved and unimproved pile groups with 3D spacing, the leading row of piles carried larger loads and bending moments than the trailing row of piles. No group interaction effects were observed in all pile groups with 7D spacing. At very large deflections, cracks developed and tension failure occurred in the CDSM block of the improved 3D pile group. Values for p-multipliers were back-calculated and incorporated into a computer code to perform a parametric study on improved pile groups with 3D spacing. It was seen that for CDSM block depths greater than 9D, increases in lateral resistance are practically negligible. At deflections less than 8 cm, lateral resistance of the improved pile groups is not sensitive to undrained shear strength of the improved clay representing typical cement contents.
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Acknowledgments
The research reported herein is a part of the NEES-pilEs (the George E. Brown, Jr. Network for Earthquake Engineering Simulation—piles in low E soils) project to study the behavior of pile foundations in improved and unimproved soft clay using centrifuge model tests, field tests, and computational simulations. The NEES-pilEs project was supported by the National Science Foundation (NSF) under Grant No. CMMI-0830328 and this support is gratefully acknowledged. Any opinions, findings, and conclusions or recommendations expressed in this paper are those of the authors and do not necessarily reflect the views of the National Science Foundation. The experiments were conducted at the Center for Geotechnical Modeling at the University of California at Davis. The authors greatly appreciate the assistance from staff of this center: Dan Wilson, Peter Rojas, Jenny Chen, Ray Gerhard, Lars Pedersen, Anatoliy Ganchenko, Chad Justice, and Tom Kohnke. Allison Quiroga, Bo Zhang, and Karrthik Kirupakaran from the University of Oklahoma helped with the centrifuge tests. Useful suggestions and discussions during the development of the centrifuge tests by Sri Sritharan, Juan Baez, Arul Arulmoli, and Steve Vukazich are also gratefully acknowledged.
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Journal of Geotechnical and Geoenvironmental Engineering
Volume 142 • Issue 4 • April 2016
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© 2015 American Society of Civil Engineers.
History
Received: Dec 8, 2014
Accepted: Oct 5, 2015
Published online: Dec 30, 2015
Published in print: Apr 1, 2016
Discussion open until: May 30, 2016
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