Liquefaction-Induced Softening of Load Transfer between Pile Groups and Laterally Spreading Crusts
Publication: Journal of Geotechnical and Geoenvironmental Engineering
Volume 133, Issue 1
Abstract
Laterally spreading nonliquefied crusts can exert large loads on pile foundations causing major damage to structures. While monotonic load tests of pile caps indicate that full passive resistance may be mobilized by displacements on the order of 1–7% of the pile cap height, dynamic centrifuge model tests show that much larger relative displacements may be required to mobilize the full passive load from a laterally spreading crust onto a pile group. The centrifuge models contained six-pile groups embedded in a gently sloping soil profile with a nonliquefied crust over liquefiable loose sand over dense sand. The nonliquefied crust layer spread downslope on top of the liquefied sand layer, and failed in the passive mode against the pile foundations. The dynamic trace of lateral load versus relative displacement between the “free-field” crust and pile cap is nonlinear and hysteretic, and depends on the cyclic mobility of the underlying liquefiable sand, ground motion characteristics, and cyclic degradation and cracking of the nonliquefied crust. Analytical models are derived to explain a mechanism by which liquefaction of the underlying sand layer causes the soil-to-pile-cap interaction stresses to be distributed through a larger zone of influence in the crust, thereby contributing to the softer load transfer behavior. The analytical models distinguish between structural loading and lateral spreading conditions. Load transfer relations obtained from the two analytical models reasonably envelope the responses observed in the centrifuge tests.
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Acknowledgments
Funding was provided by the Pacific Earthquake Engineering Research (PEER) Center, through the Lifeline Program and the Earthquake Engineering Research Centers Program of the National Science Foundation, under Contract No. 2312001. The centrifuge tests were funded by Caltrans under Contract Nos. 59A0162 and 59A0392. The contents of this paper do not necessarily represent a policy of either agency or endorsement by the state or federal government. Recent upgrades to the centrifuge have been funded by NSF Award No. CMS-0086566 through the George E. Brown, Jr., Network for Earthquake Engineering Simulation (NEES). The writers appreciate the assistance of Dr. Dan Wilson with the centrifuge tests and data analysis techniques.
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© 2007 ASCE.
History
Received: Sep 27, 2005
Accepted: Jul 19, 2006
Published online: Jan 1, 2007
Published in print: Jan 2007
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