Liquefaction-Induced Settlement of Pile Groups in Liquefiable and Laterally Spreading Soils
Publication: Journal of Geotechnical and Geoenvironmental Engineering
Volume 134, Issue 11
Abstract
The results of a series of dynamic centrifuge tests on model pile groups in (level) liquefied and laterally spreading soil profiles are presented. The piles are axially loaded at typical working loads, which has enabled liquefaction-induced settlements of the foundations to be studied. The development of excess pore pressures within the bearing layer (dense sand) was found to lead to a reduction in pile capacity and potentially damagingly large coseismic settlements. As the excess pore pressure increased, these settlements were observed to exceed postshaking downdrag-induced settlements, which occur due to the reconsolidation of liquefied sand around the pile shaft. In resisting settlement, the pile cap was found to play an important role by compensating for the capacity lost by the piles. This was shown to be achieved by the development of dilative excess pore pressures beneath the pile cap within the underlying loose liquefied sand which provide increasing bearing capacity with settlement. The centrifuge test data show good qualitative and quantitative agreement with the limited amount of model and full-scale data currently available in the literature. The implications of settlement for the design of piled foundations to serviceability conditions in both level and sloping ground are discussed, with settlement becoming an increasingly important consideration for laterally stiffer piles. Finally, empirical relationships have been derived from the test data to relate suitable static safety factors to given increases in excess pore pressure in the bearing layer within a performance-based design framework (i.e., based on limiting displacements).
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Acknowledgments
The writers would like to sincerely thank the technical staff at the Schofield Centrifuge Centre in Cambridge for their invaluable assistance with the centrifuge testing work. Financial support for the first writer and the project was provided by the Engineering and Physical Sciences Research Council, UK (EPSRC) and is acknowledged with thanks.
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© 2008 ASCE.
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Received: Mar 8, 2007
Accepted: Mar 14, 2008
Published online: Nov 1, 2008
Published in print: Nov 2008
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