Postshaking Shear Strain Localization in a Centrifuge Model of a Saturated Sand Slope
Publication: Journal of Geotechnical and Geoenvironmental Engineering
Volume 134, Issue 2
Abstract
This paper presents analyses of a test conducted on a 9-m-radius centrifuge to study the redistribution of pore water during diffusion of earthquake-induced excess pore pressures in a sand slope with embedded silt layers. The centrifuge model developed large postshaking deformations associated with shear strain localization at the interface between the sand and silt layers. Dense arrays of pore pressure transducers provided detailed measurements of pore pressure variations in time and space within the slope. A new data analysis approach is presented in which measured pore-pressures are used to compute flow rates and volumetric strains as a function of time and position throughout the slope. Hydraulic gradients were calculated by numerical differentiation of measured pore-pressure distributions with respect to position. Flow rates that were based on Darcy’s law were then integrated with respect to time to obtain flow quantities, from which volumetric strains were computed. A second data analysis approach that computes volumetric strains on the basis of soil compressibility and changes in pore pressure provided an independent computation of strains in consolidating zones. Results using these data analysis procedures confirm that a dilating (loosening) zone of significant thickness developed in the sand immediately beneath an embedded silt layer that had impeded the drainage of high pore pressures. These results support the hypothesis that the dilating zone corresponds to regions where the mobilized friction angle exceeds the critical state friction angle and that the dilating zone can be initially relatively thick before its size diminishes to the thickness of a thin shear band after the peak friction angle is mobilized. Quantification of the evolution of the size of the dilating zone is a key to understanding the magnitude of deformations associated with void redistribution.
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Acknowledgments
The National Science Foundation funded this research under Grant No. CMS-0070111. Dan Wilson provided software for data acquisition and extensive advice regarding model testing techniques and design. The writers are grateful to I. M. Idriss for his comments throughout this study and to the Geotechnical Centrifuge Research Center at Rensselaer Polytechnic Institute for loaning several pore pressure sensors. This project used upgraded capabilities of the NEES centrifuge at UC Davis that were funded by the George E. Brown, Jr., Network for Earthquake Engineering Simulation (NEES) under Award No. CMS-0086566.
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Information & Authors
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Published In
Journal of Geotechnical and Geoenvironmental Engineering
Volume 134 • Issue 2 • February 2008
Pages: 164 - 174
Copyright
© 2008 ASCE.
History
Received: Feb 14, 2006
Accepted: Mar 2, 2007
Published online: Feb 1, 2008
Published in print: Feb 2008
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