Physical Basis and Validation of a Constitutive Model for Soil Shear Derived from Microstructural Changes
Publication: International Journal of Geomechanics
Volume 13, Issue 4
Abstract
Previous work indicated that rates of change of shear stress, effective normal stress, and void ratio of a sheared soil are proportional to applied values of shear and effective normal stress; initial proportionality values decay exponentially with strain to become zero at the steady-state condition. This paper proposes that the physical basis for this behavior is an underlying stochastic process in which particles move at random shear strains into the steady-state flow structure under the action of shear stress, countered by frictional resistance generated by the effective normal stress. The resulting dynamical systems model with physical properties closely fits 130 undrained and drained triaxial and true-triaxial shear tests, exhibiting strain softening or strain hardening, using various stress paths, conducted on uncemented, resedimented clays at various overconsolidation ratios (OCRs) and uncemented sands and silts at various relative densities. Parameters varied orderly with OCRs (clays) and confining pressure (silts and sands). The model’s value is that based on a simple hypothesis of particles moving into the steady state at random shear strains, it closely matches data from a variety of tests. Present limitations of the model are that it only applies to static loading and not yet to generalized stress paths found in field situations.
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Acknowledgments
The author thanks the following persons: Dr. Gonzalo Castro and Dr. Steve Poulos; both of GEI Consultants, Inc., Winchester, MA; and Dr. J. Graham, Professor Emeritus, University of Manitoba, Winnipeg, Manitoba, Canada; Professor Lee Jones, Mathematics Department, University of Massachusetts at Lowell, Lowell, MA; and Professor Hong Qian, Mathematics Department, University of Washington at Seattle, Seattle, WA for helpful advice on some parts of this paper. In particular, Dr. Castro also helped the author clarify how the model handles postpeak behavior, Dr. Poulos helped the author clarify nonmonotonic particle behavior in the flow structure, Professor Jones rigorously reviewed the stochastic approach used, and Professor Qian provided the basis of the appendix. The author also thanks Professor P. Ooi, Professor of Civil Engineering, University of Hawaii, HI, and Dr. G. Iglezia of G2D Resources, LLC, San Diego, CA for input received. Additionally, the author thanks the editor and the anonymous reviewers of the journal for their rigorous yet sensitive handling of this paper. Their deep knowledge of the subject resulted in extremely subtle and insightful comments that have raised the standard of this paper to its present mark.
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Information & Authors
Information
Published In
International Journal of Geomechanics
Volume 13 • Issue 4 • August 2013
Pages: 365 - 383
Copyright
© 2013 American Society of Civil Engineers.
History
Received: Apr 24, 2011
Accepted: Jan 30, 2012
Published online: Feb 2, 2012
Published in print: Aug 1, 2013
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