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|Evaluation of three constitutive models for soils
|University of California, Berkeley. College of Engineering
Lucia, Patrick C.
Duncan, J. M. (James Michael)
Stress-strain relations (soils)
Finite element method
|Geotechnical Laboratory (U.S.)
Engineer Research and Development Center (U.S.)
|Miscellaneous paper (U.S. Army Engineer Waterways Experiment Station) ; GL-79-3.
Abstract: The finite element method provides a powerful technique for analysis of stresses and movements in earth masses, and it has already been applied to a number of practical problems including embankment dams, open excavations, braced excavations, and a variety of soil-structure interaction problems. If the results of soil deformation analyses are to be realistic and meaningful, it is important that the stress-strain characteristics of the soil be represented in the analyses in a reasonable way. This is difficult because the stress-strain characteristics of soils are extremely complex, and the behavior of soil is nonlinear, inelastic, and highly dependent on the magnitudes of the stresses in the soil. The purpose of this report is to compare the characteristics of the hyperbolic, the Cam Clay and the Al-Shawaf and Powell stress-strain models for use in finite element analyses of earth masses. The principal objective of the study was to investigate the potential advantages and disadvantages of the Al-Shawaf-Powell model as compared to the other, more widely used stress-strain relationships. The hyperbolic stress-strain relationships were developed in an attempt to provide a simple framework encompassing the most important characteristics of soil stress-strain behavior, using the data available from conventional laboratory tests. These relationships have been used in finite element analyses of a number of different types of static soil mechanics problems and values of the hyperbolic parameters have now been determined for about 150 different soils. Duncan et al. (1978) outlined procedures for determination of the hyperbolic stress-strain and volume change parameters for use in nonlinear finite element analyses of stresses and movements in earth masses. The Cam Clay model was developed at Cambridge, and has recently been modified by Chang and Duncan (1978) for use in finite element analyses of stresses and movements in earth masses constructed of compacted materials, such as earth dams. Chang and Duncan outlined the procedures for determination of stress-strain and volume change parameters to provide the best fit between calculated and measured triaxial data. A model recently developed by Al-Shawaf and Powell differs from the hyperbolic and Cam Clay model in two important respects. (A.) It models shear dilatancy. (B.) The tangent moduli are obtained by numerical procedures rather than through the use of analytical expressions. This report is concerned with evaluating the following characteristics of the Al-Shawaf-Powell model: (1.) The ability of the model to reproduce triaxial test data for soils exhibiting dilatant behavior. (2.) The procedures required to develop the stress-strain and volume change parameters. (3.) The potential for use of the model in practical geotechnical problems. In the following sections the characteristics of the three models are described, the procedures for evaluating the parameters are explained, and comparisons between calculated and measured stress-strain curves for three dilatant soils are presented.
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