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Title: Analysis of strain-softening behavior of soil
Authors: Peters, John F.
Leavell, Daniel A.
Johnson, Lawrence D.
Keywords: Soil mechanics
Mathematical models
Numerical models
Clay soils
Shear strength
Soil tests
Soil testing
Finite element method
Finite element code
Publisher: Geotechnical Laboratory (U.S.)
Engineer Research and Development Center (U.S.)
Description: Research Report
Purpose and Scope: The purpose of this report is to present the results of a study involving (A.) development of models for simulating strain-softening behavior of soils, (B.) laboratory triaxial strength tests to obtain stress-strain data on strain-softening soils, (C.) verification of the models by numerical analyses using results of the laboratory strength tests, and (D.) implementation of the most suitable model into a subroutine that can be incorporated into an appropriate finite element computer code. Two incremental elastoplastic models for simulating the strain-softening behavior of soils were developed as part of this study. Laboratory triaxial shear strength tests were performed on two highly plastic clay soils and one low plasticity clay to determine their drained and undrained stress-strain response. The minimum requirement to evaluate parameters for the models consisted of testing soils at two values of overconsolidation ratio (OCR). The values of OCR selected for testing of each soil were 1.2 and 15, which required a minimum of four strength tests on each soil (two drained and two undrained). These two OCR's were selected to simplify evaluation of the material parameters required to use each of the models and to evaluate the model behavior under both drained and undrained conditions. The models were analyzed for relative usefulness by first determining the material parameters from drained strength data, predicting the undrained stress-strain behavior in triaxial shear, and comparing behavior predicted by the models with observed behavior for results of the undrained triaxial shear tests. Additional tests were performed at other values of OCR to determine the ability of the models to predict behavior at intermediate values of OCR. The report is presented as five parts. Part I provides introductory background material on the significance of strain-softening to geotechnical analysis. In particular, the role of strain-softening in establishing a correspondence between traditional limit equilibrium analyses and the finite element analyses is described. Parts II and III present the description of the testing program and a summary of test results. The formulations of the two constitutive models are outlined in Part IV, and the predictions of the models are compared with laboratory data. Part V presents conclusions on the performance of the model with recommendations for future research. Appendix A presents the formulation of constitutive relationships using the theory for elastoplastic strain-hardening materials. Appendix B discusses stress-dilatancy theories and the Hvorslev failure law. Bounding surface plasticity for cohesive soils is discussed in Appendix C, reproduced from a report by Drs. Yanis F. Dafalias and Leonard R. Herrmann. The computer code for the bounded frictional-dilatant flow is described in Appendix D, while Appendix E presents laboratory test data. NOTE: This file is large. Allow your browser several minutes to download the file.
Rights: Approved for public release; distribution is unlimited.
Appears in Collections:Non-Series Report

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