THREE-DIMENSIONAL FINITE ELEMENT ANALYSIS OF three-dimensional finite element analysis of flexible pavements

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  • THREE-DIMENSIONAL FINITE ELEMENT ANALYSIS OF FLEXIBLE PAVEMENTS CONSIDERING NONLINEAR PAVEMENT FOUNDATION BEHAVIOR

    BY

    MINKWAN KIM

    B.Eng., Inha University, 1998 M.Eng., Inha University, 2000

    M.S., University of Illinois at Urbana-Champaign, 2005

    DISSERTATION

    Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Civil Engineering

    in the Graduate College of the University of Illinois at Urbana-Champaign, 2007

    Urbana, Illinois

    Doctoral Committee:

    Associate Professor Erol Tutumluer, Chair Professor Imad L. Al-Qadi Associate Professor William G. Buttlar Assistant Professor C. Armando Duarte Professor Marshall R. Thompson

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    ABSTRACT

    With the current move towards adopting mechanistic-empirical concepts in the design of

    pavement structures, state-of-the-art mechanistic analysis methodologies are needed to

    determine accurate pavement responses, such as stress, strain, and deformation. This

    research has focused on the nonlinear modulus and deformation behavior of pavement

    foundation geomaterials, i.e., fine-grained subgrade soils and unbound aggregates used in

    untreated base/subbase layers, due to repeated wheel loading. This nonlinear behavior is

    commonly characterized by stress dependent resilient modulus material models that need

    to be incorporated into finite element based mechanistic pavement analysis methods to

    predict more accurately critical pavement responses. This dissertation describes the

    development of a finite element mechanistic analysis model for both the axisymmetric

    and three-dimensional analyses of flexible pavements. To properly characterize the

    resilient behavior of pavement foundations, nonlinear stress-dependent modulus models

    have been programmed in a User Material Subroutine (UMAT) in the general-purpose

    finite element program ABAQUSTM. The developed UMAT is verified first with the

    results of a well established axisymmetric nonlinear pavement analysis finite element

    program, GT-PAVE. Next, the UMAT subroutine performance is also validated with the

    instrumented full scale pavement test section study results from the Federal Aviation

    Administration’s National Airport Pavement Test Facility. The predicted responses at

    different locations in the test sections are compared with the field measured responses

    under different sections and load levels to indicate that proper characterizations of the

    nonlinear, stress-dependent geomaterials make a significant impact on accurately

    predicting measured pavement responses from three-dimensional pavement analyses.

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    Different resilient modulus models developed from conventional and true triaxial test

    data on unbound granular materials are also studied. When the intermediate principal

    stresses are taken into account in the three-dimensional modulus model development

    unlike in the axisymmetric models, large discrepancies are obtained in the computed

    pavement responses when compared to those from the axisymmetric nonlinear finite

    element analyses. Finally, as an important application of the developed UMAT nonlinear

    material subroutine in the analysis of flexible pavements subjected to multiple axle/wheel

    loads, load spreading and nonlinear modulus distributions of pavement layers are found

    to considerably impact pavement surface deflections and critical pavement responses.

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    ACKNOWLEDGEMENTS

    I would like to express my sincere gratitude to my advisor, Professor Erol Tutumluer,

    who provided me valuable advice, encouragement, and guidance on the matter of

    academic and personal as well. He always shared his enthusiasm and knowledge with me.

    I am also grateful to the member of my graduate committee, Professor Imad L. Al-Qadi,

    Professor William G. Buttlar, Professor Armando C. Duarte, and Professor Marshall R.

    Thompson for their constructive suggestions and thoughtful advices on the many aspects

    encountered in the completion of this study.

    I want to thank my colleagues and friends at the Department of Civil and Environmental

    Engineering for their friendly and continuous supports during the complete this work.

    They will always be remembered for the wonderful times we spent together during my

    stay in Champaign, Illinois.

    Finally, I am deeply indebted to my parents and family for their endless patience,

    comprehension, and love, and especially acknowledge the endless support and

    encouragement of my wife, Ji Young.

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    Table of Contents

    List of Figures ................................................................................................................................vii List of Tables .................................................................................................................................. ix Chapter 1 Introduction ................................................................................................................ 1

    1.1 Introduction .................................................................................................................... 1 1.2 Statement of Research Need........................................................................................... 2 1.3 Objectives of Study ........................................................................................................ 3 1.4 Outline of Thesis ............................................................................................................ 4

    Chapter 2 Granular Material and Subgrade Soil Characterizations............................................ 7 2.1 Introduction .................................................................................................................... 7 2.2 Unbound Granular Materials .......................................................................................... 7 2.3 Subgrade Soils ................................................................................................................ 8 2.4 Mechanistic Based Pavement Design Concepts ............................................................. 9

    2.4.1 Resilient Behavior.................................................................................................... 10 2.4.2 Modeling Resilient Modulus of Unbound Granular Materials ................................ 12

    2.4.2.1 Confining Pressure Model ............................................................................... 13 2.4.2.2 K-θ Model ....................................................................................................... 14 2.4.2.3 Shackel’s Model .............................................................................................. 16 2.4.2.4 Bulk-Shear Modulus Model ............................................................................ 17 2.4.2.5 Uzan Model ..................................................................................................... 19 2.4.2.6 Lade and Nelson Model................................................................................... 20 2.4.2.7 Universal Octahedral Shear Stress Model ....................................................... 22 2.4.2.8 Itani Model ...................................................................................................... 22 2.4.2.9 Crockford et al. Model .................................................................................... 23 2.4.2.10 UT-Austin Model ............................................................................................ 24 2.4.2.11 Lytton Model ................................................................................................... 24 2.4.2.12 NCHRP 1-37A Mechanistic Empirical Pavement Design Guide (MEPDG) Model……. ....................................................................................................................... .25

    2.4.3 Modeling Resilient Modulus of Subgrade Soils ...................................................... 26 2.4.3.1 Empirical Relationships................................................................................... 26 2.4.3.2 Brown and Loach Models ............................................................................... 27 2.4.3.3 Semilog Model ................................................................................................ 28 2.4.3.4 The Bilinear or Arithmetic Response Model................................................... 28 2.4.3.5 Hyperbolic Model............................................................................................ 29 2.4.3.6 Dawson and Gomes Correia Model ................................................................ 30

    2.5 Summary ...................................................................................................................... 31 Chapter 3 Structural Analysis and Finite Element Modeling of Flexible Pavements............... 32

    3.1 Flexible Pavement Analysis ......................................................................................... 32 3.2 Elastic Layered Programs for Pavement Analysis........................................................ 32

    3.2.1 One Layer Approach ................................................................................................ 32 3.2.2 Multi Layer Theory .................................................................