Pavement foundation geomaterials, i.e., fine-grained subgrade soils and unbound aggregates used in untreated base/subbase layers, exhibit nonlinear behavior under repeated wheel loads. This nonlinear behavior is commonly characterized by stress-dependent resilient modulus material models that need to be incorporated into finite element (FE) based mechanistic pavement analysis methods to predict more accurately the pavement resilient responses, such as stress, strain, and deformation. Many general-purpose FE programs have been used to predict such pavement responses under various traffic loading conditions while not considering properly material characterizations of the unbound aggregate base/subbase and subgrade soil layers. This paper describes the recent pavement FE modeling research efforts at the University of Illinois focused on using both the specific-purpose axisymmetric and general-purpose three-dimensional (3D) FE programs for flexible pavement analyses. To properly characterize the resilient beh...

Nonlinear Pavement Foundation Modeling for Three-Dimensional Finite-Element Analysis of Flexible Pavements

Pavement foundation geomaterials, i.e., fine-grained subgrade soils and unbound aggregates used in untreated base/subbase layers, exhibit nonlinear behavior under repeated wheel loads. This nonlinear behavior is commonly characterized by stress-dependent resilient modulus material models that need to be incorporated into finite element (FE) based mechanistic pavement analysis methods to predict more accurately the pavement resilient responses, such as stress, strain, and deformation. Many general-purpose FE programs have been used to predict such pavement responses under various traffic loading conditions while not considering accurately material characterizations of the unbound aggregate base/subbase and subgrade soil layers. This paper describes the recent pavement FE modeling research efforts at the University of Illinois focused on using both the specific purpose axisymmetric and general-purpose three-dimensional (3D) FE programs for flexible pavement analyses. 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 commercial general-purpose finite element program ABAQUSTM. The axisymmetric pavement FE program GT-PAVE was used to verify the nonlinear material models in the ABAQUS UMAT subroutine. The results indicated that proper characterizations of the nonlinear, stress-dependent pavement foundation geomaterials significantly impacted accurate predictions of critical pavement responses and this consideration should be adequately implemented in the 3D FE analyses of flexible pavements.

Nonlinear Pavement Foundation Modeling for Three-Dimensional Finite Element Analysis of Flexible Pavements

This 1992 TRB Distinguished Lecture reviews the development of analytically based asphalt pavement design and rehabilitation during the 30-year period from 1962 to 1992. Subject headings are as follows: Introduction; Background and Foundations; Pavement Analysis; Materials Characterization; Asphalt Concrete Distress Considerations; Pavement Design and Rehabilitation; Asphalt-Aggregate Mix Design; Implications and Future Direction.

Analytically based asphalt pavement design and rehabilitation: theory to practice, 1962-1992

This paper describes the use of artificial neural networks (ANNs) as pavement structural analysis tools for the rapid and accurate prediction of critical responses and deflection profiles of full-depth flexible pavements subjected to typical highway loadings. The ILLI-PAVE finite element program, extensively tested and validated for over three decades, was used as an advanced structural model for solving the critical responses of full-depth flexible pavements. Unlike the linear elastic layered theory commonly used in pavement layer backcalculation, nonlinear stress-dependent subgrade soil response models were used in the ILLI-PAVE program to account for the softening nature of fine-grained subgrade soils under increasing stress states. ANN models then trained with the results from the ILLI-PAVE solutions have been found to be viable alternatives. The trained forward calculation ANN models were capable of predicting asphalt tensile strains and subgrade compressive stresses/strains with low average absolute...

Backcalculation of full-depth asphalt pavement layer moduli considering nonlinear stress-dependent subgrade behavior

Rutting performance of rubberized porous asphalt using Finite Element Method (FEM)

AN APPLICATION IS DESCRIBED OF THE FINITE ELEMENT TECHNIQUE TO THE ANALYSIS OF SYSTEMS REPRESENTATIVE OF PAVEMENT STRUCTURES USE IS MADE OF A DIGITAL COMPUTER PROGRAM WHICH GENERATES SUITABLE FINITE ELEMENT CONFIGURATIONS FOR AXISYMMETRIC STRUCTURES AND ACCOMMODATES APPROXIMATIONS OF NONLINEARITY WHICH APPEAR APPROPRIATE TO REPRESENT THE BEHAVIOR OF GRANULAR BASE AND COHESIVE SUBGRADE MATERIALS UNDER CONDITIONS CORRESPONDING TO MOVING TRAFFIC EXAMPLES ARE PRESENTED FOR SYSTEMS WITH LINEAR MATERIAL PROPERTIES SHOWING COMPARISONS BETWEEN DISPLACEMENTS AND STRESSES COMPUTED USING THE FINITE ELEMENT TECHNIQUE AND THOSE COMPUTED USING ELASTIC HALF-SPACE AND LAYERED SYSTEM ANALYSES TO ESTABLISH CRITERIA FOR BOUNDARY CONDITIONS IN THE FINITE ELEMENT PROCEDURE FOR THE ELASTIC HALF-SPACE SUBJECTED TO A UNIFORM CIRCULAR LOAD, DISPLACEMENTS AND STRESSES COMPUTED BY THE FINITE ELEMENT TECHNIQUE COMPARE FAVORABLY WITH THOSE DETERMINED FROM THE BOUSSINESQ SOLUTION WHERE THE NODAL POINTS IN THE FINITE ELEMENT PROCEDURE ARE FIXED AT A DEPTH OF 18 RADII FOR THE BOTTOM BOUNDARY AND CONSTRAINED FROM MOVING RADIALLY ON THE VERTICAL BOUNDARY AT A DISTANCE OF ABOUT 12 RADII FROM THE CENTER TWO ANALYSES ARE PRESENTED FOR DEFLECTION DETERMINATIONS FOR AN INSERVICE PAVEMENT NEAR GONZALES, CALIF, ONE FOR A CONDITION WHERE THE ASPHALT CONCRETE WAS AT A COMPARATIVELY HIGH TEMPERATURE (STIFFNESS MODULUS IN THE RANGE 120,000 TO 280,000 PSI), AND THE OTHER WITH THE MATERIAL AT A LOW TEMPERATURE (STIFFNESS MODULUS APPROXIMATELY 1,500,000 PSI) NONLINEAR MATERIAL PROPERTIES, DETERMINED FROM THE RESULT OF REPEATED LOAD TRIAXIAL COMPRESSION TESTS, WERE USED TO REPRESENT THE BEHAVIOR OF THE UNTREATED GRANULAR BASE AND SUBBASE AND THE FINE-GRAINED SUBGRADE SOIL DEFLECTIONS PREDICTED BY THE FINITE ELEMENT PROCEDURE ARE IN THE SAME RANGE AS THOSE MEASURED WITH THE CALIFORNIA TRAVELING DEFLECTOMETER INDICATING THAT THE METHOD HAS POTENTIAL TO SIMULATE ACTUAL PAVEMENT BEHAVIOR TO A REASONABLE DEGREE THE ANALYSIS ALSO INDICATES THAT WHEN THE EXTENSIONAL STRAINS IN THE ASPHALT CONCRETE ARE LARGE FOR THIS PAVEMENT (IE, WHERE THE STIFFNESS OF THE ASPHALT BOUND MATERIAL IS LOW), THE GRANULAR MATERIAL EXHIBITS A VERY LOW MODULUS UNDER THE LOADED AREA AND A LARGE PROPORTION OF THE SURFACE DEFLECTION CAN BE ATTRIBUTED TO DEFORMATIONS WITHIN THIS MATERIAL ON THE OTHER HAND, WHEN THE ASPHALT LAYER IS STIFF, THE MAJORITY OF THE SURFACE DEFLECTION IS CONTRIBUTED BY THE SUBGRADE AN ANALYSIS IS ALSO PRESENTED FOR THE RESULTS OF PLATE LOAD TESTS ON A TWO- LAYER PROTOTYPE PAVEMENT CONSISTING OF GRANULAR BASE AND A COHESIVE SUBGRADE SOIL USING THE SAME NONLINEAR CHARACTERIZATION FOR MATERIAL PROPERTIES AS FOR THE IN- SERVICE PAVEMENT /AUTHOR/

J M Duncan

Papers

Finite element analyses of pavements