A Comparison between Effects of Linear and Non-Linear Mechanistic Behaviour of Materials on the Layered Flexible Pavement Response (original) (raw)
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APPLICATIONS OF LAYERED THEORY FOR THE ANALYSIS OF FLEXIBLE PAVEMENTS
Unbound granular materials used in untreated base/sub-base layers, exhibit nonlinear behavior under repeated wheel loads. The properties of the granular materials play a significant role in the performance of these pavements. Therefore, accurate modelling of the granular layers is essential in the evaluation of critical pavement responses under the application of loads, these materials exhibit stress dependent characteristics. Thus, consideration of non-linearity in these layers is necessary for accurate estimation of the pavement responses of a flexible pavement structure. The pavement responses are computed using Kenlayer computer program developed by Huang. Using the Kenlayer program, this paper examines the effect of nonlinearity in granular on critical pavement responses by conducting parametric analysis. The results indicate that the consideration of nonlinearity yields 23.13% reduction in tensile strains at the bottom of bituminous layers and 0.76% increase in compressive strains on the top of the sub grade layers and same surface deflections compared to the value obtained using linear elastic analysis. This indicates that nonlinear analysis is more realistic and accurate.
2011
Resilient modulus is an important input for computation of the structural response of pavements in Mechanistic -Empirical Methods. It has a significant effect on computed pavement responses and predicted pavement performance. The main objective of the research study that is introduced here is to develop a material model subroutine applicable to Finite Element program to simulate the nonlinear behavior of unbound granular materials, and evaluate the influence of using different constitutive models for characterization of unbound granular materials on critical responses of Flexible pavements. These constitutive models include Linear Elastic, Uzan and Universal models. For this purpose, three different pavement sections are assumed and FE models for these sections were verified by comparing elastic responses with KENLAYER Program. A granular base with known material constants for these three models was selected and sections were analyzed using different constitutive models. The results...
NonPAS: A Program for Nonlinear Analysis of Flexible Pavements
2015
Normal 0 false false false EN-US X-NONE FA MicrosoftInternetExplorer4 The primary step in design of a pavement using Mechanistic-Empirical (M-E) method is the analysis of pavement and calculation of the critical responses of pavement under various loadings. This confirms the need for developing pavement analysis software as an analytical base of the M-E method. To this end, NonPAS program has been developed for linear and nonlinear analysis of flexible pavements. Developed program allows nonlinear analysis of flexible pavements using five nonlinear models, including K-θ, Uzan, Uzan-Witczak, MEPDG 2002 and Bilinear models. Nonlinear Analysis of flexible pavements by utilizing these constitutive models provides a more accurate modeling of granular material behavior. Developed program can be used to analyze a pavement system consists of maximum of 10 layers, which is subjected to a maximum of six circular loads. Developed program allows for calculating the responses at 400 different po...
Effects of Interface Condition on Performance of Road Pavements with Non-linear Granular Materials
The main results of a numerical investigation into the effects of interface condition on the critical response and predicted performance of flexible pavements with granular bases are presented. In addition, the influence of using linear elastic and non-linear elastic models for granular base characterization, on the design life of typical road structures with granular bases under various combinations of layer interface conditions is examined. Repeated load triaxial tests are carried out and non-linear regression analyses on tests results are performed to determine the constitutive model parameters. The Asphalt Institute distress models for fatigue cracking and rutting using both linear and non-linear analyses are utilized to estimate the pavement design life. It is shown, among others, that interface condition affects significantly the critical response of pavement structures and hence their predicted performance. Furthermore, the results indicate that the use of linear assumption to characterize granular base and sub-base behaviour, grossly over-estimates the design life of pavement structures. This effect strongly depends on interface conditions used between the pavements layers.
In the past few years, LCPC has been implementing in its finite element code CESAR-LCPC a module for pavement modelling, including non-linear models for asphalt materials and unbound granular materials. This program has been used to model results of a full scale experiment on a flexible pavement, with a granular base, performed on the LCPC accelerated pavement testing facility. The experimental results indicated that the response of the pavement depends strongly on the level of load and on the water content of the unbound granular layers. The modelling of the pavement was performed in 3D, and several modelling hypotheses were successively tested : linear elasticity, a non-linear elastic model for the unbound layers (Boyce model) and a visco-elastic model for the asphalt concrete (Huet-Sayegh model). The most complete model, coupling non-linear elasticity for the unbound materials and visco-elasticity for the asphalt concrete, led to realistic predictions of the pavement response for different levels of load and different loading speeds.
In the mechanistic pavement design, it is common practice that the coarse and fine grained materials are modelled as linear elastic materials. The main reason for this is to use a simple set of parameters to represent each layer which in this case are the elastic modulus and Poisson ratio. However, it is well known that the unbound coarse granular materials and the fine grained subgrade materials behave nonlinearly under the traffic loading. The Australian mechanistic empirical design method (AUSTROADS) uses a simplified approach to account for the nonlinear behaviour of the unbound coarse and fine grained materials. In this paper the Austroads quasi-linear analysis is compared with the exact nonlinear analysis to examine the validity of this approach. The Austroads quasi-linear analysis provided better solutions than the linear elastic analysis without sublayering, however, it needs some adjustment to provide better match with the exact nonlinear analysis solution.
This paper explains the importance of using a nonlinear anisotropic three-dimensional (3D) finite-element (FE) pavement model to simulate the granular base layer and predict viscoelastic pavement responses under moving vehicular loading. The FE model was built using the general-purpose FE software ABAQUS, and a user material subroutine was developed to implement the constitutive model of granular material using a modified Newton-Raphson approach with secant stiffness. The FE model utilizes implicit dynamic analysis and simulates the vehicular loading as a moving load with 3D contact stresses at the tire-pavement interface. The analysis results indicate that it is important to consider the viscoelastic nature of the asphalt layer and the moving load for accurately capturing the nonlinear granular base modulus in the mechanistic pavement model. The modulus distribution in the granular base layer is affected not only by wheel load and pavement structure (such as asphalt layer thickness and subgrade support) but also by temperature and vehicle speed because of the viscoelastic behavior of the asphalt surface layer. Excluding the cross-anisotropic stress-dependent behavior of the granular base layer could cause significant error in predicting fatigue cracking and rutting potential in thin asphalt pavements. In addition, the model results captured the trends of field measurements at different loading and temperature conditions.
This paper explains the importance of using a nonlinear anisotropic three-dimensional (3D) finite-element (FE) pavement model to simulate the granular base layer and predict viscoelastic pavement responses under moving vehicular loading. The FE model was built using the general-purpose FE software ABAQUS, and a user material subroutine was developed to implement the constitutive model of granular material using a modified Newton-Raphson approach with secant stiffness. The FE model utilizes implicit dynamic analysis and simulates the vehicular loading as a moving load with 3D contact stresses at the tire-pavement interface. The analysis results indicate that it is important to consider the viscoelastic nature of the asphalt layer and the moving load for accurately capturing the nonlinear granular base modulus in the mechanistic pavement model. The modulus distribution in the granular base layer is affected not only by wheel load and pavement structure (such as asphalt layer thickness and subgrade support) but also by temperature and vehicle speed because of the viscoelastic behavior of the asphalt surface layer. Excluding the cross-anisotropic stress-dependent behavior of the granular base layer could cause significant error in predicting fatigue cracking and rutting potential in thin asphalt pavements. In addition, the model results captured the trends of field measurements at different loading and temperature conditions.
Deformational properties of unbound granular pavement materials
Selection of pavement materials takes very important role in pavement design procedure. The understanding of pavement structure behavior under cyclic loading is necessary in order to assure its serviceability during a predicted structure life. Unbound granular material layers in pavement structure represent a base for upper construction and their compaction and deformational behavior under cyclic loading have significant impact on the bearing capacity of upper layers and overall pavement construction. Unbound granular materials show complex behavior under cyclic loads with gradual accumulation of permanent deformation. Accumulation of a large number of small permanent deformation in unbound granular material usually affects on behavior of the sub-base layer and larger irreversible deformations in the upper layers of the pavement structure. Several analytical models have been developed to describe the development of the permanent deformations and behavior of unbound granular materials affected by these deformations. Recent studies and analyses are oriented on laboratory testing of different types of unbound materials under triaxial loading. These studies aim at developing analytical models which are more accurate in predicting deformation behavior of particular local materials under specific stress and moisture conditions. The purpose of this paper is to present an overview of the models that describe permanent deformation in unbound granular materials and correlation between permanent deformation and number of load cycles. Particular emphasis in the analyses would be on models that can be applied on unbound pavement layers constructed of local materials used in Croatia.
Non-linear finite element analysis of flexible pavements
Advances in Engineering Software, 2003
A research study is being undertaken to incorporate the realistic material properties of the pavement layers and the moving traffic load, in the analysis of flexible pavements, using the finite element theory. As a preliminary step taken herein in this direction, a pavement structure where field measurements have been carried out when subjected to a cyclic loading, is selected and modelled as a finite element model. The analysis is being carried out using the finite element computer package ABAQUS/STANDARD, when this pavement model is subjected to static and cyclic loading while considering the linear and non-linear material properties of the pavement layers. The results indicate that displacements under cyclic loading when non-linear materials are present, are the closest to field measured deflections. q