Selection and evaluation of models for prediction of permanent deformations of unbound granular materials in road pavements Draft report (original) (raw)
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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.
Permanent deformation models for a granular material used in road pavements
Construction and Building Materials, 2006
This paper analyses the permanent deformation performance of an unbound granular material that has been subjected to repeated triaxial loads. The study focuses on the evolution of the cumulative strain and includes a classification of the specimens according to the shakedown concept. This was done by fitting models that express the cumulative strain to cyclic loads and stress level. The predictions of the models were not absolutely perfect. The results with the granular material were not satisfactory enough to warrant their use in a low traffic road pavement section in Galicia (Spain).
Prediction of Permanent Deformations of Unbound Granular Materials in Low Traffic Pavements
Road Materials and Pavement Design, 2007
Permanent deformations of unbound granular layers and soils, caused by unfavourable moisture conditions, are one of the most common mechanisms of deterioration of low traffic pavements, with unbound granular bases. The paper presents permanent deformation models, developed by LCPC and by the University of Limoges, for the prediction of permanent deformations of unbound granular materials : a simple empirical model and two elastoplasticity based models for cyclic loading : one of them is based on the time independent plasticity with kinematic hardening, and the second one on the shakedown theory. The model parameters have been determined with cyclic triaxial tests performed on a granular base course material, at different moisture contents. An application of the models to finite element calculation of permanent deformations in a pavement structure is presented. RÉSUMÉ: Les déformations permanentes des graves non traitées et du sol support, causées par des conditions d'humidité défavorables, sont un des principaux mécanismes de dégradation des chaussées souples, à assises non liées. L'article présente des modèles de déformations permanentes développés par le LCPC et par l'Université de Limoges, pour la prédiction des déformations permanentes des matériaux granulaires non liés : un modèle expérimental empirique et deux modèles élastoplastiques : l'un d'eux est basé sur la plasticité à écrouissage cinématique et le deuxième sur la théorie de l'état limite. Les paramètres des modèles ont été déterminés au moyen d'essais triaxiaux à chargements répétés effectués sur une grave non traitée, à plusieurs teneurs en eau. Une application de ces modèles a été réalisée au travers d'une modélisation éléments finis 3D d'une structure de chaussée souple.
Predicting permanent deformation behaviour of unbound granular materials
International Journal of Pavement Engineering, 2014
This Ph.D. project was carried out at the Swedish National Road and Transport Research Institute (VTI) in cooperation with the KTH Royal Institute of Technology. It was financed by the Swedish Transport Administration (Trafikverket). The Danish aggregates used here were provided by the Danish Road Directorate. This work was supervised by Professor Sigurdur Erlingsson at VTI. First, I would like to express my gratitude to VTI for allowing me the opportunity to work on this project. I am very grateful to my supervisor Professor Sigurdur Erlingsson for all his guidance, support, inputs, insightful ideas, constructive comments, patience and very warm and friendly attitude. I am also thankful to our former head of the Department of Pavement Technology at VTI, Gunilla Franzén, and the current head of the department, Björn Kalman, for administrative support. My special thanks go to Håkan Arvidsson for helping me in the laboratory. I am also indebted to my fellow Ph.D. students at VTI, Abubeker Ahmed, Farhad Salour, Jonas Wennström and Markus Svensson, who have always helped and inspired me in many ways. I am also thankful to my colleagues for the friendly environment and for their help and support directly and indirectly all through the project. I would like to specifically mention Hassan Hakim for his help and invaluable suggestions in many different aspects. Finally, I am grateful to my wife Nadia Sharmin and my daughters Farishta and Aura for all their love and support. I am also thankful to my parents and siblings for their inspiration.
A simplified method of prediction of permanent deformations of unbound pavement layers
This paper presents a simplified method for modelling of permanent deformations of unbound granular layers. This method is based on three steps: first, the material is characterised using repeated load triaxial tests, with different stress levels. Then, the test results are analysed using a model of prediction of permanent deformations as a function of maximum applied cyclic stresses and number of load cycles. Two different models can be selected at this stage: an empirical relationship and an elastoplastic model. Finally, a finite element analysis with the program CESAR-LCPC, is used to determine the stress distribution in the pavement. The stresses calculated at different points in the structure allow the permanent vertical strains at each point to be determined, by applying one of the selected permanent deformation models. Finally the permanent strains are integrated along the vertical direction to obtain the vertical displacements in the structure (i.e. rutting of the layer). An example of application of the method is presented.
Journal of Building Materials and Structures, 2020
This research paper deals with experimental characterisation and numerical modelling of the resilient behaviour of Unbound Granular Materials (UGMs) usually used in road construction. The first part of this paper describes the main results of an experimental program that was carried out to assess the mechanical properties of two local Unbound Granular Materials (UGMs) for construction purposes in road pavement. The second part of this paper is devoted to the numerical modelling of the resilient behaviour of UGMs used in flexible pavements. For this purpose, several nonlinear unbound aggregates constitutive models are implemented within an axi-symmetric finite element code developed to simulate the nonlinear behaviour of pavement structures. In addition, deflection data collected by Falling Weight Deflectometer (FWD) are incorporated into the analysis in order to assess the sensitivity of critical pavement design criteria and pavement design life to the constitutive models. Finally, ...
Construction and Building Materials, 2012
The present paper reports the results of a laboratory experiment that aimed to investigate the permanent deformation behaviour of two unbound granular materials for road subbase layers under repeated triaxial loading. In the first part of research the shakedown concept was used to classify the mechanical response of the granular mixtures. The obtained results confirmed the potential usefulness of this theoretical approach for ranking granular materials with regard to their rutting potential. The second part was entirely dedicated to the development of an analytical model to describe the long-term permanent deformation behaviour of these materials. The proposed model allowed permanent strain accumulation as function of the number of load applications and applied stress level to be described. The results, besides being consistent with the shakedown concept, showed the ability of the model to reflect the change in mechanical behaviour due to the different nature of materials, under specific stress and moisture condition. In addition, the model allowed the permanent deformation accumulation resistance of the material to be properly investigated through specific strain rate envelope curves defined on a Mohr-Coulomb diagram. Therefore, this study could propose an innovative and practical design approach for permanent deformation behaviour assessment of unbound granular material and consequently for evaluating its suitability in the pavement in order to avoid undesirable response.
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.
International journal of geosynthetics and ground engineering, 2024
The behaviour of unbound granular materials (UGMs) used in road construction is crucial in determining the longevity and performance of road pavement. Geotechnical analysis can assist engineers in selecting suitable materials and designing road pavements that meet industry standards. This paper presents the results of laboratory geotechnical tests conducted on unbound granular materials (UGMs) collected from three sites (Roses Gap, Rules East, and Polkemmet Road) in Horsham, Victoria, Australia. UGMs were investigated for their mechanical behaviour and suitability as subgrade materials for road pavements. The study utilised laboratory geotechnical tests, including particle size distribution (PSD), Atterberg limits, compaction (Proctor) test, unconfined compressive strength (UCS), California Bearing Ratio (CBR), and repeated load triaxial (RLT) tests, to evaluate the physical and mechanical properties of the UGM samples. The study indicates that UGM samples collected from different locations displayed variations in their geotechnical properties, such as particle size distribution, water absorption, and CBR strength. Roses Gap samples showed weak cohesion properties, and significant vertical displacements after repeated triaxial tests. However, among the samples in this site, samples with higher clay content (RG21) demonstrated the most promise in triaxial tests. Similarly, the Rules East samples were found to be suitable for low-traffic subgrades due to their satisfactory CBR and RLT testing results, albeit with little cohesion from clay content. Out of three locations, Polkemmet samples were identified as potential subgrade applications, with PR12 being the top recommendation overall. It satisfied PSD, CBR, and RLT test conditions due to acceptable particle size in the largest range, highest CBR strength value, and lowest permanent displacement. The study's findings provide useful information for the design of road pavements using these materials and the characterisation of rural materials around the Horsham region for future use in various other contexts.