Thèses sur le sujet « Repeated load triaxial test »

FundaÃÃo Cearense de Apoio ao Desenvolvimento Cientifico e TecnolÃgico
Permanent deformation or rutting is a major distress in asphalt pavements. To predict permanent deformation of asphalt mixtures the dynamic creep test is often used in laboratory, with the result presented in terms of the so called flow number. However, for this work it was performed the triaxial repeated permanent deformation load test, a confined test that better represents field conditions. The models that incorporate the flow number do not represent the main zone of the dynamic creep test result, denoted secondary region, in which the permanent deformation rate of growth is constant. In this work the Shift Model was used, which is a viscoplastic model that accesses the permanent deformation from the superposition principles, i.e., time-temperature superposition and time-stress superposition. Thus, the asphalt mixtures were tested under different loading conditions, temperature, load time and rest period, in order to assess three parameters of the test: parameter C, which indicates where the secondary region begins (parameter that governs the primary region of the test); the parameter α (alpha) is the slope of the secondary region; and the parameter B represents the level of permanent deformation of the secondary region. The results show that the TRLPD test is more severe than the conventional dynamic creep test. Nevertheless, the use of TRLPD test represents an advance in the understanding of the behavior of asphalt mixtures with respect to rutting performance, and has the advantage of allowing the use of results in computational simulations.
A deformaÃÃo permanente à um dos principais defeitos em pavimentos asfÃlticos. Para prever esta falha em revestimentos, por meio de ensaios laboratoriais, à frequentemente utilizado o ensaio de creep dinÃmico cujo resultado final à apresentado em termos do chamado flow number. No entanto, para este trabalho foi realizado o triaxial repeated load permanent deformation (TRLPD) test, que à um ensaio sob condiÃÃes de confinamento, a fim de melhor se aproximar das condiÃÃes encontradas em campo. Os modelos que incorporam o flow number nÃo representam a principal regiÃo de ensaio de creep dinÃmico, denominada regiÃo secundÃria, na qual o incremento de deformaÃÃo permanente cresce em valor constante. No presente trabalho utilizou-se o Shift Model, o qual à um modelo viscoplÃstico que avalia a deformaÃÃo permanente a partir da superposiÃÃo dos efeitos tempo-temperatura e tempo-tensÃo. Dessa forma, as misturas asfÃlticas foram testadas sob diferentes condiÃÃes de carregamento, temperatura, tempo de aplicaÃÃo de carga e perÃodo de repouso. Foram avaliados trÃs parÃmetros do ensaio em questÃo: o parÃmetro C, que fornece os dados de onde a regiÃo secundÃria se inicia (parÃmetro que governa a regiÃo primÃria do ensaio); o parÃmetro α (alfa), que à o aclive da regiÃo secundÃria; e o parÃmetro B, que representa o nÃvel de deformaÃÃo permanente da regiÃo secundÃria. Os resultados obtidos mostram que o ensaio TRLPD à mais severo do que o ensaio convencional de creep dinÃmico, porÃm considera-se que a utilizaÃÃo de ensaios confinados representa um avanÃo para o entendimento do comportamento das misturas asfÃlticas quanto à resistÃncia à deformaÃÃo permanente das mesmas, e este traz a vantagem de poder ser usado em simulaÃÃes computacionais.

Unbound Granular Materials (UGMs) are used in the base/subbase layers of flexible pavements for the majority of roads around the world. The deterioration of pavements increases with the increase of traffic loadings. To ensure the long-term performance and serviceability of pavement structures through a realistic design, the precise evaluation and comprehensive characterisation of the resilient and permanent deformation behaviour of pavement materials are essential. The present PhD study aims to investigate the characterisation of the resilient and permanent deformation behaviour of four road base UGMs sourced from quarries in Victoria, Australia, using Repeated Load Triaxial (RLT) testing. The triaxial system used in this study is instrumented with four axial deformation measurement transducers to achieve highly precise measurements and to evaluate the effect of instrumentation on the resilient modulus of UGMs. The resilient Poisson’s ratio of the studied UGMs is also determined using a radial Hall-Effect transducer. Moreover, a series of permanent deformation tests is performed to precisely characterise the axial and radial permanent deformation behaviour of UGMs and investigate the factors that may significantly influence the accumulated axial and radial permanent deformations. Finally, three permanent deformation models incorporated with a time-hardening procedure are employed to predict the magnitude of permanent strain for multiple stress levels of the RLT test. The predictions using the employed models are then compared against the measured values to evaluate the suitability of the models and to identify the model that best predicts the strain accumulation behaviour of the tested UGMs. While this study focuses on the resilient and permanent deformation behaviour of four Victorian UGMs under repeated loading, the knowledge generated from this comprehensive investigation will contribute towards the global development of more reliable methods for evaluating the long-term performance of pavement structures and minimising road maintenance and repair costs.
Doctor of Philosophy

Unbound granular materials (UGMs) used in the base and sub-base layers of flexible pavements play a significant role in the overall performance of the structure. Proper understanding and characterization of the deformation behaviour of UGMs in pavement structures are, therefore, vital for the design and maintenance of flexible pavements. In this study, the resilient deformation (RD) and the permanent deformation (PD) behaviour of UGMs were investigated for the better understanding and improved modelling of these deformation characteristics. The study is based on a series of repeated-load triaxial (RLT) tests carried out on several UGMs commonly used in pavement structures. Here, the influences of stress level and moisture content - two of the most significant factors affecting the deformation behaviour of UGMs - were analysed. The effects of the grain size distribution and the degree of compaction were also considered. The study on the RD behaviour indicated that the resilient stiffness (MR)of UGMs increases with the increased bulk stress level, which can be satisfactorily described by the k-θ model. Moisture was found to negatively impact the MR as long as the deformation was mostly resilient with a negligible amount of accumulated PD. Analysis of the influence of moisture on the parameters k1 and k2 of the k-θ model showed that k1 decreases with increased moisture and k2 is relatively insensitive to moisture. Based on these observations, a simple model was developed for the impact of moisture on MR. The performance of this model was comparable to an existing moisture dependent MR model. In contrast, it was further observed that at the later stages of the RLT tests, after a relatively large number of load applications, the MR increased with increased moisture up to the optimum moisture content. This occurred when the RD was accompanied by a significant amount of PD. Further investigation suggested that moisture aided the post-compaction (PC) and possible particle rearrangement that resulted in the increased PD and increased MR. In this case k1 decreased, whereas k2 increased, with increased moisture. The existing MR-moisture model did not work for this behaviour. This suggests that the effect of PC on MRshould be considered in modelling. However, although not explored in this study, it may be possible to simulate this effect of increase in MR with increased moisture due to PC using the proposed model if k2 is expressed as a function of moisture. The PD characteristics of UGMs were investigated based on the multistage (MS) RLT test. In contrast with the single stage (SS) RLT test, the MS RLT test accounts for the effect of stress history and enables a comprehensive study of the material behaviour under cyclic stresses of various magnitudes. Since the existing PD models cannot be directly applied for the MS loading procedure, a general formulation based on the time hardening concept was derived that can be used to extend the models for the MS loading conditions. Based on this formulation, some of the current models were calibrated and their performance in predicting the PD behaviour in MS RLT tests was compared. The investigation regarding the impact of moisture on PD showed that moisture significantly increases the accumulation of PD. Generally, materials with finer grading showed more sensitivity to moisture with regards to both PD and RD. To characterize the impact of moisture, moisture sensitivity of different grain size distributions and the impact of the degree of compaction on PD with reduced effort, a simple model was proposed. Unlike some of the well-performing existing models, this model can be calibrated using a single MS RLT test without requiring any separate static failure triaxial tests. This model was validated using the MS RLT test data with satisfactory results. The sensitivity of the parameters of this model was studied with respect to moisture content, degree of compaction and grain size distribution. Some reasonable trends for the sensitivity of the parameters to these influential factors were obtained, which suggests that these may be further developed to incorporate into the model.

QC 20150325

O módulo de resiliência é um parâmetro de crucial importância nas análises mecanísticas que envolvem a estimativa das tensões e deformações na estrutura do pavimento e no seu subleito, quando da ação do tráfego. Embora ensaios de campo possam ser empregados para se determinar o MR, a grande maioria das pesquisas nesse sentido são desenvolvidas em laboratório, onde é possível um maior controle das condições da amostra, dos sistemas de aplicação de carregamento e de medida dos deslocamentos. Entretanto, os ensaios em laboratório que visam à determinação do MR ainda são considerados especiais e exigem equipamentos relativamente complexos, ensejando portanto, pesquisas com a finalidade de se obter expressões que estimem o MR a partir de parâmetros advindos de ensaios mais simples e rotineiros. Neste trabalho foram realizados ensaios triaxiais dinâmicos para a determinação do módulo de resiliência de três solos empregados em rodovias do nordeste brasileiro. Através dos resultados de laboratório, verificou-se o desempenho dos modelos mais comumente empregados para se representar a variação do módulo de resiliência em função do estado de tensão. Observou-se para os três solos desta pesquisa, que o MR foi mais influenciado, quanto ao estado de tensão, pela tensão de confinamento e pela tensão principal maior. Analisou-se, por fim, a existência de uma expressão matemática entre o módulo de resiliência obtido a partir dos ensaios triaxiais dinâmicos e o módulo tangente inicial proveniente de ensaios de compressão simples, sob diversos níveis de tensão. Os resultados mostram que este tipo de associação é promissora, mas exige-se que o universo de solos estudados seja ampliado para que se estabeleça uma inferência decisiva.
Resilient modulus is a crucial parameter in mechanistic analysis involving the estimation of stress and strains under the pavement structure subjected to traffic loading. While field tests can be used to determine the dynamic behavior of soils, most researches favor laboratory tests. Such preference is based on the fact that laboratory tests are less constrained because of their carefully controlled conditions. Unfortunately these tests are still unusual due to relative complex equipment, therefore researches involving the correlation of resilient modulus from repeated load triaxial tests with other test results is needed. In this work, repeated load triaxial tests were performed on three soils used in northeastern Brazilian roadways to estimate the resilient modulus. The performance of the models most commonly adopted to represent resilient modulus as a function of state of stress were verified. lt was observed for the three soils in this research, that confining stress and principal major stress influenced resilient moduli values. Predictive equations correlating the resilient modulus from repeated load triaxial tests and parameters from compressive strength tests, considering different states of stress were investigated. lt was shown that this type of empirical correlation presented satisfactory results, although incisive conclusions can\'t be drawn without a wider number and variety of soils.

O conhecimento do módulo de resiliência dos materiais constituintes do pavimento e do seu subleito é indispensável quando o objetivo é projetá-lo, ou analisar o seu comportamento frente à solicitação das cargas rodoviárias. O módulo de resiliência é determinado, na maioria das vezes, a partir de resultados de ensaios triaxiais dinâmicos, que exigem equipamentos complexos para a sua realização. Assim, é desejável que se disponha de métodos que possibilitem a sua avaliação a partir de resultados de ensaios mais simples. Neste trabalho, foram realizados ensaios triaxiais dinâmicos para a determinação do módulo de resiliência de dois solos, um argiloso e outro arenoso fino, compactados nas energias normal e intermediária. A partir dos resultados dos ensaios cíclicos foi possível modelar a variação do módulo de resiliência com a variação do carregamento aplicado e identificar, entre as variáveis de tensão, aquelas que exercem maior influência no valor deste módulo. A existência de discrepâncias significativas entre os valores de módulo de resiliência obtidos a partir de sucessivos ensaios de um mesmo corpo-de-prova foi também investigada. Finalmente, analisou-se a existência de uma relação entre o módulo de resiliência obtido nos ensaios dinâmicos e o módulo tangente inicial proveniente de ensaios de compressão simples, sob diversos níveis de tensão. Os resultados mostram que este tipo de associação é promissora, mas exige-se que o universo dos solos estudados seja ampliado para que se estabeleça uma conclusão definitiva.
The knowledge about the resilient modulus of the pavement constituent materials and subgrade is essential in order to design or to analyze theirs behavior subjected to traffic loading. Often, the resilient modulus is obtained from repeated load triaxial tests demanding complex equipment for their execution. Thus, is desirable to develop methods to permit its evaluation from more simple tests. In this work, repeated load triaxial tests are carried out to the determination of the resilient modulus of two soils, a clay and a fine sand, compacted in the normal and intermediate AASHTO compretion efforts. From the repeated load triaxial test data it was possible to model the variation of resilient modulus with the variation of applied loading as wellos to identify, among the stress parameters, those of more influence on the value of this modulus. The significant discrepancy among the resilient modulus values obtained from successive tests in the same sample was also investigated. Finally, equations were developed in order to correlata the resilient modulus from repeated load triaxial tests to parameters from compressive strength tests, considering different states of stress. lt was shown that this type of empirical correlation presented satisfactory results, although incisiva conclusions could not be drawn without using a lager number and variety of soils.

O conhecimento do módulo de resiliência (MR) é fundamental ao se projetar um pavimento, pois ele é necessário para o cálculo de tensões, deformações e deflexões nas suas camadas e subleito, bem como, a análise do desempenho do sistema. Embora ensaios de campo possam ser empregados para se determinar o MR, a grande maioria das pesquisas nesse sentido são desenvolvidas em laboratório, onde é possível um maior controle das condições da amostra, da aplicação de carregamento e medida dos deslocamentos. Porém, pela complexidade e alto custo dos ensaios de laboratório, há a necessidade de pesquisas que disponibilizem expressões que permitam estimar o MR a partir de resultados de ensaios mais simples que o triaxial cíclico e usuais na pavimentação. Nesta pesquisa, foram realizados ensaios triaxiais cíclicos para a determinação do MR de três solos empregados em rodovias de Campo Grande - MS. A partir dos resultados dos ensaios triaxiais cíclicos, verificou-se o desempenho dos modelos mais comumente empregados para se representar a variação do módulo de resiliência em função do estado de tensão. Foram propostas e analisadas expressões matemáticas entre o MR obtido a partir dos ensaios triaxiais cíclicos e o módulo tangente inicial proveniente de ensaios de compressão simples, sob diversos níveis de tensão. Finalmente, analisou-se a existência de relações que englobem, além dos solos estudados nesta pesquisa, os solos estudados anteriormente em outras pesquisas desenvolvidas na EESC-USP. Os resultados mostram que este tipo de associação é promissora, mas exige-se que o universo de solos estudados seja ampliado para que se estabeleça uma inferência decisiva.
The resilient modulus knowledge (MR) is fundamental for pavement design, once it is necessary for stresses, strains and deflections calculus in its layers and subgrade, as well as, the analysis of system performance. Although field tests may be used to determine the dynamic behavior of soils, most of researchers favor laboratory tests, based on the fact that such tests are less constrained because of their carefully controlled conditions. Because laboratory procedures are considered complex and highly expensive, it is desirable to establish relationships among MR and other index properties that are relatively simple and usual in pavement construction. In this research, cyclic triaxial tests were performed to determine MR of three soils used in Campo Grande-MS roads. The performance of the models most commonly adopted to represent resilient modulus as a function of state of stress were verified. A mathematical expression among MR, obtained from the cyclic triaxial tests, and the initial tangent modulus, obtained from unconfined compression strength tests, were developed considering different states of stress. Finally, were analyzed the existence of relationships among soils studied in this research, and soils used in previous studies developed at EESC-USP. Results show that this type of empirical correlation presents a satisfactory results, however incisive conclusions cannot be taken without a large number and variety of soils.

Composite geogrids can successfully be used as a pavement-reinforcement material to increase the performance of pavement structures. This thesis presents a comprehensive study that has investigated the effectiveness of composite geogrids as subgrade reinforcement in unpaved granular pavements that are subjected to cyclic loading and constructed with local materials available in Queensland, Australia. The research outcomes suggest guidelines to design and construct unpaved granular pavements with the composite geogrid reinforcement at the base-subgrade interface. These guidelines benefit the industry by reducing construction and maintenance costs, and environmental pollution.

Studies conducted in 2016 show that 58% of the highways in Brazil presents any deficiency in the pavement, signaling or in its geometry. These deficiencies are, on average, the cause for about 6% of the accidents and for the increase of the operational cust by 91,6%. Among them we can stress the permanent deformation, the so called wheel tracks, which is harmful to the dynamic of the loads, to the comfort provided by the pavement, increasing its risk. To the correct design of the pavement it is very important to better know the characteristics of the materials to be used. In this context, stands out the subgrade, the foundation for the whole structure of the pavement, which one is studied in the present reseach by considering three typical soils used as highway subgrade in Santa Maria, Rio Grande do Sul State, and having the permanent deformations as the main focus. The metodology aplied in this work consisted in the location, sampling and characterization of the soil fields, lab tests and empirical machanistic design. Besides the physical, chemical and mechanical characterizations, it was performed the repeated triaxial load test aiming to obtain the resilient modulus and the permanent deformation parameters, according to the Brazilian Petroleum Corporation Manual (PETROBRAS). The Resilient Modulus model presented the better results with frequencies of 1 Hz and 2 Hz, and the presence of silt in one of the soils affected its resilient behaviour. The permanent deformation tests were performed with the frequency of 2 Hz and 150.000 load cicles. The average statistic correlation, according to Guimaraes (2009)´s methodology, was 0.91, bigger than the one provided by the Monismith and Barksdale´s models. However, the dominance of fine grained soils, along with low compactation energy, lead to a higher deformation rates, motivating the use of intermediate energy. With this new approach the permanent deformation was reduced 40% and the resilient modulus increased 78,8%. However, the numerical simulation according to the mechanistic approach, and using the layer thickness obtained from the Departamento Nacional de Infraestrutura de Transportes (DNIT) method, under 8,2 ton standard axle load, showed that the wheel tracks deeping would be small, based on the low stresses observed in the subgrade. On the other hand, the fatigue behaviour presented an inferior performance, reducing the project´s useful life. It was observed the presence of shakedown in the ranges A, B and C.
Pesquisas realizadas no ano de 2016 mostram que 58,2 % das rodovias de todo o país apresentam alguma deficiência no pavimento, na sinalização ou na geometria da via. Em média, esses defeitos são responsáveis por cerca de 6% do número de acidentes, além de aumentar o custo operacional das vias em até 91,6%. Dentre essas anomalias, destaca-se a deformação permanente denominada de afundamento na trilha de roda (ATR), que prejudica a dinâmica das cargas, afeta o conforto ao rolamento e causa risco à segurança. Para o adequado dimensionamento de um pavimento, é fundamental o conhecimento dos materiais que o compõem. Neste contexto, destaca-se o subleito, por ser a fundação sobre a qual são assentes todas as camadas, motivo pelo qual o objetivo geral desta pesquisa é analisar três solos típicos de subleitos rodoviários de Santa Maria, estado do Rio Grande do Sul, em especial quanto aos parâmetros de deformação permanente. A metodologia aplicada neste trabalho consistiu na localização, coleta e caracterização das jazidas de solos, realização de ensaios laboratoriais e dimensionamento mecanístico - empírico. Assim, além da caracterização física, química e mecânica, foram realizados ensaios triaxiais de cargas repetidas para obtenção do módulo de resiliência e dos parâmetros de deformação permanente, segundo recomendações do manual de execução de trechos monitorados da empresa Petróleo Brasileiro Sociedade Anônima (PETROBRAS). O modelo composto do módulo de resiliência apresentou os melhores resultados, a partir de ensaios com frequência de 1 Hz e 2 Hz, sendo que a presença de silte em um dos solos afetou seu comportamento resiliente. Os ensaios de deformação permanente foram conduzidos a 2 Hz, com 150.000 ciclos de aplicação de carga, cuja correlação estatística média, empregando a metodologia de Guimarães (2009), foi de 0,91 – superior a dos modelos de Monismith e Barksdale. Entretanto, a predominância de materiais finos, aliada à baixa energia de compactação (normal), resultaram em elevadas taxas de deformação, o que motivou o estudo de um dos solos também com uso da energia intermediária. Esse procedimento reduziu a deformação permanente em 40% e elevou o módulo de resiliência em 78,8%. Entretanto, a simulação numérica do pavimento sob a ótica mecanicista, a partir das espessuras calculadas pelo método do Departamento Nacional de Infraestrutura de Transportes (DNIT), aplicando-se a carga padrão de 8,2 toneladas, mostrou que o ATR seria pequeno, em face das baixas tensões atuantes no subleito, em contraposição ao desempenho à fadiga, que reduziu sensivelmente a vida útil de projeto. Constatouse a ocorrência de shakedown nos domínios A, B e C.

Les matériaux granulaires sont souvent utilisés les chaussées à faible et moyen trafic, pour la réalisation des couches d’assise, des couches de forme et de la couche de sol support. Les sollicitations dues au trafic sont les principales causes d’endommagement de ces chaussées qui conduisent à deux modes de dégradation: l’orniérage à grand rayon et la fissuration par fatigue de la couverture bitumineuse. L’influence de la non saturation et de la teneur en fines sur la capacité portante des sols granulaires joue un rôle très important sur la rigidité mécanique ainsi que l’endommagement des structures de chaussées soumises aux chargements répétés du trafic. En plus, le phénomène d’hystérésis produit par les conditions environnementales, notamment les conditions hydriques a également une influence importante sur la rigidité de ces matériaux non liés. Cependant, la méthode de dimensionnement des chaussées neuves en France ne permet pas de prendre en compte correctement l’effet de teneur en fines et l’effet de l’hystérésis hydrique. L’objectif de la thèse est d’étudier l’effet de la non-saturation, de la teneur en fines et de l’hystérésis hydrique sur le comportement mécanique des matériaux granulaires de chaussées soumis aux chargements répétés du trafic. Nous avons réalisé une campagne d’essais à différentes teneurs en eau sur deux chemins d’humidification et de séchage, avec mesure de la succion, de la résistance au cisaillement et du comportement résilient (essais triaxiaux à chargements répétés). Finalement, à l’aide de ces résultats expérimentaux, nous avons déterminé les paramètres des modèles classiques d’élasticité non linéaire. Ces modèles sont implantés dans le code de calcul aux éléments finis CAST3M pour déterminer la déflexion de chaussées souples lorsqu’elles sont soumises à des sollicitations mécaniques de trafic et des sollicitations hydriques environnementales
Granular materials are often used in low traffic pavement structures, with unbound granular base and sub-base layers. The load due to traffic is one of the principal damage modes for these pavements. The main design criteria for these pavements are a rutting criterion for the subgrade, a fatigue criterion for the asphalt layer. The variation of the unsaturated state and the clay content in granular materials have a significant influence on their mechanical behavior. In addition, the hysteresis phenomenon produced by the environmental conditions, including water conditions also has a very important influence on the rigidity of the unbound material. Whereas, the French design method is based on linear elastic calculations. It does not take into account theinfluence of clay content of pavement materials and the influence of the hysteresis phenomenon. Then, the objective of this thesis is to study the unsaturated state, the clay content and the hysteresis phenomenon on mechanical behavior of unbound granular materials for roads subjected to traffic loading. A series of tests for different water contents on both wetting and drying paths have been carried out with matrix suction measurements, shear tests and repeated load triaxial tests for the resilient behavior. Finally, the experimental results were simulated using the nonlinear elastic model (modified Boyce model) generally used for the resilient behavior of granular soils. These models are implemented in the finite element code and calculations have been performed with CAST3M to determine the deflection of full scale pavements at different environmental conditions

The structural behaviour of pavements in cold regions can considerably be affected by seasonal variation in environmental factors such as temperature and moisture content. Along with the destructive effect of heavy traffic loads, climatic and environmental factors can considerably contribute to pavement deterioration. These factors can influence the structural and functional capacity of the pavement structures which, as a result, can trigger and accelerate pavement deterioration mechanisms. Studies on the influence of variation of the environmental factors on the response and behaviour of pavement materials have shown that proper consideration to these factors must be given in realistic pavement design and analysis. In flexible pavement structures, particularly with a thin hot mix asphalt (HMA) layer, unbound materials and subgrade soil largely contribute to the overall structural behaviour of the pavement system. In unbound materials, moisture content and its variation can significantly affect pavement layer stiffness and permanent deformation characteristics. Therefore, the moisture condition of pavements and its influence on the mechanical behaviour of pavement materials has been of interest among the pavement research community. A proper understanding of moisture transformation in pavement systems and its effects on pavement performance are important for mechanistic pavement design. The present summary of this doctoral thesis is based on four main parts. The first part of the thesis covers field measurements and findings from a test section along county road 126 in southern Sweden and consists of two journal papers (paper I and II) tackling different aspects of the research topic. This test section is located in a relatively wet ground condition and consists of a thin flexible pavement structure with a deep drainage system. It is instrumented with subsurface temperature, volumetric moisture content and groundwater probes. The mechanical response of the pavement structure was investigated using Falling Weight Deflectometer (FWD) measurements. The second part of the thesis (paper III and IV) are based on laboratory experiments and investigates different recent approaches that have been proposed to apply principles of unsaturated soil mechanics for incorporating seasonal variation of moisture content into the resilient modulus models using matric suction. The third part of the thesis (paper V) builds a bridge that spans between the laboratory and field investigations with an attempt to evaluate one of the predictive models presented in Paper III. The fourth part of the thesis (paper VI) mainly focuses on the laboratory-based investigation of the permanent deformation characteristic of subgrade soils. In this part, the permanent deformation characteristics of two different silty sand subgrade soils were investigated and modelled using the data obtained from repeated load traxial tests. Paper I mainly focuses on the spring-thaw weakening of the pavement structure. The environmental data collected using different sensors and the FWD tests were used to investigate variations in moisture content with thaw penetration and its influence on the stiffness of unbound layers and the pavement’s overall bearing capacity. Using the backcalculated layer stiffness and corresponding in situ moisture measurements in the unbound layers, a degree of saturation-based moisture-stiffness model was developed for the granular material and the subgrade. In Paper II, the drainage system of the structure was manually clogged during a three month period in summer to raise the groundwater level and increase the moisture content of the layers. Along with the subsurface groundwater level and moisture content monitoring, the structural response of the pavement was studied. In this research work, the FWD tests were conducted at three different load levels. The stress dependent behaviour of the unbound granular layer and the subgrade soil were further studied using the multilevel loads FWD test data. Additionally, parameters of a nonlinear stress-dependent stiffness model were backcalculated and their sensitivity to in situ moisture content was studied. In Paper III and IV, series of suction-controlled repeated load triaxial (RLT) tests were conducted on two silty sand (SM) subgrade materials. Several resilient modulus prediction models that account for seasonal moisture content variation through matric suction were summarized and after optimizing the model parameters, the capability of the prediction models in capturing the material response were evaluated. In Paper V, an attempt was made to evaluate the proficiency of one of the suction-resilient modulus models using the field moisture content and FWD measurements from the Torpsbruk test site. The backcalculated subgrade stiffness dataset at different moisture contents were compared with resilient modulus models obtained from the suction-resilient modulus predictive model. Paper VI presents an evaluation of several permanent deformation models for unbound pavement materials that incorporate the time-hardening concept using a series of multistage repeated load triaxial (RLT) tests conducted on silty sand subgrade materials. The permanent deformation tests were conducted at four different moisture contents with pore suctions measurement throughout the test. The effect of moisture content (matric suction) on the permanent deformation characteristics of the materials and the predictive model parameters were further investigated.

QC 20150324

Les matériaux granulaires sont souvent utilisés dans les chaussées à faible trafic, pour la réalisation des couches d'assise non liées. L'objectif de la thèse est une meilleure compréhension du comportement hydromécanique des matériaux granulaires insaturés sous charge répétée en tenant compte des différents effets couplés: teneur en eau et teneur en fines. Une série d'essais triaxiaux à chargements répétés (TCR) est réalisée avec les différents échantillons de sable de Missillac remodelés à différentes teneurs en eau et en fines pour caractériser les comportements de déformation permanent et résilient. En outre, les courbes de rétention sont obtenues par des essais de succion. Puis, sur la base des résultats expérimentaux, les modèles de déformations permanentes et réversibles existants sont améliorés pour prendre en compte les teneurs en fines et en eau variables. Finalement, le comportement de l'état limite du sable Missillac est estimé avec les effets des teneurs en fines et en eau
Granular materials are often used in low traffic pavement structures as unbound granular base and sub-base layers. The objective of this context is a better understanding of hydromechanical behaviour (deformation behaviour mainly) of the unsaturated granular materials under repeated loading taking into account the various coupled effects: water content and fine content. A series of RLTTs are conducted with the different remolded Missillac sand samples at different water contents and fine contents to characterize the permanent and resilient deformation behaviour. Besides, the soil water retention curves (SWRCs) are obtained by suction measurement. Then, based on the experimental results, the existing permanent and resilient deformation models are improved to accommodate to the changeable fine content and water content. In the end, the shakedown behaviour of Missillac sand is estimated with the effects of fine content and water content

Este estudo tem como objetivo principal comparar estruturas de pavimentos flexíveis projetadas através dos métodos empírico do DNER e mecanístico, considerando-se alguns materiais de pavimentação utilizados na região de Campo Grande, estado do Mato Grosso do Sul. Como objetivos decorrentes, pode-se destacar a obtenção das características resilientes e de fadiga destes materiais e a proposta de um catálogo simplificado de estruturas de pavimentos para a referida região. Para a efetivação da pesquisa, foram coletados materiais típicos do subleito da região e daqueles mais utilizados na composição de bases e capas dos pavimentos locais. Após as suas caracterizações, realizaram-se ensaios de compactação, CBR, triaxiais cíclicos e compressão diametral estática e dinâmica. As análises mecanísticas foram realizadas utilizando-se o programa computacional FEPAVE, que leva em conta o comportamento elástico não-linear dos materiais, considerando-se o critério de confiabilidade. A partir da análise comparativa dos métodos de dimensionamento, observou-se que, ora as estruturas estabelecidas pelo método mecanístico são idênticas às determinadas pelo método do DNER, ora são mais esbeltas, ora são menos esbeltas, dependendo do tipo de material que constitui as camadas e do nível de confiabilidade adotado. Verificou-se ainda que a caracterização dos materiais através dos ensaios de módulo de resiliência, vida de fadiga e deformação permanente é imprescindível quando se deseja projetar um pavimento empregando-se o método mecanístico. Por fim, elaborou-se um catálogo simplificado de pavimentos flexíveis para a região de Campo Grande – MS, com as intenções de contemplar o uso de materiais locais e auxiliar os engenheiros na concepção de seus projetos
This study has as main objective to compare structures of flexible pavements designed by two different methods, the DNER empirical method and the mechanistic method, being considered some paving materials used in the area of Campo Grande, state of Mato Grosso do Sul. As secondary objectives, it can stand out the obtaining of the mechanical properties of these materials and the proposal of a simplified catalog of flexible pavements for the referred area. For the accomplishment of the research, typical materials of subgrade, base course and surface layer were collected. After their characterizations, tests of compaction, CBR and repeated load were executed. The mechanistic analyses were accomplished being used the software FEPAVE, that takes into account the non-linear resilient modulus of the materials, being considered the reliability criterion. Starting from the comparative analysis of the design methods, it was observed that the structures established by the mechanistic method can be identical, more slender or less slender to the ones obtained by the empirical method, depending on the type of the material that constitutes the layers and the reliability level adopted. It was also verified that the characterization of the materials by repeated load tests (resilient modulus, fatigue’s life and permanent deformation) is indispensable when one want to project a pavement being used the mechanistic method. Finally, a simplified catalog of flexible pavements was elaborated for the area of Campo Grande – MS, with the intentions of to contemplate the use of local materials and to aid the engineers in the conception of their projects

This diploma work takes focus in elastic modulus of unbound granular aggregates, which was determined by repeat load triaxial test and in deformation behaviour of unbound granular aggregates - elastic and plastic deformation. It was examine the propriety of this aggregate for its service as underlying granular material in pavement. Further, there was observed the influence of elastic modulus of unbound granular aggregates on concrete characteristics - compressive and bending strength. Finally, it was observed the influence of individual fractions of aggregates on its elastic modulus and strength of concrete.

Les Agrégats d’Enrobés (AE) proviennent de la démolition des chaussées. Leur réemploi est une alternative aux matériaux vierges, et réduit l’impact environnemental. Le projet ORRAP développe un recyclage à froid des AE sans addition de liant, en couche d’assise de chaussées à faible trafic. Les charges routières répétées causent des dégradations : orniérage et fissuration par fatigue. L’objectif de la thèse est d’étudier le comportement thermo-hydro-mécanique d’AE. Une campagne d’essais triaxiaux a été menée à plusieurs températures, teneurs en eau et fréquences, afin de caractériser les comportements permanent et résilient. A partir des résultats expérimentaux, le comportement résilient a été décrit par un premier modèle analytique élastique non linéaire, puis par un second viscoélastique. Le module résilient a été prédit par des simulations numériques aux éléments discrets, avec un modèle de contact viscoélastique. Finalement, deux planches d’essais expérimentales ont été construites
Reclaimed Asphalt Pavement (RAP) comes from the demolition of pavements. Its reuse is an alternative to virgin materials, to reduce the environmental impact. The ORRAP project develops a cold recycling without binder addition, in base and subbase layers of low traffic pavements. The traffic solicitations lead to damages: the rutting and the fatigue cracking. The objective of this thesis is to study the thermo-hydro-mechanical behaviour of RAP. A series of triaxial tests was carried out at several temperatures, water contents and frequencies. The experimental work allowed to characterise permanent and resilient behaviours. Based on experimental results, the resilient behaviour was described by a first non-linear elastic analytical model, and then by a second viscoelastic analytical model. Using the discrete element method, numerical simulations with a viscoelastic contact model predicted the resilient modulus. Finally, two full scale test sections were built

There is an impetus in the UK to move away from empirical pavement foundation design and the current method specification, towards an analytical design approach. For an analytical design approach to be adopted, the required performance properties of stiffness and resistance to permanent deformation of the foundation materials (sub grade and capping) need to be measured, both in the laboratory for design and in the field in order to ensure compliance. This thesis studies the influence of the sub grade on the constructability and performance of a series of full-scale pavement foundations. This has been achieved by measuring the performance parameters of several sub grade materials in the laboratory, using repeated load triaxial testing. These data have been compared to comparable data collected in situ using dynamic stiffness measuring devices during the construction of trial pavement foundations. The performance of the trial foundations has been measured during the placement and compaction of the different foundation materials, and again after their subsequent trafficking. The testing demonstrates the stress dependency of the foundation materials. The laboratory testing shows that the sub grade permanent deformation under cyclic loading (used to simulate construction operations) becomes unstable at a deviator stress of half the deviator stress at failure (0.5qmax)· The stiffness at this applied stress and above is shown to be approaching a consistent value. This indicates that large changes in the stiffness of inversely stress dependent fine grained soils occur below the deviator stress at which the permanent deformation becomes unstable. Significant variability of data has been found in the performance parameters measured (both in the laboratory and in the field) for samples of subgrade collected from small areas of the same site. However comparable patterns of stress dependency have been observed between measured laboratory and field performance using the different apparatus. The resistance to permanent deformation is shown to be a more critical design load case for construction than the need for adequate stiffness of support required to compact the foundation layers. The performance of a composite road foundation is shown to be material and site specific, and this will have important implications for design and site compliance testing.

This thesis developed an alternative laboratory element testing method to evaluate the response of the unsaturated soils of rail track foundations under repeated moving wheel loadings. The novel laboratory testing method is more capable of producing the realistic strength-deformation characteristics of the unsaturated soils with the effects of principal stress axis rotation (PSAR), which can be used to redesign the conservative rail track guidelines.

This thesis deals with compares the procedures carried out in the cyclical load triaxial testing device according to CSN EN 13286-7, and the procedures performed in the United States of America. In the practical part elasticity moduls of mixed recycled material are experimentally compared with mixed recycled material containing binder(connective material) and with fine-grained soil in the cyclical load triaxial testing device. Further the thesis assesses the use of mixed recycled material in the construction of a third class low-load pavement.

Este trabalho apresenta um estudo sobre o comportamento de tubos metálicos enterrados, submetidos ao carregamento móvel de um veículo. Foram realizadas análises numéricas utilizando o método de elementos finitos para o cálculo da tensão vertical no solo, momento fletor, tensão normal e deformação diametral vertical do tubo. Foram analisados 630 modelos, obtidos da variação das características do solo (módulo de elasticidade) com o objetivo de representar diferentes níveis de compactação do solo, características do tubo (espessura da parede do tubo) e da altura da camada de recobrimento do solo. O programa utilizado nas análises numéricas foi o SIGMA/W do pacote Geostudio. Os resultados encontrados apontam que as maiores tensões no solo, momentos, tensões normais e deformações no tubo ocorrem devido ao carregamento móvel quando este se localiza exatamente acima do tubo. Observou-se que o aumento da espessura da camada de solo que recobre a tubulação causa uma diminuição de 15% a 55% das tensões verticais no solo, momentos fletores, tensões normais e deformações no tubo. Foram desenvolvidas equações para o cálculo das deformações para os casos estudados. Foi também desenvolvido um procedimento para a moldagem de corpos de prova de areia no estado fofo (índice de vazios máximo) para realização de ensaios triaxiais.
This paper presents a study on the behavior of buried metal pipes, subjected to the vehicle live load. Numerical analysis using the finite element method to calculate the vertical stress were made on the ground, bending moment, normal stress and diametral vertical pipe deformation. 630 models were analyzed, obtained from the variation of the soil characteristics (modulus) in order to represent different levels of soil compaction, the pipe characteristics (thickness of the pipe wall) and the height of the soil cover layer. The program used in numerical analysis was the SIGMA/W Geostudio package. The results show that the highest stresses on the ground moments, normal stresses and strains in the tube occur due to live loading when it is located just above the tube. It was observed that increasing the thickness of the layer of soil covering the pipe causes a decrease from 15% to 55% of the vertical tensions in the ground, bending moments, normal stress and strain on the pipe. Equations were developed to calculate the deformations in the cases studied. It has also developed a procedure for molding sand specimens into the soft state (maximum void ratio) to perform triaxial tests.

This research was a step forward in investigating the characteristics of recycled concrete aggregates to use as an unbound pavement material. The results present the guidelines for successfully application of recycled concrete aggregates in high traffic volume roads. Outcomes of the research create more economical and environmental benefits through reducing the depletion of natural resources and effectively manage the generated concrete waste before disposal as land fill.

Key factors that influence the design of paved and unpaved roads are the strength and stiffness of the pavement layers. Among other factors, the strength of pavements depends on the thickness and quality of the aggregates used in the pavement base layer. In India and many other countries, there is a high demand for good quality aggregates and the availability of aggregate resources is limited. There is a need for the development of sustainable construction methods which can handle aggregate requirements with least available resources and provide good performance. Hence it is imperative to strive for alternatives to achieve improved quality of pavements using supplementary potential materials and methods. The strength of pavement increases with increase in the thickness of the base which has a direct implication on construction cost whereas decreasing the thickness of the base makes it weak which results in low load bearing capacity especially for unpaved roads. The use of different types of geosynthetics like geocell and geogrid are a potential and reliable solution for the lack of availability of aggregates and studies are conducted in this direction. To better understand the performance of any geosynthetically reinforced base layers, it is essential to characterize the pavement material by studying the behavior of these materials under static as well as repeated loading. For unpaved roads, the base layer, made of granular aggregates plays a crucial role in the reduction of permanent deformation of the pavements. The resilient modulus (Mr) of these materials is a key parameter for predicting the structural response of pavements and for characterizing materials in pavement design and evaluation. Usually, during the design of flexible pavements, pavement materials are treated as homogeneous and isotropic. The use of rollers in the field during pavement construction leads to a higher compaction of material in the vertical direction which introduces stress-induced anisotropy in the base material. The effect of stress-induced anisotropy on the properties of the granular material is studied and discussed in the first part of the research by conducting repeated load triaxial tests. Isotropic consolidated and anisotropically consolidated samples were prepared to investigate the behavior of base materials under stress induced anisotropic conditions. An additional axial load was applied on the isotropically consolidated sample to create anisotropically consolidated sample. The axial loading was provided such that the stress ratio (σ1/σ3), during anisotropic consolidation was kept constant for all the tests at different confining pressures. The effect of repeated loading on the permanent deformation and the resilient modulus for both isotropically and anisotropically consolidated samples, at different confining pressure and loading conditions, are discussed. The behavior of both anisotropically and isotropically consolidated samples has been explained using the record of the excess pore pressures generated during the experiments. The experimental studies show that the permanent strains measured in the vertical direction of the anisotropically consolidated samples are less compared to the results obtained for isotropically consolidated samples. The resilient moduli of the anisotropically consolidated samples were also observed to be higher than that of the isotropically consolidated sample. The study conducted on the pore pressure of both the samples explains better performance of the anisotropically consolidated samples. The studies showed that the isotropically consolidated samples showed higher pore pressures compared to the anisotropically consolidated specimens. Another factor which influences the resilient modulus of the pavement materials is the geosynthetic reinforcement. Geocell and geogrid reinforced triaxial samples were prepared to study the effect of reinforcement in the resilient modulus of the base materials. From the literature, it can be seen that most of the research in the triaxial testing equipment were carried out in the non-destructive range of confining pressure and deviatoric stress. Several studies have been conducted by the researchers to visualize the pavement response in the elastic range. However, the studies in the plastic creep range and incremental collapse range were highly limited. In the current study, testing is carried out on the triaxial samples for two different stress ranges. In the first sections, loading was applied in the elastic and elastic shakedown range as per AASTHO T-307. For various loading sequences, a comparative analysis has been done for the resilient modulus of the geogrid and geocell. In the next section, the loading was applied on the sample in the plastic shakedown range and incremental collapse range. The results of the permanent strains and resilient modulus of the sections are compared with the corresponding results of the unreinforced section. In the plastic shakedown and incremental collapse range also the permanent strains of reinforced samples were less than those observed in the unreinforced section. The performance of geosynthetically reinforced pavement layers can be better understood by studying the samples prepared under realistic field conditions. In the case of triaxial experiments the sample size is very less compared to the field conditions and the effect of other pavement layers on the performance of the base layers cannot be studied on triaxial samples. Samples were prepared in the laboratory by modeling the pavement sections in a cuboidal tank, in which different pavement layers are laid one over the other, and a static loading or repeated loading is applied to overcome the bottleneck of small sample size in the triaxial setup. The experiments were conducted on the unreinforced section; geocell reinforced section and geogrid reinforced section placed above strong and weak subgrade. The results of the study are examined regarding the resilient deformation, permanent deformation, pressure distribution and strain measurements for different thicknesses of base layers under repeated loading. The initial parts of the study present the results of experiments and analysis of the results to understand the behavior of geocell reinforced granular base during repeated loading. In this study, an attempt is made to understand the various factors which influence the behavior of geocell reinforced granular base under repeated loading by conducting plate load tests. The loads applied on the pavements are much higher than the standard axle loading used for the design of pavements. High pressure was applied on all the test sections to simulate these higher loading conditions in the field. The optimum width and height of the geocell to be provided, to get maximum reduction in permanent deformation is studied in detail. The effect of resilient deformation of reinforced and unreinforced base layers is quantified by calculating the resilient modulus of these layers. The studies showed that the geocell reinforcement was effective in reducing the permanent and resilient deformations of base layer when compared to the unreinforced samples. The resilient modulus calculated was higher for the reinforced sample with half of the thickness of the unreinforced sample. The effect of reinforcement in the stress distribution within the base layer is also studied by measuring the pressures at different depths of the base layer. The results showed that the pressure getting transferred to the subgrade level was much lower in the case of geocell reinforced base layer. The ultimate aim of any pavement design method is to reduce the distress in the subgrade level and thus leading to increased life of pavements. Pressures at the subgrade level for reinforced and unreinforced sections are studied in detail, the main parameter under study being the stress distribution angle, to investigate the distress in the subgrade level. It was observed that the geocell reinforced sample showed higher stress distribution angle when compared to its unreinforced counterpart. Another important factor that has to be studied is the strains at the subgrade level since it is the governing factor of causing rutting in the pavements. From the experiments conducted in the study, it was shown that the reinforcement is very effective in reducing the strains at the top of subgrades. The implications of the current study are brought out in terms of improved pavement performance as the carbon emission reductions. It is important to analyze the performance of reinforced section under realistic field conditions. To do that experiment were conducted on reinforced and unreinforced base layers placed on top of weak subgrade material. The study showed that the reinforcements are effective in reducing the deformations under weak subgrade conditions also but not as effective as it was under strong subgrade case. The experimental results were then validated with the two-dimensional mechanistic-empirical model for geocell reinforced unpaved roads for predicting the performance of pavements under a significant number of cycles. The modified permanent deformation model which incorporates the triaxial test results and strains measured directly from the base sections were used to model and validate. Plate load experiments were also conducted on base layers reinforced with geogrid to understand the behavior of these reinforced samples under repeated loading. Several factors like the width of the geogrid to be provided and the depth of placing the geogrid in the base layer were studied in detail to achieve maximum reduction in deformations. Permanent and resilient deformation studies were carried out for both reinforced and unreinforced sections of varying thicknesses, and a comparison was made to understand the effect of reinforcement. The geogrid reinforcement could effectively reduce the permanent and resilient deformations when compared to the unreinforced sections. A study was also carried out on the resilient modulus, which explained the better performance of the geogrid reinforced samples by showing higher resilient modulus for reinforced samples than the unreinforced specimens. The performance of the geogrid reinforced base layers was further verified by studying the pressure distribution at the subgrade level and by calculating the stress distribution angle corresponding to the reinforced and unreinforced samples. The strains at the subgrade level were also studied and compared with the unreinforced sample which showed a better performance of geogrid reinforced samples. The results from the strain gauges fixed in the geogrid were further used to model and validate the permanent deformation model. Experiments were conducted on geogrid-reinforced base layer placed above weak subgrade conditions. The results showed that the reinforcement was effective in reducing the deformations under weak subgrade conditions also. Apart from conducting the laboratory studies, experimental results were numerically modeled to accurately back-calculate the resilient moduli of the layers used in the study. 3D numerical modeling of the unreinforced and honeycomb shaped geocell reinforced layers were carried out using finite element package of ANSYS. The subgrade layer, geocell material, and infill material were modeled with different material models to match the real case scenario. The modeling was done for both static and repeated load conditions. The material properties were changed in a systematic fashion until the vertical deformations of the loading plate matched with the corresponding values measured during the experiment. The experimental study indicates that the geocell reinforcement distributes the load in the lateral direction to a relatively shallow depth when compared to the unreinforced section. Numerical modeling further strengthened the results of the experimental studies since the modeling results were in sync with the experimental data.

碩士
中原大學
土木工程研究所
90
When AC applying vehicle loading，It is a kind of “dynamic type” Load. Because of the interlock effect between the coarse grains formed by natural confining pressure. Tests under tensile failure model is not able to demonstrate the behavior of AC Mixture. This research develops a more suitable AC slab dynamic creep test as a practicable methop for estimate the AC’s ability of resisting rutting. By the result of AC slab dynamic creep test，this method is truly suitable to estimate the AC’s ability of resisting permanent deformation, especialy for SMA.The result of wheel tracking test also shows that SMA has better ability of rutting-resisting than DGAC.Analyzing the creep test data by Power Law method could get a reasonable result；for this reason, it can estimate the permanent deformation development from regression function. In this study, the AC’s slab dynamic creep test honestly can reflect AC’s characteristic of resisting rutting under different test condition.