Apresenta-se um processo de retroanálise de pavimentos flexíveis baseado na teoria do ponto inerte para a retroanálise do subleito, readaptado para bacias de deflexões teóricas obtidas com o carregamento para o ensaio com a viga Benkelman. Além da retroanálise do subleito, foi desenvolvido um modelo matemático fatorial para a obtenção do módulo resiliente equivalente das camadas presentes sobre o subleito, consideradas como uma única, denominada camada equivalente. Para a readaptação da teoria do ponto inerte e elaboração do modelo fatorial foram utilizados bancos de dados de bacias deflectométricas teóricas geradas pelo programa ELSYM5. Avaliou-se o erro na retroanálise do subleito e da camada equivalente para o processo proposto mediante comparações com outras metodologias semelhantes de retroanálise. A teoria do ponto inerte proporciona o desenvolvimento de um algoritmo simples, convergente e de resposta única para retroanálise de subleito de pavimentos flexíveis, minimizando a influência da experiência do engenheiro na resposta do problema. O procedimento de retroanálise elaborado nesta pesquisa caracteriza-se por simplicidade, sendo de uso adequado, entre outros, para avaliações em nível de rede. / A backcalculation procedure for flexible pavements is introduced based on inertial point theory for subgrade backcalculation readapted to theoretical deflection basins obtained with the load to Benkelman beam test. Beside subgrade backcalculation, it was developed a factorial mathematical model to obtain equivalent resilient modulus from the layers presents upon subgrade, considered as unique and denominated equivalent layer. To the readaptation of inertial point theory and preparing of factorial model were used theoretical deflection bowls data base generated by ELSYM5 program. The subgrade and equivalent layer modulus backcalculation were evaluated to the proposed process through others similar backcalculation methodologies. The inertial point theory provides the development of simple algorithms, convergent and with unique solution for flexible pavements subgrade backcalculation minimizing the influence of engineer experience in the problem answer. The backcalculation procedure developed in this research is characterized by simplicity being of suitable use at network evaluation level among others.

The deployment of a modern road system, with all necessary infrastructure needed for users to travel in safety and comfort, requires high levels of financial investments. The expenses with substantial maintenance and early reconstruction of our tracks are unacceptable, as we have field and laboratory equipment that allows us for a better understanding of materials and design methods. Thus, this research had as general objectives structuring a database with materials and typical elastic parameters of flexible pavements of Rio Grande do Sul roads, through the process of modulus backcalculation, and determine the best structural options regarding the cost-benefit relationship, making flexible pavement project engineers job easier. There were got the resilient modules of five federal highways located in our state (BR 158, BR 285, BR 287, BR 290 e BR 392), through backcalculated deflectometric basins collected with FWD equipment, provided by DNIT. After the application of a statistical filter based on the coefficient of variation percentage, in order to eliminate the spurious data, a typical module database of the resilient materials evaluated was generated. Based on the data and on the literature, there were defined structural groups based on different structural assemblies through different combinations between resilient modules and thicknesses of layers commonly used in flexible pavements. Using mechanistic analysis concepts, it was evaluated by the AEMC software, specific tensile strains in lower fiber coating (t), and subgrade top compression (c), which, later subsidize the implementation of performance models for fatigue and permanent deformation consolidated in the literature, enabling obtaining the N number of standard axles for each structural assembly set. At the same time, using DNIT road cost system (SICRO II), pavement services were budget, determining the cost per km for the structures previously defined. Comparing the cost/km and critical N data (evaluated from the comparison of results obtained by the models of performance) there was obtained the cost/benefit ratio for all data sets. Evaluating the 100 most economic positions, it is observed that 100% of structural assemblies have the highest arbitrated asphalt concrete thicknesses (12.5 cm). It is also evident, the influence that the asphalt concrete has, as 88% of occurrences among the top 100 positions have the highest resilient arbitrated module. Thus, it is concluded that the variables that produce the best cost/benefit relationship are the modulus and the thickness of the asphalt concrete layer. / A implantação de sistemas viários modernos, com toda infraestrutura necessária para que o usuário trafegue com segurança e conforto, requer elevados níveis de investimentos financeiros. Os gastos substanciais com manutenção e reconstrução precoce de nossos pavimentos são inaceitáveis, uma vez que dispomos de equipamentos de campo e laboratório que permitam melhor entendimento acerca dos materiais e métodos de projeto. Desta forma, esta pesquisa teve como objetivos gerais estruturar-se um banco de dados com materiais e parâmetros elásticos típicos de pavimentos flexíveis do Rio Grande do Sul, através do processo de retroanálise, determinando-se as melhores opções estruturais com vistas à relação custo-benefício, facilitando o trabalho de engenheiros em projetos de pavimentos flexíveis. Foram obtidos os módulos resilientes de cinco rodovias federais localizadas no estado (BR 158, BR 285, BR 287, BR 290 e BR 392), através de retroanálise das bacias deflectométricas coletadas com o equipamento FWD, disponibilizadas pelo DNIT. Após a aplicação de um filtro estatístico baseado no coeficiente de variação percentual, no intuito de eliminarem-se os dados espúrios, gerou-se um banco de dados de módulos resilientes típicos dos materiais avaliados. A partir do banco de dados e de consulta bibliográfica, definiram-se conjuntos estruturais por meio de diferentes combinações entre módulos resilientes e espessuras de camadas comumente utilizadas em pavimentos flexíveis. Utilizando-se os conceitos de análise mecanicista, avaliou-se através do software AEMC, as deformações específicas de tração na fibra inferior do revestimento (t), e de compressão no topo do subleito (c), as quais, posteriormente, subsidiaram a aplicação de modelos de desempenho para fadiga e deformação permanente consolidados na literatura, permitindo a obtenção do número N de eixos padrões para cada conjunto estrutural definido. Em paralelo, empregando-se o sistema de custos rodoviários (SICRO II) do DNIT, orçaram-se os serviços de pavimentação, determinando-se o custo/km para as estruturas previamente definidas. Cruzando-se os dados de custo/km e N crítico (avaliado a partir da comparação dos resultados obtidos pelos modelos de desempenho), obteve-se a relação custo/benefício para todos os conjuntos de dados. Avaliando-se as 100 posições mais econômicas, observa-se que 100% dos conjuntos estruturais possuem as maiores espessuras de concreto asfáltico arbitradas (12,5 cm). Percebese também, a influência do módulo do concreto asfáltico, onde, 88 % das ocorrências entre as 100 primeiras posições possuem o maior módulo resiliente arbitrado. Desta forma, conclui-se que as variáveis que produzem as melhores relações custo/benefício são o módulo e a espessura da camada de concreto asfáltico.

Petróleo Brasileiro S/A / It is unusual practice, in national projects of new pavements and restorations, the consideration of viscoelastic behavior and non-linear elastic of materials that compound or will compound the layers of pavement. However, the linear elastic response is a simplification of the actual behavior of the pavements layers, since the materials used in the structure have dependent stiffness of the stress state (granular layers and subgrades) or temperature and load application time (asphalt concrete). Therefore, it was aimed to study the behavior of the pavements structures of three monitored sections in the city of Santa Maria/RS. For this, tests were performed with the equipment FWD applying four different loads in each stake that compounds the extension of the three sections. It was found from deflection basins and backcalculated resilient moduli the nonlinear elastic behavior of granular layers (base and sub-base) of the sections 1 and 2, with resilient modulus directly proportional to the increase of the confining pressure. The subgrades of both sections exhibited varied behavior and can be simplified by the linear elasticity without considerable loss. The same happened to the asphalt concrete of section 1. On the other hand, the coating of the section 2 resulted in resilient modules dependent of the increase of vertical surface tension in the center of the load plate. In relation to section 3, the results related only to deflection measures indicated mostly behavior near of linearity in all evaluated reading distances, except for that carried out under the load application. Sequentially to load pulses, also were determined deflections with the Benkelman beam, aiming to find a local correlation between the results obtained from different equipments. The deflections basins indicated higher values, measured with the beam, in relation to those determined by FWD. Consequently, the resilient modules were higher when determined from the backcalculation of the readings taken with FWD, in relation to Benkelman beam. In parallel, it was verified and quantified the influence of bounding conditions between the layers and correction, total or partial, of deflections basins, depending on the temperature, in backcalculated resilient moduli. It was found that the assignment of total bounding in the interfaces between the layers reduces considerably the backcalculated resilient moduli of granular materials. Regarding to the temperature correction, it is appropriate the determination of the rigidity of the granular materials and the subgrade by performing backcalculation without any adjustment in the field basins. Taking these values as a basis, it was considered appropriate to repeat the iterative procedure, with adjustment of the deflections depending on the temperature in the initial readings, thereby determining the new asphalt concrete resilient moduli. / Não é prática usual, em projetos nacionais de pavimentos novos e restaurações, a consideração do comportamento viscoelástico e elástico não linear dos materiais que constituem, ou que irão constituir as camadas do pavimento. Todavia, a resposta elástica linear é uma simplificação do comportamento real das camadas dos pavimentos, já que os materiais empregados na estrutura possuem rigidez dependente do estado de tensões (camadas granulares e subleitos) ou da temperatura e tempo de aplicação de carga (concretos asfálticos). Em vista disso, buscou-se estudar o comportamento das estruturas dos pavimentos de três trechos monitorados, na cidade de Santa Maria/RS. Para isso, foram realizados ensaios com o equipamento FWD, aplicando quatro diferentes carregamentos em cada estaca que compõe a extensão dos três trechos. Verificou-se, a partir das bacias deflectométricas e dos módulos de resiliência retroanalisados, o comportamento elástico não linear das camadas granulares (base e sub-base) dos Trechos 1 e 2, com módulo de resiliência diretamente proporcional ao incremento da tensão confinante. Os subleitos de dois trechos exibiram comportamento variado, podendo ser simplificados pela elasticidade linear, sem prejuízo considerável. O mesmo aconteceu para o concreto asfáltico do Trecho 1. Já o revestimento do Trecho 2 resultou em módulos resilientes dependentes do incremento da tensão vertical na superfície no centro da placa de carga. Em relação ao Trecho 3, os resultados, referentes apenas às medidas deflectométricas, indicaram comportamento majoritariamente próximo da linearidade em todas as distâncias de leitura avaliadas, com exceção daquela medida abaixo do centro da placa de carga. Sequencialmente aos pulsos de carga, foram determinadas também as deflexões com a viga Benkelman, objetivando encontrar uma correlação local entre os resultados obtidos a partir dos diferentes equipamentos. As bacias deflectométricas indicaram valores superiores, medidos com a viga, em relação àqueles determinados pelo FWD. Consequentemente, os módulos de resiliência foram maiores quando determinados a partir da retroanálise de leituras efetuadas com o FWD, em relação à viga Benkelman. Em paralelo, foi verificada e quantificada a influência das condições de aderência entre as camadas e da correção, total ou parcial, das bacias deflectométricas, em função da temperatura, nos módulos de resiliência retroanalisados. Constatou-se que a atribuição de aderência total nas interfaces entre as camadas reduz consideravelmente os módulos de resiliência retroanalisados dos materiais granulares. Em relação à correção de temperatura, verificou-se adequada a determinação da rigidez dos materiais granulares e subleito mediante a realização da retroanálise sem nenhum ajuste nas bacias de campo. Tomando estes valores como base, julgou-se pertinente a repetição do procedimento iterativo, com ajuste das deflexões em função da temperatura nas leituras iniciais, determinando assim o novo módulo de resiliência do revestimento.

The use of recycled concrete material (RCM) as pavement base material is a promising but unproven technique for road rehabilitation and construction. A telephone survey conducted to investigate the state of the practice concerning RCM usage in Utah County revealed that RCM is infrequently used in this application due primarily to a lack of practical knowledge about the engineering properties of the material. Therefore, this research was aimed at evaluating the physical properties, strength parameters, and durability characteristics of both demolition and haul-back sources of RCM available in Utah County for use as pavement base material. The study included extensive laboratory and field testing. Laboratory tests included California bearing ratio (CBR), unconfined compressive strength (UCS), stiffness, freeze-thaw cycling, moisture susceptibility, abrasion, salinity, and alkalinity evaluations. Non-destructive testing was utilized in the field to monitor seasonal variation in stiffness of an RCM pavement base layer over a 1-year period. The testing included a dynamic cone penetrometer, ground-penetrating radar, a heavy Clegg impact soil tester, a soil stiffness gauge, and a portable falling-weight deflectometer. The laboratory testing indicated that the demolition material exhibited lower strength and stiffness than the haul-back material and reduced UCS loss after freeze-thaw cycling. However, the demolition material received a moisture susceptibility rating of good in the tube suction test, while the haul-back material was rated as marginal. Both materials exhibited self-cementing effects that led to approximately 180 percent increases in UCS over a 7-day curing period. Seven-day UCS values were 1260 kPa and 1820 kPa for the demolition and haul-back materials, respectively, and corresponding CBR values were 22 and 55. The field monitoring demonstrated that the RCM base layer was susceptible to stiffness changes due primarily to changes in moisture. In its saturated state during spring testing, the site experienced CBR and stiffness losses of up to 60 percent compared to summer-time values. RCM compares well with typical pavement base materials in many respects. Given the laboratory and field data developed in this research, engineers should be able to estimate the strength and durability parameters of RCM needed for pavement design.

L'incidence de l'infection par le VIH, définie comme le nombre de sujets nouvellement infectés par le VIH au cours du temps, est le seul indicateur permettant réellement d'appréhender la dynamique de l'épidémie du VIH/SIDA. Sa connaissance permet de prévoir les conséquences démographiques de l'épidémie et les besoins futurs de prise en charge, mais également d'évaluer l'efficacité des programmes de prévention. Jusqu'à très récemment, l'idée de base pour estimer l'incidence de l'infection par le VIH a été d'utiliser la méthode de rétro-calcul à partir des données de l'incidence du SIDA et de la connaissance de la distribution de la durée d'incubation du SIDA. L'avènement, à partir de 1996, de nouvelles combinaisons thérapeutiques très efficaces contre le VIH a contribué à modifier la durée d'incubation du SIDA et, par conséquent, à augmenter la difficulté d'utilisation de la méthode de rétro-calcul sous sa forme classique. Plus récemment, l'idée d'intégrer des informations sur les dates de diagnostic VIH a permis d'améliorer la précision des estimations. La plupart des pays occidentaux ont mis en place depuis quelques années un système de surveillance de l'infection à VIH. En France, la notification obligatoire des nouveaux diagnostics d'infection VIH, couplée à la surveillance virologique permettant de distinguer les contaminations récentes des plus anciennes a été mise en place en mars 2003. L'objectif de ce travail de thèse est de développer de nouvelles méthodes d'estimation de l'incidence de l'infection par le VIH capables de combiner les données de surveillance des diagnostics VIH et SIDA et d'utiliser les marqueurs sérologiques recueillis dans la surveillance virologique dans le but de mieux saisir l'évolution de l'épidémie dans les périodes les plus récentes. / The knowledge of the dynamics of the HIV/AIDS epidemic is crucial for planning current and future health care needs. The HIV incidence, i.e. the number of new HIV infections over time, determines the trajectory and the extent of the epidemic but is difficult to measure. The backcalculation method has been widely developed and used to estimate the past pattern of HIV infections and to project future incidence of AIDS from information on the incubation period distribution and AIDS incidence data. In recent years the incubation period from HIV infection to AIDS has changed dramatically due to increased use of antiretroviral therapy, which lengthens the time from HIV infection to the development of AIDS. Therefore, it has become more difficult to use AIDS diagnosis as the basis for back-calculation. More recently, the idea of integrating information on the dates of HIV diagnosis has improved the precision of estimates. In recent years, most western countries have set up a system for monitoring HIV infection. In France, the mandatory reporting of newly diagnosed HIV infection, coupled with virological surveillance to distinguish recent infections from older, was introduced in March 2003. The goal of this PhD thesis is to develop new methods for estimating the HIV incidence able to combine data from monitoring HIV and AIDS diagnoses and use of serologic markers collected in the virological surveillance in order to better understand the evolution of the epidemic in the most recent periods.

A avaliação estrutural é muito importante para os sistemas de gerência de pavimentos, principalmente, para as análises em nível de projeto. Os métodos de dimensionamento de reforço em uso no Brasil, baseado apenas na deflexão recuperável máxima, não exploram todas as potencialidades das avaliações estruturais não destrutivas, pois utilizam expressões empíricas, não associadas diretamente ao comportamento mecanístico do pavimento. Este trabalho tem por objetivo analisar os métodos existentes no Brasil para o dimensionamento de reforço de pavimento flexíveis e compará-los com o dimensionamento mecanístico, baseado nas propriedades mecânicas das camadas do pavimento existente, obtidas mediante retroanálise de avaliações estruturais não destrutivas. Também são analisados fatores que influenciam interpretação dos dados obtidos pelas avaliações estruturais e o processo de retroanálise, como os efeitos da temperatura, as correlações de valores de deflexões obtidas com FDW em valores de deflexões obtidas com Viga Benkelman e as correlações entre os módulos de resiliência das camadas com índices obtidos a partir das deflexões medidas a diferentes distâncias do ponto de aplicação de carga. / Pavement management systems, particularly at project level, are very dependent upon structural evaluation. The pavement rehabilitation design methods used in Brazil are based only on the maximum deflection. They do not explore all the capabilities of non-destructive structural evaluations since they use empirical equations not directly associated to the mechanistic behavior of pavements. This work aims to analyze the Brazilian methods for overlay design and compare them to a mechanistic approach, based on fundamental properties of an elastic-layer system. It is also analyzed factors associated to the interpretation of field data and to the process of back calculation of in situ moduli, such as the effects of pavement temperature during the test, the conversion of deflection values obtained with F.W.D. to deflections values obtained with Benkelman Beam, and the correlations between resilient moduli and indices obtained from deflection values at different distances from the load application point.

A avaliação estrutural é muito importante para os sistemas de gerência de pavimentos, principalmente, para as análises em nível de projeto. Os métodos de dimensionamento de reforço em uso no Brasil, baseado apenas na deflexão recuperável máxima, não exploram todas as potencialidades das avaliações estruturais não destrutivas, pois utilizam expressões empíricas, não associadas diretamente ao comportamento mecanístico do pavimento. Este trabalho tem por objetivo analisar os métodos existentes no Brasil para o dimensionamento de reforço de pavimento flexíveis e compará-los com o dimensionamento mecanístico, baseado nas propriedades mecânicas das camadas do pavimento existente, obtidas mediante retroanálise de avaliações estruturais não destrutivas. Também são analisados fatores que influenciam interpretação dos dados obtidos pelas avaliações estruturais e o processo de retroanálise, como os efeitos da temperatura, as correlações de valores de deflexões obtidas com FDW em valores de deflexões obtidas com Viga Benkelman e as correlações entre os módulos de resiliência das camadas com índices obtidos a partir das deflexões medidas a diferentes distâncias do ponto de aplicação de carga. / Pavement management systems, particularly at project level, are very dependent upon structural evaluation. The pavement rehabilitation design methods used in Brazil are based only on the maximum deflection. They do not explore all the capabilities of non-destructive structural evaluations since they use empirical equations not directly associated to the mechanistic behavior of pavements. This work aims to analyze the Brazilian methods for overlay design and compare them to a mechanistic approach, based on fundamental properties of an elastic-layer system. It is also analyzed factors associated to the interpretation of field data and to the process of back calculation of in situ moduli, such as the effects of pavement temperature during the test, the conversion of deflection values obtained with F.W.D. to deflections values obtained with Benkelman Beam, and the correlations between resilient moduli and indices obtained from deflection values at different distances from the load application point.

A presente pesquisa teve como objetivo principal a realização de estudos laboratoriais, de campo e numéricos, buscando viabilizar duas misturas de concreto permeável que foram utilizadas na construção de duas calçadas experimentais localizadas no campus da USP em São Paulo. Nas pistas experimentais foi realizado o acompanhamento da capacidade permeável ao longo do tempo, além da avaliação das suas respostas estruturais frente à aplicação de carregamentos dinâmicos por meio de equipamento FWD, considerando a variação do teor de umidade no interior das estruturas. Por fim, foram realizadas retroanálises com uso de diferentes softwares procurando entender qual das camadas da estrutura apresenta maior vulnerabilidade estrutural frente à presença de volumes excessivos de água. Os resultados da etapa laboratorial indicaram que há uma sensibilidade muito grande no comportamento das misturas em função do teor de aditivo superplastificante, uma vez que houve segregação severa da pasta de cimento no fundo dos corpos de prova quando esse teor ultrapassou determinado limite. Os resultados dos ensaios de taxa de infiltração em campo possibilitaram a proposição um modelo empírico para estimativa do desempenho da capacidade hidráulica para calçadas em concreto permeável executadas na região de São Paulo. Os resultados dos levantamentos deflectométricos e das retroanálises indicaram variação considerável na capacidade de suporte do conjunto base+subleito entre as calçadas, além de evidenciar considerável perda da capacidade de suporte dessas estruturas quanto submetidas à presença de elevados volumes de água no seu interior. Palavras chave: concreto permeável, calçada, pavimento, taxa de infiltração, levantamento deflectométrico, análise estrutural, retroanálise. / The main goal of this research was to carry out laboratorial, field and numerical studies with the purpose of defining two feasible pervious concrete mixtures to be used as the surface layer of two experimental sidewalks in the campus of the University of São Paulo. The permeability capacity of the sidewalks was monitored along time, as well as its structural responses in terms of deflections due to application of FWD dynamic loadings, assessing how the structural behavior was impacted by the presence of high volumes of water into the permeable structure. A backcalculation procedure was used in order to assess the elastic behavior of the structure layers, as well as find out which layer of the structure is the most vulnerable in terms of mechanical behavior under the presence of excessive volumes of water. The results in the laboratory indicates that pervious concrete mixtures are considerable sensitives to the amount of superplasticizer additive, since a severe mortar segregation was observed on the bottom of the specimens casted using some of the mixtures produced. The results of infiltration tests in field made it possible to develop an empirical model capable of estimating the hydraulic performance of pervious concrete permeable sidewalks in São Paulo region. The results of the deflection measurements and the backcalculations indicated a considerable variation on the bearing capacity of the infrastructure (base+subgrade) between the two sidewalks. In addition, it is evident the loss of bearing capacity of the structure under the presence of excessive amount of water into the sidewalk.

The bearing capacity of a road decreases greatly during spring thaw, when the previously frozen road begins to thaw. The extent of this decrease can be evaluated by making Falling Weight Deflectomter (FWD) measurements on the road, measuring the deflection of the road when an impact load is applied to it. The bearing capacity of the road can then be evaluated by backcalculating the layer modules with backcalculation programs, or through more simple calculations based on the deflection basin indices. Both analyses were carried out in this thesis with data from FWD measurements which were carried out on county road Lv 126 in Southern Sweden during the year 2010. The temperature and moisture content of the road were monitored during the same time. The aim with the thesis was to compare the two ways of analyses, and to find out if there is some relationship between them and the measured environmental data. The results showed that the base course layer and subbase decreased in stiffness during spring thaw about 50% while the decrease in the subgrade was 20%, compared to the backcalculated summer and autumn value. The results of the simple calculations from the deflection basin indices were well comparable to the backcalculation results. By comparing the backcalculated stiffness values to the moisture content measurements it was stated that the stiffness decreased as the moisture content increased.

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. / <p>QC 20150324</p>