Falling weight deflectometer (FWD) is currently used by most highway agencies to determine the structural condition of the highway network. Utilizing the deflections measured by the FWD, the resilient moduli of layers in the flexible pavement is determined using backcalculation software packages. The moduli can be input into semi-empirical mechanistic equations to estimate the remaining life of the pavement system and aid in informing pavement engineers about timing of maintenance and rehabilitation needs. There have been concerns among practitioners and the research community about the adequacy of the resilient moduli determined by the backcalculation software. Some of the backcalculation models have been simplified and field verification may be needed. Field-measured stresses and strains may be used to quantify the reliability of the backcalculated moduli. The Virginia Smart Road, which has 12 different flexible pavement designs and was built and instrumented with pressure cells, strain gages, thermocouples, frost probes and moisture sensors. To validate the backcalculated moduli theoretically and through instrument response, this research was conducted with following objectives: 1) to determine the resilient moduli of the unbound granular materials on the Virginia Smart Road using small and large plates of the FWD; 2) to investigate the extent of spatial and temporal variability of the FWD deflections among pavement sections; 3) to develop a temperature correction model for the backcalculated HMA resilient moduli; 4) to define an appropriate backcalculation approach and compare the four widely used software approaches; and 5) to correlate backcalculated and laboratory measured moduli. In addition, the FWD measurements were used to establish a comparison between in-situ measured and computed stresses and strains in the pavement. The analytical approaches used are linear elastic, viscoelastic, and viscoelastic combined with nonlinearity. Results show that estimation of unbound granular materials moduli using surface deflections is more reliable when 457-mm-diameter loading plate is used. Analysis of deflections from different sensors showed evidence of spatial and temporal variability. The lowest coefficient of variation of deflections (7%) within sections occurred at low temperatures (2 to 6 °C), while the highest coefficient of variation (42%) occurred at temperatures between 35 to 40 °C. This resulted in the development of a deflection temperature correction model. The model was validated at different temperature ranges. A backcalculation procedure was defined to achieve good root mean square error using four selected software packages. This resulted in the selection of the most reliable software to perform moduli backcalculation. A correlation was established between the nonlinear models produced by backcalculation and laboratory testing of the granular 21-B material. However, for the HMA materials, difference in loading period between laboratory testing and FWD loading pulse could affect the results. The study found that when utilizing the backcalculated moduli, computed strains using viscoelastic modeling were comparable to in-situ measured values. Similarly, calculated stresses compared well with the field-measured stresses; especially at high temperatures. Mix properties, temperature of testing and loading were found to have an effect on the agreement between the measured and computed strains in the wearing surface. The study also recommended further validation of FWD measurements using embedded instruments to calibrate analytical models and further analysis of deflection data so that optimum number of testing points can be determined to limit amount of testing performed for determination of deflection variability. / Ph. D.

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Le diagnostic du parc routier est une étape indispensable préalable à l'entretien et la réparation des structures de chaussées. L'importance d'une plus grande finesse de l'analyse des résultats issus des méthodes de contrôle non destructif peut permettre de réaliser, à terme, des économies sur les coûts et énergie mis en jeu lors de la maintenance et la construction. Ces travaux de doctorat présentent un modèle thermo-visco-elastique permettant d'intégrer le comportement des matériaux bitumineux composant une chaussée par l'utilisation du module et de l'amortissement complexe issu des courbes maitresses. La résolution du problème dynamique est réalisée à l'aide d'une approche fréquentielle. Cette approche est appliquée en particulier à un essai FWD sur lequel des variations climatiques sont étudiées. Des essais in situ, réalisés sur deux sites instrumentés, permettent de valider le modèle. Les bons résultats obtenus suggèrent l'utilisation de ce modèle à travers une analyse multicritère sur les bassins de déflexion et les historiques pour le développement futur d'un modèle de retro calcul dynamique. / The diagnosis of the road fleet becomes a necessary step prior to themaintenance and the repair of pavement structures. The importance of a finer analysis of the results of the non-destructive testing methods can eventually achieve to cost and energy savings for the maintenance and construction. This phD thesis introduces a thermo-visco-elastic model for intersting the behavior ofbituminous pavement materials, using the complex modulus and damping from master curves. The resolution of the dynamic problem is performed thanks to a frequency approach. This approach is particularly applicable to a FWD test on which climatic variations are studied. In situ tests, carried out on two instrumented sites, are used to validate the model. The obtained of good results suggests the use of this model through a multi-criteria analysison deflection basins and of the records for the future development of a backcalculation dynamic model.

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Analizuojama asfalto dangos konstrukcijos elgsena Lietuvos klimato sąlygomis, įvertinant temperatūros ir drėgnio, kaip vienų iš svarbiausių klimato veiksnių, įtaką kelio asfalto dangos konstrukcijos stipriui. Pateikta krintančio svorio deflektometro matavimo metodikų apžvalga kitose šalyse. Atlikta temperatūros ir drėgnio kiekvienos dienos pokyčių analizė, įvertinant jų įtaką dangos konstrukcijai. Nustatyta kelio dangos stiprio ir Eo modulio priklausomybė nuo dangos temperatūros, matuojant kelio dangos įlinkius krintančio svorio deflektometru. Kai asfalto dangos stipris matuojamas skirtingu metų laiku ar įvairiu paros metu, tai Eo modulio reikšmės turi būti redukuojamos priimtai standartinei temperatūrai. Eksperimentiniame asfalto dangų konstrukcijų ruože atliktu tyrimu patikslintas temperatūrinis redukcijos koeficientas, kuris leidžia krintančio svorio deflektometru nustatytas asfalto dangos sluoksnių Eo modulio vertes redukuoti standartinei +20 °C temperatūrai. / This final master thesis performs asphalt pavement structural behavior of the Lithuanian climate conditions, taking into account the temperature and moisture, as one of the most important climatic factors that influence the road asphalt pavement structural strength. The Falling Weight Deflectometer (FWD) measurement methods used in other countries are presented. The temperature and moisture changes in the day are analysed, evaluating their impact on pavement design. The strength of asphalt pavement layers, as well as Eo modulus values, measured using the falling weight deflectometer, strongly depend on the pavement temperature. When we use deflectometer for measuring asphalt pavement strength at different environmental conditions and in different season, the values of Eo modulus should be reduced to the assumed standard temperature. So during this research at the experimental asphalt pavement structure the temperature correction factor was revised. The use of this factor enables to adjust the Eo modulus values of asphalt pavement layers measured by the Falling Weight Deflectometer to the standard temperature of +20 °C.

Currently, Scania is not offering full air suspended AWD trucks, which it seems to be a demand for. This study acts as a first step to fulfill this demand. Including, a benchmarking of what competitors offer as well as an investigation and an evaluation of Scania’s current suspension system. Moreover, a requirement specification and a concept generation for a front air suspension system on AWD trucks have been presented. Eight concept were generated, where two were chosen for further study of design, force analysis and roll gradient analysis. It was concluded that there is a market for this configuration, however, implementing it would require extensive design work. / I nuläget erbjuder inte Scania luftfjädring för samtliga hjulaxlar på AWD lastbilar, vilket det tycks finnas ett kundbehov av. Denna studie agerar som ett initialt steg till att uppfylla detta kundbehov. Studien inkluderar inledningsvis en analys av vad konkurrenter erbjuder samt en undersökning och utvärdering av Scanias nuvarande fjädringssystem. Utöver det, har en kravspecifikation och en konceptgenerering för främre luftfjädring på AWD lastbilar presenterats. Åtta stycken koncept genererades, varav två stycken valdes för vidare studie av design, kraftanalys samt krängstyvhetsanalys. Slutsatserna var att det finns en marknad för denna typ av konfiguration, dock skulle det behövas omfattande designarbete för att implementera det.

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