| Railways are well-known for being the most reliable and energy efficient means of transport for passengers and goods. Nowadays, the railway sector is considered to experience a boost-up, so that it represents the topic of high interest for fast development. Traditional methods applied to observe the main properties of a railway track system are not able meet the requirements of the new engineering projects. One of the major disadvantages of the railway transport is considered to be represented by the high cost of construction as well as the one of maintenance. Furthermore, the demand for new technologies to obtain accurate information about the railway track system components is more and more pronounced. Railway foundations represent geotechnical structures which are highly dependent on the quality of ballast and subgrade to facilitate easy construction and distribute stresses more evenly.A traditional railway system consists of several components such as rail, fasteners, sleepers, ballast and subgrade, all these forming a structural system designated to withstand various effects of traffic and climate. The use of faster trains which have heavier axle loads require a better comprehension of the loads transmitted by the moving train to the railway track system as well as the mode of transmitting stresses, strains or any other deformations to the subgrade layers. In order to better understand the behavior of the entire railway track system, numerical models need to be built to properly represent the components of the superstructure and substructure. In order to determine the effects of train loads on the components of the railway track system, we need to accurately determine elastic parameters for each layer of the substructure.In this work, the use of FWD is presented and testing results are depicted for Oasis railway and Tanhan railways, K33 and DK1 sections respectively. Furthermore, a numerical approach was presented to back-analyze the material properties of the railway substructure from FWD deflection data obtained from another test field. The results of the numerical analysis were represented by the sensor deflections which were placed at different distances from the point where the FWD load was imparted. After getting the peak deflections from the numerical analysis, they had to be compared to the ones from the test field in order to check that they are not exceeding a certain value of error percentage. The peak deflection values attained by performing the numerical analysis were as following: 200.049 μm, 154.497μm, 144.023μm, 113μm, 79.925μm, 66.7μm and 56.5μm respectively, which proved the validity and importance of the finite element model for the case presented herein.In the last part of the thesis, a dynamic analysis was performed by using the subgrade elastic modulus values from the previous numerical analysis. The outputs of this analysis consisted of stresses and accelerations encountered in different components of the railway track system, great attention being focused on the three layers of the subgrade.The results indicated that for different speeds of the moving train, the stresses and accelerations might suffer some fluctuations. It has also been highlighted the decreasing tendency of stresses and accelerations with time and distance. Both numerical analyses offered a good overview of the peak deflections from a FWD test as well as a better understanding of the stresses and accelerations within the subgrade layers. |
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