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Geosynthetic reinforced & unreinforced rail track foundation comparison of analytical methods and numerical modelling

Design of Railway track foundations (RTF) given by Research Designs & Standards Organ-ization, India (RDSO) is studied for its reference methods, material specifications and the design criteria. Considering the new demands of heavier and fast freight transport there is a need to optimize and economize the design and maintenance of the RTF. An analytical design method for design of geogrid reinforced RTF is discussed and modified aiming for its application in the same. The design considers loading mechanism of the wheel, rail and sleeper in pseudo static nature, elastic properties of track elements, geogrid ballast interaction, stress diffusion in the ballast and sub ballast and empirical distress formulae for critical rutting under cyclic loading. Modifications in the design are done by changing the critical rut ratio, subgrade strength criteria and the applied dynamic augment. A detailed parametric study is done which encompasses the various design cross sections thus obtained with different granular layer thicknesses and properties (Resilient modulus) possible in Indian Scenario using a plane strain finite element (FE) model in Plaxis 2D. Deviator stress transferred on the subgrade top due to train loads is used for the design. The three designs thus obtained are compared. It was found that different layers of RTF can be optimized by using geogrid. Also maintenance period of RTF can be increased for same thickness of the granular layers. Modified analytical method of geogrid reinforced RTF corroborates with results of numerical model