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An investigation into the use of asphalt layers to control stress and strain levels in railway track foundations

A hot mixed asphalt layer can be inserted between the ballast and subgrade layers in the foundations of rail tracks to improve the stress and strain distributions in these layers and also reduce track vibrations and level of damage in the track’s superstructure. These phenomena depend on various parameters such as the manner of operation of the railway and the mechanical characteristics of the foundations. This study is devoted to the derivation of analytical equations that describe the tensile strain on the asphalt layer and compression stress in the subgrade layer in terms of these parameters. A series of numerical analyses have been performed using the KENTRACK simulation code in which the railway axle load, asphalt thickness, ballast modulus and California bearing ratio of the subgrade were varied. The obtained values of the maximum tensile strain in the asphalt and compression stress on the subgrade were analysed using a least squares method in order to extract correlation equations that consider the maximum tensile strain in the asphalt layer and compression stress on the subgrade layer in terms of the varied parameters. A comparison of the obtained simulation results with measured data reported in the literature shows a good agreement between the results.