Keywords: ballast, ballast specifications and standards, ballast fouling, finite element method, power trend line.

Ballast is formed from crushed stone and consists of particles in the size range 20 to 63 mm. Ballast supports the rails and sleepers uniformly and provides a stable layer to the rolling stock by transmitting their high imposed loads to the subgrade layer. The ballast layer maintains an adequate stability to the sleepers against vertical, lateral and longitudinal forces generated by rolling stock. On the other hand, the ballast layer provides sufficient dynamic resilience for the railway track and provides sufficient permeability for drainage. In addition, ballast layer absorbs noise and in parallel ensures comfort in the trains and around the railway line. In order to accomplish these functions adequately, ballast must conform to certain characteristics.

Therefore, various standards and specifications have been prepared by railway organizations throughout the world to meet their design requirements. Generally the specification for ballast for use in the installation and maintenance gives consideration to material, shape, flakiness index, elongation index, wet attrition value, grading, aggregate crushing value and etc. Consequently, the purpose of these standards and specifications are to define the mandatory requirements relating to the design, installation and maintenance of the ballast. In this paper ballast standards and specifications throughout the world are summarized and compared with each other.

Railway ballast is renewed when it loses its geotechnical properties and is no longer able to support the track adequately and provide drainage because of contamination. Ballast contamination causes the ballast layer to lose its functional and structural integrity. The contamination may result from the abrasion of the ballast under repeated train loads, the movement of fine particles from the subgrade, spillage of products carried by the trains and windblown material. In this study ballast contamination is assessed by reviewing existing methods commonly used for evaluating the degree of ballast fouling with their limitations.

Eventually within the scope of the above studies, a numerical model for realistic prediction of stresses and displacements inside the track support structure is developed by using the finite element method. The track is modelled as a multi-layer system and two-dimensional finite element models were built. The analyses results of the multi layered system modelled using a finite element method. In addition, the power trend line was used to present the vertical displacement, moment on the rail element and stresses in the ballast layer that compare measurements increasing at a specific rate. The power trend equations were obtained for displacement of railway track, moment on rail element and stresses in the ballast material.

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