In this paper a first time attempt has beenmade tomeasure the lowstrain shearmodulus of clean and fouled ballast using a seismic survey ofMulti-channel Analysis of SurfaceWave (MASW).Amodel rail track was built with nine sub-sections, each having different fouling characteristics.MASWsurveywas performed in the top of each section of ballast and shear wave velocitywas measured. The shearmodulus of ballast fouled by pulverized rock, clayey sand and coal was calculated by using shear wave velocities and densities of each section and presented. The optimum and critical fouling points are defined considering the shear stiffness and drainage criteria for ballast fouled by clayey sand and coal. In both cases the shear stiffness increased to amaximumand then decreased as the percentage of fouling increased. The degree of fouling corresponding to themaximumshearwave velocity is defined as the optimum fouling point. After a particular degree of fouling the shear stiffness decreased less than clean ballast and the corresponding drainage condition become unacceptable. This point is defined as the critical fouling point. The results obtained from the model track were compared with the field data.
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