This paper presents the equipment and Spectral Analysis of Surface Wave (SASW) approach for non-invasively characterizing railroad track ballast and foundation layers. Surface wave testing on a railroad track is more complicated than that on soil sites or pavements because of the presence of ballast, crossties, and rails as well as the complexity of ballast-soil foundation structure in terms of the variation of shear-wave velocity with depth. Using portable SASW equipment, the Young’s Modulus of the ballast was calculated for both clean and fouled ballast in wet and dry conditions. In addition, the local modulus is determined at different locations under the tie, e.g. tie center or edge, to investigate modulus variation and tie support under a single tie. Expansion of the system to measure the modulus under two adjacent ties is also discussed and may be suitable for evaluating ballast performance under §213.103, which requires ballast to perform the following serviceability functions: (1) transmit and distribute the load of the track and railroad rolling equipment to the subgrade; (2) restrain the track laterally, longitudinally, and vertically under dynamic loads imposed by railroad rolling equipment and thermal stresses exerted by the rail; (3) provide adequate drainage for the track; and (4) maintain proper track crosslevel, surface, and alignment”.

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