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A new design method has been developed to determine the granular layer thickness required to prevent and remedy railroad subgrade failures caused by repeated traffic loads. The design method emphasizes the effect of repeated loading on subgrade performance, and a procedure is incorporated to convert actual traffic conditions to a design dynamic wheel load and the equivalent number of repeated loads for the design period. The procedures for practical application of the design method are given in this paper. The design method was evaluated for several field cases and results were found to be consistent with field performance. These field cases include two test tracks and three track sites on two major railroads, where soft subgrade failures due to repeated axle loads were evaluated. Although the new design method is believed to provide the best approach currently available in taking into account the main load and track variables, future studies are recommended for further improvements and verifications.
Li et al. (Wed,) studied this question.