In order to reduce buckling problems of railway ballasted tracks, efforts have been made to improve lateral resistance of sleepers. There have been several researches on the development of new shapes of sleepers which may increase lateral resistance. However, detailed investigation on the mechanism of improvement has not been studied. Based on the above mentioned, in this study, a series of model tests were attempted. Six types of sleepers were prepared for model tests. Single-sleeper pullout tests and track panel pullout tests were conducted on the sleepers. The model test results revealed that lateral resistance of the sleepers are significantly affected by their shapes. The idea that the lateral resistance measured at a horizontal displacement of 2.0 mm in full-scale (or 0.4 mm in 1/5-scale) single-sleeper pullout tests corresponds to that in track panel pullout tests is only valid for limited conditions. This is because of the piled group effect in track panel pullout tests, which affects the lateral resistance. Because the degree of the piled group effect is controlled by the ratio of the sleeper width to the sleeper spacing, a significant reduction of lateral resistance may be observed in track panel pullout tests depending on the sleeper type.
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