The track bed was simulated with the discrete element method.The model of bonded ballast particles clumps was established to model real ballast particles.The ballasts box model was built for the track bed com-posed of ballasts of diversified gradation and different grain shapes.The influence of gradation and grain shapes on the mechanical properties of the track bed was analyzed.The results show as follows:The reasonably graded track bed has better mechanical properties than a track bed of single-size grains;under the condition that ballast grain shapes are the same,a track bed of a wider range of gradation has better mechanical properties but has a lower porosity;grain shapes affect the mechanical properties of the track bed significantly,regular grain shapes degrade the mechanical properties of the track bed obviously.%用离散元法对道床进行模拟，建立能拟合真实道砟颗粒形态的球簇单元模型。对由不同级配、颗粒外形道砟组成的道床建立箱体模型，重点分析颗粒级配与颗粒外形对道床力学性能的影响。分析结果表明：合理级配的道床比单一粒径的道床具有更好的力学性能；在颗粒外形相同的情况下，级配范围较大的道床力学性能较好，但孔隙率较低；道砟颗粒外形对道床力学性能影响大，由规则外形的颗粒组成的道床力学性能明显降低。
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