Experimental investigation of the characteristics of a granular ballast bed under cyclic longitudinal loading

•Dynamic behavior of ballast bed under cyclic longitudinal loading are investigated.•Resistance-displacement hysteretic curve of ballast bed is obtainted and analyzed.•Longitudinal bearing performances of ballast bed are described.•Images of ballast movement at different points of hysteresis curve are obtainted. In this study, tests are performed for studying the characteristics of a ballast bed under cyclic longitudinal loading at different loading rates and a displacement amplitude based on a full-scale test model. The deformation and resistance characteristics of the granular ballast bed are investigated under cyclic loading. The results show that the resistance of a track panel with different number of sleepers to the longitudinal displacement is obviously lower than the sum of the resistances per sleeper. In addition, monotonic and repeated loading can cause plastic deformations to accumulate continuously on the ballast bed, whereas cyclic densification occurs without much additional breakage owing to the rearrangement of the ballast particles, causing the resistance amplitude of the ballast bed to increase. Moreover, the loading and unloading curves of the granular ballast bed do not coincide with each other under cyclic loading, forming a closed hysteretic curve, and the ballast bed is subject to cyclic softening with the increase in the number of cycles. Furthermore, the response degree of the granular ballast bed is related to the displacement amplitude, and the cyclic softening behaviour of the granular ballast bed is dependent on the exerted displacement amplitude. Thus, a higher exerted displacement amplitude implies a more severe cyclic softening.