Railroad ballast serves to transfer moving train loads to the subgrade and maintain track stability. The profile of repeated train loading is observed to be irregular and periodical with a rest time caused by the nature of railway cars. The cyclic loading pulses applied in large-scale triaxial testing are then simplified with varying rest times in prior research, but this simplification leaves its effect on the response of ballast movement ambiguous. In this study, SmartRock, an intelligent sensor, is employed in large-scale triaxial tests to examine the vertical acceleration of ballast under various loading pulses. An index called cyclic loading duration ratio (CLDR) is introduced to establish the correlation between vertical accelerations and loading pulses. The findings suggest that there are settling acceleration and rebound acceleration under various loading pulses. With the decreasing of CLDR, both accelerations show a clear growth, and their growth rates are highly dependent on the applied deviator stress. Besides, under CLDR = 0.05, the ballast particles tend to vibrate with the high deviator stress. These insights are crucial for making informed decisions about waveform selection in future triaxial testing.

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