The deformation and degradation of granular material under high-frequency cyclic loading
In order to understand the permanent deformation and degradation of railway ballast under high speed train loading, a series of cyclic triaxial tests were conducted using large-scale cylindrical apparatus. The frequency was used from 5 Hz to 60 Hz corresponding to the train speeds from about 40 km/h to 400 km/h. Three types of permanent deformation mechanisms were observed in response to the applied cyclic loads, namely, plastic shakedown at relatively lower frequency, ratcheting at an increased frequency, and plastic collapse at higher frequencies. Correspondingly, four types of particle degradation were observed. The magnitudes of ballast deformation and degradation were found to increase with the frequency and number of load cycles. A critical train speed was identified. Moreover, a good correlation was obtained between particle breakage and volumetric strain under cyclic loading.