The compressive creep of rockfill

Abstract Multistage constant stress rates loading-creep tests were carried out on air-dried slate rockfill. The influences of the loading history on the creep deformation of rockfill were investigated, including the prior loading stress rate, the stress increment size of prior loading, and the history of early loading and early creep, in which 'prior loading' was defined as the loading just before the creep in the current loading-creep step, while 'early loading' or 'early creep' was that before prior loading. Regardless of the size of the prior loading stress increment, as long as there was a loading-creep process before this step of loading-creep, the time development process of the subsequent creep strain and strain rate was related to the creep stress and the prior stress rate before creep. The creep process had no obvious relationship with the early stress rate in the last step, as well as the earlier loading history before the last creep. The subsequent creep strain was positively correlated with the creep stress and prior stress rate. When the prior stress rate before creep was high, the subsequent creep rate and time were linear in the double logarithmic coordinate. The creep rate and time accorded with a power-law relationship which appeared to be the baseline for creep development. Whatever the prior loading rate, the creep rate time progression in the middle and later stages of the subsequent creep conformed to this baseline. Besides, when the prior stress rate was lower than a certain value, the initial strain rate of subsequent creep was significantly lower than the baseline, which decreases less until several minutes after the start of creep. The development law of creep rate at the initial stage could be generalized as a straight horizontal line in double logarithmic coordinates, which is kept almost unchanged for a certain time. The strain rate would not resume the power-law relationship with time until it approached the base creep rate. The inheritance and hysteresis of different prior strain rates to the initial stage of subsequent creep due to prior stress rate with the discrepancy, result in differences in the creep magnitude and time development process of creep rate. Moreover, the prior low strain rate both depressed the initial rate of subsequent creep and pushed back the initiation time of subsequent creep according to the power law.