Abstract: To investigate the volumetric creep characteristic of rockfill in depth, we conduct a series of confined creep tests on air-dried slate rockfill materials, using different prior loading stress rates and different pre-consolidation states. We find that the subsequent initial stage creep rate is positively correlated with the prior stress rate, but it is less affected by the latter if the prior stress rate is higher than a certain value. In normal consolidation state, if a higher prior loading rate is adopted, the time developing process of the subsequent creep rate conforms to the Singh-Mitchell model. If the prior loading rate is low, the creep rate in the initial stage is less than that at a faster prior loading, and then decreases slowly. This slow decrease continues for a certain time period until the creep rate varies with time in the same trend as the case of high prior loading rate－a negative linear relationship that exists between creep rate and time in double logarithmic coordinates. In over-consolidation state caused by prior loading or compaction, the subsequent initial stage creep rate and the total amount of creep deformation are still positively correlated with the creep stress and the prior loading stress rate, but their values are far smaller than those in the normal consolidation of the same creep stress and prior loading stress rate. Similar to the situation with lower prior loading stress rate in normal consolidation, the initial subsequent creep rate with a high prior loading stress rate in over-consolidation decreases slowly for a certain period, until the creep rate starts to decrease in the same way as the high prior stress rate case in normal consolidation. For the subsequent creep in over-consolidation with the same pre-consolidation stress, the higher the creep stress, the lager the subsequent creep deformation and the subsequent creep rate.

Key words: rockfill, prior stress rate, pre-consolidation stress, creep rate, creep value