Abstract: In this work, large-scale confined compression and creep tests are conducted using the dry rockfill of slate, which is designed for the shell material of the Lianghekou high gravelly-soil-core rockfill dam. We adopt two types of tests, i.e. single stage loading and multi-stage loading, and examine the confined creep under the loading at a constant stress rate and the confined creep under the loading-unloading-reloading at a constant stress rate, focusing on the influence of historical loading conditions on volumetric creep deformation and the influence of creep deformation on subsequent compression deformation. We find that except for two special creep processes, i.e. after loading-unloading-reloading and after low constant stress rate loading, all the time variations in volumetric creep deformation under different stresses follow a similar normalized trend－creep deformation is positively correlated with stress. The creep rate generally decreases with time, and follows a good double logarithmic linear relationship. The initial creep rate is positively correlated with stress, but its time decay rate seems to be irrelevant to stress, previous loading, or creep history. For the two special creep processes, we find that creep rate increases with time gradually or keeps unchanged in a short initial period, and creep deformation is smaller than in other cases. And the creep deformation in the early stage leads to an increase in the degree of over-consolidation, which generates an obvious hardening effect on the subsequent reloading process. Thus, the confined compression modulus under the initial reloading is significantly higher than that of normal loading. But with more reloading applied, it gradually approaches to the latter, which is less affected by the number and time of previous creeping and shows a similar evolving process.

Key words: rockfill, compression deformation, creep, normalization, hardening