Abstract: The deformation behaviors of rockfill material are time-dependent. In this work, large scale confined compression tests with the loading at different stress rates, successive unloading-reloading tests, and successive creep tests after the loading are conducted using test materials from the dry rockfill of slate designed for the shell material of the Lianghekou high gravelly-soil-core rockfill dam. The stress deformation process of the test material is obviously affected by its stress rate. For confined compression under medium-low stress, a higher stress rate leads to a larger deformation increment and a smaller confined compression modulus. Under high stress, the influence of stress rate on stress strain process weakens; however, a higher stress rate leads to a smaller deformation increment and a larger confined compression modulus, which is opposite to the medium-low stress case. During loading, rockfill deformation generally increases with the rising of stress rate. A hysteresis curve is formed during successive unloading-reloading at a constant stress rate after confined compression. A certain deformation is accumulated in each unloading-reloading cycle; the accumulation increment of each cycle is gradually decreased with the times of cycles, and the average rebound/recompression index is also decreased. Generally, for each cycle, a higher stress rate is related to smaller unloading deformation and reloading deformation, smaller accumulated deformation increment as well as faster convergence. The relationship between creep rate and creep time after loading is nearly linear in double logarithmic coordinates. As stress or stress rate increases, the initial creep rate grows, while the decay rate of creep rate is lowered.

Key words: stress rate, rockfill, compression deformation, loading-unloading cycle, creep rate