Abstract: The reservoir water level of a high earth core rockfill dam can fluctuate by over 60 m during operation. Rockfill materials in the zone affected by water level fluctuations may undergo significant deformation due to cyclic wetting-drying cycles, resulting in longitudinal cracks on the dam’s surface and impacting its safe operation. Extensive research has been conducted on the effect of cyclic wetting-drying on the long-term deformation and deterioration of rockfill materials. Nevertheless, there is a scarcity of studies on the cyclic wetting-drying behavior of rockfill grains of varying sizes. We conducted comprehensive single grain crushing tests on slate rock grains of various sizes subjected to different wetting-drying cycles. The findings indicate that the load-displacement curves and fragmentation patterns of slate rock grains can be categorized into four types. The peak loads for grain crushing and the average crushing strengths decrease with the increase of the number of cycles. The crushing strengths of slate rock grains of varying sizes exposed to different wetting-drying cycles conform to the Weibull distribution. A power exponential relationship exists between the characteristic crushing strengths and the number of cycles, suggesting a gradual slowdown in the deterioration of the mechanical properties of slate grains. The characteristic crushing strengths exhibit a clear size effect across different wetting-drying cycles, with this effect showing a negative correlation with the number of cycles.

Key words: rockfill grains, grain crushing, cyclic wetting-drying, crushing strength, size effect