Abstract: Gradation is crucial factor influecing the mechanical properties of high dam rockfills. During the filling period of a high dam, frequent particle breakage due to heavy equipment rolling leads to significant changes in the grading curve. Exceeding the design values of rockfill grading can result in unqualified areas, posing a risk to the safe operation of the dam. The traditional grading evolution research is mostly based on the reduced rockfill materials with a maximum particle size smaller than 60 mm, making it challenging to effectively describe on-site grading of rockfills with large particle sizes and multiple groups. This paper provides a novel approach to developing a prototype rockfill gradation evolution model. By utilizing the Weibull distribution of particle-crushing energy consumption of each particle group of rockfill body, the proportion of particle crushing amount of each particle group under different rolling passes was obtained. A fractal distribution matrix of crushing particles was developed to estimate the particle content of each new group, resulting in a new grading curve. Model parameters were determined through laboratory single grain strength test and field rolling test. The validity of the new model is verified by comparing with the measured values of the on-site rolling test pit of Shuangjiangkou Hydropower Station, the world's highest rockfill dam (315 m) currently under construction.

Key words: prototype gradation, rockfills, Weibull distribution, fractal distribution；particle crushing