Abstract: Soft rock, easily broken during mining, filling, and rolling, is used as dam filling material in some pumped storage power plants. The relationship between filling and particle composition varies, greatly affecting the strength and deformation characteristics of dam materials. Currently, research on the particle breaking characteristics of soft rock damming materials is lacking, as is the differentiation from hard rock damming materials. This paper performs particle screening, scanning, and crushing studies on soft rock damming material from a pumped storage power station. The particle crushing mode, fractal dimension, crushing strength, and size effect differences between soft and hard rock are compared. The influence of particle shape and size on particle crushing mode and crushing strength of soft rock is investigated, and the relationship between particle shape and crushing strength of soft rock is quantified. The results show that the crushing mode of soft rock particles can be classified as crushing, splitting, or mixed. For hard rock particles with low strength and soft rock, the crushing mode is unique. The fractal dimension of 2.198 for soft rock is much smaller than marble and limestone, yet it is comparable to limestone, basalt, and sandstone. More tiny pieces form on the surface during soft rock particle disintegration. The crushing strength of soft rock particles is much lower than that of hard rock particles, with an average Weibull modulus of 1.48, also lower than most hard rock particles. The size effect and dispersion of the crushing strength of soft rock particles are stronger. The crushing modes of soft rock particles are mainly affected by particle shape, while the crushing strength is mainly affected by particle size. The formula proposed in this paper describes the quantitative relationship between particle shape and crushing strength.

Key words: soft rock, particle shape, crushing mode, fractal dimension, Weibull statistics