Under the high stress of a 300-m dam, the particle breakage patterns of rockfill material may differ from those under low-stress levels. The existing studies on the particle breakage of rockfill material under ultra-high dams are relatively rare. In this study, by performing a series of large-scale triaxial shear tests under different relative densities and confining pressures, the stress-strain relationships and particle breakage characteristics of a sandstone rockfill material were investigated. The development of four particle breakage indexes before and after the triaxial test, the evolution of the gradation curves, and the applicability of three gradation formulas to the data of this study were analyzed. Based on the distribution of one relative breakage index, its relationship with strength and compressibility was established. Finally, three failure modes for the sandstone rockfill material after the triaxial test were given. And the relationships among failure modes and confining pressure, and particle size were discussed.
