There is substantial evidence that crushable soils (e.g., sands, gravels, rockfills, etc.) undergo particle crushing upon shearing or over creeping. To investigate the evolution of grading and particle crushing of coarse-grained materials, a series of consolidated and drained triaxial shearing and creep tests were conducted on rockfills using a large-scale triaxial apparatus. The test data from the sieve analysis test, both before and after the triaxial tests, were subjected to a comprehensive qualitative and quantitative analysis of the variation of grading or breakage index. Research findings indicate a decrease in the percentage of coarser particles in the particle components of rockfills, accompanied by an increase in the amount of particle crushing upon shearing or over creeping. Furthermore, a series of empirical expressions were proposed through nonlinear fitting of test data to characterize the relationship between the breakage index and two variables (i.e., the normalized plastic work and mean effective stress) under various confining pressures and stress levels upon shearing or over creeping. These findings can provide a scientific basis for the design, construction, and maintenance of rockfill dams or high rockfill embankments in the practical engineering application.
