Abstract: To investigate the variation law of particle grading in soft rock fill before and after testing, a series of large-scale experiments were conducted on soft rock fill in the construction of two reservoir dams. Quantitative analysis was performed using the Marsal particle crushing rate and grading equation parameters. Results are as follows: 1) In the compaction tests, the Marsal particle crushing rate reaches its maximum value near the optimum moisture content. 2) With increasing confining pressure, the Marsal particle crushing rate increases in the triaxial tests. However, such rate increase becomes less significant when a specific confining pressure is reached. 3) The Marsal particle crushing rate in super-large-scale compaction tests is higher than that in large-scale compaction tests. The rate of Marsal particle crushing after wetting and creep tests is lower than that in saturated triaxial tests. The Marsal particle crushing rate in large-scale lateral compression tests is also lower than that in triaxial tests. 4) Parameters of the grading equation show a monotonic change before and after the tests, tending to converge to a specific value. These research findings provide a scientific basis for optimizing the grading design.

Key words: soft rock fill, particle crushing, grading equation, type of test, gradation optimization, large-scale triaxial test