Critical State and Grading Evolution of Rockfill Material under Different Triaxial Compression Tests

One of the most important features of soil behavior is the dependence of stress path. A series of large-scale triaxial compression tests was conducted to investigate the effect of stress path on critical state and particle breakage–induced grading evolution of rockfill material. All tests were first consolidated under constant principle stress ratio condition, and then sheared under three different stress paths, including constant lateral stress ${\sigma }_3$, constant mean effective stress $p^{\prime }$, and constant vertical stress ${\sigma }_1$. Test results indicate that the mean effective stress $p^{\prime }$, deviatoric stress $q$, and void ratio $e$ along different stress paths reached the consistent critical state line (CSL) in the $p^{\prime }\text{-}q\text{-}e$ space. There was a power function between $p^{\prime }$ and $q$, and a linear relation between $e$ and ${(p^{\prime }/p_a)}^{\xi }$ with $\xi =0.5$ at the critical state. The particle breakage under different stress paths was found to be consistent at the same critical state, and a unique relation among $e$, $p^{\prime }$, and the particle grading parameters at the critical state existed irrespective of stress paths. The test results at the critical state formed a straight line in the $e\text{-}{(p^{\prime }/p_a)}^{0.5}\text{-}{I}_G$ space.