Estimations of Three Characteristic Stress Ratios for Rockfill Material Considering Particle Breakage

Abstract

The particle breakage during specimen shearing has a significant influence on the critical-state line (CSL) of the rockfill material. A series of large-scale triaxial compression tests on the rockfill material from Henan Province (HPR) were conducted in a wide range of initial void ratios and confining pressures. The influences of the particle breakage on the critical-state stress ratio $M_{\mathrm{c}}$, the peak stress ratio $M_{\mathrm{p}}$ and dilatancy stress ratio $M_{\mathrm{d}}$ were investigated. The deviatoric stress and particle breakage of the HPR at the critical state increase with the increase in confining pressure, while the influences of the initial void ratio on these behaviors are too little to be considered. The gradient of the CSL in the $q\hbox {-}p$ space of the rockfill, $M_{\mathrm{c}}$, was found to be passively correlated with the particle breakage index $B_{\mathrm{r}}$, rather than being a constant. Additionally, the observed values of $M_{\mathrm{c}}$ at low confining pressures (low particle breakage occur) will be substantially undervalued if $M_{\mathrm{c}}$ is estimated as a constant. In the critical-state-theory-based constitutive models, $M_{\mathrm{p}}$ and $M_{\mathrm{d}}$ are estimated as the combinations of $M_{\mathrm{c}}$ and state parameter $\psi$. It is believed that the simulations of $M_{\mathrm{p}}$ and $M_{\mathrm{d}}$ when $M_{\mathrm{c}}$ is correlated with $B_{\mathrm{r}}$ are obviously more favorable than those when $M_{\mathrm{c}}$ is constant.