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

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 Mc, the peak stress ratio Mp and dilatancy stress ratio Md 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-p space of the rockfill, Mc, was found to be passively correlated with the particle breakage index Br, rather than being a constant. Additionally, the observed values of Mc at low confining pressures (low particle breakage occur) will be substantially undervalued if Mc is estimated as a constant. In the critical-state-theory-based constitutive models, Mp and Md are estimated as the combinations of Mc and state parameter . It is believed that the simulations of Mp and Md when Mc is correlated with Br are obviously more favorable than those when Mc is constant.