Development and application of state-dependent fractional plasticity in modeling the non-associated behavior of granular aggregates

To characterize the constitutive behavior of granular aggregates, a non-associated plasticity model with two different yield and plastic potential surfaces was usually used. However, in this paper, a state-dependent fractional elastoplastic model is proposed by only performing the first- and fractional-order differentiations of the yield function. The non-associated plastic flow is obtained without using any plastic potential functions. The state dependence is considered by correlating the fractional order with a state parameter. The model is then validated by simulating a series of test results of different granular aggregates, including sand, ballast and rockfill, under a variety of loading conditions.