On the Stress-Path Dependent Response and Yield Surface of Bonded Soft-Rigid Mixes

The mechanical behaviour of bonded soft-rigid granular materials is governed by complex interactions among constituent phases, with responses varying as a function of their relative volume or mass fractions. This study investigates a three-phase granular system comprising soft particles (waste tyre rubber), rigid particles (crushed rock), and flexible binder. Experimental evidence suggests that the mechanical response is sensitive to the changes in soft/binder proportions in the mix. The macroscopic response of these mixes under different stress paths and the evolving yield characteristics are explored through a Discrete Element Method (DEM) framework. The mechanical response from 1-D compression experiments is calibrated using a modelling framework developed for these mixes. The calibrated model parameters are then applied to simulate loading scenarios, including triaxial, unconfined, isotropic, biaxial compression, and indirect tension tests, representing different stress paths. Beyond analysing the mechanical response under various stress paths, the yield points identified from distinct discontinuities in fabric metrics are used to construct the yield surface. When mapped in deviatoric–mean stress space, the yield loci conform to a two-yield surface formulation, delineating transitions between compressive and dilative regimes. Additionally, the yield surface in the deviatoric plane is tracked along with its evolution as strain levels increase.