Experimental observation and an empirical model of enhanced heap stability resulting from the mixing of granular materials

We report the existence of enhanced heap stability as a result of the mixing of granular materials. Our setup consists of a rectangular container, filled with a binary mixture of granular matter up to some height h, that is rapidly opened at one wall to allow repose angle (θc) formation. We develop an empirical model for θc based on the Mohr–Coulomb failure criterion. The model is parameterized by an effective cohesion c and an effective coefficient of friction μ that depend on: (1) the granular proportions and (2) the c and μ for pure cases. Good agreement is achieved between the experiment and the model. We note that even the experimental fluctuations of θc as a function of granular proportions are well correlated (<2% deviation) with the computed uncertainty of the empirical model.