  The behavior of granular column collapses is associated with the dynamics of
geohazards, such as debris flows, landslides, and pyroclastic flows, yet its
underlying physics is still not well understood. In this paper, we explore
granular column collapses using the spheropolyhedral discrete element method
(DEM), where the system contains two types of particles with different
frictional properties. We impose three different mixing ratios and multiple
different particle frictional coefficients, which lead to different run-out
distances and deposition heights. Based on our previous work and a simple
mixture theory, we propose a new effective initial aspect ratio for the
bi-frictional granular mixture, which helps unify the description of the
relative run-out distances. We analyze the kinematics of bi-frictional granular
column collapses and find that deviations from classical power-law scaling in
both the dimensionless terminal time and the dimensionless time when the system
reaches the maximum kinetic energy may result from differences in the initial
solid fraction and initial structures. To clarify the influence of initial
states, we further decrease the initial solid fraction of granular column
collapses, and propose a trial function to quantitatively describe its
influence. Due to the utilization of a simple mixture theory of contact
occurrence probability, this study can be associated with the
friction-dependent rheology of granular systems and friction-induced granular
segregations, and further generalized into applications with multiple species
of particles in various natural and engineering mixtures.
