Combined Effect of Particle Shape and Interparticle Friction on the Collapse Mobility and Deposition Morphology of a Granular Column

ABSTRACT Geophysical mass flows of granular materials composed of irregular‐shaped particles with different frictions are ubiquitous in catastrophic events such as landslides, snow, and rock avalanches; however, their mobilities and deposition morphologies remain poorly understood. Employing two‐dimensional discrete element simulations, we investigate the combined effect of polygonal particle shapes and interparticle friction coefficient on these physical properties. The interparticle friction coefficient systematically varied over a wide range, and the polygonal grains were irregularly changed from triangles to disks, which were controlled by their number of sides. We showed that interparticle friction coefficient affects monotonically the collapse mobility and deposition morphology for all polygonal particle shapes except particles exhibiting high angularities. In particular, all trends change for low interparticle friction coefficients and then saturate for higher frictions, but the evolution rates for triangles and squares are significantly different from other particle shapes. Contrarily, both collapse mobility and deposition morphology depend nonmonotonically on the particle angularity for low friction coefficients, especially for highly angular grains. These physical properties then recover a monotonic behavior with particle shape for higher friction conditions. Remarkably, the monotonic and nonmonotonic dependences of the collapse mobility and deposition morphology on the interparticle friction coefficient and irregular‐shaped grain are deeply explained via the microscopic origins, including the friction mobilization, contact coordination number, angular velocity, and relative tangential velocity. In particular, friction mobilization primarily governs the nonmonotonic behavior of highly angular grain flows where particle interlocking is negligible, while contact coordination number, rotational and translational constraints mainly control the monotonic characteristics of kinetic energy, runout distance, and deposit height. These observations show a good agreement with the shear strength of simple shear flows of frictional‐irregular particle shapes. The findings also highlight the necessity of incorporating particle angularity and friction coefficient as well as contact coordination number and friction mobilization into current constitutive frameworks, leading to probably improving the reliability in describing natural geophysical flows such as landslides and debris flows.