The effects of interparticle cohesion on the collapse of granular columns

The presence of interparticle cohesion can drastically change the behavior of granular materials. For instance, powders are challenging to handle, and one can make a sandcastle using wet grains. In this study, we report experimental results for columns of model cohesive grains collapsing under their own weight in air and spreading on a rough horizontal surface. The effects of two different sources of interparticle cohesion on two collapse geometries are compared and rationalized in a common framework. Grains are made cohesive by adding a small amount of water, such that they are in the pendular state, or by applying a polymer coating. The effects of cohesion are reported for a cylindrical column that spreads unconfined axisymmetrically and a confined rectangular column that flows in a single direction. A dimensionless number, comparing macroscopic cohesive strength to particle weight, is shown to capture the effects of cohesion on the final morphology. To this end, a characterization of the cohesive strength of the granular materials is obtained, independent of the physical source of cohesion at the particle scale. Such a framework allows for a common description of cohesive granular materials with different sources of cohesion.