Submerged cohesive granular collapse: Influence of packing density

We explore the submerged collapse of cohesive granular columns, as a function of packing density and cohesive force strength, via grain-resolving direct numerical simulations. We investigate both randomly packed granular columns as well as densely packed columns with an initial hexagonal close-packed (HCP) structure. The cohesive force acts to reduce the final runout distance of the collapsing column, and it entirely prevents the collapse when it exceeds a critical value. This critical value decreases with increasing packing density. The collapsing column has distinct failure planes, whose angle with the horizontal increases with the packing density. A force-chain network analysis indicates that strong cohesive force chains form more easily in the failure region and have a larger size as the cohesive force and packing density increase, which induces a larger macroscopic cohesive resistance. The cohesive force significantly accelerates the contraction of loosely packed columns and decelerates the dilation of densely packed columns, resulting in a more complex evolution of the local porosity and pore pressure.