Effects of initial packing density and cohesion on submerged granular collapse

We investigate the collapse of submerged cohesive granular columns as a function of their packing density and the cohesive force strength, via grain-resolving direct numerical simulations. The cohesive force acts to reduce the final runout distance of the collapsing columns. In addition, it significantly accelerates the initial contraction for loosely packed columns and decelerates the dilation for densely packed columns, leading to a larger or smaller excess pore pressure, respectively. Early on, the collapsing column exhibits distinct planar failure surfaces, whose angle with the horizontal increases with the packing density. We employ a network science-based approach to analyze the cohesive and contact force chains. Pronounced force-chain network structures form preferentially in the failure region. They tend to be larger for higher packing density, which induces a larger macroscopic cohesive resistance. The cohesive force tends to reduce the normal contact force, which results in shorter contact force chains.