Submerged granular collapse: different cohesion strength and initial packing densities

We investigate the submerged cohesive collapse of cohesive granular columns, as a function of packing densities and cohesive force strength, via grain-resolving direct numerical simulations. We not only obtain the randomly packed granular columns but also the regular densely packed columns by Hexagonal close-packed (HCP) structure. The cohesive forces act to reduce the final runout distance of the collapsing column, which will no longer collapse when the cohesive force is larger than a critical value. This critical value decreases with the increase of the packing density. The cohesive forces significantly accelerate the contraction for loosely packed columns and decelerate the dilation for densely packed columns, resulting in a larger positive excess pore pressure and a smaller negative excess pore pressure, respectively. The collapsing column has distinct straight-like failure surfaces at the initial time, whose angle with the horizontal plane increases with the packing density. The force-chain network analysis indicates that the strong cohesive force chains form more easily in the failure region and have a larger size with increasing the cohesive force and packing density, which induces a larger macroscopic cohesive resistance. The cohesive force has a canceling effect on the normal contact force, which results in a smaller size for the contact force chains.