Onset of submerged granular collapse in densely packed condition

Granular materials are widespread in nature, and understanding their transport is important in geophysics. This study investigated the initiation of submerged granular collapse and collapse types, which affect transport processes. Laboratory experiments and failure analysis were performed; four particles and five liquids were experimentally examined. The experimental results reveal that the failure angle increases with decreasing particle size and increasing liquid viscosity. As the failure angle approaches π/2, the breaching collapse dominates; otherwise, sliding collapse occurs. Furthermore, the failure analysis indicated that the failure angle depends on the dimensionless parameter Darcy number; this was validated experimentally. The critical value of the Darcy number to distinguish between breaching and sliding collapse was devised on the basis of the experimental results.