Collapse of submerged granular columns in loose packing: Experiment and two-phase flow simulation

Abstract

This study examines, both experimentally and numerically, the collapse process of a submerged granular column in loose packing, with an emphasis on the effects of the grain size and the initial aspect ratio of the granular column. A two-phase flow continuum model, developed based on the rheological characteristics of solid-water mixtures, is used to perform the numerical simulations. Two particle sizes representing very fine particles and coarse particles are examined in this study. The two-phase flow model is validated and verified by comparing with the measured characteristics of the collapse process. Compared to the collapse of a granular column of coarse particles, the runout distance of a granular column with very fine particles is longer and the spread velocity is higher. Based on the two-phase flow simulation results supported by the experimental results, critical initial aspect ratios are identified to classify the types of the initial collapse process and the final deposit morphology, and the empirical expressions are provided to describe the changes of the runout distance, collapse duration, final deposition height, and spread velocity with the initial aspect ratio. A phenomenon similar to the so-called Kelvin-Helmholtz instability can be observed in both the experiment and the simulation at the later stage of the collapse, which causes the formation of several vortexes in the two-phase flow during the collapse process. The presence of these vortexes is responsible for the pressure drop on the bed after the passage of the flow front and the wavy feature on the final deposit morphology.