ABSTRACT
Experimental and numerical studies were made on the onset of collapse and the growth of two-dimensional macroscopic cavity regions due to viscous flow. Particular attention is paid to hydrodynamic interaction of two initially circular cavities of equal radii, with varied center-to-center distance and orientation. In certain configurations, downstream cavity experienced stronger stream due to the presence of the other cavity, so that the critical velocity of collapse became lower than that for a single cavity case. For larger fluid velocities, the collapse of the upstream cavity proceeded monotonically, whereas the collapse of the downstream cavity paused for a moment, and resumed after the other one was completely filled by the grains. At the same time the fluidized region grew rapidly toward upstream direction. In the presence of distributed cavities, these fluidized regions may be connected by the flow, which induces natural disasters like landslides, collapses of river banks and cliffs.
