Experimental measurement of the angle of repose of a pile of soft frictionless grains
Piles of perfectly smooth spherical particles are able to sustain a non-zero angle of repose as a result of geometrical constraints. Here we report on a study of piles made of soft frictionless grains and their angle of repose. The piles are formed by a continuous bubbling of air into a soapy solution in a narrow container of rectangular cross section. For wide containers, the angle of repose of the pile is \(3.75\pm 0.11\) degrees, independent of bubble flow rate. However, we find that the angle of repose is sensitive to confinement effects. In contrast with sand piles, surface avalanches are nearly absent and the fluidized region along the interface is several layers deep. In addition, the bubble pile is metastable, i.e. upon interruption of the gas flux the slope relaxes back to zero as a result of liquid drainage.
KeywordsAngle of repose Sand piles Bubbles Foams
We gratefully acknowledge financial support provided by James Madison University Program of Grants for Faculty Assistance.
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Conflict of interest
The authors declare that they have no conflict of interest.
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