Modeling deformation with cereal

An earthen dam filled with rocks and covered by an impervious surface provides one economical water-management solution. But if capillary action from below draws water into the porous rocks, the dam’s lowest layer may saturate and destabilize. Eventually the entire dam can fail. To investigate how earthen dams collapse, Itai Einav and François Guillard from the University of Sydney used a surprising yet effective proxy for the rocks: puffed rice. Rheologically, both are brittle, porous media.

The researchers modeled a simplified rockfill dam (upper figure) by packing puffed rice into a cylinder (lower figure). The constant pressure applied at the top of the chamber mimics the weight of the rocks at the top of the dam. Then the researchers added milk to the cereal from the bottom. The lower section of rice became saturated as the milk filled more and more micropores. The capillary action sapped the rice dam’s ability to counteract the constant downward pressure, which caused the upper unsaturated portion of rice to repeatedly collapse in events the researchers called “ricequakes.” Also associated with those quakes were audible crackling that “resembled the clicking beats of a metronome slowing down over time.” You can hear the crackling in this audio file.