Dilatancy in slow granular flows
A. Kabla and T. Senden
Physical Review Letters 102:228301 (2009), doi:10.1103/PhysRevLett.102.228301
Abstract
When walking on wet sand, each footstep leaves behind a temporarily dry impression. This counter intuitive observation is the most common illustration of the Reynolds principle of dilatancy: that is, a granular packing tends to expand as it is deformed. As a consequence, the amount of porous space increases, resulting in the apparent drying of the footprint. Although widely called upon in areas such as soil mechanics, geomechanics, as well as many industrial processes, a deeper understanding of this principle is constrained by the lack of analytical techniques to study this behaviour. Using X-ray radiography we track a broad variety of granular flow profiles and quantify their intrinsic dilatancy behaviour. These measurements frame Reynolds dilatancy as a kinematic process. Closer inspection demonstrates however the practical importance of flow induced compaction which competes with dilatancy, leading more complex flow properties than expected.