Citation
A. Kabla and T. Senden
Physical Review Letters 102:228301 (2009)
Abstract
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.
Figure sample
Series of radiographs describing the flow and density profiles for a shear flow (top) and gravity driven flow (bottom). Material: monodisperse acrylic spheres, 1 mm in diameter. Numbers on the top right corner of each image indicate the upward displacement of the moving wall. See EPAPS [24] movies Nos. 1 and 2 for the complete sequence of images. Letters designate specific regions discussed in the text and Fig. 4b.
