When a granular material such as sand is mixed with a certain amount of liquid, the surface tension of the latter bestows considerable stiffness to the material, which enables, for example, sand castles to be sculpted1, 2, 3, 4. The geometry of the liquid interface within the granular pile is of extraordinary complexity and strongly varies with the liquid content5, 6, 7. Surprisingly, the mechanical properties of the pile are largely independent of the amount of liquid2, 8, 9, 10, 11, 12, 13 over a wide range14, 15, 16. We resolve this puzzle with the help of X-ray microtomography, showing that the remarkable insensitivity of the mechanical properties to the liquid content is due to the particular organization of the liquid in the pile into open structures. For spherical grains, a simple geometric rule is established, which relates the macroscopic properties to the internal liquid morphologies. We present evidence that this concept is also valid for systems with non-spherical grains. Hence, our results provide new insight towards understanding the complex physics of a large variety of wet granular systems including land slides, as well as mixing and agglomeration problems.

---

I thought this might be important. Microtubular hydraulic nodes supporting variable-pressure open-strucutred liquid patterns could conceivably provide a breakthrough in construction of large configurable shelters or other supporting structures.


A