Why is (wet) granular rheology so complicated?
Institute of Physics
University of Amsterdam
Granular rheology is everywhere around us; the book by Duran quotes the stunning figure that the handling and transport of granular materials consumes roughly 10% of the world energy consumption. You might think that is a ridiculous figure, but if you think, for instance, about how much concrete is being manufactured and transported on this planet, that mining is an incredibly important industry, or that most of agriculture actually deals in some way with granular materials, you get a better feeling for how much energy is actually involved in dealing with these materials. I will discuss the rheology and mechanical properties of wet granular materials, and show why the behavior can be very subtle. Once one understands the mechanical properties, I will show that one can use this knowledge to construct the perfect sandcastle, or to understand why the ancient Egyptians wetted the desert sand with water before sliding heavy stones over it (Figure).
One of the mysteries of sand is why the Egyptians wetted the sand with water if they wanted heavy constructions to slide over it, as is shown explicitly in this wall painting of 1880 BC on the tomb of Tehuti-hetep (Fig.1(a)). Was this done to facilitate the sliding? According to archaeologists, this is not the case: “Another figure standing from the base pours water from a jar in front of the sledge, perhaps only a ceremonial act, since even in large quantities water poured upon the ground could not assist the dragging.”