Natural slope: experimental methods and computational models searching for shape generated by controlled falling sand flows

Controlled falling sand flows are governed by complex mechanisms so that their behavioral model, showing properties of both solids and liquids, represents a barely explored research field, within the contest of form finding. This paper recounts the explorative process on controlled falling sand flows conducted by the corresponding author at the University of Naples Federico II during her Master's Degree thesis research activities. In particular, it presents an experimental study on the sedimentation processes of sand piles obtained by pouring sand from a point of emission with fixed flow rate. After that, the equilibrium condition achieved by the sand flows on a collision plane, defined by Frei Otto as the "natural angle of repose", is observed. The research is focused on the analysis of behavioral reaction of the sand to addition and subtraction. It investigated three typologies of experimental systems, in order to define geometric solutions, consistent with the conical surfaces derived by Eurelian principles, and two computational methods, capable of processing the same physical simulations and of generating approximate solutions in terms of three-dimensional surfaces, although using non-mechanical algorithms. Finally, the presented work highlights the potential of the self-organization of the sand that make ridged and developable surfaces and generate repeatable and controllable solutions, despite the complexity of the shape.