Impact of the heap shape formation on the local vertical force profile of ensiled granular materials

The free surface, which results from the filling of a container by a dry granular material, takes the shape of a heap. This shape is induced by the particle properties like their size, their friction, their restitution coefficient but also by their kinetic energy induced by the filling conditions. The stabilisation of the intergranular contact network inside the heap leads to the formation of a specific local stress field. For five wheat-based powders of same origin but with contrasted properties, beds are formed in a quasi-2D semi-confined cell using a point source. The free surface of the bed is captured from photos taken at different filling states. The local vertical force is measured in the center of the cell for different depths. This work highlights a correlation between the local vertical force profile and the shape of the heap during the filling. Two modes of force distribution can be distinguished and classified according to a parameter of uniformity. These distinctions are linked to the different shapes of the heap, quasi layering or dune. Our experimental study demonstrates that the history of the powder filling has a direct impact on the resulting local force profile. (C) 2018 Published by Elsevier B.V.