Smoothing out sandpiles: rotational bulldozing of granular material

Predicting the dynamics of dense granular flow plays an important role in engineering and geophysical flow which involve the transport of granular materials such as for instance cereals, rocks or sand. In the past decade, most of the studies have focused on the flow of granular material on inclined surface due to the obvious applications in rock avalanches, landslides and pyroclastics flows [14, 7] (for a review, see e.g. [6]). However, the bulldozing of granular materials, i.e. the action to push the granular material with a blade on a flat plane, has not received so much attention. Indeed, it is not straightforward to build an experimental setup which allows the study of the steady dynamics of bulldozing granular material in a reproducible way. Moreover, the theoretical description of such flow remains complicated as the rheology of dense granular flow is difficult to capture and until quite recently there was no acceptable continuum model for a granular material [9]. In this project, we explore a problem of granular flow on a plane layer: the rotating bulldozing of a sandpile. Starting from an initial sandpile, we use a rotating blade to transport this sandpile and characterize the motion of the granular materials and the shape of the dune built against the blade. The use of a rotating blade instead of a straight blade with a rectilinear motion allows the system to be recirculated and thereby observing the dynamics over long times. In addition, the variation of speed along the blade potentially allows for richer dynamics. Therefore, the aim of this work is to provide the first experimental results with a rotating bulldozer and characterize the key features of the dynamics.