Experimental study of heaping in a two-dimensional ‘‘sand pile’’

In connection with recent vibrationally excited sand-heaping observations we performed a series of experiments dealing with 2D compact triangular packings of monodisperse metallic beads under vibration. We report for the first time the observation of spontaneous heaping and associated convections for this system. We establish the mechanical conditions leading to this phenomenon and the domain of occurrence. We identify the microscopical mechanism to be a block-slip motion generated by the walls and we show that the heaping dynamics obeys a ln(t) law.