- Three main mechanisms governing the behavior of a heap and its shape have been visualized: rolling on the heap surface, sliding on the base surface and sliding within the heap to fill air voids. It has been shown that as the friction force between the particles and the base surface reduces, the sliding on the base surface dominates the process. According to the experimental study carried out in this paper, the angle of repose varies within 5° as the heap is piled up on different surface, from very smooth to adhesive ones. The effect of the friction coefficient between the particles and the base surface on the angle of repose has been graphically correlated. Also, other effects such as heap size, particle size, particle density and vibrations on the angle of response have been studied.