Heap formation in two-dimensional granular media

Using molecular dynamics (MD) simulations, we find the formation of a heap in a system of granular particles contained in a box with oscillating bottom and sidewalls. The simulation includes the effect of static friction, which is found to be crucial in maintaining a stable heap. We also find another mechanism for heap formation in systems under constant vertical shear. In both systems, heaps are formed due to a net downward shear by the sidewalls. We discuss the origin of net downward shear for the vibration-induced heap.