Effect of Grain Geometry on Angle of Repose and Dynamics
  With simulation and experiment we examine the effect of grain anisotropy on the angle of repose in a two-dimensional geometry. We find that the structure of the granular packing can be directly controlled by changing the aspect ratio of the grains, and that the specific type of order strongly affects the angle of repose and the resulting dynamics. The angle of repose is largest for dimer grains, and is smaller for both monomer and trimer grains. The motion of a collapsing grain heap consists of large scale collective shear when monomer grains are considered, but occurs via tumbling of grains on the surface for dimers, and via disorderly bulk tumbling for trimer grains. 
C.J. Olson, C. Reichhardt, M. McCloskey, and R.J. Zieve