  By means of contact dynamics simulations, we investigate a dense packing
composed of polyhedral particles under quasistatic shearing. The effect of
particle shape is analyzed by comparing the polyhedra packing with a packing of
similar characteristics except for the spherical shape of the particles. The
polyhedra packing shows higher shear stress and dilatancy but similar
stress-dilatancy relation compared to the sphere packing. A harmonic
approximation of granular fabric is presented in terms of branch vectors
(connecting particle centers) and contact force components along and
perpendicular to the branch vectors. It is found that the origin of enhanced
shear strength of the polyhedra packing lies in its higher force anisotropy
with respect to the sphere packing which has a higher fabric anisotropy.
Various contact types (face-vertex, face-face, etc) contribute differently to
force transmission and fabric anisotropy. In particular, most face-face
contacts belong to strong force chains along the major principal stress
direction whereas vertex-face contacts are correlated with weak forces and
oriented on average along the minor principal stress direction in steady
shearing.
