  Particle shape is a key to the space-filling and strength properties of
granular matter. We consider a shape parameter $\eta$ describing the degree of
distortion from a perfectly spherical shape. Encompassing most specific shape
characteristics such as elongation, angularity and nonconvexity, $\eta$ is a
low-order but generic parameter that we used in a numerical benchmark test for
a systematic investigation of shape-dependence in sheared granular packings
composed of particles of different shapes. We find that the shear strength is
an increasing function of $\eta$ with nearly the same trend for all shapes, the
differences appearing thus to be of second order compared to $\eta$. We also
observe a nontrivial behavior of packing fraction which, for all our simulated
shapes, increases with $\eta$ from the random close packing fraction for disks,
reaches a peak considerably higher than that for disks, and subsequently
declines as $\eta$ is further increased. These findings suggest that a
low-order description of particle shape accounts for the principal trends of
packing fraction and shear strength. Hence, the effect of second-order shape
parameters may be investigated by considering different shapes at the same
level of $\eta$.
