  We investigate the structure and distribution of arches formed by spherical,
hard particles shaken in an external field after they come to rest. Arches (or
bridges) are formed during a computer-simulated, non-sequential deposition of
the spheres after each shaking cycle. We identify these arches by means of a
connectivity criterion and study their structural characteristics and spatial
distribution. We find that neither the size distribution nor the shape of the
arches is strongly affected by the packing fraction of the deposit. Conversely,
the spatial distribution and orientation of the bridges do depend on the volume
fraction occupied by the spheres.
