  By means of tree-dimensional contact dynamics simulations, we analyze the
vibrational dynamics of a confined granular layer in response to harmonic
forcing. The sample is composed of polyedric grains with a shape derived from
digitalized ballast. The system involves a jammed state separating passive
(loading) and active (unloading) states. We show that an approximate expression
of the packing resistance force as a function of the displacement of the free
retaining wall from the jamming position provides a good description of the
dynamics. We study in detail the scaling of displacements and velocities with
loading parameters. In particular, we find that, for a wide range of
frequencies, the data collapse by scaling the displacements with the inverse
square of frequency, the inverse of the force amplitude and the square of
gravity. We show that the mean compaction rate increases linearly with
frequency up to a characteristic frequency of 10 Hz and then it declines in
inverse proportion to frequency.
