  Compacted unbound granular materials are extensively used as sub-layer in
pavement design. Most pavement design guides assume that they are responsible
for the degradation and deformation of the roads and railways that they
support. Biaxial tests are usually employed to investigate the elasto-plastic
response of these materials to cyclic loading. A particularly interesting
question is whether a limit load exists, below which the excitations shake
down, in the sense that the material does not accumulate further deformations.
We have carried out a detailed study of the elasto-plastic behavior of a simple
model of unbound granular matter submitted to cyclic loading. The dissipated
energy through out the simulation has been used for the characterization of the
different regimes of responses.
