The ballast module is a magnitude associated with the rigidity of the ground.[1]​ Its practical interest is found above all in civil engineering since it allows us to know the settlement of a building on the ground, as well as the distribution of forces in certain foundation elements. It is measured by applying a vertical load to a surface and measuring the subsidence or displacement from the applied load.

Where:.

Obviously the previous definition is only valid for a certain range of pressures, since once creep or plasticity phenomena appear, the force is no longer proportional to the subsidence and therefore the force-subsidence relationship is not a linear relationship and it does not make sense to speak of a constant module.