In this paper, coarse soils are modeled by granular packings, because both of them have similar characteristics, such as: gaseousity, duality, dilatancy, fragility and hyperbolicity. By virtue of these properties, it is assumed that the contact force ensemble remains the same, while the packing changes because of its dual character, regarding the compactness of the soil. For the dense state, both assemblages coincide themselves, forming chains of contact forces; the transmission of stresses obeys the Trollope's hypothesis of centroidal reactions; and the volumetric strain increases. For the loose state, the packing adopts a "passive" distribution, yielding a constant angle of internal friction at failure; so that, the strain is contractive and the stress transmission occurs fundamentally by shear, in a similar fashion to the Rowe's mechanism. In the figures, the good correspondence between the results of the theory and the reported experimental data is shown.