2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/26632Experimental data from axially symmetric compression test at constant mean pressure p on Hostun sand from Bouvard experiments are used to study the validity of an "isotropic" modelling as a function of the density .The isotropic assumption is found to be quite good for loose samples and/or in the range of large pressure. For smaller mean pressure, anisotropic response is observed at few percents of axial deformation. Relation with anisotropic distribution of local force is made. Pacs # : 5.40 ; 45.70 ; 62.20 ; 83.70.Fn6 pages + 1 page, 1 figureSoft Condensed Mattertext