  Experimental data from axially symmetric compression test at constant mean
pressure p on Hostun sand from Flavigny experiments on loose sands are used to
study the validity of an "isotropic" modelling at different densities . It is
found that the material response is not isotropic even at small deviatoric
stress. As an "isotropic" behaviour is found for compression test at constant
volume on the same sand, this new result questions the unicity of the
trajectory in the classical phase space of soil mechanics (q,p,v), with q being
thed deviatoric stress, v the specific volume. This asks whether the space
shall be taken larger than 3d or not. Pacs # : 5.40 ; 45.70 ; 62.20 ; 83.70.Fn
