p=constant compression on loose Hostun sand: The case of an anisotropic response

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