  Experimental data from axially symmetric compression test at constant mean
pressure p on kaolinite clay are used to study the validity of an "isotropic"
modelling as a function of the overconsolidation ratio (OCR).The isotropic
assumption is found to be quite good for 2<OCR<3 and/or in the range of small
deformation for OCR>4. For very large OCR (OCR >10), anisotropic response is
observed at few percents of axial deformation. Relation with anisotropic
distribution of local forces is made. Pacs # : 5.40 ; 45.70 ; 62.20 ; 83.70.Fn
