Experimental
Test of the "Isotropic"
Approximation for Granular Materials using p=constant Compression

** **

**Abstract: **Experimental data from axially symmetric
compression test at constant mean pressure p=(s_{1}+s_{2}+s_{3})/3 on
Hostun sand from Bouvard experiments are used to study the validity of an
"isotropic" modelling as a function of 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.Fn

*poudres &
grains* **12** (1), 11-16 (février 2001)