From Particle to Material Behavior: the Paths Chartered by Jean Biarez - Multiscale Geomechanics: From Soil to Engineering Projects - page 18

Biarez understood that this description of the geometric anisotropy of the
granular assembly allowed not only the initial anisotropy to be characterized (due to
the preparation of the sample or to the natural consolidation of the soil layer in the
gravity field), but also the induced anisotropy (due to an anisotropic loading path) to
be explained. Anisotropy in a granular material can be detected from an analysis of
mechanical behavior or from geometric measurement, as defined above. Thus Figure
2.4 below shows, first, the mechanical demonstration of the anisotropic behavior of
a sand sample (Figure 2.4a) when it was first subjected to triaxial compression and,
second, the evolution of geometrical anisotropy in an analogical assembly composed
of Schneebeli rolls as the sample was made to undergo deformations (Figure 2.4b).

(a) (b)

Figure 2.4. Effect of anisotropy for granular materials in Jean Biarez's thesis [BIA 62]:
(a) Cycles with uniform pressure after a deviatoric strain Δ H/H=1.2%: macroscopic
mechanical response; and (b) measurement of tangent plane orientations in
cylindrical rods assemblies with respect to deformations

The use of software based on the DEM has allowed us to analyze more
accurately the relationship between changes in the geometric anisotropy and the
mechanical behavior of numerical granular samples. For instance, the results of
numerical simulations of biaxial tests, performed with software based on the contact
dynamics method [JEA 95, MOR 94] on samples whose particles are polygonal
[NOU 03, NOU 05] showed that: