Strona 2_redak - Instytut Agrofizyki im. Bohdana Dobrzańskiego ...

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same porosity need not have identical mechanical properties. The author distinguished
two elements of the packing structure: 1) spatial orientation of the long axes of nonspherical
granules (characterized by two parameters) and 2) packing density.
x
y
z
z
10%
10%
a) V - section b) H - section
Fig. 3.1. Distribution of density of probability of angle of inclination to horizontal line of long
axis of sand grains [129]
Figure 3.1 [127] presents the density distribution of probability of sand grains
long axis inclination angle. The sample was formed by pouring sand into a mould
filled with water, then compacted by tapping on the walls of the mould. V-section is
the vertical section and H-section is the horizontal section of the sample. In the vertical
section, the density of probability in the horizontal diretcion is considerably
higher, while in the horizontal section no distinct orientation of long axes of the
granules is observed. The manner of characterizing the geometric structure of
a granular material illustrated in figure 3.1 has been later frequently used by other
researchers, especially in the case of 2D models.
Konishi et al. [83] made an elasto-optical study of biaxial deformation of
2D systems of particles in the form of rods with oval cross-section. The authors
recorded force values at various strain stages while taking elasto-optical photographs.
They estimated the effect of anisotropy related to the sample forming
method, friction between the particles, and their form on the response of the
material to mechanical loading. They used particles with two section forms and
three size classes. The length ratio of the long to short axes of the elliptical
cross-section was 1.1 in the first group, and 1.4 in the second. The dimension of
the long axis of the cross-section ellipse in the first group was 14.8, 9.9 and 6.3 mm,
and in the second – 16.0, 10.7 and 7.1 mm. To examine the effect of interparticle
friction two series of measurements were performed; one with non-lubricated
particles with internal friction angle of 52° and another with particles lubricated with
talcum, for which the internal friction angle was 26°. Samples were poured into
a cubicoid mould with different angles θ of mould bottom inclination to the
horizontal. The sample, compressed horizontally with a constant force, had freedom
to deform vertically. Measurements included vertical loads as well as vertical and