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

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(β = 0 o ), positioning the outlet hole of the funnel along the sample axis of symmetry
and not close to the mould wall as before. Every time the same quantity of grain
filled the whole volume of the mould, therefore every time the same density of the
medium was obtained.
To estimate the degree of arrangement of the long axes of the grains, the
samples prepared according to the method described above were flooded with
polyester resin. Once the resin was set, the samples were cut along horizontal and
vertical planes. The sections obtained were used to determine the measure of grain
arrangement after [129], in accordance with the formula:
preferred angle of inclination of long axes of grains with relation to chosen
system of coordinates:
⎛
⎜
1
θ = arctg
⎜
2 ⎜
⎜
⎝
n
∑
i=1
n
∑
i=1
⎞
sin2θi
⎟
⎟
, (3.3)
⎟
cos2θi
⎟
⎠
intensity of parallel orientation of the long axes
V ⋅ M =
⎛
⎜
⎝
n
∑
i=1
2
⎞ ⎛
sin 2θi⎟
+ ⎜
⎠ ⎝
n
∑
i=1
2
⎞
cos 2θi⎟
⎠
100
⋅ ,
n
(3.4)
where:
n – number of measurements,
θ i – the angle of inclination of the long axis of a given grain with relation to the
adopted system of reference.
The value of the expression V·M varies within the range from 0 to 100%. The
value of 0% corresponds to totally random orientation of the long axes of the grains,
while 100% represents ideally parallel orientation of the long axes of the grains. For
angle β = 20 o and for the vertical sample section, the measures had values of θ = 38 o ,
V·M = 65%, respectively, and therefore the sample was characterized by considerable
anisotropy.
The effect of spatial orientation of grains of three cereals and of rape on the
angle of internal friction was examined with the triaxial compression method and
with the direct shear method. The methods were chosen due to their popularity in
experimental studies on the mechanics of granular materials. It was assumed that