From Particle to Material Behavior: the Paths Chartered by Jean Biarez - Multiscale Geomechanics: From Soil to Engineering Projects - page 28

In particular, experimental studies conducted by Biarez and his students [BIA 97,
KIM 95] showed the influence of particle size distribution on the rate of breakages:
subjected to the same loading, a sample of crushed granite with a broadly graded
particle size distribution produces less breakage than a sample made from the same
material but with a narrowly graded particle size distribution (see Figure 2.15).
These same studies also highlighted the role of the loading path: for the same
particle size distribution and the same confining stress, the particles in the sample
will break into a greater quantity if subjected to triaxial rather than isotropic
compression or an oedometer test.
Due to the numerical simulation by DEM, breakable particles can also be
modeled. For example, if PFC software is used [ITA 02], we can create an aggregate
(called a cluster ) consisting of several spheres (or disks in two-dimensions),
according to a chosen geometry (elongated, with a surface more or less rough, with
growths more or less pronounced, etc.) linked by bonds that break when the tensile
force reaches a certain limit.
Attempting to simulate the behavior of dams that could take into account the
breakage of blocks, Deluzarche used this model by considering breakable clusters
[DEL 04, DEL 05]. In his study, he used a bond strength that was dependent on the
size of the blocks, according to the results obtained by [MAR 73]. His numerical
simulations of biaxial tests on samples with particle size distributions, either
narrowly or broadly graded, led to the same result as the tests of [KIM 95], see
Figure 2.16.
The explanation for this phenomenon is related to the transmission of forces
through force chains and to the number of contacts per particle, easily
measurable parameters in a discrete element simulation. Indeed, in a sample with a
narrowly graded particle size distribution, the coordination number is generally low
and all the particles have roughly the same number of contacts. The larger particles
that are less resistant because they have more defects will thus break into greater
quantities.
On the other hand, in a broadly graded sample, the coordination number is higher
(the particles have more points of contact on average) because the largest particles
may have a large number of contacts.