Abstract
The soil structure can be described as an assembly of elements of various sizes separated by a complex system of cracks and fractures, since the grains of the soil are differentiated by their shape, size and orientation. They are thus differently associated and related, their masses can form complex and irregular configurations which are in general extremely difficult to characterize in exact geometric terms. To understand the mechanical behavior of granular materials, it is then necessary to characterize the grains using the fractal dimension which is a characteristic that indicates the degree of irregularity and fragmentation of the latter.
 This experimental work consists in studying the influence of the parameters variation: granular class, grain size and normal stress applied during Casagrande's direct shear tests on the roughness fractal dimension calculated with the method of Box counting. The analysis of the results obtained at the end of a granulometric variation which caused a variation of the fractal dimension of grain roughness. This variation made it possible to analyze the level of fragmentation suffered by the sandstone grains during the various shear tests. This fragmentation produces fines that are the source of variations in the mechanical properties of the sandstone material.
Highlights
The behavior of granulate material is influenced by several parameters such as: granulometry, the size and shape of the grains, their hardness and applied stress, etc
The samples are subjected, in the dry state, to the direct shear tests at the Casagrande box, applying three shear stresses 100 kPa, 300 kPa and 400 kPa (AFNOR, 1994), these tests show that relative displacements occur between the grains, which result in friction at the points of contact and engender their crushing (Figure 7)
The box counting method gives the fractal dimension of roughness DF which indicates the degree of roughness with respect to a given grain sample
Summary
The behavior of granulate material is influenced by several parameters such as: granulometry, the size and shape of the grains, their hardness and applied stress, etc. Its calculation is a theoretical tool for interpreting problems from the dimensions of the physical quantities involved. It has been used among others in the field of civil engineering. It describes well the irregularity of a grain of the granular material. The most used techniques are the new theories of image analysis that are important after photographing the grains (Sezer & al., 2008). They make it possible to quantify and study the crushing variation of the grains of the different granular classes studied by varying several parameters
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