Traduction technique français anglais de la thèse de doctorat de Bassels Seif El Dine intitulée « Etude du comportement mécanique de sols grossiers à matrice »
Université : École des ponts ParisTech (École nationale des ponts et chaussées)
Copyright : Bassels Seif El Dine 2010
French english scientific translation series : Phd thesis entitled : « A study of the mechanical behavior of matrix coarse-grained soils ».
Phd Student : Bassels Seif El Dine
University : École des ponts ParisTech (former : École nationale des ponts et chaussées), FRANCE
Chapter 1 : Bibliographic Elements (IV)
Table I.8 shows the results of the tests conducted by Valle  to study the effect of the gravel’s grain size using gravel from Criquebeuf-sur-Seine. This author used the following maximum diameters: 6.3, 12.5 and 25 mm. He conducted the tests on the large shear box with dimensions 500 x 500 x 300 mm. The spacing between the two semi-boxes that was adopted is dmax/2. Below are the results of Table I.8:
We can observe that the shear strength of the soil tends to increase with increasing grain size. Besides, cohesion increases while the angle of friction varies little (Figure I.29). These results show that the size of the box does influence shear strength.
However, Afriani  conducted several series of tests related to the effect of grain size using a large shear box on the natural material from Criquebeuf-sur-Seine. Maximum diameters used were 25, 50, and 80 mm and spacing between the 2 semi-boxes t = 12 mm (t > dmax/2). Afriani found that the values of cohesion c and angle of friction φ increase with the increase in the maximum diameter of the grains as shown in table I.9 below. Figure I.30 shows the variations of c and φ as a function of dmax.
Pedro  also conducted a study of the influence of gravel size on soil behavior using an average-sized triaxial device on soil mixtures with 20 and 35% gravel content (Fontainebleau sand matrix). He used relatively tight granulometric cuts: 4/5 mm, 8/10 mm and 16/20 mm. Figure I.31 shows that inclusion size does not influence the increase in shear strength.
Influence of granulometric spread on inclusions
In order to study the mechanical behavior of coarse-grained soils using classically sized laboratory devices, we are often lead to sieve or substitute a portion of the used soil (the largest particles: scale effect I.2.1.1). As such, it is important to study the effect of spread.
In general, we study this parameter by conducting tests in which volume fraction is kept constant while varying the granulometric spread of inclusions. This parameter is then directly linked to the uniformity coefficient CU of the granulometric curve of coarse-grained soils.
Research conducted by Torrey and Donagh  and Valle  showed that the angle of friction and shear strength increase with increasing dmax and CU. Figure I.32 shows that cohesion and angle of friction increase with increasing grain size. Torrey and Donagh  also concluded that the angle of friction increases with increasing uniformity coefficient CU (Figure I.33).
These authors used the reduction technique in their work. This technique is used to change the granulometric spread of coarse-grained soils but also results in a decrease of the volume fraction of inclusions. It is thus difficult to draw conclusions about the influence of this parameter based solely on these works.
Influence of the shape of inclusions
In order to study the influence of the shape of inclusions, we compare the mechanical characteristics of test tubes containing inclusions of various shapes. In general, we can distinguish between two types of inclusion shapes: round and angular. Several authors studied the influence of the shape of inclusions on the mechanical behavior of coarse-grained soils.
Yagiz  studied the influence of the shape of inclusions on shear strength of coarse-grained soils using a shear box with dimensions 65 x 65 x 38 mm. He chose gravel shapes that are either angular or round with a maximum grain size of 6.3 mm, a maximum grain size of sand grains of 0.4 mm, and a size ratio of 0.10. Figure I.34 below shows that gravel shape has little influence of the internal angle of friction.
Afriani conducted a series of shear tests on material that was reconstituted through removal and substitution from an original 0/50 mm natural soil sample extracted from Criquebeuf-sur-Seine (Figure I.35). Substitution was carried out using crushed 20/50 mm material extracted from Vignats (Figure I.36). These series of tests were conducted using a large shear box with dimensions 500x500x250 mm, 12 mm spacing, and by varying substitution ratios from 15% to 38%. The crushed material comes original from quartz solid rock.
Figure I.37 and table I.10 show that cohesion c and internal angle of friction φ increase with increasing proportions of Vignats material and consequently, with inclusion shape. This increase proportional to the percentage of Vignats material becomes very significant beyond 30% of incorporated crushed material.
Pedro  studied the influence of this parameter across small and large deformations. He conducted a series of triaxial tests with test tubes containing 20% of spherical shaped inclusions (glass balls (Figure I.38)) and other tests using angular inclusions (gravel (Figure I.39)).
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