# Sandy Loam Soil Shear Strength Parameters and Its Colour
## 4 Shear Cohesion and Internal Friction Angle of Sandy Loam Soil Results Analysis  
The cohesion (physical cohesion) resulting from the bonding between similar atoms reflects how these particles are bonded to each other and, thus, is a step for understanding the behaviour of the soil.  
As mentioned in the introduction, even though shear cohesion is different from soil physical cohesion, these two terms are related. The soil cohesion forms initial stress acting as compressive stress to the shear cohesion [1].  
Based on the obtained results of the tested soil type, as the moisture content increases, the shear cohesion increases to a value around 21 kPa and remains approximately constant in the moisture content range from 6% to 9%, and, beyond this point, the shear cohesion increases with the increase in the moisture content, reaching a maximum point (breaking point) of a value 27.17 kPa at 11.25% moisture content. Beyond the breaking point, as the moisture increases, the shear cohesion decreases to a low value, reaching 12.72 kPa at 15.25%. The shear cohesion results are shown in Figure 5.  
For loam soils, cohesion decreases with the increase in the moisture content (this can be recognised in Figure 5 at the high moisture values) and, inversely, the cohesion in sandy and clayey soils increases with increasing moisture [18].  
Figure 4: (**a–h**) Sandy loam soil Mohr–Coulomb diagrams at different moisture contents.  
The interaction between the soil particles leads to friction between them, and this friction acts as a resistance to the shearing load. The shear strength based on the Coulomb equation consists of two values, the first of which is the shear cohesion (\(C\)) and the second value resulting from the product of the internal friction coefficient (\(\upmu\)) and the applied normal stress.  
\[\tau=C+\sigma\tan\Phi \tag{1}\]  
where:  
\(C\) (kPa) is the shear cohesion;  
\(\sigma\) (kPa) is the normal stress applied on the soil (consolidation load divided by the area);  
\(\phi\) (degree) is the internal friction angle (\(\tan(\phi)\), which is equal to \(\upmu\); it is the friction coefficient and it indicates the slope of the line).  
The increase in the applied normal load increases the compaction of the soil, thus increasing the density (density increases to a limit due to the decrease in the voids), which leads to the increase in the particle interaction. When there is not normal stress applied to the soil, the internal friction will not influence the shear strength of the soil (its influence is neglected).  
The internal friction angle results of the sandy loam soil show that, at ambient conditions (no water added; moisture in the soil is due to humidity), the internal friction angle of the soil is the highest, with a value of 31.15 degrees, and, with the increase in the moisture content, the internal friction decreases to a value of 24.87 at 9.6%. Beyond the 9.6% moisture, the results remain approximately constant with the increase in the moisture content till reaching 12.65% (the results are decreasing but at a slow rate; thus, they are considered constant). Beyond 12.65% moisture content, with the increase in the moisture, the internal friction angle continues to decrease, reaching 17.04 degrees at 15.25%. The internal friction angle results are shown in Figure 6. Low moisture content means high soil friction, and the high moisture content decreases the soil friction [18].  
Figure 5: Sandy loam soil shear cohesion at different moisture contents.