## 4 Results and Discussion
### SEM Analysis  
SEM is a technique that provides many magnified images and explains differences that soil enhancement produces in physical, chemical, and mechanical behavior, including shape, size, composition, and crystallography properties [46]. SEM was used in this study to investigate the microstructure particles for the natural, contaminated, and treated soils, in order to detect the structure of the bonding between sand particles in the previous cases.  
Figures 6(a)-d and 6(a)-d illustrate the geometric arrangement for the natural, contaminated, and treated soils, respectively. In natural soil fabric, the diameter in the singular grains can be observed. However, it is not possible to distinguish individual floccules in these micrographs, as indicated in Figure 6(a). Subsequently, the morphological shape of the natural soil, as shown in Figure 7(a), indicated the appearance of burrs in the soil grains, confirming its non-coated properties.  
Crude oil firmly coated the singular soil particles via hydrogen bonding and van der Waals forces. As a result, it was shown in the form of a dense-packed structure with almost no visible voids, as shown in Figure 6(b), since the lining oils created a water-resistant layer that blocked the voids, causing a reduction in permeability. Moreover, in the photomicrograph of Figure 7(b), the surface of the contaminated soil appeared as one flock with no distinct pore spaces, indicating that it was filled with oil.  
Figure 6(c) illustrates a significant improvement in the soil treatment with CEM II. The similarity of the microscopic surface of the treated soil to the natural soil was obvious, in addition to agglomerated morphology of the soil sample. The change in color from dark to light in the samples signifies that the crude oil was removed from the soil in a satisfactory proportion. These results are in agreement with the chemical results shown in Table 7, which indicate a decline in total organic carbon from 11.7% to 0.8% and in oil and grease from 14% to 0.96%, simultaneously, which is a significant performance. However, the structural features for the soil sample in Figure 7(c) showed a small proportion of oil covering some of the grains with the presence of apparent voids in the surface element.  
In comparison, no considerable improvement was noticed in the soil that was stabilized with OPC, as shown in Figure 6(d), compared to CEM II. The microscopic surface of the treated soil was more similar to the contaminated soil than it was to the natural soil. The crude oil still coats the soil particles. If we combine the impact of the oil and cement, the influence of oil is still dominant. This result is consistent with the chemical results; soil treated with OPC had 8.2% total organic carbon and 9.8% oil and grease. Although the soil grains became aggregated, they were formed in the shape of flocks coated with oil, as shown in the microscopic image in Figure 7(c).  
Figure 6: Stress versus vertical displacement for (a) un-soaked and (b) soaked samples.  
Figure 8: _Cont._  
Figure 7: SEM photograph of 200 nm: (**a**) natural soil; (**b**) contaminated soil; (**c**) soil stabilized with CEM II; and (**d**) soil stabilized with OPC.