# Geotechnical Evaluation of Diesel Contaminated Clayey Soil
## 3 Results and Discussion  
### Diesel Retention in the Contaminated Soil  
At 4% diesel concentration, the natural soil readily absorbed the contaminant (Figure 1b). In contrast, at 14% diesel concentration, the soil could not retain the contaminant at all (Figure 1c). After analyzing the contaminated soil, it was found that the soil retained only 12.62% \(\pm\) 0.27% of diesel. Figure 1: Evolution of soil aspects as diesel concentration increased from: **(a)** natural soil, **(b)** 4% added diesel, and (c) 14% added diesel. Clay fractions of soil can adsorb non-polar molecules--such as diesel--due to the van der Waals attraction forces [30]. Such attraction forces between particles rapidly decay with the surface-to-surface distance (varying inversely as the seventh power of distance between the plates). However, attractive forces are additive. So, van der Waals attraction forces can be calculated by adding the attractions among all the particles. This may result in a higher total force and a lower decay (varying inversely as the third power of distance between the plates) with the surface-to-surface distance [30]. Nonetheless, [PERSON] and [PERSON] [31] found that van der Waals attraction forces get reduced when fluid other than water fills the medium between the attracted particles. Further, [PERSON] and [PERSON] [32] showed that organic compounds that are not potent wetting agents have lower sorption capacity on polar mineral surfaces [32]. Hence, this makes water a stronger opponent to displace non-ionic organic solutes from minerals in aqueous systems. In the absence of water, clay particles can behave as conventional organic compound absorbers, its large surface area being the main contributor to its high absorptive capacity [33]. However, in the presence of water, the absorption of non-polar hydrocarbons can be suppressed since non-polar organic molecules are not solid competitors for adsorption sites on the clay surface compared to highly polar water [30]. Thus, in the present study, since the soil was contaminated at its natural water content, diesel adsorption by the soil minerals was limited to those places where soil absorption sites were available. This means that soil could only retain the required diesel to satisfy its hydration needs. Diesel is a non-polar mixture of aromatic (including naphthalene) and saturated (including isoparaffins and cycloparaffins) hydrocarbons obtained from petroleum. Diesel hydrocarbons have carbon numbers in the range of C9-C28 with high boiling points between 170 and 430 \({}^{\circ}\)C. As previously stated, the term \"water content\" was transformed to \"liquids content\" to consider the difference in specific gravity between diesel and water [17]. Thus, Equation (2) was used to consider the contribution of the liquid's specific gravity on the liquids content of the soil [17]. \[E_{\text{{nrc}}}=l_{c}\left(\frac{c+1}{c+G_{f}}\right), \tag{2}\]  
where \(E_{\text{{nrc}}}\) is the equivalent water content, \(l_{c}\) corresponds to the liquid content, \(c\) is the water to diesel volume ratio in the pore's liquid, and \(G_{f}\) is the specific gravity of diesel. It must be mentioned that in Equation (2), for water that has not been mixed with any contaminant, \(c=0\). Table 3 presents the impact on the \(E_{\text{{nrc}}}\) and the saturation rate (\(s_{r}\)) of the soil due to its contamination. Diesel contamination increased the \(E_{\text{{nrc}}}\) and the \(s_{r}\) of the contaminated soil by 18% and 12%, respectively, compared to the natural soil. Such an increase in both parameters influences the engineering behavior of the contaminated soil. It can even make it complicated to directly compare the results obtained by both soil conditions.