# Geotechnical Evaluation of Diesel Contaminated Clayey Soil
## 1 Introduction
These authors reported that contaminated soils with a water content of 5% had higher electrical resistivities and decreased permittivity compared to uncontaminated soils. In contrast, contaminated soils having a water content of 15% showed smaller resistivities and higher permittivity compared to non-contaminated soils. It has been reported that soil contamination affects its consistency limits. [PERSON] et al. [12] reported that the plastic limit of a crude-oil-contaminated soil increased as the contaminant concentration increased, but the plastic index decreased as the contaminant concentration increased. [PERSON] and [PERSON] [7] found that the liquid limit of a gasoline-contaminated soil increased, reaching maximum value at a contaminant concentration of 6%. Although a further increase of gasoline concentration reduced the liquid limit of the soil, it was higher than the one obtained for the natural soil. [PERSON] et al. [12] reported that swelling pressure of natural soil was higher than that of contaminated soil. However, for 12% oil content, the contaminated soil had a higher free swell percentage than the natural soil. Other researchers have studied the effects of diesel [5], oil [13], gasoline [6], and crude oil [12] on the shear resistance of different clay soils, finding that soils' cohesions tended to decrease as the contaminant concentration increased. However, while in some cases, the internal friction angle was reported to increase as the contaminant concentration increased [5; 6], in other cases, a reduction of its value was reported as the contaminant concentration increased [7; 12; 13]. These results may mean that clay minerals exhibit different behaviors according to the hydrocarbon used to contaminate the soil. [PERSON] and [PERSON] [7] showed that the settlement and ductility of a gasoline-contaminated soil increased as the contaminant concentration increased. They also found that the soil failure mechanisms changed depending on the contaminant concentration in the soil. [PERSON] et al. [9] studied the effects of soil contamination in a soil that was simultaneously contaminated with lead and diesel. These authors found that the increase in diesel concentration reduced the hydraulic conductivity of the contaminated soil. Suchdecrease was because diesel occupied the pore spaces and limited the water flow through the soil samples. [PERSON] et al. (2012) found that the settlement of the contaminated soil increased as the crude oil concentration increased because the contaminant reduced the specific surface area of the soil, decreasing the water absorption of the particles of the soil facilitating the water drainage. Although many efforts had been carried out to study the effects of diesel contamination on the geotechnical properties of soils, most of the studies had focused on saturated soil conditions. As a result, the available information about the effect of diesel contamination on unsaturated soils is scarce. Moreover, to the widest knowledge of the authors, there is no available information about the maximum diesel retention that natural soil can have and its effect on the geotechnical behavior of the soil. Thus, the objective of this study was to determine the maximum diesel retention by an unsaturated clayey soil, and to evaluate the impact of diesel contamination on its geotechnical properties. The test performed in both natural and contaminated soil conditions showed that although the soil could not retain more diesel, its saturation rate did not exceed 80%. Furthermore, the changes in the geotechnical properties of the contaminated soil promoted an increase in its shear strength resistance. Such difference was due to an increase in the osmotic suction in the contaminated soil.