# Geotechnical Evaluation of Diesel Contaminated Clayey Soil
## 1 Introduction  
Hydrocarbons are the main energy source used to satisfy our energy needs, but during their life cycle, they can produce many environmental impacts. Hydrocarbon leaks/spills, which can occur from its exploitation to use, cause environmental pollution, where, commonly, the first receptor is the soil. Soil contamination by hydrocarbons can be originated by accidental spills during its transportation and disposal, leakage of storage tanks and pipes, and/or by clandestine fuel intakes. The unsaturated (aerated) zone of the soil, that is, the area in which the infrastructure's foundations are frequently laid, is the first one to be contaminated by hydrocarbon leaks and/or spills. It is also possible that hydrocarbons permeate through the soil up to the groundwater level zone, contaminating the saturated zone of soil. Therefore, hydrocarbon leaks and spills can affect the deep foundations located on it as well as it can contaminate groundwater. In this case, the hydrocarbons can be transported by the groundwater to the surrounding areas contaminating the soil and may affect the foundations located in such areas. The permanence of hydrocarbons in the unsaturated zone depends on different factors, such as the solubility, volatility, toxicity, biodegradation rate, and sorption of the hydrocarbons; the nature and permeability of the soil or soils forming the unsaturated zone; and the natural or man-made liquid flow (water and/or contaminants). Unfortunately, soil contamination by different hydrocarbons has rapidly expanded worldwide, surpassing, in many cases, the self-purification capacity of soils. As a result, the number of hydrocarbon-contaminated sites has increased in both developed and developing countries, latter being the more affected ones. Soil is the most frequent source of risk to construction projects [1] due to not only the geotechnical or geological aspects but also the contaminants present in it. Nevertheless, there is still limited available information about the impact of hydrocarbons contamination on the geotechnical properties of the soils. Some of the risks associated with soil contamination are loss of foundation and structural integrity, damage to construction materials, and loss of facility [1]. Independent from the time the soil gets polluted--before or after the infrastructure construction--the changes caused in its engineering properties can place both the integrity of the structures and its users at risk. It is known that soil contamination by hydrocarbons affects its engineering properties. However, such an effect depends on many variables, such as the type of soil and the physical and chemical properties of the spilled/leaked hydrocarbon [2; 3; 4]. Published papers have been focused on the effect of diesel contamination on the geotechnical properties of soil by varying the contaminant concentration from 0% to 20% (weight basis) [5; 6; 7; 8; 9]. However, none of them has been focused on the quantity of diesel that soil is capable to retain. This can have important repercussions since the exceeding hydrocarbons can be subjected to evaporation or transportation depending on the type of hydrocarbon and the local environmental conditions. Nevertheless, the retained hydrocarbons can have a major influence on the geotechnical behavior of the contaminated soil. [PERSON] and [PERSON] [10] reported that after contaminating a clay sample with diesel, clay particles showed a change in their microstructure, resulting in a denser structure due to change in the pore size distribution. [PERSON] [4] studied the effects of used motor oil on the properties of lateritic soil and found a reduction in the amount of fine-grained size particles of the soil as the concentration of the contaminant was increased from 0% to 8%. [PERSON] et al. [11] estimated the effect of diesel contamination on the electrical properties of unsaturated soils.