# Geotechnical Evaluation of Diesel Contaminated Clayey Soil
## 2 Materials and Methods  
### Experimental Procedure  
The experiment was performed in two phases: natural soil characterization and soil contamination and characterization. In the first phase, the extraction of disturbed natural (uncontaminated) soil samples from a place in the north of Queretaro City, Mexico, was done. An undisturbed cubic soil sample was extracted to evaluate the natural soil's water content and volumetric unit weight. All soil samples were stored in a controlled temperature chamber (20 \(\pm\) 1 \({}^{\circ}\)C) until its use for geotechnical characterization.  
All the disturbed soil samples were mixed into the controlled temperature chamber to obtain a uniform mass of soil to perform the remaining geotechnical tests. This soil mass was divided into subsamples, poured into hermetically sealed containers, and stored in the same chamber. The soil sample quantity that is required for each test could now be taken with ease, avoiding opening and manipulating the whole soil sample every time a quantity of soil was needed for analysis.  
The tests were performed according to the methods described in the Test Methods section. The unit weight of the natural soil was \(\gamma_{m}=15.10\) kN/m\({}^{3}\)\(\pm\) 0.10 kN/m\({}^{3}\), and its water content was \(w=36.94\%\)\(\pm\) 0.19%; this corresponded to an average saturation rate of \(s_{r}=70.82\%\)\(\pm\) 0.18%. After finished the natural soil characterization, the soil contamination process was started.  
In the second phase of this work, the remaining soil sample was contaminated with diesel for its geotechnical characterization. Table 1 shows the characteristics of the commercially available diesel used to contaminate the soil. To define the quantity of diesel needed for soil contamination, a 50-g natural soil sample was placed in a sealed glass container. Then, this soil subsample was contaminated with diesel, at an initial concentration of 4% by weight, and stored for seven days in the temperature-controlled room.  
During this curing period, the contaminant could distribute throughout the soil and react with the pore fluid to achieve ionic stability ([PERSON], 2012). After the curing period, the sample was visually inspected to verify if the soil could retain the added diesel. This process was repeated by increasing the diesel concentration (i.e., 4%, 8%, 12%, and 14%) until the soil could not retain more diesel.  
When the soil could not retain more diesel, it was transferred to a smaller glass container to allow the soil to drain the exceeding contaminant. Then, a contaminated soil subsample was taken from the top of the container to determine the retained diesel concentration by a gravimetric method [15]. The retained diesel concentration was 12.62% \(\pm\) 0.27%. Therefore, such a concentration of diesel was used to contaminate the natural soil to be used during this second phase.  
Once the diesel concentration to contaminate the soil was defined, the following procedure was applied. First, the remaining natural soil was air-dried to reduce its water content. This was done because in the previous experiment, a considerable increase in the liquids content of the contaminated soil was noticed (see Section 3.1). Then, the soil was placed in a container to mix it manually with diesel to simulate the long-term contamination effect [16].  
Next, the contaminated soil was poured into hermetically sealed containers and stored in the temperature-controlled room for six weeks. After this curing period, the contaminated soil was tested as indicated in the Test Methods section.  
The selected contamination procedure is an alternative way to reduce the sample preparation time [16]. It also allows the contaminant to bring about a long-term change in the initial soil structure [16]. Although a curing time of seven days is enough to allow the soil to react with the contaminant [2], the curing period was extended to six weeks to enhance the long-term contamination effect.