The Influence of Oil Pollutants on the Mechanical Properties of Clayey Sand

Oil pollutants affect the mechanical properties of soils differently. The effect of the kind of oil pollutants on the geotechnical characteristics of a type of soil is an interesting subject that has been examined less in previous studies. The results of this research can be used in designing structures built on soils that are likely to be contaminated with oil pollutants. This study comprehensively investigated the effect of the type of pollutants on the mechanical properties of sandy clay soil to provide the necessary parameters in the remediation plan for soils contaminated with various oil pollutants. A series of laboratory tests, including pH, standard compaction, one-dimensional consolidation, unconfined compressive strength (UCS), ultrasonic pulse velocity (UPV), falling head permeability, and direct shear, was conducted on the clean and polluted samples. Scanning electron microscopy (SEM) micrographs confirmed that oil pollutants change the soil structure into a flocculated but dispersed one. In addition to the low dielectric constant of oil pollutants, their high viscosity played an important role in altering the geotechnical parameters of clayey sand. The higher the viscosity of the oil pollutant, the higher the maximum dry density (MDD), cohesion coefficient, compression index (Cc), swelling index (Cs), and permeability coefficient of oil-polluted soil. The samples polluted with used motor oil and crude oil, due to their high viscosity, had the greatest drop in compressive strength and shear strength, respectively; whereas the kerosene-polluted sample, due to its low viscosity compared to other oil pollutants, had the greatest rise in compressibility. Thus, in geotechnical plans, special attention should be paid to the bearing capacity and settlement of clayey sand contaminated with crude oil and kerosene, respectively.