The effect of various oil pollutants on the compressibility properties of clayey sand

Abstract:

Soil pollution by oil and its derivatives is a highly controversial environmental problem that also causes geological and geotechnical harm. The effect of oil pollutant type on geotechnical characteristics, especially soil compressibility, is an interesting topic neglected in previous studies, which needs further investigation. The results of research on this topic can be used in the compressibility analysis of structures built on soils likely to be contaminated with oil pollutants. Using a one-dimensional consolidation test, this study evaluated the compressibility properties of clayey sand contaminated with 3, 6, and 9% (dry weight of the soil) of four oil pollutants: used motor oil, crude oil, diesel, and kerosene. Scanning electron microscopy (SEM) was also employed to assess the microstructural interaction between the soil and the four oil pollutants. In addition to the low dielectric constant of oil pollutants, their high viscosity played a crucial role in altering the compressibility properties of clayey sand. The SEM micrographs confirmed that oil pollutants change the soil structure into a flocculated but dispersed one. The higher the viscosity of the oil pollutant, the larger the formed clots. Besides increasing the pore space between particles and facilitating the movement of water by covering the soil particles, oil pollutants reduced the soil's specific surface area (SSA) and water absorption by the soil particles. This caused the water to drain faster, ultimately increasing the compaction coefficient (CC), consolidation settlement, consolidation coefficient (CV), and permeability coefficient (k). The higher the viscosity of the oil contaminant, the higher the surface energy at the oil-water interface, which decreased water drainage. The highest compressibility belonged to the samples contaminated with kerosene, followed by those contaminated with diesel, crude oil, and used motor oil, respectively. Thus, in geotechnical plans, special attention should be paid to the settlement of clayey sand contaminated with kerosene.