Effect of Long-Term Hydrocarbon Contamination on Physical Properties and Pore Size Distribution of Clay Soil

Due to their physicochemical properties different from water, petroleum hydrocarbons significantly change the geotechnical properties of cohesive and non-cohesive soils. Most of the studies have been performed for soils contaminated in laboratory under controlled conditions. In this study, undisturbed samples of soils contaminated in situ were tested. Soil samples were collected from the area that had been exposed to chronic contamination with petroleum fuels for about 30 years. Reference samples of uncontaminated soil were collected at a distance of about 30 m. Compared to uncontaminated soil, the contaminated samples showed lower natural moisture content and porosity, higher bulk density, redistribution of particle size content and reduction of plasticity. Mercury intrusion porosimetry confirmed the conclusions on the increase in soil porosity and revealed changes in pore size distribution. Analysis of the results indicated increase in coefficient of permeability and decrease in pores tortuosity. These studies provide valuable insight in properties of clay soils exposed to a long-term hydrocarbon contamination in natural conditions. The obtained results indicate substantial changes in geotechnical behavior and filtration conditions in contaminated soil.