Abstract
This paper is focused on analyzing the engineering properties and geotechnical changes of the soil contaminated by petroleum hydrocarbons, compared to non-contaminated soil. Also, identifying the physical and chemical behaviors and the interaction mechanisms between soil and contaminants at the time of contamination is far-reaching. This study aims to investigate the effects of petroleum contaminants on Atterberg limits, cation-exchange capacity, electrical conductivity and acidity, maximum dry density, and optimum moisture content of clay soil compared to non-contaminated samples with similar geological conditions in Gachsaran petroleum refinery region. The significant effects of contaminants on clay soil include an increase in cation-exchange capacity and electrical conductivity, but a decrease in acidity compared to non-contaminated samples. The results of the Atterberg limit as a physical index of the soil showed an increase in the petroleum hydrocarbon concentration, which enhanced the plastic and liquid limits, but decreased the plasticity index. The results of compaction tests using water and oil fluids indicated that the concentration of petroleum hydrocarbons in sandy soil increased maximum dry density and decreased optimum moisture content. Moreover, in a soil sample with stable pollution levels, maximum dry density and optimum moisture content were higher and lower in the compaction test using water fluid compared to those in compaction tests using oil fluid, respectively. Finally, increasing the soil pollution level reduced the difference between maximum dry density and the optimum moisture content in the compaction test using water fluid compared to the same test using oil fluid.
Highlights
The pollution of soil and underground water causes many environmental problems
Influenced by the amount of contamination in the soil, soil PH decreases with an increase in the number of pollutants, which can be due to the presence of organic compounds containing hydrogen that can be separated (Laurent et al, 2012)
Since some parts of soil particles are covered by oil, they do not let water molecules reach double layers; more water is needed for the soil to get to the plasticity
Summary
The pollution of soil and underground water causes many environmental problems. Among all the environmental pollutants, oil and petroleum hydrocarbons have been attracting more attention as global concerns. The leakage of petroleum compounds leads to soil contamination and physical and chemical transformations in the soil. This could happen due to the leakage of oil-transferring pipes, worn-out and old petroleum reservoirs, underground and sea oil transmission systems, natural leakages, as well as oil well fires. There are different methods for the removal of the contaminants from soil. To achieve an accurate and adequate design, it is necessary to examine different soils and oil pollutants to minimize the probable expenses and damages caused by the geotechnical risks of petroleum contaminated soils. Few studies have been conducted to investigate the physical and chemical characteristics of oil-contaminated soils under natural conditions
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