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The extraction of crude oil worldwide is estimated to be about 4 billion tons annually, 10% of which leaks into the environment. Iran is in great risk of pollution because of the extensive natural oil reservoirs and the spread of the oil industry. During the past 10–15 years soil washing methods have gathered much attention due to their rapid and easy implementation and high clean up efficiencies in removing organic contaminants from polluted soils. This paper investigates the effects of soil washing at various temperatures and pH levels of the washing solutions on the removal of gasoline constituents from contaminated soils. Aliphatic and aromatic fractions of gasoline were studied for this purpose. Raw soil samples were spiked with gasoline for soil washing tests. Sodium dodecyl sulfate surfactant (with concentration of 1 g/L) was used as the washing solution for the samples. The results of this study indicate that an increase in both pH and temperature of the solution enhances the removal efficiencies of aliphatic and aromatic contaminants from soil samples. The removal efficiencies of aliphatic contaminants from coarse and fine fractions of the samples increased from 81.12 to 92.34% and 62.41 to 76.47%, as the temperature rose from 20 to 40°C, respectively. A nearly similar trend of increase was noted for the aromatic compounds. With regard to pH of the washing solutions, the removal efficiencies of the contaminants increased as the pH changed from 5.76 to 8.14. Thus, concluding that the implementation of soil washing is more efficient when the soil has naturally high pH values.

Swelling and shrinkage of expansive subgrade soils in North Texas causes deep cracks and surficial distresses in pavements. Since this behavior is affected by changes in water content of the soil, evaluating moisture variation in the subgrade soil could provide an estimation of pavements deformation. The objective of the current research is to investigate the moisture variation of a pavement site due to real time environmental factors. For this study, a 2-lane rural road in Kaufman County, Texas was selected for data acquisition and monitoring purposes. Soil test borings were conducted to determine subgrade condition and moisture sensors were installed at 1m and 4.5m depth to monitor in-situ moisture content every hour. In addition, a rain gauge was used to record the precipitation at the site. The main wetting branch of the soil water characteristics curve (SWCC) was estimated from soil's physical properties and incorporated into Finite Element (FE) software PLAXFlow for transient analysis of moisture variation. The FE results were compared with direct field measurements. Model outputs and sensor readings indicated significant variation of moisture content due to rainfall. Lower moisture content accompanied with considerable variations was recorded at shallow depths, while moisture variation at greater depths was mainly controlled by groundwater. The FE results were in line with direct field measurements, confirming the validity of the estimated parameters. The FE analysis could be utilized for determination of the hydraulic balance of the subgrade and has the potential to be considered as part of the future design procedures.

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