A series of unconfined compression tests performed on fine-grained soils contaminated with varying amounts of chemicals showed a decrease in shear strength and stress-strain behavior. These observations were attributed to changes in dielectric constant and pore fluid viscosity. Consolidated drained triaxial tests performed on a granular soil showed a similar behavior, even though granular soils do not show a physicochemical interaction between soil and pore fluid. This is attributed to mechanical interactions at particle contacts, caused by enhanced lubrication by viscous pore fluids. For fine-grained soils, the observed reduction in shear strength is attributed to physicochemical effects caused by a reduction in dielectric constant and mechanical interactions caused by high pore fluid viscosities. Observations show that the reduced physicochemical interactions seem to have been overshadowed by mechanical interactions. The clayey silt tested showed a marginal reduction in shear strength, indicating that the net effect is insignificant.
An experimental study was performed to investigate factors that control the compression index of contaminated soils and to evaluate the applicability of the correlations proposed by Skempton (1944) and Arulanandan et al. (1983) for contaminated soils. The literature search indicated that the compressibility of a soil depends on mechanical as well as physicochemical factors. The addition of chemicals to a soil changes its pore-fluid properties, and causes a change in mechanical and physicochemical factors and hence its settlement characteristics. Experimental results indicated that the compressibility of the two soils used in this study changed with the type and amount of chemicals in pore fluids. It was also found that the pore fluid viscosity influenced the compressibility of contaminated soils. Both correlations were unable to provide reasonable estimates of the compression indices for contaminated soils. The electrical properties reflect the changes in physicochemical interactions but not the changes in mechanical factors due to soil contamination. Both mechanical and physicochemical factors control the compressibility and liquid limit of a soil but to a different degree. Therefore, the changes in mechanical factors brought about by changes in the pore fluid viscosities were included in the above correlations as correction factors. With the correction factors, both correlations appear to predict the settlement characteristics of the contaminated soils used in this study.
An experimental investigation was performed to evaluate the effects of oil contamination on soils and to establish a methodology to identify and classify contaminated soils. Identification and classification tests were performed before treatment, cleaning, stabilization, or disposal of contaminated soils. There are no standards for identification and classification of contaminated soils. Fine-grained, oil-contaminated soils are often identified and classified as granular soils with large particle sizes and may result in selection of improper treatment techniques. In this study, four uncontaminated soils were first identified and classified; then, all four soils were mixed with 3% motor oil. The oil-contaminated soils were first tested for identification and classification and then treated by (1) heating in ovens at various temperatures (low-temperature desorption), (2) adding solvents (solvent extraction), and (3) adding surfactants (treatment with surfactants). The processed soils were then reidentified and reclassified. Test results showed that treatment with a surfactant produced near-virgin soils for all four soil types. The solvent extraction was adequate only for the silty sand and the silty clay. The low-temperature thermal treatment was inadequate for all four soils. To further confirm the above test results, the low-plastic clay was mixed with 6% motor oil and the above test program repeated. This soil with a higher degree of contamination produced the same results. To provide an explanation for the change in soil behavior due to oil contamination, low-plastic soil was mixed with oil up to 70% by weight and Atterberg limit tests performed. It was concluded that fine-grained soils when contaminated with oil behave as granular soils with particle aggregation. Since soils in this study were artificially contaminated, one should exert caution when applying the results of this study to soils in contact with oil for many years.
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