Geotechnical Behavior of Surfactant-Contaminated Soils

Untreated surfactant-rich greywater is uncontrollably discharged into the environment in underdeveloped countries and even in some areas of developing countries, which may change soil characteristics. However, there is hardly any research concerning geotechnical behavior of soils contaminated by surfactant. The present study investigates mechanical properties of two types of surfactant-contaminated sandy soils experimentally. Soil samples were collected from Bam County and Shahriar County located in the central parts of Iran. The clean specimens were contaminated by a series of prepared surfactant-rich aqueous solutions containing different amounts of a widely used detergent. The weight ratio of detergent to water was selected equal to 1/20, 1/15, 1/10, and 1/5. Physical characteristics of the contaminant solutions were examined by performing surface tension and viscosity tests. Additionally, geotechnical behavior of the clean and the contaminated samples was investigated through conducting compaction and direct shear tests. Results indicated that the geotechnical properties of the contaminated soils declined by increasing the surfactant concentration in the contaminant. Compared to clean specimens and at the highest contamination level, the optimum water content of both Bam and Shahriar soils reduced from 7.70% and 11.00% to 4.05% and 6.75% as well as the maximum density decreased from 17.87 kN/m(3) and 18.52 kN/m(3) to 17.37 kN/m(3) and 17.88 kN/m(3), respectively. Moreover, Bam and Shahriar soils with a maximum degree of contamination showed a reduction in the friction angle from 23.06 degrees and 20.52 degrees to 10.52 degrees and 12.17 degrees as well as a decrease in the formed apparent cohesion of the unsaturated samples by near 56% and 78%, respectively.