effect of phytoremediation on compression characteristics of silty clayey sand contaminated with crude oil

In the present study, the effects of phytoremediation using ophiopogon japonicus and platycladus orientalis on the compressibility of silty clayey sand contaminated with 3%, 5%, or 7% crude oil was examined over a period of 2 months. phytoremediation led to a decrease in the total petroleum hydrocarbons. the scanning electron microscopy images showed that an increase in the crude oil content increased flocculation of the fine particles in the soil## however, phytoremediation decreased flocculation of the soil structure. the replacement of water by crude oil decreased the dielectric constant of the fluid in the void space, which decreased the thickness of the double-layer water. these changes caused the soil particles to move closer together and become more flocculated. the atterberg limits of the contaminated soil increased after phytoremediation. a decrease in soil permeability was observed after phytoremediation in the permeability and consolidation tests. the compression index and coefficient of consolidation increased as the crude oil content and the contamination time period increased. the increase in the compression index at 30 and 60 days of phytoremediation was 6% and 18% less, respectively, than for the untreated samples. the increase in the coefficient of consolidation after phytoremediation also was 15% less than for the untreated samples. it could be concluded that phytoremediation decreased the negative effects of crude oil on the geotechnical properties of the soil over time. it also was effective in decreasing settlement of the soil contaminated with crude oil and decreased the coefficient of volume compressibility.