Effect of Bentonite Addition on Geotechnical Properties of Oil-Contaminated Sandy Soil

Oil and its derivatives not only change the chemical and biological properties of the soils, but also affect their geotechnical properties. Effects of oil contamination on a sandy soil which mixed with bentonite was assessed in terms of compaction, shear strength, and consolidation behavior. The experiments were carried out by polluting dry sandy soil with 2.5, 5, 7.5, 10% w/w crude oil at different bentonite contents (0, 5, 10, 15, 20% w/w). Results of compaction tests indicated that at a fixed bentonite content, with increasing crude oil content, the maximum dry density increases, while the optimum water content decreases. Similarly, at a fixed contaminant content, increasing the bentonite content in the soil leads to increase in soil maximum dry density and the optimum moisture content. Moreover, direct shear tests revealed that at a specific bentonite content, higher contamination concentration causes lower internal friction angle. The effect of oil content on the coefficient of consolidation (Cv) and void ratio of soils with 0, 5, 10, 15, and 20 percent bentonite contents was studied. The results of consolidation tests indicated that at a fixed bentonite content Cv has an overall increasing pattern which is in its maximum amount at 5% oil content