Effect of Oil- Contamination on Shear Strength Parameters of Grain Soils with Emphasis on the Effect of Dimensions of Direct Shear Test Box

Petroleum contamination in soils induced by oil products such as crude oil, gasoline, and motor oil is an issue raised widely in oil-rich countries like Iran. Contaminated soil with oil products is considered as a common environmental problem, but under the physical-chemical processes that occurred between these contaminants and soil, new geotechnical behavior is expected, which can reduce the soil bearing capacity, change the soil strength parameters and vary engineering and geotechnical properties of soil. Once the leakage occurs, resulted by self-gravity, the oil flows towards the groundwater level, which will cause soil-saturation with this hydrocarbon liquid. In spite of this, lateral propagation of the liquid may result in a wider scale of contamination. Oil pollution near the shore, contaminates the soil across the entire coastline. In this case, to account for the pollution of soil, regarding the environmental conditions, soil type, and type of contaminants the geotechnical properties are revised. The largest oil contamination in soil occurred in recent decades due to the Persian Gulf war in Kuwait, where a volume of 9 million cubic meters of soil in 19.05 million square meters was contaminated to oil; about 69 lakes were created to gather the diffused crude oil. Another case is the destruction of tanks of the refinery of Tehran and Abadan in the war between Iran and Iraq, which caused intense oil-pollution.