Soil pollution is one of the most dangerous sorts of environmental pollutions because of waste materials, fossil fuels, etc. Unfortunately in developing countries, there are very few arrangements to prevent soil pollution due to the fossil fuels and to improve polluted soil. In this research, influences of gas oil on properties of Kalmand protected area's sandy soil near Yazd, Iran, were studied. It was found that gas oil constituted 5.25% of soil weight in the refueling station in the region. Therefore, cleaning and strengthening of the soil by adding cement rather than expensive and complicated methods were the most important goals of this research. First, the influence of gas oil on soil properties was studied, and to improve the soil, different percentages of ordinary portland cement were added to the polluted sand to study the improved soil properties using laboratory tests. It was found that unconfined compressive strength, cohesion, and angle of internal friction of sample with 16% cement and 8% gas oil after 28 days of curing were higher than those of the specimen of 6% cement and 14% gas oil, at 4.6, 5.4, and 1.3 times, respectively. Moreover, based on falling head tests it was observed that permeability of the stabilized specimens decreased substantially. From SEM tests, fewer voids were observed in the stabilized samples, which led to less pollutant penetration into the soil. According to EDX, although dangerous elements in the contaminated specimen made up 3.99% of the specimen total weight, addition of cement introduced considerable amounts of elements that are vital for pozzolanic reactions. Therefore, it can be concluded that addition of cement to the gas oil-polluted soil not only can improve geotechnical properties of the soil and reduce its permeability, but also is very efficient for environmental issues.
Keywords: Cement; Cohesion; EDX; Highway; Oil-polluted sand; Permeability; Protected area; SEM; Unconfined compressive strength.