Nowadays, crude oil and its products are considered as the one of most important causes of environmental pollution. Soil contamination by petroleum products is one of the important issues of geoenvironment, which, in addition to harmful effects on human health and ecology of the earth, also affects the basic geotechnical properties of soil. Therefore, it is necessary to take measures to clear contaminated areas or prevent the spread of these contaminants. There are various methods for purifying and controlling soil oil pollution. Among these, the use of oil absorbent geotextiles is considered as a new method, and its performance requires more research. The absence of chemicals in the process of separation, less energy, simple control and implementation are the advantages of separating by geotextiles. In this thesis, it is attempted to evaluate the performance of these geotextiles in absorption crude oil and improving the geotechnical properties of contaminated soil. In this research, various geotextiles were tested to achieve the highest oil absorption capacity. In this tests, 5 layers of geotextiles (the area of each layer of geotextile is 176.625 ) are located in a mold with a diameter of 15 and a height of 7.5 cm that contains two kg of soil with 8% oil, and after one week was pulled out. The highest crude oil absorption capacity was about 30% for the spacer fabric getextile. Therefore, in this research, this type of geotextile has been used to continue the experiments. In order to achieve the stated objectives of the research, large-scale direct shear tests were performed on natural soil samples, soil contaminated with 8, 12 and 16 percent crude oil and treated soils with 1, 3, and 5-layer of spacer geotextile. Investigating the effect of the number of absorbent geotextile layers on the removal efficiency (percentage of crude oil removed) shows that with increasing number of absorbent geotextile layers, the amount and percentage of crude oil removed has increased. Also, increasing the number of layers has a positive effect on the evaporation process and increases the amount of evaporated oil. So that the efficiency of oil removal in the sample contaminated with 16% crude oil and 5 layers of absorbent geotextile was more than 50%. The results of the large-scale direct shear test indicate that with increasing the contamination, the internal friction angle of the soil decreases and its cohesion increases. Evaluation of the behavior of treated soils after 7 days shows that with increasing number of absorbent geotextile layers, the internal friction angle of the soil and its cohesion is increased. The results of CBR test on natural soil samples, soil with 8% oil and treated soil with 1, 3 and 5 layers of adsorbent geotextile (respectively 27.3, 20.8, 30, 35.4 and 43.9) show that increasing the number of geotextile layers increases the number of CBRs. Keywords: Oil pollution, Oil absorbent geotextile, Oil removal efficiency, large shear box test, CBR test
