Abstarct: Due to the nature of external contaminants into the soil, it can cause changes in the physical structure and chemical soils. One of the most important and most common of these factors, or one of its derivatives, which are petroleum hydrocarbons in the family fit. Leakage and emissions of these substances can leak due to natural factors such as natural or Earth Summit in production and storage sites And human factors such as accident tankers, pipelines and reservoirs injury, etc. The entry and release into the soil in addition to environmental hazards such as pollution of underground water can be multiple causes changes in soil parameters. It changes according to the type and structure of the soil can cause changes in the physical properties or texture.Changes in soil geotechnical parameters may improve or decline in performance on the part of soil.However, due to the costly and time-consuming cleanup of soils contaminated with this material, as well as economical construction in the affected area, It is necessary to have the contaminated soil geotechnical characteristics and parameters studied engineering in the design of the structures in question, the results are considered to be.Since the soil shear strength as one of the most important factors that determine soil quality appear and analyze issues such as the horizontal pressure against the separation fence and shield and bracing, the slope stability and the bearing capacity of the soil and ... plays an important role, this parameter was investigated in the present thesis. The above study is baxsed on direct shear tests performed on your particular device. The soil used in the study of coarse sand that has been collected from the area shahrood oil site.To determine the effect of pollution, contamination and over time, samples without contamination as pilot-tested at the beginning and then the results were compared with samples of contaminated. After two hydrocarbon contaminated soil samples with kerosene (oil) and gas oil (diesel) and in quantities of 2% and 4% and after 10 days of large-scale direct shear tests with box cutter 15*30*30 And 2.067 mm per minute rate cut has been applied.In addition to observing the effect of resistance over time, examples were made from time to relax after 2 previous testing was done.The results showed a significant reduction of resistance after exposure to gasoline and similar behavior after exposure to oil, but the process by increasing the amount of contaminants increases. As a result, given the structural differences between the two oil and diesel, compared to the same samples contaminated with diesel oil contaminated with less resistance than the show itself. The increase of pollution, internal friction angle () reduce adhesion (C) increases.