Stability Analysis of Forest Roads Cutslope According to Mechanics Properties of Soil (Case Study: Stakhrposht Region-Neka)

Slope instability and mass movement of soil are the most important concerns of road construction scientists and experts as well as environmentalists. Soil is the main material of forest road construction and forms the road bed. In this research in order to avoid time and cost waste in mechanic soil laboratory, the region was divided into same units based on landform in GIS software. 10 soil samples were taken through systematic randomize sampling method from 20 land units. Totally, 200 soil samples were taken and the soil moisture, bulk density and texture were analyzed. New homogenous units were produced using the classification of soil experiments results. Therefore, in optimizing process of sample numbers the sampling intensity dramatically decreased to 100 samples without changing accuracy and reliability. Atterberg and shearing resistance tests were done on these samples. Results showed that the percentage of Fine-Grained Soil at both depth (10-30 and 70-90 cm) of instable units was more than that of stable units. Liquid index in instable and stable units were 0.38 and 0.09, respectively. Plastic index in instable and stable unites was recorded as 45.88 and 19.07. Moreover, the mean of shear resistance of soil in instable units was lower than that of stable units. Drainage services are proposed for instable units with plastic properties.