stabilization of subgrade soil for highway by recycled polyester fiber

subgrade soil stabilization is one of the primary and major processes in the construction of any highway; also environmental authorities are concerned about the growing amount of polyethylene (pet) bottles produced by household sectors. this research in order to study effect of adding recycled polyester fiber on soil engineering properties, especially shear strength and california bearing ratio (cbr) used clay soil with low liquid limit (cl) and atterberg limits used high liquid limit (ch). clay soil with recycled polyester fibers are mixed with soil in three different percentages 0.1%, 0.3% & 0.5% (the portion of stabilizer matters to soil net weight). shear strength, cbr, atterberg limits of stabilizer samples were measured by direct shear test and cbr test and atterberg limits test. experiments results show this fact that using of recycled polyester leads to increasing shear strength and cbr and reduction, plasticity index. it is remarkable that according to economic problems, the most optimum quantity of recycled polyester fiber to reach to favorite strength is 0.5%.