عنوان مقاله [English]
In the most of the construction and roading projects, the natural subsoil layers do not meet the mechanical requirements such as stiffness and shear strength and need soil improvement. There are several mechanical and chemical soil improvement methods that using reinforcement elements such as geotextiles, geogrids and natural or artificial fibers are among the mechanical methods. Because of the ease of application, low produce casts and short construction time, the use of randomly distributed discrete fibers are increasing in the recent decades. In this research, the shear strength of a silty sand reinforced by randomly distributed discrete glass fibers was studied in the laboratory. The study was focused on the effect of the length and content of the fibers on the shear strength parameters of the soil such as cohesion and internal friction angle. The shear strength of specimens of the improved soil prepared in 28 different configurations using fibers with 5, 10, 20 and 30 mm length and 0.1, 0.2, 0.3, 0.4, 0.5 and 0.6 % of weight contents were investigated using direct shear test device. the results of this study show that the inclusion of the fibers increases the shear strengths of the soil. The improvement of the shear strength of the soil resulted from improving of both cohesion and the internal friction angle. Increasing the length and the content of the fibers, increases the shear strength of the soil but further increment from optimum length and content of fibers reduces the shear strengths of the reinforced soil. The shear strength of the fiber reinforced soil is always more than that of unreinforced soil. The internal friction angle and cohesion of the fiber reinforced soil in the optimum condition increased about 30% and 40% respectively. The optimum length and content of the fibers to achieve the maximum shear strength were 10 mm and 0.4% respectively.
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