Shear modeling of fiber reinforced soil composite on the base of fiber pull-out test

The concept of reinforcing soil with natural fibers was originated in ancient times. However, short natural and synthetic fiber soil composites have recently attracted increasing attention in geotechnical engineering for the second time. Consequently in this work, shear behavior of fiber reinforced soil composite was modeled by using force-equilibrium method. The proposed model indicated that fiber percentage, fiber diameter, fiber aspect ratio, Elastic Modulus of fiber, coefficient of friction between fiber and matrix, the thickness of shearing zone and vertical compressive stress determine the shear resistance of a fiber reinforced soil composite. In the next step, a set of laboratory direct shear tests was performed on different samples including both neat soil and fiber reinforced treatments. In order to compare model outputs and experimental results, it was necessary to measure the coefficient of friction between fiber and soil. Therefore, a novel apparatus based on fiber pull-out test was designed to determine the interfacial shear stress between fiber and soil. Since, soil considers as a soft material and its mechanical properties depend on vertical stress, therefore, the Instron Tensile Tester was modified to provide fiber pull-out test through the soil matrix. Consequently, the proposed model adequately predicted shear behavior of fiber reinforced soil composite based on fiber pull-out test results.