Studying the Effect of Roughness on Soil-Geotextile Interaction in Direct Shear Test

One of the methods of increasing soil resistance against failure is soil reinforcement using geosynthetics. Soilgeosynthetic interactions are of great importance and are affected by friction and adhesion at their interface. Soil gradation, contact surface roughness and geotextile density are among the factors affecting soilgeotextiles interaction this study, to investigate the effects of these factors, largescale direct shear tests have been conducted using a well and a poorly graded sand at a relative density of 80% reinforced with two geotextiles having different tensile strengths and mass per unit area. Samples were subjected to normal pressures of 12.5, 25 and 50kPa and sheared at a rate of 1 mm/min. Geotextile surface roughness was achieved by gluing two different single sized sand particles. Results show that increasing geotextile surface roughness increases shear strength at soilgeotextile interface. Geotextile tensile strength mobilization is shown to depend on soil grain size at the interface. The coarser and more angular the soil particles, the more effective the soilreinforcement interactions. Geotextile tensile strength and its mass per unit area are shown to less important factors.