Geosynthetics have been extensively used in pavement systems, either by placing the geosynthetic at the interface between the base and subbase layers or at the interface between the subbase and subgrade layers or within the unbound base course layer to enhance the performance of roadways under repeated traffic and environmental loads. Gaining a better understanding on the geosynthetic and soil-geosynthetic interaction properties along various directions is important for geosynthetics that are subjected to multi-directional loads. Previous studies have investigated the effect of geosynthetic orientation on the unconfined tensile properties of biaxial and triangualr geogrids, whether by using numerical software or by using analytical analysis. However, the effect of geosynthetic orientation on the soil-geosynthetic interaction properties has not extensively been studied. Furthremore, properties of geotextiles have also not extensively been studied along various directions. The objective of this research is to gain a better understanding of the impact of the geosynthetic orientation on the geosynthetic and soil-geosynthetic interaction properties. Two types of test were used to achieve the objective of this research: (1) Wide-width tensile tests, which were used to investigate the impact of geosynthetic orientation on the geosynthetic properties, and (2) Soil-geosynthetic interaction tests, which were used to study the impact of geosynthetic orientation on the soil-geosynthetic interaction properties. Three types of geosynthetics that have similar mass per unit area were used in this study. This included: a triangular geogrid, a biaxial geogrid, and a woven geotextile. Geosynthetic and soil-geosynthetic interaction properties were evaluated for each geosynthetic along various directions. Variation of these properties were also compared between the three products tested. Effect of various components of the experimental setup and the test design on the findings were also evaluated. Evaluation of the results obtained from the wide-width tensile tests indicated that the ultimate tensile strength and tensile stiffness of the geogrid with triangular aperture shapes, were comparatively uniform along all tested directions. However, the ultimate tensile strength and tensile stiffness of the woven geotextile and the geogrid with rectangular aperture shapes, were highly dependent on the direction of tensile load. When the tensile load was applied along the machine or the cross-machine directions, the ultimate tensile strength and tensile stiffness of the woven geotextile and the biaxial geogrid were noticeably high. However, when the tensile load was applied along other directions (i.e., 30˚, 45˚, and 60˚), the ultimate tensile strength and tensile stiffness were comparatively low. Evaluation of the results obtained from the soil-geosynthetic interaction tests indicated that the ultimate pullout resistance and the stiffness of the soil-geosynthetic composite (KSGC) of the triangular geogrid were relatively uniform along all tested directions. However, the ultimate pullout resistance and the stiffness of the soil-geosynthetic composite (KSGC) of the woven geotextile and the biaxial geogrid were highly dependent on the direction of tensile load. When the pullout load was applied along the machine or the cross-machine directions, the ultimate pullout resistance and the stiffness of the soil-geosynthetic composite (KSGC) were found to be comparatively high. However, when the pullout load was applied along other directions (i.e., 30˚, 45˚, and 60˚), the ultimate pullout resistance and the stiffness of the soil-geosynthetic composite (KSGC) were found to be comparatively low. Overall, findings from this study indicate that the triangular geogrid tested in this study provided an isotropic in-plane behavior both in-isolation and under confinement of soil. However, the in-isolation and under confinement responses of the biaxial geogrid and the woven geotextile evaluated in this study were found to be highly anisotropic. Specifically, although the biaxial geogrid and the woven geotextile were found to have high mechanical properties in the machine and cross-machine directions, their properties along other directions were found to be comparatively low.Civil, Architectural, and Environmental Engineerin
