Laboratory Evaluation of Geosynthetics to Stabilize/Reinforce the Subgrade/Base in Unpaved Roadways

This research study evaluates the performance of geosynthetic material for subgrade stabilization and base reinforcement of unpaved test sections. For this purpose, extensive large-scale in-box static plate load tests were conducted on several unreinforced and geosynthetic reinforced, unpaved test sections. This research was conducted in Geotechnical Engineering Research Laboratory (GERL) at Louisiana Transportation Research Center (LTRC). The in-box static plate load tests (ASTM D1196-93) were conducted to evaluate the performance and benefits of geosynthetic material for subgrade stabilization/base reinforcement. A total of forty-seven tests were performed in this regard. The quality control of the section was maintained using non-destructive in-situ tests such as nuclear-density gauge, geogauge, dynamic cone penetrometer (DCP), and light falling weight deflectometer (LFWD). These devices were used as effective tools in the assessment of subgrade and base course layers and for the evaluation of stiffness modulus of the different sections. The test results showed that the presence of geosynthetic reinforcement can significantly improve the bearing capacity of the unpaved test section, thus reducing the accumulated permanent deformation in the subgrade layer. The test results showed that the inclusion of reinforcement improved the bearing capacity ratio, and redistributed the applied load to a wider area, thus minimizing stress concentration, as well as achieving a more uniform stress distribution on top of subgrade layer. In addition, single-stage and multi-stage repeated load triaxial tests were also conducted on two layered (base-subgrade), small specimens to assess the effectiveness of placing the geosynthetic material (type and tensile modulus) at the interface of the base-subgrade specimens. These test results also demonstrated that inclusion of reinforcement reduced the permanent vertical deformation of the specimens