Effectiveness of geogrid and its position on the performance of unpaved roads under repetitive loading

Road network provides access to communities and plays a vital role in the economic development of a country. These days, the transportation sector is given the utmost importance as premature failures are very common owing to rapid industrialization and urbanization. Also, subgrade failure is a very common scenario in pavement failures. To prevent these failures, geosynthetics have been used widely. In this study, model pavement sections were built in a steel tank with black cotton soil as subgrade forming a weak subgrade layer followed by granular sub-base (GSB) and sacrificial layer at the top. Two biaxial geogrids were considered as reinforcing material, and their position was varied within the GSB layer. The pavement thickness was varied by varying the thickness of GSB. The GSB of thickness 0.25 m, 0.30 m, and 0.35 m were considered. The effectiveness of geogrid on the pavement performance was evaluated by varying the position (one-third from the top, middle, two-third from the top and interface of subgrade and GSB) of geogrid within GSB. The pavement was subjected to repeated load test to simulate traffic loading. The loading frequency was kept at 0.01 Hz. The settlement of the pavement was recorded in terms of total and plastic settlements along the surface below the load point and away from the load point. Based on the test results, the geogrid placed at a depth of two-third thickness of GSB from the top showed improved performance and is effective compared with other positions. With geogrid reinforcement at optimal position, the reduction in plastic settlement is in the order of 34% to 52% depending on the geogrid stiffness and GSB thickness thereby improving the rutting performance of the pavement. Also, with geogrid reinforcement, it is possible to reduce the pavement thickness with equivalent and/or better performance of the pavement when compared to unreinforced pavement depending on the tensile strength of the geogrid. Thus, geogrid can be used to design pavements that are durable and with low maintenance cost making sustainable pavements.