Effect of Geogrid Type and Subgrade Strength on the Traffic Benefit Ratio of Flexible Pavements

In this study, extensive large-scale model pavement experiments consisting of a total of twenty-one pavement sections overlying different subgrade conditions (poor to firm) were conducted to determine the traffic benefit ratio (TBR). TBR is quantified as the ratio of a cumulative number of load cycles to reach a defined deformation/failure state in the reinforced section to that of the unreinforced section with the same pavement geometry and material constitutions. Biaxial geogrids made up of polyester and polypropylene of varying tensile strengths were considered. The controlled experimentation was carried out in a large-sized test chamber of dimensions equal to 1.5 m in length, 1.5 m in width, and 1.0 m in depth. To simulate the wheel loading on the pavement in a real field condition, repetitive loading was applied in the form of haversine loading using a linear actuator system of 100 kN capacity. Based on the studies, geogrid placed at one-third thickness of the base layer was found to be the optimal depth of reinforcement. TBRs of the reinforced pavement were found to range from 1 to 52. The study, however, recommends the use of TBR ranging from 1.5 to 4 for a conservative design. Finally, the TBR-based design of pavements was illustrated through a worked-out example for given input parameters. The thickness of aggregate layers was found to reduce by 7.5–29% for the range of California bearing ratios and TBRs considered in this study.