Geogrid Base Reinforcement with Aggregate Interlock and Modeling of Associated Stiffness Enhancement in Mechanistic Pavement Analysis

The main mechanism by which geogrids reinforce unbound aggregate base and subbase layers of flexible pavements is the geogrid aggregate interlock. Geogrids prevent aggregate material from moving laterally under applied wheel loading; this enhances local strengthening and stiffness in the base layer. This higher stiffness zone essentially benefits the geogrid's pavement response by better bridging over the weak subgrade soil and transmitting reduced critical stresses and strains on top of subgrade. The University of Illinois developed a mechanistic model for the analysis of geogrid reinforced flexible pavements based on the finite element approach. This approach was used to model successfully the development of a stiffer layer associated with aggregate interlock around the geogrid reinforcement by considering compaction-induced residual stresses as the initial condition in the mechanistic analysis. The predicted critical pavement responses matched with the measured values from full-scale pavement test studies. Further, field-observed stiffening and strengthening of the geogrid-reinforced base courses were documented from dynamic cone penetrometer (DCP) test results. Significant reductions in measured pavement responses, especially in base course lateral movements caused by geogrid inclusion, were apparent in the University of Illinois full-scale test sections. Therefore, the longer traffic lives observed established the pavement performance benefits. When the same DCP evaluations were conducted on geogrid base reinforced in-service pavements in California, similar trends were observed in increased base course strength, and stiffness properties were successfully linked to immediate (enhanced compaction) and long-term (retained-improved stiffness) benefits.