Influence of Geogrid Properties on Rutting and Stress Distribution in Reinforced Flexible Pavements under Repetitive Wheel Loading

Geogrid reinforcement effectively controls the rutting of pavements under traffic loads, especially when constructed over soft subgrades. In this study, extensive large-scale model pavement experiments (LSMPEs) were performed to quantify the rut depths of flexible pavements. In all, 20 LSMPEs were performed on pavement sections overlying subgrades of different strengths with California bearing ratio (CBR) values varying from 1% to 5%. Three geogrid types were considered to study the effects of material type [polypropylene (PP) and polyester (PET)] and tensile strengths ($30–60\mathrm{kN}/\mathrm{m}$) on the rutting behavior of flexible pavements. LSMPEs were first performed under monotonic loading to obtain the optimum depth of reinforcement within the base layer of flexible pavement. Thereafter, a series of repetitive load (haversine loading) was applied on paved sections of reinforced flexible pavements using a high-end, linear, double-acting actuator system. Rut deformations were measured at both the surface and the subgrade levels of the model pavements. The rut deformations were found to distinctly vary in accordance with the condition of the subgrade, the thickness of the pavement layers, and the type of geogrid used. The rut depth reduction (RDR) at the pavement surface was found to range from 22% to 69% for PP- and PET-geogrid reinforced base layers. Geogrid reinforcement significantly reduced the rut depths at the subgrade level (as high as 90%) compared to unreinforced sections. In addition, the model pavements were instrumented with the earth pressure cells to measure the vertical pressures transferred to the subgrade due to surface loading. The ability of geogrid reinforcement to distribute loads to wider areas was quantified in terms of the vertical stress distribution angle, ${\alpha }_{\max }$, at the end of the load cycles ($N=\mathrm{100,000}\mathrm{cycles}$). The ${\alpha }_{\max }$ maximum values for geogrid (GG1/GG2/GG3)-reinforced pavements built over weak subgrade ($\mathrm{CBR}=1\%$) varied from 28.4° to 32.2°, while it was 25.7° for unreinforced pavements. Likewise, ${\alpha }_{\max }$ values for geogrid-reinforced pavements overlying a relatively fair subgrade ($\mathrm{CBR}=5\%$) varied from 34.5° to 43.6° against 30.4° for an unreinforced case.