Geogrid mechanism in low-volume flexible pavements: accelerated testing of full-scale heavily instrumented pavement sections

This study uses full-scale accelerated testing to provide new insight into the effectiveness of geogrids on the performance of low-volume flexible pavements. Although several previous studies reported that geogrids improve pavement performance by enhancing its structural capacity and reducing distress potential, this study goes further to quantify the effectiveness of geogrids, specify the mechanism of the reinforcement they provide and identify the optimum placement of geogrid in low-volume flexible pavements. Full-scale, low-volume flexible pavement sections were constructed on weak subgrade (California bearing ratio=4%) and heavily instrumented with 170 sensors. The pavement was divided into three cells with each cell having three sections. The granular base and hot-mix asphalt layer thicknesses varied, and each cell had at least one control and one geogrid-reinforced pavement section. The instruments were embedded to measure stress, strain, deflection, moisture, pore-water pressure and temperature and were used to monitor pavement response to a moving load using the Accelerated Transportation Loading ASsembly (ATLAS). The testing programme was divided into two parts: response testing and performance testing. The response testing considered tyre configuration, loading, inflation pressure, speed and travelling offset. The performance testing considered number of passes to failure. This paper presents the various pavement responses to different loading configurations and pavement performances when a repetitive moving dual-tyre assembly at 8km/h and 44kN was applied. Based on the performance testing and visual observation of the pavement cross sections after excavation, the reinforced sections showed reduced rutting and delayed surface cracking compared to the control sections. Specifically, the pavements' measured response showed that geogrid-reinforced pavement sections exhibited less vertical pressure and less vertical deflection in the subgrade when tested at a low speed. Therefore, the study's most notable conclusion is that geogrid reinforcement reduces the horizontal movement of the granular material, especially in the longitudinal direction. The study also concludes the following about geogrid placement: (1) for a relatively thick granular base layer, placing the geogrid in the upper one-third of the base reduces the shear strains in the longitudinal and transverse directions. (2) For weaker pavements, the geogrid reinforcement at the base-subgrade interface reduces the vertical deflection. In the second case, the effectiveness of geogrid shall be compared to the increase in pavement structure or using other geosynthetic materials such as geotextiles.