Large-Scale and Bench-Scale Test Systems for Assessing Impact of Geogrids on Pavements Founded on Problematic Soils

Geogrid reinforcement is an economically viable alternative to achieve improved performance in highway pavement construction in regions with soft problematic subgrade soils. To examine the potential benefits of using geogrids in pavement foundations, measurement of permanent deformation using laboratory triaxial tests is typical practice. However, since the performance improvement of pavement foundation systems is achieved by distribution of vertical stresses at the reinforcing layer through the tensile properties of the geogrid material, it is desirable to conduct large-scale testing to more accurately monitor the behavior of the geogrid-reinforced aggregate and soil system. This article describes the development of laboratory large-scale and bench-scale pavement testing systems to evaluate the behavior of geogrid-reinforced pavement systems through wheel tests performed with problematic subgrade soils found in North Georgia. The large-scale test specimens are prepared in a 1.8 (6 ft) by 1.8 (6 ft) by 0.6 m (2 ft) metal box and consist of 305 mm (12 in.) of unbound aggregate base (UAB) overlying 305 mm (12 in.) of subgrade soil. Geogrid is placed at the interface between the subgrade soil and UAB layer. Pressure sensors are installed near the bottom of the UAB layer and near the top and bottom of the subgrade layer to monitor stress distributions within the pavement foundation system. The bench-scale system, which measures 914 (36 in.) by 203 (8 in.) by 152 mm (6 in.) is also described. This system is advantageous because not only does it expedite rapid testing but also allows for relative micro- and macroscale comparisons of aggregate-geogrid behavior. This article presents test results showing vertical stress variations obtained experimentally in the UAB and subgrade soils under simulated traffic tire loading. The two systems are shown to be effective in establishing the influence of geogrid reinforcement in pavement systems.