Laboratory Evaluation of Geogrid Base Reinforcement and Corresponding Instrumentation Program

The performance of geogrid base reinforcement in pavement on weak subgrade under cyclic plate load testing was studied. The performance of instrumentation sensors was also evaluated to improve future instrumentation programs. The tests were conducted inside a test box of dimensions of 2.0×2.0×1.7 m3 using a servo-hydraulic actuator. A 40-kN load at a frequency of 0.77 Hz was applied through a 305-mm-diameter steel plate. The sensors used included linear variable displacement transducers, pressure cells, bondable foil strain gages, and piezometers. The test results showed that the inclusion of geogrid at the subgrade/base course layer interface can significantly improve the performance of flexible pavement on weak subgrade (California bearing ratio=0.5 %) and that the traffic benefit ratio can be increased up to 3.5 for a rutting depth of 25 mm. The test results also showed that the reinforcement can redistribute the applied load to a wider area, thus achieving an improved stress distribution on the subgrade, which will eventually reduce the permanent deformation of subgrade. The bondable foil strain gages are unsuitable for long-time continuous monitoring of strain development within geogrid under high number of cyclic loading.