Shakedown Analysis of Geogrid-Reinforced Granular Base Material

This research study was performed to examine the shakedown behavior of geogrid-reinforced unbound granular materials and evaluate the factors that affect the shakedown stress limits. To achieve this objective, the study was performed through conducting repeated load triaxial (RLT) tests on both unreinforced and geogrid-reinforced unbound granular specimens. A multistage RLT test, in which only one sample is needed to determine the shakedown stress limits, was selected in preference to a single-stage RLT test, in which several tests on multiple samples are required. Five geogrids of different tensile modulus and different aperture geometries (three rectangular or biaxial and two triangular or triaxial) were used. The test results clearly demonstrated the potential benefits of placing the geogrid within the unbound granular base specimen in terms of permanent deformation reduction. The benefits of the geogrid are more prevalent at higher stress levels and for higher tensile modulus geogrids. The inclusion of the geogrid has more of an effect on delaying the occurrence of range B shakedown behavior (i.e., increasing the plastic shakedown limit) than that of range C shakedown behavior (i.e., increasing the plastic creep limit) for specimens prepared at the optimum and the dry side of optimum. For specimens prepared at the wet side of optimum, geogrids have a negligible effect on delaying the occurrence of range B shakedown behavior (i.e., increasing the plastic shakedown limit) but have a significant effect on delaying the occurrence of range C shakedown behavior (i.e., increasing the plastic creep limit). Of the five geogrids used, the triaxial geogrid TX2, with triangular geometry and the highest tensile modulus, performed consistently better than the other four geogrids.