Effect of Reinforcement on Resilient and Permanent Deformations of Base Course Material

Deformational response of base course material under traffic loading is characterized by resilient (recoverable) and permanent (irrecoverable) deformation. A series of repeated load triaxial tests was conducted on unreinforced and geogrid-reinforced crushed limestone samples to evaluate the effects of the geogrid stiffness, location, number of layers, and crushed limestone moisture content and state of stress on the resilient and permanent deformations of these samples at different number of load cycles. Three types of geogrids were used. For each geogrid type, three reinforcement arrangements were investigated. The effect of the moisture content of the crushed limestone was investigated by conducting repeated load triaxial tests on samples prepared at three different moisture contents: optimum moisture content and ±2.5% of the optimum moisture content. Statistical analyses were conducted on the collected data. Results indicated that the geogrid inclusion within crushed limestone samples significantly reduced permanent deformations but did not show appreciable effect on resilient deformations. Improvement was significantly affected by the geogrid stiffness and arrangement. However, the effect of the geogrid stiffness was found to be smaller than the effect of the geogrid arrangement. For stress levels less than the plastic shakedown stress limit, the geogrid had a minimum contribution to the permanent deformation resistance during primary postcompaction stage; however, it significantly increased the permanent deformation resistance during the secondary stage. In addition, the geogrid reinforcement was found to have a small effect on the permanent deformation resistance mechanisms when the imposed stress level was greater than the plastic shakedown stress limit. Results illustrate that change in the moisture content of the crushed limestone material alters the material state of stress and this significantly affects the geogrid improvement.