Resilient and permanent deformation characteristics of unbound pavement layers modified by geogrids

The benefits of geogrids in reducing permanent deformation of flexible pavements are generally recognized and have been shown in numerous studies. In contrast, although resilient moduli of unbound materials are important property inputs in mechanistic-empirical pavement design, the impact of geogrids on the resilient behavior of unbound layers remains unclear from previous studies. This paper focuses on resilient behavior of unbound layers and permanent deformation of subgrades modified by geogrids at the base-subgrade interface. Two sets of tests were conducted on scaled pavements built over two types of soil. Each set of tests consisted of four sections. Three were modified with different geogrids and one was left unmodified as a control. Instruments were installed to measure the subgrades' resilient and permanent deformations. The pavement layers were tested with a lightweight deflectometer (LWD). Surface deflections and subgrade resilient deformation under impulsive LWD loads were recorded. The test sections were then subjected to repetitive reduced-scale moving-wheel loading. Subgrade resilient and permanent deformations were measured at select intervals of the wheel passes. The measurements of surface deflection and subgrade resilient deformation under the LWD load indicate that the geogrids did not have an appreciable impact on the resilient behavior of the base layer and subgrade. Subgrade resilient deformations, along with the repetitive wheel loads, also suggest that the effects of the geogrids on the resilient responses of the subgrade were not evident. However, two of the geogrids consistently exhibited benefits in reducing permanent deformation in the subgrade.