Equivalent Modulus of Geogrid-Stabilized Granular Base Back-Calculated Using Permanent Deformation

Geogrids have been increasingly used for stabilization of base courses and subgrade. In the design of the geogrid-stabilized roads, the benefit of geogrids is usually quantified by a modulus improvement factor (MIF) so that the geogrid-stabilized base course can be simplified as a nonstabilized base course with an equivalent modulus. In previous studies, the equivalent moduli of base courses were usually back-calculated by using the measured vertical stresses and/or resilient deformations of the road surface. However, these responses (i.e., stress or resilient deformation) fail to or cannot fully capture the benefits of the geogrid in reducing the permanent deformation of roads. In this study, the equivalent moduli of the geogrid-stabilized base courses were back-calculated by using the measured permanent deformations. Burmister’s layered elastic solution and a modified mechanistic empirical pavement design guide (MEPDG) soil damage model were used for this back-calculation. The results show that the MIFs of the geogrid-stabilized bases determined by using the measured permanent deformations were mostly higher than those determined by using the measured vertical stresses at the interface. The equivalent modulus of the geogrid-stabilized base back-calculated by using the permanent deformation captured the benefits of the geogrid at both the loading and unloading stages.