Quantifying the Benefit of Triaxial Geogrid in Stabilizing Granular Bases over Soft Subgrade under Cyclic Loading at Different Intensities

Abstract

Since it was introduced in the market, triaxial geogrid has been used successfully for subgrade improvement and base course stabilization. Because triaxial geogrid can provide uniform tensile resistance in all directions, it is more efficient to interact with granular material and provide lateral restraint under cyclic loading. The benefit of geosynthetic in stabilizing granular bases has been mostly evaluated by researchers in terms of surface permanent deformation and stress distribution under cyclic loading at a constant intensity. In real applications, applied cyclic loads from vehicles may have different intensities. How the loading intensity affects the benefits of geosynthetics in stabilizing granular bases has not been well understood. In this study, cyclic plate loading tests at different loading intensities were performed on 0.23 m thick unstabilized and triaxial geogrid mechanically stabilized granular bases over soft subgrade with a CBR of 2.0% constructed in a geotechnical testing box (2 m × 2.2 m × 2 m) at the University of Kansas. Two types of triaxial geogrid were used in this study. The intensities of loading applied on a steel plate of 0.30 m in diameter increased from 5 to 45 kN. In these tests, surface deformation, subgrade deformation, and vertical/horizontal stresses at the interface between base and subgrade were monitored by transducers placed at varying distances from the center of the loading plate. Test results indicated that the surface and subgrade permanent deformations and the vertical stresses at the interface between base and subgrade were reduced by the inclusion of a triaxial geogrid. A majority of the surface permanent in each section was contributed by the subgrade permanent deformation. In the mechanically stabilized section, the horizontal stress in the base increased in contrast to the decreased stresses that were measured in the subgrade. The benefits of geosynthetic mechanical stabilization were even more obvious when a heavier-duty geogrid was tested in the geotechnical testing box.