Resilient behavior and permanent deformations of triaxial geogrid stabilized bases over weak subgrade

Abstract

Geogrid has been playing an important role in solving geotechnical problems such as paved/unpaved roads constructed on weak subgrade. Geogrid provides lateral confinement to resist the lateral movement of aggregates by the interlocking action that occurs between geogrid apertures and surrounding aggregates. The inclusion of geogrid influences the resilient behavior of stabilized bases and benefits the stabilized bases by reducing permanent deformations (i.e. rutting). However, the resilient behavior and the accumulation mechanism of permanent deformations have not been well understood. In this study, cyclic and static plate loading tests were conducted on test sections of geogrid stabilized bases over subgrade under various loading intensities. The test sections were constructed in a geotechnical box with dimensions of 2 m (W) × 2.2 m (L) × 2 m (H) at the University of Kansas. The vertical and horizontal pressures along the interface were monitored by earth pressure cells with varying distances away from the centerline of test sections. Permanent and resilient deformations were monitored by LVDTs installed at 0, 0.25, 0.5, and 0.75 m away from the center. The results show that both the vertical and horizontal stresses were redistributed due to the inclusion of geogrids. Vertical stresses were distributed to a wider area, while horizontal stresses were confined to a smaller area close to the loading plate. The presence of geogrids reduced permanent deformations but increased resilient deformations. An analytical solution of the geogrid-stabilized layered elastic system was derived to evaluate the change of earth pressures induced by the inclusion of geogrids. Confinement effect and tensioned membrane effect were treated as external stresses applied at the interface. The base course was treated as transversely-isotropic to capture the modulus degradation at the horizontal direction. Results show that vertical stresses at the interface decreased and horizontal stresses along the centerline increased due to the inclusion of geogrids. The geogrid stabilized sections had higher lateral earth pressure coefficients along the centerline. A simple hypoplastic model was adopted to simulate the resilient behavior of stabilized soils (i.e. with higher lateral earth pressure coefficients). The results show that the soil sample under a stabilized condition had a higher resilient deformation under unloading n as compared with that under an unstabilized condition. The confinement and tensioned membrane effect due to the inclusion of geogrids reduced the permanent deformations not only at the loading stage, but also at the unloading stage.