The geogrid is a type of spatial network structure with a certain thickness; through its interactions with the surrounding soil, the soil can be reinforced. In this study, the characteristics of the interface between the geogrid and gravelly soil were investigated with a pull-out test. To investigate the mesoscopic characteristics of the geogrid-soil interface, the Particle Flow Code 3D (PFC3D) program was employed to simulate the pull-out test, which can reproduce the evolution of the influencing zones of the geogrid during the pull-out test from macroscopic and mesoscopic perspectives. Both sides of the geogrid were characterised by a shear zone and an advanced influencing zone. The geogrid indirectly reinforced the soil within the influencing zones to a certain extent, and the thickness of this zone was rarely related to the normal pressure. Additionally, the widths of the influencing zones above and below the interface were different; the above one was wider.

Centrifuge model tests were conducted to investigate the geogrid-gravelly-soil-reinforced steep slope embankments. A control experiment was carried out on a set of unreinforced embankments. The following test results were obtained. Under a centrifugal force, the unreinforced gravelly soil steep embankments failed in sudden collapse and circular sliding. By contrast, the reinforced embankments exhibited a local deformation on the slope surface and a continuous progressive deformation on the slope due to the failure of geogrid-soil interface. The geogrid reinforcement strengthened the soil and enhanced the integrity of the embankment. Thus, the stability of the slope was improved, and the horizontal lateral displacement of the slope and the settlement at the slope crest were reduced. In the design of a geogrid, reinforcements should be sparsely arranged in the upper section of the embankment and densely arranged in the lower section. For equally spaced reinforcements, the geogrid should be strengthened in the middle and lower sections of the embankment.