Macro- and meso-scopic analysis of pullout characteristics of 3-D geogrid-sand interface

Three-dimensional (3-D) geogrids exhibit greater advantages over planar geogrids in reinforcement engineering due to the stronger bearing capacity of transverse ribs. To investigate the interaction and interfacial mechanical response of the three-dimensional geogrid-sand system at macroscopic and mesoscopic scales, three-dimensional geogrids with four different transverse rib thicknesses were fabricated using 3D printing technology. Experimental pullout tests under three normal stresses, combined with DEM simulation of the tests, were conducted. The findings showed that as the transverse rib thickness increases, the peak pullout force, residual pullout force, geogrid strain, and interfacial friction performance all exhibit a nonlinear growth trend, with the growth rate slowing down after the thickness reaches 9 mm. The numerical results indicate that a thicker transverse rib enhances the horizontal disturbance of the geogrid on the sand, weakens the vertical mobility of the lower particles, and imposes greater confinement on them. When the rib thickness increased to 11 mm, the strong contact force chains within the sand increased by 42.9%, and the particles coordination number grew by 5.29%. Overall, thicker transverse ribs enhance the displacement consistency of sand particles, resulting in tighter and more stable interparticle contacts, and contributing to a more uniform stress distribution within the model.