Interface behavior of geogrid-reinforced sub-ballast: Laboratory and discrete element modeling
This paper shows a study on the interface behavior of biaxial geogrids and sub-ballast using a direct shear box and computational modeling. A series of large-scale direct shear tests are performed on sub-ballast (capping layer) with and without geogrid inclusions. The laboratory test data indicate that the interface shear strength is mainly decided by applied normal stresses and types of geosynthetics tested. Discrete element modeling approach is used to investigate the interface shear behavior of the sub-ballast subjected to direct shear loads. Irregular-shaped sub-ballast particles are modeled by clumping of many spheres together in pre-determined sizes and positions. Biaxial geogrids are simulated in the DEM by bonding small balls together to build desired geogrid shapes and opening apertures. The numerical results reasonably match with the measured test data, showing that the introduced DEM model can simulate the interface behavior of sub-ballast stabilized by the geogrids. In addition, the triaxial geogrid presents the highest interface shear strength compared to the biaxial geogrids; and this can be associated with the symmetric geometry of grids' apertures that can distribute load in all directions. Evolutions of contact forces of unreinforced/reinforced sub-ballast specimens and contour strain distributions during shear tests are also investigated.