Anisotropic pullout behavior of bauxite slag-geogrid interfaces

This study investigated the anisotropic pullout behavior of dry bauxite slag-geogrid interfaces to address a critical knowledge gap in abandoned bauxite slag deposits reinforcement. Laboratory tests were conducted on coarse sand (slag of 2.5-4.75 mm) and fine gravel (slag of 10-12 mm) using biaxial (SS40) and triaxial (TX150) geogrids across 0°, 22.5°, 45°, 67.5° and 90° by the self-developed pullout apparatus that provide a new test method under normal stresses of 20-60 kPa. Results revealed that the slag-geogrid interface pullout strength increases with increasing normal stress. A new parameter η was proposed that representing the magnitude of pullout strength anisotropy and was defined as the difference between the maximum and minimum pullout strength divided by the average pullout strength across orientations. It exhibited values of 0.47-1.36 across tested conditions, with this anisotropy diminishing significantly as normal stress increased to 60 kPa. Fine gravel-geogrid interfaces showed higher peak η values than coarse sand counterparts. The interface pullout strength of bauxite slag-SS40 and bauxite slag-TX150 disparity amplified with increasing normal stress. The rectangular mesh of SS40 increased normal stress sensitivity compared to TX150's stable triangular structure. Results demonstrated that design approaches assuming η = 0 neglect directional effects, potentially explaining recurrent geogrid-reinforced structure failures. This research provided essential data for optimizing geosynthetics reinforcement slag deposit under complex stress orientations.