Pullout Behavior of Triaxial Geogrid Embedded in a Transparent Soil

Geogrids with triangular apertures are increasingly being used as a reinforcement element in various geotechnical structures because of their characteristics to offer uniform resistance in all directions. In the present study, the load-displacement characteristics of triaxial geogrid in longitudinal (machine direction, MD) and transverse (cross-machine direction, XMD) directions under pullout conditions were evaluated for various normal stresses. Transparent soil made of fused quartz sand and transparent fluid (mineral oils) was used to quantify the soil and geogrid displacement under pullout conditions through image analysis, so that both the global and local failure modes of the triaxial geogrid can be assessed. The geogrid strain at failure under pullout and multirib tensile test conditions was compared to understand the failure modes of the triaxial geogrid in MD and XMD. The triaxial geogrid in XMD had experienced larger geogrid displacement when compared with MD, and the difference in the displacement is prominent with the increase in the normal stress. For identical normal stress and clamp displacement, the extent of the shear zone was larger for geogrid tested in XMD than MD. The test results also reveal that the triaxial geogrid has failed by pullout under lower normal stresses but has also failed by rupture under relatively higher stresses, irrespective of geogrid orientation. Interestingly, under lower normal stresses, the triaxial geogrid oriented in XMD had a deformed in-plane, while in MD, out-plane geogrid deflection was noted. With the increase in the normal stress, the node rupture was noted when oriented in XMD but failed by rib rupture when oriented in MD. (c) 2021 American Society of Civil Engineers.