Abstract: Most of the existed studies of soil-geogrid interaction mainly focus on uniaxial and biaxial geogrids. Nevertheless, the interface behavior between triaxial geogrid and soil has not been fully understood by experimental study. A series of laboratory pull-out tests is conducted on triaxial geogrid considering the effect of two kinds of pullout directions, referred to as TX_0 and TX_90, respectively. The displacements of specimens are measured and recorded at 4 sections along the pullout direction, and then the tensile strain, relative displacement between geogrid and soil, distribution pattern of interface friction, and deformation and failure mode of the geogrid specimens are all analyzed. Based on the peak shear strength and the residual shear strength, the variation laws of the interface behavior between geogrid-soil and apparent friction coefficient are investigated. The experimental results demonstrate that the interlocking of transverse rib increases with the increase of normal stress due to out-of-plane bending in the case TX_0, which leads to a better pullout performance than that in the case TX_90. The interface friction develops in a progressive mode along with constant adjustment of the distribution pattern and an elastoplastic softening characteristic is observed for interface behavior. The interface friction angles in the case TX_0 are significantly larger than that in the case TX_90, while the interface cohesions are just opposite. Higher normal stress can contribute to a better pullout performance in the case TX_0.

Key words: triaxial geogrid, pull-out test, pullout direction, interface behavior between geogrid and soil, geogrid deformation