现有关于格栅与土的筋-土界面特性研究多以单、双向格栅为研究对象，而对三向土工格栅筋-土界面特性开展的试验研究较少。以三向土工格栅为研究对象并考虑0°和90°两种拉拔方向的影响（记为TX_0工况和TX_90工况），开展了一系列室内拉拔试验，通过对三向土工格栅沿拉拔方向4个断面的位移进行量测，分析了格栅拉伸应变、筋-土相对位移、界面摩阻力分布及格栅变形与破坏模式，并分别从峰值剪切强度和残余剪切强度两个方面对筋-土界面强度参数和表观摩擦系数的变化规律进行了探讨。研究结果表明：由于平面外挠曲变形的影响，TX_0工况下横肋的嵌锁作用随法向应力增大而增强，从而使TX_0工况的拉拔性能逐渐优于TX_90工况；拉拔过程中，筋-土界面摩阻力的发挥是一个渐进的过程，其分布形式不断发生调整，筋-土界面呈弹塑性-软化特征；TX_0工况的筋-土界面摩擦角显著大于TX_90工况，黏聚力则刚好相反，法向应力较高时TX_0工况的筋-土界面强度更高，更有利于材料性能的发挥。

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.