The interface interaction between geogrid and soil is one of the key issues on geosynthetic reinforced soil structures. Comparative analysis of properties of geogrid clay interface under the different normal stresses and water contents of clay were conducted by medium sized pullout tests. The results show that ultimate pullout force of geogrid

interfacial cohesion and frictional coefficient are significantly affected by water content of clay. Ultimate pullout force of geogrid tends to be remarkably different when subjecting to different normal stresses at a lower water content. And frictional coefficient of interface decreases with the increase of water content

and interfacial cohesion has a tendency to increase followed by decrease with the increase of water content. Moreover

aforementioned three parameters can keep constant when water content is close to value at plasticity limit. The curves of load and displacement possess three stages: linear increase

non linear increase and ultimate pullout. As water content increases

the interval nonlinear changing stage is not conspicuous. Furthermore

it is found that geogrid strains in transversal ribs tend to increase but to reduce in longitudinal ribs when last level load is kept for given hours and then followed by unloading pullout force.