Abstract: Understanding the reinforcement mechanism is necessary to establishing a reasonable design method for reinforced-soil structure. In this purpose, pullout test was carried out on HDPE(High Density Polyethylene) geogrid using large scale multi-ring shear apparatus. Firstly, characteristics of the interface between soil and geogrid was analyzed, which is the key to understanding the reinforcement mechanism. The frictional resistance in the interface restricts the soil deformation at the contact zone along the interface, thus enhances the anti-deformation capability of soil, which can be regarded as a direct reinforcement. The frictional resistance also  alters the stress distribution in both sides of the reinforced soil, which can be named as  indirect reinforcement action. The latter occurs in a certain area at both sides of the interface due to soil particles in this area disturbed by the shearing, hence the strength of the reinforced soil is increased. The scope influenced by the above actions is obtained by tests, which can help determine the reasonable interval between the geo-grids. Numerical analysis was also conducted to verify the above understanding. Besides, a number of triaxial tests on the reinforced soil were carried out to investigate the overall properties of reinforced soil  and its failure pattern. All these research results are helpful to establish a reasonable design method for reinforced soil structures.

Key words: reinforced soil with geogrid, reinforcement mechanism, pullout test, indirect reinforcement action, reasonable design method