Abstract: At present, the safety factors are improved little with circular failure analysis method stated in the criterion(Technical standard for applications of geosynthetics, GB50290-98) for preventing deep sliding of reinforced underlying layer of embankment with geofabric, which doesn’t agree with the actual effects. It shows that the circular arc analysis method doesn’t reflect the whole effects of reinforced geofabric. By analyzing interactional mechanism between soil and geofabric in detail, it considers that geofabric with middle tensile strength and modulus will exhibit the intercross sliding resistance mechanism of shearing resistance, of pulling-out resistance and of tension resistance, when embankment and its foundation achieve the state of limit equilibrium as the height of filling soil increases. By comparing the full scale test of embankment without reinforced underlying layer with the other two sections being provided with one or two reinforced underlying layers, the sliding resistance and reinforcement effects are revealed. Considering the above sliding resistance mechanism respectively, the minimum safety factors of the embankment with one reinforced underlying layer are worked out with circular failure analysis method. They also show the sliding resistance and reinforcement effects. It should be pointed out that in practice there is a leading sliding resistance mechanism. Further, making use of the data of the full scale test, a new circular sliding surface passing the point of maximum vertical settlement, which is the center point of interface between embankment and geofabric, is put forward. The computed safety factors of the embankment without or with one or two reinforced underlying layers are improved obviously with the new sliding surface and more closer to actual situation than the old one

Key words: geofabric, reinforced underlying layer, mechanism and effects of sliding resistance, full scale test, circular failure analysis method