Abstract:In-situ testing study on the mechanical behavior of soil nailing and the displacement characteristics of miscellaneous fill slope is carried out. A number of significant conclusions are proposed. For the first time,double arciform strain of the soil nailing is observed in the miscellaneous fill. It is considered as the result that there are two (or more) potential slide planes in the miscellaneous fill. The critical anchorage length is analyzed and determined for the first,which is 9 m in this experiment. The ritical anchorage length is formed because of the transfer of the peak value point,the zero value point of the stain (stress) and the wreck point at the same time. It is found out that all anchorage structure (anchor-bolt,anchor-cable and soil nailing) have this characteristic.