Soil nailing technology is currently adopted as a cut slope retaining system, generally in nonplastic soils. Design methods that have been mostly used are Davis[8], German[11], and French methods[10], on which the limit equilibrium approaches are based[6]. Recently, a kinematical limit equilibrium design method has been proposed by Juran[5] and Byrne[1]. This method has the advantage that the force in each nail can be obtained from the horizontal force equilibrium of the slice comprising the nail. But, there is possibility of argument about the problem of boundary condition and the vertical force equilibrium[7]. Besides, all of the above methods cannot appropriately take into account for the construction characteristics of the top-down nailing system.
In this study, a new analysis and design method was developed by using Discrete Element Method(DEM). The DEM which have been used for a general stability analysis was extended to be applicable to a nail reinforced steep slope. The analytical technique adopted in this study was originally proposed by Chang[2] for non-reinforced slopes. In order to apply the DEM to reinforced steep slopes, a formulation in replacing nails by elastoplastic springs is presented. The present method is capable of estimating tensile and shear stresses mobilized in nails and thus providing individual safety factor of soil and each nail-reinforcement, especially with considering the realistic sequence of construction. Thus, excavation steps followed for the real sequence of construction was also considered in the analysis. For this purpose, a mechanism to simulate characteristics of interactive behavior of nail and surrounding ground was established, and it was replaced by elastoplastic springs. By utilizing the developed method, tensile forces mobilized in nails could be predicted to some degree of accuracy, and local safety factors can also be calculated. This results give assistance for stability analysis of reinforced structure. Excavation steps followed for the real sequence of construction was also considered in the analysis.
In this study, a relatively large scale experiment was also carried out to compare between analysis results and measured data. The magnitude of tensile forces is predicted relatively well. It is mainly due to the consideration of real construction sequence in the proposed method.
