Soil nailing has been widely used during the last two decades to stabilize steep slopes in several countries. The design methods that have been mostly used are Davis method, German method, and French method, on which the limit equilibrium approach is based, and Juran method, in which the kinematical limit equilibrium design concept is utilized. These methods have been developed on the basis of experimental results and practical experience, and postulate some simplifying assumptions. Therefore these methods may give reasonable predictions for any given condition that agrees with those assumptions. Moreover, the nail force is estimated from the overall safety factor that is assumed to be same as that for the soil. Since the nail is a passive structural element, the estimation does not present an actual nail force.
In this paper, the discrete element method(DEM) that can obtain not only working stresses on interfaces but also the relative displacement of each element is used for the analysis of an excavated slope reinforced by nails. For applying DEM to the reinforced slope, a function is proposed for obtaining shear and tensile forces in a nail from the relative displacement between the nail and the adjacent soil. On the basis of the adopted and proposed techniques a computer program that could perform a stability analysis for steep excavated slope reinforced with nails is developed.
The predicted and measured tensile forces in nails are compared in order to investigate the validity of the developed program. In taking into account for the sequence of excavation, the developed method is capable of predicting the measured tensile force of nails that the other methods give a very different pattern of the tensile forces. The results are also compared with those obtained from both Davis and German methods for several values of design parameters(soil strength, nail length, slope shape, etc.). It can be shown that the developed program gives reasonable results for a wide range of design values. Furthermore, the method can evaluate local and partial safety factors and hence the local failure condition can also be considered.
