Abstract：A new method is proposed for three-dimensional stability analysis of symmetrical or approximately symmetrical slopes. By using a simple equilibrium condition，the normal stress distribution over the three- dimensional slip surface is assumed，which is then multiplied by a modification function involving two unknown parameters. According to three equilibrium conditions of three-dimensional symmetrical slope，three equilibrium equations in terms of the factor of safety and two parameters are derived that are then reduced to a cubical equation in terms of the factor of safety and finally yield the explicit solution to the three-dimensional factor of safety. The presented method does not need consideration of the inter-column forces，rigorously satisfies the equilibrium conditions，and costs fewer computation efforts than the conventional methods of columns. Example studies show that the assumption regarding the initial normal stress distribution over the slip surface and the selection of modification functions has relatively insignificant effect on the value of factor of safety，thus ensures the reasonableness and effectiveness of the proposed method.
