Abstract：The two-dimensional Spencer method is extended to three-dimensional slope stability analysis，in which all forces acting on the discretized blocks are taken into account. The static force equilibrium in all three directions is satisfied；and the total moment equilibrium is also satisfied. In this method，the potential sliding mass is divided into rigid blocks. The inter-block forces and their direction are involved in the computing process. It does not need previously known main sliding direction of the slope. Hence，the number of assumptions being introduced is less than that in other three-dimensional analysis methods. This method can be applied to various types of potential sliding surfaces，complicated geological boundaries and stratifications，water pressure，and earthquake loading，especially for the slope with asymmetrical profile. This proposed method holds the advantages of the 2D Spencer method. The convergence of the iterative calculating process in this method is better than that of other methods. In addition，this method not only gives one value of the safety factors for an integrated slope，but also analyzes the safety factor and its sliding direction for each block according to the characteristics of its sliding surface. The numerical approaches and steps are provided to achieve the program of the proposed method for 3D slope stability analysis. Some programming techniques are also proposed to ensure the practicability and validity of the method. Moreover，an asymmetrical example is employed to show how this method works. The results calculated by this 3D method are given in detail such as the factors of safety and sliding directions of blocks. The results obtained by 3D Janbu method are also presented for comparison. By comparing this 3D Spencer method with other 3D analysis methods，it is shown that the proposed method can provide more parameters and information useful for a landslide control and treatment.
