Abstract:For a general slice,force equilibrium equations are developed,and the recurrence equation of inter-slice force and the general formulation based on force equilibrium to solve the factor of safety are established. Hence,the general slice method based on force equilibrium to solve the factor of safety is developed. The vertical slice method based on force equilibrium to solve the factor of safety is a special case of this method. Analyzing the applicability of Sarma¢s method,a new inter-slice shear force equation is presented based on the compatible relationship among slices displacements. It clarifies the relationship between the inter-slice shear forces and slip surface geometry,and indicates that the reduction factor for shear strength along inter-slice boundaries varies from one boundary to the next,depending on the geometry of the slices and the slip surface. A non-rigorous method of general slice can be developed based on the proposed new inter-slice shear force equation. It assumes that the reduction factors for shear strength along inter-slice boundaries are different from that for shear strength along the slip surface. An example analysis indicates that the proposed new method is better than the Sarma¢s method,and leads to more reasonable values of safety factor. Even if the shape of slice is varied,the proposed new method can also give consistent values of safety factors and ensure that the iteration is stably convergent.