Determination of Interslice Force in Slope Stability Analysis

Limit equilibrium analysis within the framework of method of slices is one of the most commonly used methods for analyzing the stability of a slope. Since the equilibrium condition, along with failure criterion, is insufficient to render the problem to be determinate, various assumptions were evoked. In the past, the problem of indeterminacy was solved either by iteration method together with the assumption of the same mobilization of shear strength along the potentially sliding surface and by making assumptions regarding the direction of interslice forces. In this paper, a direct method for determining the interslice forces is proposed via the hypothesis of least resistance. A simple equation is derived for determining the inclination angle of the interslice force. It is shown that the inclination is dependent upon the geometry and soil properties of a given slope. Use of the derived equation for calculating the factor of safety of a given slope is computationally efficient. Results obtained from this method are compared with that of the existing methods. The numerical cases studied indicated that the factor of safety as well as the interslice forces and line of thrust obtained from the proposed method is close to those obtained from the existing methods. There is no convergency problem in the proposed method. The proposed method eliminates the need to make assumptions on the interslice force direction or location.