Abstract：Imbalance thrust force method (ITFM) is originally developed approach for slope stability analysis in China，which has been widely used in the field of landslide stability analysis. But few papers are interested in the accuracy of results obtained by ITFM. It has been proved that the error by ITFM is high enough not to be negligible，and the hidden danger will take place in practice if misusing it. By theoretical analysis and comparison of examples，it is considered that the accuracy of ITFM is influenced by the increments of slip segment obliqueness，and the accuracy can be improved by adjusting the increments of slip segment obliqueness. The increments of slip segment obliqueness must be less than or equal to 10 degrees when using ITFM，otherwise the other slope stability analysis methods should be selected or the slip line should be improved. A new inter-slice shear force equation is presented in this paper to solve the existing problems in the inter-slice shear force equation of Sarma′s method. The presented equation meets the demands of slope stability analysis，and can properly express inter-slice shear forces for general slices. Sarma′s method is improved，based on the new inter-slice shear force equation. The improved Sarma′s method considers that the reduction factor for shear strength along inter-slice boundary is different from that for shear strength along slip surface. Corresponding examples indicate that the improved Sarma′s method works better than Sarma′s method and a more reasonable value of safety factor can be obtained by the improved Sarma′s method. The consistent values of safety factor can be given and the iteration is stably convergent even if the shape of slices is varied.
