Abstract: In the coordinate system of strength parameters, utilizing the concept of strength reserve area can deduce the FOS expression of double reduction method (DRM), which is more rational than several existing expressions, and the results do not have enormous deviations from results of existing expressions. In this new method, for the same K, adopting different mathematical expressions gets different virtual initial points. There are two approaches that are based on the ratio of reduction. The first approach only adjusts tan?, and the other only adjusts friction. In theory, these two reduction paths are different. However, this research shows that the difference has no influence on results of DRM, and selecting the shortest reduction path can reduce calculation time. The reduction strategy of traditional strength reduction method (SRM) is different from double reduction method. In DRM result, the critical friction and cohesion appear in such a way that critical friction is over initial friction, or critical cohesion is over initial cohesion, which is not reasonable. By analyzing DRM calculation results given various K, and focusing on the essence of strength reduction method to get two types of results. The first type result is the result that has to conform to calculation accuracy, and the other result is that the result has to align with the fact that critical points must embody the phenomenon of parameters of the weakening.

Key words: slope stability analysis, finite element strength reduction method, double reduction method (DRM), expression of safety factor, DRM applicable scope