Review and Comparative Analysis of Factor of Safety Definitions in Slope Stability.

There are several definitions of the factor of safety used to quantitatively characterize slope or landslide stability, which can yield varying results. A comprehensive comparison of the differences among various definitions is necessary for practitioners. In this study, the characteristics of the existing definitions are comprehensively summarized. They can essentially be classified into five categories, including the rotation moment ratio defined by Fellenius, the shear strength-stress ratio defined by Bishop same as the shear strength reduction coefficient, the amplification coefficient of driving forces defined in the China code, the work rate ratio alternatively suitable for the analytical kinematical limit method, and the square root of deformation energy ratio with rigorous physical meaning. Some examples show that the safety factor based on the Fellenius definition is the smallest, while that by the Kulhawy definition is the largest, and relatively increasing by (6.6–13.4)%. The difference among the safety factors defined by Fellenius, Bishop, and Kulhawy is mainly due to distinct assumptions on the interslice forces using different slice methods rather than the different definitions. The shear strength reduction via numerical simulation method is the most complicated approach for slope stability in terms of execution and computation time. The two definitions using the work rate ratio and strength reduction in the limit analysis method are close only for slopes initially approaching the limit state. The square root of the work rate ratio is consequently proposed for comparability. The definitions of the shear strength-stress ratio and square root of deformation energy ratio are generally recommended. [ABSTRACT FROM AUTHOR]