VALIDATION OF THE DEFINITION OF THE FACTOR OF SAFETY USED IN THE FINITE ELEMENT SLOPE STABILITY ANALYSIS

In this paper, it proves that the necessary and sufficient condition for the potential sliding body reaching the ultimate limit equilibrium state is that the summation of shear stresses along the sliding surface equals to that of resistant shear strength. Based on the rigorous theory analyses and derivatives, it is clearly shown that the definition of factor of safety (FOS) in the slip surface stress method (SSSM) is irrelevant with the shape of slip surface. Thus, the authors demonstrate that the FOS of noncircular slip surface can also be defined as the ratio of the sum of resistant sliding force along slip surface to that of sliding force. Furthermore, the physical meaning of the FOS in the SSSM, which can be taken as the average evaluation of the strength reduction coefficient that makes the sliding body reach the ultimate limit equilibrium state along the slip surface in nature, is formulated on the basis of strength reserving theory rather than the overloading theory like that in the limit equilibrium method (LEM) and the shear strength reduction method (SSRM). Finally, the factors of safety (FOS) and the locations of critical failure surfaces obtained by the SSSM, LEM and SSRM are compared for various geotechnical practices. It is found that the SSSM can achieve precise and reasonable stability assessments for the soil slopes on the basis of actual stress field. Consequently, compared with the LEM and SSRM, the SSSM is demonstrated to be effective and efficient alternative approach for routine analysis and design in geotechnical engineering practice with a high level of confidence.