The extended simplified Bishop method (ESBM) provides another convenient way to calculate the safety factor of non-circular slip. But a new question arises when to format the equations of overall moment equilibrium of the forces acting on each slice

namely

different positions of moment centers can lead to different safety factors. Just so

the application of ESBM is limited. The authors address the question of the effect of the moment centers on safety factor of non-circular slip. Moreover the principle has been suggested to position the moment center in order to obtain relative accurate safety factor. According to analysis of many examples

the results show that it is possible to make the precision of safety factors calculated by ESBM equivalent to that of by rigorous method such as Morgenstern-Price method as long as the moment centers is choose properly.