Abstract:The strength reduction method and explicit finite difference method are used to calculate the global safety factor of the compound soil-nailed wall(CSNW). Compared with the traditional slice method,such as simplified Bishop¢s method,Janbu¢s method,Spencer¢s method and Morgenstern-Price¢s method,the strength reduction method reduces a lot of assumptions,such as the shape of the failure surface and the location of the failure band. Thus,the strength reduction method makes the concept of safety factor more clear and the failure surface more intuitive. In the calculation,only the strength of the soil and the cement deep mixing pile are reduced during the process. The strength parameters of the nail bar and that of the interface between the grouting body and the soil are regarded as constant. A compound soil-nailed wall project of typical soft clay of Shanghai is presented. The contour map of shear strain increment is recommended to recognize the failure surface or failure band of the CSNW. The failure surface calculated with strength reduction method is identical to the actual failure pattern of the CSNW. The traditional slice methods based on the limit equilibrium theory are also used to calculate the global safety factor. The result of strength reduction method and that of the traditional computing technology are compared and the difference between them is smaller than 10%. The tiny discrepancy of the safety factors calculated by the different methods mentioned above is acceptable. So it is concluded that the strength reduction method can be used in practice.