Abstract：A new technique is described for computing rigorous upper bound on stability factors of vertical cut under the condition of plane strain. A perfectly plastic soil model is assumed. The failure of soil is governed by nonlinear yield criterion. Sequential quadratic programming(SQP) is used in conjunction with the limit analysis of classical plasticity theory. A new kinematically admissible velocity field is constructed. When using linear failure criterion that exceeds the actual nonlinear failure criterion，the stability factor formulation of the upper bound theorem leads to a classical nonlinear programming problem，where the objective function，which is to be minimized，corresponds to the dissipated power. The upper bound optimization problem may be solved efficiently by applying a nonlinear SQP algorithm，and stability factors are obtained，which agree well with previous achievements.
