Abstract:The ultimate bearing capacity of soil mass is analysed by elastoplastic finite element method through step loading under plane strain condition;and non-convergence in finite element program is taken as discriminant criterion of failure. Slip surface stress analysis method in finite element analysis of slope stability is used to validate whether the safety factor tends to 1.0 when soil mass arrives at the state of limit equilibrium and to search for the critical slip surface. The critical slip surface given by the method is compared with that obtained by the classical Prandtl solution. The example shows that different yield criteria affect the results greatly. Namely,for slope and foundation without self-weight,the solution obtained by Mohr-Coulomb inside-tangent circle yield criterion under associated flow rule or Mohr-Coulomb matched D-P yield criterion under non-associated flow rule is close to the classical Prandtl solution. But the critical slip surface obtained by Mohr-Coulomb matched D-P yield criterion under non-associated flow rule is not in accordance with the classical Prandtl solution;and the corresponding safety factor is not tend to 1.0. The solution obtained by Mohr-Coulomb inside-tangent circle yield criterion under associated flow rule makes the safety factor tend to 1.0 along critical slip surface and the corresponding slip surface accord with the classical Prandtl solution. For the slope with self-weight,the solution obtained by Mohr-Coulomb inside-tangent circle yield criterion makes the safety factor tend to 1.0 along critical slip surface and the critical slip surface in the limit state accord with that obtained by finite element stability analysis. These show that the solution obtained by Mohr-Coulomb inside-tangent circle yield criterion under associated flow rule is the true ultimate bearing capacity of soil mass structure.