When the conventional strength reduction finite element method is used to determine the plastic zone of slopes

the results obtained are not so accurate

the shape of plastic zone and the position of sliding surface can not be directly visualized. Using the method of local mesh refinement around the plastic zone

one can not only improve the accuracy of the safety factor calculated greatly but also solve the shape and position of sliding surface. For the specific problems of searching the sliding surface in the plastic zone

a plastic strain limit is presented as a mesh refinement criterion. The shape and position of the sliding surface and the safety factor is determined by local mesh refinement method. A lot of numerical computations are carried out

the results have shown that the criterion used is effective for determining the shape and position of the sliding surface

and the error of the safety factor between the computed value and the accurate value is only 0.2 %.