The shear strength reduction technique has been commonly incorporated into the elastroplastic FEM.Based on the computed displacements and generalized shear strain of slope for a given state

nonconvergence state of finite element analyses for displaying an unstable condition of slope will be certainly defined. At the moment of overall failure

the variations and distributions for some physical variables such as plastic strain

stress level

will take a certain characteristics. Therefore

the evaluation criteria by preassuming an allowable iteration number employed in current practice is fairly inappropriate. Furthermore

the evaluation criteria for limiting allowable minimum ratio of unbalanced force to external load less than 10-3 will

in some cases

lead to numerically computational nonconvergence and also display a certain uncertainties. The distribution zone of generalized shear strain can be manifested based on the results of elastoplastic FEM by use of strength reduction technique. If the generalized shear strain zone with a given value is developed from the toe to the top

the slope will approach a critical instable state. However

the critical value of generalized shear strain at which a critical state will be initiated cannot be determined beforehand and therefore the safety factor determined by this type of methods is not sufficiently meaningful. In fact

the generalized shear strain or displacement is composed of both plastic and elastic components. Therefore

it is not rational and accurate to evaluate the initiation and development of plastic zone or shear failure zone based on the feature of variations and distributions of these variables. However

shear failure of soil is directly associated with the initiation

development and redistribution of plastic zones

and plastic strain can give a clear representation of development of plastic zone. Therefore

in this paper

the elastoplastic FEM by using shear strength reduction procedure （SSRFEM） is incorporated with the dynamic display technique of computed numerical results. Elastoplastic FEM is the essential part of this method. In the procedure

the following main issues have been effectively solved

e.g.

（1） Considering the elastoplastic behavior of soil

an efficient nonlinear iterative algorithm in FEM is developed; （2） The appropriate formulation together with numerical scheme for stress modification is established to assure that the updated stress state computed is compatible with the current yield surface in a fair accuracy. （3） The basic rules for evaluating critical overall instable state of slope is proposed based on the development pattern of generalized plastic strain or plastic zone and is compared with the conventional procedures by controlling maximum allowable iterative number. The reasonable safety factor can be defined by the proposed method. Through numerical analyses for a natural vertical slope

it is indicated that the proposed method can rather rationally predict both safety factor of slope and the corresponding shape and position of the potential slip surface. The computed safety factor can agree well with those obtained by other SSRFEM analyses based on the conventional procedures. For an actual excavated slope and an excavated slope with reinforcement of soil nailing

numerical analyses are performed. Accordingly

practical applicability of the proposed technique to complicated cases is verified.