For the slope failure caused by excavation unloading effect

the reasonable stability analyses result always can not be obtained by the traditional limit equilibrium method. With loosened zone as the stability analysis object for cutting slope

deviatoric stress increment was chosen as the analysis indicator and its numerical analysis method to determine the range of loosened zone was put forward. The loosened zone was defined as the sum of elastic relaxation zone and plastic flow zone which should distribute continuously and have adverse effect on slope stability.The adjustment of deviatoric stress field is the main reason f

or slope failure after excavation. Calculation program of deviatoric stress and its increment was written in FLAC

3D

software. Taking a dip bedded cutting slope as example

the development process of deviatoric stress and displacement during the excavation was calculated by the FLAC

3D

. The results indicate that there exists a remarkable correlativity between the deviatoric stress and displacement. The deviatoric stress increment contours were characterized by abnormal phenomena which contain local salience and partition of positive and negative values etc. The sequential connection line of salience vertexes is the boundary line between zones in which deviatoric stress redistribution is abnormal or not

and so it can be considered the inner boundary of loosened zone. The proposed method can provide some references for the stability analyses and pre-reinforcement design of cutting slopes.