Three-dimensional analysis of slope stability is developing. Compared with two-dimensional method

this method can reflect the condition of slope more closely to the fact. Based on the upper bound limit analysis method

a new three-dimensional rotation-translation combined mechanism is proposed to study the stability of slope with weak interlayer. And this combined mechanism can be expended longitudinally through the plane insert; so the method could be used to analyze the slope stability with different lengths. The proposed failure mechanism is finally verified by comparisons with the elastoplastic finite element method. The comparisons show that the proposed mechanism improves the efficiency of the previously-developed rigid block mechanism to account for the presence of the weak interlayer in the slope and can be used as a simple evaluation method for the engineering design.