Abstract: Slope instability is a dynamic progressive failure process from qualitative to quantitative, which is one of the key points and difficulties in slope investigations. A theoretical framework of the slope progressive failure is constructed by considering strain-softening behavior of geotechnical materials and the calculation of kinetic. The simulation of slope progressive failure is implemented into the dynamic explicit solution module of ABAQUS software. The extension process of shear band is revealed according to the developments of plastic strain. The partition evolution law of material parameters at the slip surface is determined by the softening constitutive model. The slope slip surface is obtained by the equivalent plastic strain. Slope can be divided into landslide body, sliding zone and slide bed by the location of the sliding plane. The development of kinematic variables of internal characteristic points in the partition zones is studied to reveal the progressive failure process of the slope. Based on temporal-spatial distribution of material parameters along the sliding plane, the safety factors of slopes are obtained at different evolutionary stages using the vector sum method. By comparing the vector sum method with the Bishop method, it is found that the safety factors corresponding to peak and residual strength parameters are relatively close using these two methods. The sliding plane determined by vector sum method is also located among sliding planes by Bishop method, which to a great extent demonstrates the procedure is rational and reliable. Finally, the influence of material softening characteristics on slope stability is analyzed. It is noticed that when the residual cohesion is increased but other parameters are constant, the sliding plane is deepened, the initial value of safety factor is reduced, the appearance time of rapid decreasing phase of the safety factor is delayed, the duration of rapid decreasing phase is extended, and the safety factor after slope stability is increased. When the threshold of the corresponding equivalent plastic strain of the residual cohesion is increased but other parameters are constant, the sliding plane is deepened, the initial value of safety factor is reduced; however the appearance time of rapid decreasing phase of the safety factor is substantially constant, the stable time is delayed, and the stability safety factor is slightly increased .

Key words: strain-softening, progressive failure, dynamics, partition evolution of material parameters, vector sum method, slope stability