Abstract: The conventional limit equilibrium and finite element analysis with strength reduction methods have difficulties in simulating the progressive failure of the materials in the slope stability analysis. This disadvantage has impeded the research developments in this area. A 10 meters high soil slope with grain size of 0.1 meters was numerically analyzed by the Particle Flow Code software. At its initial stage, the soil slope is stable. Three failure modes have been imposed on the existing soil slope: reduction of the cohesion; reduction of the coefficient of friction among particles and imposing a 0.1 g horizontal seismic force on the existing soil slope. 30 particle groups with a vertical spacing of 1 meter have been monitored for the progressive failure of each 20,000 time step. The progressive failure of a total of 200,000 time steps has been studied. The results indicate that, for the reduction of the cohesion, the initial local failure is close to the rigid body assumption. The failure mode belongs to the progressive failure. The deformations of the sliding body are relatively small and the sliding body movement is not far. The final slip surface is close to an arc. A global failure mode can be found in the reduction of coefficient friction among the particles. The plastic deformations are found in the sliding body and therefore, large deformations are observed in the sliding body. A long distance of movement in the sliding body can be found. Under the seismic condition, the global instability and a broken sliding body can be found. The sliding impact zone and sliding body movement are the largest among three failure modes. The following failure ranking can be obtained from the strongest to the weakest global failure: seismic condition, reduction of internal friction and the reduction of cohesion. The slope failure is a progressive process of reduction of the potential energy and re-stabilization of the sliding body as well as the accumulation of the sliding materials.

Key words: Soil Slopes, Progressive Failure, Strength Reduction, Seismic Excitation, Particle Flow Code, Numerical Analysis