Progressive failure feature of slope is difficult for numerical simulation of slope. Also practical slope failure process is rarely a whole and sudden slipping one

is often step by step one from local deformation to final and overall instability

which is a chain domino style failures triggered by small disturbance under critical condition. Here by particle flow code(PFC)

a numerical slope with cohesion between particles being 36 kPa

friction coefficient between particles being 0.36

0.1m particle size and 10m height is designed

initial models damage will not occur under gravity condition. Slope failure is done by cohesion strength between particles reduced to half of initial one. Slope shapes of each 20 000 steps

total steps being 200 000

are obtained by monitoring change of vertical particle groups at horizontal intervals of 1m

which directly reveals progressive failure of slope. Found that failure is always beginning from local part

movement of slope body material results in secondary damage in slope

which forms final arc sliding surface. These account for sliding isn’t a whole declining of slope body

the body isn’t a rigid one. Stress conditions along slip surface don’t reach limit state at the same time. Change of stress in slope body isn’t a monotonous one

but a process with rises and falls. All these conclusions contradict assumptions in current limit equilibrium methods such as rigidity of finite slice

simultaneously reaching limit sate on slip surface

making statically indeterminate problem solved by force transfer mode between slices given

overall analytical method not presenting localization and progressive feature of failure

which hints future of slope computing method lies in discrete element methods can present dynamic practical problem and material real failure characteristics.